Thorium: will it save the planet from the energy crisis? Distant relatives of the bomb.

Uranium, element number 92, is the heaviest element found in nature. It was used at the beginning of our era; fragments of ceramics with a yellow glaze (containing more than 1% uranium oxide) were found among the ruins of Pompeii and Herculaneum.

Uranium was discovered in 1789 in uranium tar by the German chemist Marton Heinrich Klaproth, who named it after the planet uranium, discovered in 1781. Metallic uranium was first obtained by the French chemist Eugene Peligo in 1841, by reducing anhydrous uranium tetrachloride with potassium. In 1896, Antoine-Henri Becquerel discovered the phenomenon of uranium radioactivity by accidentally exposing photographic plates to ionizing radiation from a nearby piece of uranium salt.

Physical and chemical properties

Uranium is a very heavy, silvery-white, shiny metal. In its pure form, it is slightly softer than steel, malleable, flexible, and has slight paramagnetic properties. Uranium has three allotropic forms: alpha (prismatic, stable up to 667.7 °C), beta (tetragonal, stable from 667.7 to 774.8 °C), gamma (with a body-centered cubic structure, existing from 774.8 °C to the melting point), in which uranium is the most malleable and easy to process. The alpha phase is a very remarkable type of prismatic structure, consisting of wavy layers of atoms in an extremely asymmetrical prismatic lattice. This anisotropic structure makes it difficult to alloy uranium with other metals. Only molybdenum and niobium can create solid-phase alloys with uranium. True, uranium metal can interact with many alloys, forming intermetallic compounds.

Basic physical properties of uranium:
melting point 1132.2 °C (+/- 0.8);
boiling point 3818 °C;
density 18.95 (in alpha phase);
specific heat capacity 6.65 cal/mol/°C (25 C);
tensile strength 450 MPa.

Chemically, uranium is a very active metal. Quickly oxidizing in air, it becomes covered with a rainbow film of oxide. Fine uranium powder spontaneously ignites in air; it ignites at a temperature of 150-175 °C, forming U 3 O 8 . At 1000 °C, uranium combines with nitrogen to form yellow uranium nitride. Water can corrode metal, slowly at low temperatures and quickly at high temperatures. Uranium dissolves in hydrochloric, nitric and other acids, forming tetravalent salts, but does not interact with alkalis. Uranium displaces hydrogen from inorganic acids and salt solutions of metals such as mercury, silver, copper, tin, platinum and gold. When shaken vigorously, the metal particles of uranium begin to glow.
Uranium has four oxidation states - III-VI. Hexavalent compounds include uranyl trioxide UO 3 and uranium uranium chloride UO 2 Cl 2 . Uranium tetrachloride UCl 4 and uranium dioxide UO 2 - examples of tetravalent uranium. Substances containing tetravalent uranium are usually unstable and turn into hexavalent uranium when exposed to air for a long time. Uranyl salts such as uranyl chloride decompose in the presence of bright light or organic matter.

Uranium has no stable isotopes, but 33 of its radioactive isotopes are known. Natural uranium consists of three radioactive isotopes: 238 U (99.2739%, T=4.47⋅10 9 years, α-emitter, ancestor of the radioactive series (4n+2)), 235 U (0.7205%, T=7.04⋅10 9 years, the ancestor of the radioactive series (4n+3)) and 234 U (0.0056%, T=2.48⋅10 5 years, α-emitter). The last isotope is not primary, but radiogenic; it is part of the radioactive series 238 U. Atomic mass of natural uranium is 238.0289+0.0001.

The radioactivity of natural uranium is due mainly to isotopes 238 U and 234 U, in equilibrium their specific activities are equal. The specific radioactivity of natural uranium is 0.67 microcurie/g, divided almost in half between 234 U and 238 U; 235 U makes a small contribution (specific activity of the isotope 235 U in natural uranium is 21 times less active 238 U). Natural uranium is radioactive enough to expose a photographic plate in about an hour. Thermal neutron capture cross section 233 U 4.6 10 -27 m2, 235 U 9.8 10 -27 m2, 238 U 2.7 10 -28 m2; fission cross section 233 U 5.27 10 -26 m2, 235 U 5.84 10 -26 m2, natural mixture of isotopes 4.2 10-28 m2.

Isotopes of uranium are usually α-emitters. Average α-radiation energy 230 U, 231 U, 232 U, 233 U, 234 U, 235 U, 236 U, 238 U is equal to 5.97, respectively; 3.05⋅10 -4 ; 5.414; 4.909; 4.859; 4.679; 4.572; 4.270 MeV. At the same time, isotopes such as 233 U, 238 U and 239 In addition to alpha, U also undergoes another type of decay - spontaneous fission, although the probability of fission is much less than the probability of α decay.

From the point of view of practical applications, it is important that natural isotopes 233 U and 235 U fission under the influence of both thermal and fast neutrons ( 235 U is capable of spontaneous fission), and the nuclei 238 U are capable of fission only when capturing neutrons with energies greater than 1 MeV. When capturing neutrons with lower nuclear energy 238 U turn into nuclei first 239 U, which then undergo β-decay and first transform into 239 Np, and then - at 239 Pu, whose nuclear properties are close to 235 U. Effective capture cross sections for thermal neutrons of nuclei 234 U, 235 U and 238 U are equal to 98⋅10 -28, 683⋅10 -28 and 2.7⋅10 -28 m2 respectively. Complete division 235 U leads to the release of “thermal energy equivalent” 2⋅10 7 kWh/kg.

Technogenic isotopes of uranium

Modern nuclear reactors produce 11 artificial radioactive isotopes with mass numbers from 227 to 240, of which the longest-lived is 233 U (T = 1.62 10 5 years); it is obtained by neutron irradiation of thorium. Uranium isotopes with a mass number greater than 240 do not have time to form in reactors. The lifetime of uranium-240 is too short, and it decays before it can capture a neutron. However, in super-powerful neutron fluxes of a thermonuclear explosion, a uranium nucleus manages to capture up to 19 neutrons in a millionth of a second. In this case, uranium isotopes with mass numbers from 239 to 257 are born. Their existence was learned from the appearance in the products of a thermonuclear explosion of distant transuranium elements - descendants of heavy isotopes of uranium. The “founders of the genus” themselves are too unstable to β-decay and pass into higher elements long before the products of nuclear reactions are extracted from the rock mixed by the explosion.

In thermal neutron power reactors, isotopes are used as nuclear fuel 235 U and 233 U, and in fast neutron reactors 238 U, i.e. isotopes capable of supporting a fission chain reaction.

U-232

232 U – technogenic nuclide, not found in nature, α-emitter, T=68.9 years, parent isotopes 236 Pu(α), 232 Np(β+) and 232 Pa(β-), daughter nuclide 228 Th. Capable of spontaneous division. 232 U has a spontaneous fission rate of 0.47 divisions/s⋅kg. In the nuclear industry 232 U is produced as a by-product during the synthesis of the fissile (weapons-grade) nuclide 233U in the thorium fuel cycle. When irradiated 232 Th main reaction occurs:

232 Th + n → 233 Th → (22.2 min, β-decay) → 233 Pa → (27.0 days, β-decay) → 233U

and a two-step side reaction:

232 Th + n → 231 Th + 2n, 231 Th → (25.5 h, β) → 231 Pa + n → 232 Pa → (1.31 days, β) → 232 U.

Running time 232 U during a two-stage reaction depends on the presence of fast neutrons (neutrons with an energy of at least 6 MeV are needed), because the cross section of the first reaction is small for thermal rates. A small number of fission neutrons have energies above 6 MeV, and if the thorium breeding zone is located in a part of the reactor where it is irradiated with moderately fast neutrons (~ 500 keV), then this reaction can be practically eliminated. If the original substance contains 230 Th, then education 232 U is complemented by the reaction: 230 Th + n → 231 Th and further as above. This reaction also works well with thermal neutrons. Therefore, suppression of education 232 U (and this is necessary for the reasons indicated below) requires loading thorium with a minimum concentration 230 Th.

Isotope produced in a power reactor 232 U poses a health and safety problem because it breaks down into 212 Bi and 208 Te, which emit high-energy γ-quanta. Therefore, drugs containing a large number of This isotope must be processed in a hot chamber. Availability 232 U in irradiated uranium is also dangerous from the point of view of handling atomic weapons.

Accumulation 232 U inevitable in production 233 U in the thorium energy cycle, which hinders its introduction into the energy sector. What is unusual is that the even isotope 232 U has a high fission cross section under the influence of neutrons (for thermal neutrons 75 barns, resonance integral 380), as well as a high neutron capture cross section - 73 barns (resonance integral 280).

There are also benefits from 232 U: It is often used in the radiotracer method in chemical and physical research.

U-233

233 U was discovered by Seaborg, Hoffmann and Stoughton. Uranium-233 - α-emitter, T=1.585⋅105 years, parent nuclides 237 Pu(α) 233 Np(β+) 233 Pa(β-), daughter nuclide 229 Th. Uranium-233 is produced in nuclear reactors from thorium: 232Th captures a neutron and turns into 233 Th, which breaks down into 233 Ra, and then in 233 U. Nuclei 233 U (odd isotope) is capable of both spontaneous fission and fission under the influence of neutrons of any energy, which makes it suitable for the production of both atomic weapons and reactor fuel (expanded reproduction of nuclear fuel is possible). Uranium-233 is also the most promising fuel for gas-phase nuclear rocket engines. The effective fission cross section for fast neutrons is 533 barns, the half-life is 1,585,000 years, and does not occur in nature. Critical mass 233 U is three times less than critical mass 235 U (approx. 16 kg). 233 U has a spontaneous fission rate of 720 fissions/s⋅kg. 235U can be obtained from 232Th by neutron irradiation:

232 Th + n → 233 Th → (22.2 min, β-decay) → 233 Pa → (27.0 days, β-decay) → 233U

When a neutron is absorbed, the nucleus 233 U usually fissions, but occasionally captures a neutron, becoming 234 U, although the share of non-fission processes is less than in other fissile fuels ( 235 U, 239 Pu, 241 Pu) it remains small at all neutron energies. Note that there is a molten salt reactor design in which protactinium is physically isolated before it has a chance to absorb a neutron. Although 233 U, having absorbed a neutron, usually divides, yet it sometimes retains a neutron, turning into 234 U (this process is significantly less probable than fission).

Running time 233 U from raw materials for the thorium industry is a long-term strategy for the development of the Indian nuclear industry, which has significant thorium reserves. Breeding can be carried out either in fast or thermal reactors. Outside India, there is not much interest in the thorium-based fuel cycle, although the world's thorium reserves are three times greater than uranium reserves. In addition to fuel in nuclear reactors, it can be used 233 U in a weapon charge. Although now they rarely do this. In 1955, the United States tested weapons quality 233 U by detonating a bomb based on it in Operation Teapot. From a weapons point of view 233 U, comparable to 239 Pu: its radioactivity is 1/7 (T=159200 years versus 24100 years for plutonium), its critical mass is 60% higher (16 kg versus 10 kg), and the rate of spontaneous fission is 20 times higher (6⋅10-9 versus 3⋅10 -10 ). However, since its specific radioactivity is lower, the neutron density 233 U is three times higher than that 239 Pu. Creation of a nuclear charge based on 233 U requires more effort than plutonium, but the technological effort is approximately the same.

The main difference is the presence in 233 U impurities 232 U, which makes it difficult to work with 233 U and makes it easy to discover finished weapons.

232 U content in weapons grade 233 U should not exceed 5 ppm (0.0005%). In the commercial nuclear fuel cycle, the presence 232 U is not a major drawback, even desirable, since it reduces the possibility of proliferation of uranium for weapons purposes. To save fuel, after recycling and reusing the level 232 U reaches 0.1-0.2%. In specially designed systems, this isotope accumulates in concentrations of 0.5-1%.

During the first two years after production 233 U containing 232 U, 228 Th remains at a constant level, being in equilibrium with its own decay. During this period, the background value of γ-radiation is established and stabilized. Therefore, the first few years the mass produced 233 U emits significant γ radiation. Ten-kilogram sphere 233 Weapon grade U (5 ppm 232U) produces a background of 11 millirem/hour at a distance of 1 m 1 month after production, 110

millirem/h after a year, 200 millirem/h after 2 years. The annual dose limit of 5 rem is exceeded after only 25 hours of working with such material. Even fresh 233 U (1 month from date of manufacture) limits assembly time to ten hours per week. In a fully assembled weapon, the radiation level is reduced by absorption of the charge by the body. In modern lightweight devices, the reduction does not exceed 10 times, creating safety problems. In heavier charges the absorption is stronger - 100 - 1000 times. A beryllium reflector increases the level of neutron background: 9Be + γ-quantum → 8Be + n. γ-rays 232 U form a characteristic signature, they can be detected and the movements and presence of an atomic charge can be tracked. Produced using the thorium cycle, specially denatured 233 U (0.5 - 1.0% 232 U), creates an even greater danger. A 10-kilogram sphere made of such material at a distance of 1 m after 1 month creates a background of 11 rem/hour, 110 rem/hour after a year and 200 rem/hour after 2 years. Contact with such an atomic bomb, even with a 1000-fold reduction in radiation, is limited to 25 hours per year. Presence of a noticeable share 232 The U in fissile material makes it extremely inconvenient for military use.

Natural isotopes of uranium

U-234

Uranium-234 (uranium II) is part of natural uranium (0.0055%), T = 2.445⋅10 5 years, α-emitter, parent radionuclides: 238 Pu(α), 234 Pa(β-), 234 Np(β+), daughter isotope in 230 Th. Contents 234 U in the ore is very minor due to its relatively short half-life. 234 U is formed by the reactions:

238 U → (4.51 billion years, alpha decay) → 234 Th

234 Th → (24.1 days, beta decay) → 234 Pa

234 Pa → (6.75 hours, beta decay) → 234 U

Usually 234 U is in equilibrium with 238 U, decaying and forming at the same rate. However, decaying atoms 238 U exist for some time in the form of thorium and protactinium, so they can be chemically or physically separated from the ore (leached by groundwater). Because the 234 U has a relatively short half-life; all of this isotope found in the ore was formed in the last few million years. Approximately half of the radioactivity of natural uranium comes from 234 U.

Concentration 234 The U in highly enriched uranium is quite high due to preferential enrichment in light isotopes. Because the 234 U is a strong γ-emitter; there are limits on its concentration in uranium intended for processing into fuel. Basically, an increased level 234 U is acceptable for modern reactors, but reprocessed spent fuel contains unacceptable levels of this isotope.

Absorption cross section 234 U of thermal neutrons is 100 barn, and for the resonance integral averaged over various intermediate neutrons is 700 barn. Therefore, in reactors at

thermal neutrons it is converted into fissile 235 U with higher speed than a much larger number 238 U (with a cross section of 2.7 barn) is converted to 239 Pu. As a result, spent nuclear fuel contains less 234 U, than fresher.

U-235

Uranium-235 (actinouranium) is an isotope capable of producing a fast-growing fission chain reaction. Discovered by Arthur Jeffrey Dempster in 1935.

This is the first isotope in which the reaction of forced nuclear fission under the influence of neutrons was discovered. Absorbing a neutron 235 U goes to 236 U, which splits into two parts, releasing energy and emitting several neutrons. An isotope fissile by neutrons of any energy, capable of spontaneous fission 235 U is part of natural uranium (0.72%), α-emitter (energy 4.679 MeV), T=7.038⋅10 8 years, parent nuclides 235 Pa, 235 Np and 239 Pu, daughter - 231 Th. Intensity of spontaneous fission 235 U 0.16 divisions/s⋅kg. When one nucleus divides 235 U released 200 MeV energy=3.2⋅10 -11 J, i.e. 18 TJ/mol=77 TJ/kg. However, 5% of this energy is carried away by virtually undetectable neutrons. The nuclear cross section for thermal neutrons is approximately 1000 barn, and for fast neutrons - about 1 barn.

Net 60kg mass 235 U produces only 9.6 fissions/s, making it simple enough to make an atomic bomb using a cannon design. 238 U creates 35 times more neutrons per kilogram, so even a small percentage of this isotope raises this figure several times. 234 U creates 22 times more neutrons and is similar to 238 U undesirable action. Specific activity 235 U is only 2.1 microcuries/g; its contamination is 0.8% 234 U raise it to 51 microcuries/g. Critical mass of weapons-grade uranium. (93.5% 235 U) in aqueous solutions is less than 1 kg, for an open ball - about 50 kg, for a ball with a reflector - 15 - 23 kg.

In natural uranium, only one, relatively rare, isotope is suitable for making the core of an atomic bomb or maintaining a reaction in a power reactor. Enrichment degree according to 235 U in nuclear fuel for nuclear power plants ranges from 2-4.5%, for weapons use - at least 80%, and more preferably 90%. IN THE USA 235 Weapons-grade U is enriched to 93.5% (industry is capable of producing 97.65%). Such uranium is used in reactors for the navy.

Comment. Uranium with content 235 U more than 85% is called weapons-grade uranium, with a content of more than 20% and less than 85% - uranium suitable for weapons use, since it can be used to make a “bad” (ineffective bomb). But it can also be used to make a “good” bomb if you use implosion, neutron reflectors and some advanced tricks. Fortunately, only 2-3 countries in the world can implement such tricks in practice. Nowadays, bombs from uranium are apparently not produced anywhere (plutonium has replaced uranium in nuclear weapons), but the prospects for uranium-235 remain due to the simplicity of the cannon design of the uranium bomb and the possibility of expanded production of such bombs if the need suddenly arises.

Being lighter 234 U is proportionally enriched to an even greater extent than 235 U in all processes of separation of natural uranium isotopes based on differences in mass, which poses a certain problem in the production of atomic bomb charges. Highly enriched 235 U usually contains 1.5-2.0% 234 U.

Division 235 U is used in atomic weapons, for energy production, and for the synthesis of important actinides. Natural uranium is used in nuclear reactors to produce neutrons. The chain reaction is maintained by the excess of neutrons produced by fission 235 U, at the same time, excess neutrons unclaimed by the chain reaction are captured by another natural isotope, 238 U, which leads to the production of plutonium, which is also capable of fission under the influence of neutrons.

U-236

Found in nature in impurity quantities, α-emitter, T=2.3415⋅10 7 years, breaks up into 232 Th. Formed by neutron bombardment 235 U then splits into a barium isotope and a krypton isotope, releasing two neutrons, gamma rays, and releasing energy.

In small quantities it is part of fresh fuel; accumulates when uranium is irradiated with neutrons in a reactor, and is therefore used as a “signaling device” for spent uranium nuclear fuel. 236 U is formed as a by-product during the separation of isotopes by gas diffusion in the case of regeneration of used nuclear fuel. This isotope has some significance as a target material in nuclear reactors. When using recycled (processed) uranium in a nuclear reactor, there is an important difference compared to using natural uranium. Uranium isolated from spent fuel contains the isotope 236 U (0.5%), which, when used in fresh fuel, stimulates the production of the isotope 238 Pu. This leads to a deterioration in the quality of energy-grade plutonium, but can be a positive factor in the context of the problem of nuclear non-proliferation.

Formed in a power reactor 236 U is a neutron poison; its presence in nuclear fuel must be compensated for by a higher level of enrichment 235 U.

U-238

Uranium-238 (uranium I) - fissile by high-energy neutrons (more than 1 MeV), capable of spontaneous fission, forms the basis of natural uranium (99.27%), α-emitter, T = 4.468⋅10 9 years, directly breaks down into 234 Th, forms a number of genetically related radionuclides, and through 18 products turns into 206 Pb. The constant rate of decay of the series makes it possible to use the ratio of concentrations of the parent nuclide to the daughter in radiometric dating. The half-life of uranium-238 by spontaneous fission has not been precisely established, but it is very long - about 10 16 years, so the probability of fission in relation to the main process - the emission of an alpha particle - is only 10 -7 . One kilogram of uranium produces only 10 spontaneous fissions per second, and during the same time α-particles emit 20 million nuclei. Mother nuclides: 242 Pu(α), 238 Pa(β-) 234 Th, daughter - 234 Th.

Although uranium-238 cannot be used as a primary fissile material, due to the high energy neutrons required for its fission, it has an important place in the nuclear industry. Having high density and atomic weight, 238 U is suitable for making charge/reflector shells in atomic and hydrogen bombs. The fact that it is fissioned by fast neutrons increases the energy output of the charge: indirectly, by the multiplication of reflected neutrons or directly by the fission of the nuclei of the charge shell by fast neutrons (during fusion). Approximately 40% of the neutrons produced by fission and all fusion neutrons are sufficient for fission 238 U energies. 238 U has a spontaneous fission rate 35 times higher than 235 U, 5.51 divisions/s⋅kg. This makes it impossible to use it as a charge/reflector shell in cannon-type bombs, because its suitable mass (200-300 kg) will create too high a neutron background. Clean 238 U has a specific radioactivity of 0.333 microcurie/g. An important area of ​​application of this uranium isotope is the production 239 Pu. Plutonium is formed through several reactions that begin after being captured by an atom 238 U neutron. Any reactor fuel containing natural or partially enriched uranium in the 235th isotope contains a certain proportion of plutonium after the end of the fuel cycle.

Depleted uranium

After extraction 235 U from natural uranium, the remaining material is called “depleted uranium” because it is depleted in isotopes 235 U and 234 U. Reduced content 234 U (about 0.001%) reduces radioactivity by almost half compared to natural uranium, while the decrease in content 235 U has virtually no effect on the radioactivity of depleted uranium.

Almost all depleted uranium in the world is stored in the form of hexafluoride. The United States has 560,000 tons of depleted uranium hexafluoride (UF6) at three gas diffusion enrichment plants, and hundreds of thousands of tons in Russia. Depleted uranium is half as radioactive as natural uranium, mainly due to the removal of 234 U. Due to the fact that the main use of uranium is energy production, in nuclear reactors with thermal neutrons, depleted uranium is a useless product with low economic value.

From a safety perspective, it is common practice to convert depleted uranium hexafluoride gas into uranium oxide, which is a solid. Uranium oxide is either subject to burial as a form of radioactive waste, or can be used in fast neutron reactors to produce plutonium.

The decision on how to dispose of uranium oxide depends on how a country views depleted uranium: as radioactive waste to be disposed of, or as material suitable for further use. For example, in the USA, until recently, depleted uranium was considered as a raw material for further use. But since 2005, this point of view began to change and now in the United States it is possible to bury depleted uranium oxide. In France, depleted uranium is not considered radioactive waste, but is supposed to be stored in the form of uranium oxide. In Russia the leadership Federal agency on atomic energy considers waste uranium hexafluoride to be a valuable material that is not subject to burial. Work has begun on creating an industrial installation for converting waste uranium hexafluoride into uranium oxide. The resulting uranium oxides are supposed to be stored long time for their further use in fast neutron reactors or additional enrichment of it 235 U followed by combustion in thermal reactors.

Finding ways to use depleted uranium poses a big challenge for enrichment plants. Its use is mainly associated with the high density of uranium and its relatively low cost. The two most important uses of depleted uranium are as radiation shielding and as ballast in aerospace applications such as aircraft control surfaces. Each Boeing 747 aircraft contains 1,500 kg of depleted uranium for these purposes. Depleted uranium is largely used in oil drilling in the form of shock rods (in wireline drilling), its weight driving the tool into wells filled with drilling fluid. This material is used in high-speed gyroscope rotors, large flywheels, as ballast in space landers and racing yachts.

But the most famous use of uranium is as cores for armor-piercing projectiles. With a certain alloy with other metals and heat treatment (alloying with 2% Mo or 0.75% Ti, rapid quenching of the metal heated to 850° in water or oil, further holding at 450° for 5 hours), uranium metal becomes harder and stronger than steel (strength at gap > 1600 MPa). Combined with its high density, this makes hardened uranium extremely effective at penetrating armor, similar in effectiveness to the significantly more expensive monocrystalline tungsten. The process of armor destruction is accompanied by the grinding of the main part of the uranium into dust, the penetration of dust into the protected object and its ignition there. 300 tons of depleted uranium remained on the battlefield during Desert Storm (mostly the remains of shells from the 30 mm GAU-8 cannon of A-10 attack aircraft, each shell containing 272 g of uranium alloy). Depleted uranium is used in tank armor, for example, the M-1 Abrams tank (USA). -4 % by weight (2-4 ppm depending on the region), in acidic igneous rocks 3.5 10 -4 %, in clays and shales 3.2 10 -4 %, in basic rocks 5·10 -5 %, in ultramafic mantle rocks 3·10 -7 %. The amount of uranium in a 20 km thick layer of the lithosphere is estimated at 1.3⋅10 14 t. It is part of all rocks that make up the earth's crust, and is also present in natural waters and living organisms. It does not form thick deposits. The bulk of uranium is found in acidic rocks with a high silicon content. The lowest concentration of uranium occurs in ultramafic rocks, the maximum in sedimentary rocks (phosphorites and carbonaceous shales). The oceans contain 10 10 t of uranium. The concentration of uranium in soils varies in the range of 0.7 - 11 ppm (15 ppm in agricultural soils fertilized with phosphorus fertilizers), in sea water 0.003 ppm.

Uranium is not found in free form in the earth. There are 100 known uranium minerals with a U content of more than 1%. In approximately one third of these minerals, uranium is tetravalent, in the rest it is hexavalent. 15 of these uranium minerals are simple oxides or hydroxyls, 20 are complex titanates and niobates, 14 are silicates, 17 are phosphates, 10 are carbonates, 6 are sulfates, 8 are vanadates, 8 are arsenates. Undetermined forms of uranium compounds occur in some carbonaceous shales of marine origin, lignite and coal, as well as in intergranular films in igneous rocks. 15 uranium minerals are of industrial importance.

The main uranium minerals in large ore deposits are represented by oxides (uranium pitch, uraninite, coffinitite), vanadates (carnotite and tyuyamunite) and complex titanates (brannerite and davidite). Titanates are also of industrial importance, for example, brannerite UTi 2 O 6 , silicates - cofinite U 1-x (OH) 4x , tantalonium bates and hydrated phosphates and uranyl arsenates - uranium micas. Uranium does not occur in nature as a native element. Due to the fact that uranium can exist in several stages of oxidation, it is found in a very diverse geological environment.

Applications of uranium

In developed countries, uranium production is mainly aimed at generating fissile nuclides ( 235 U and 233 U, 239 Pu) - fuel of industrial reactors intended for the production of both weapons-grade nuclides and components of nuclear weapons (atomic bombs and projectiles for strategic and tactical purposes, neutron bombs, hydrogen bomb triggers, etc.). In an atomic bomb the concentration 235 U exceeds 75%. In the rest of the world, uranium metal or its compounds are used as nuclear fuel in power and research nuclear reactors. A natural or low-enriched mixture of uranium isotopes is used in stationary reactors of nuclear power plants, a highly enriched product is used in nuclear power plants (sources of thermal, electrical and mechanical energy, radiation or light) or in reactors operating on fast neutrons. Reactors often use uranium metal, alloyed and unalloyed. However, some types of reactors use fuel in the form of solid compounds (for example, UO 2 ), as well as aqueous compounds of uranium or a liquid alloy of uranium with another metal.

The main use of uranium is the production of nuclear fuel for nuclear power plants. A pressurized water nuclear reactor with an installed capacity of 1,400 MW requires 225 tons of natural uranium per year to produce 50 new fuel elements, which are exchanged for the corresponding number of used fuel rods. To load this reactor, about 130 tons of SWU (separation work unit) and a cost level of $40 million per year are required. The concentration of uranium-235 in fuel for a nuclear reactor is 2–5%.

Uranium ores are still of some interest from the point of view of extracting radium from them (the content of which is approximately 1 g per 3 tons of ore) and some other natural radionuclides. Uranium compounds are used in the glass industry, for coloring glasses red or green color, or giving them a beautiful greenish-yellow hue. They are also used in the production of fluorescent glasses: a small addition of uranium gives the glass a beautiful yellow-green fluorescence.

Until the 1980s, natural uranium was widely used by dentists, including it in ceramics, which allowed them to achieve a natural color and induce original fluorescence in dentures and crowns. (A uranium jaw makes your smile brighter!) The original patent from 1942 recommends a uranium content of 0.1%. Subsequently, natural uranium was replaced by depleted uranium. This had two advantages - cheaper and less radioactive. Uranium was also used in lamp filaments, and in the leather and wood industries as a component of dyes. Uranium salts are used in mordant and staining solutions for wool and leather. Uranyl acetate and uranyl formate are used as electron-absorbing decorative agents in transmission electron microscopy, to increase the contrast of thin sections of biological objects, and for staining viruses, cells and macromolecules.

Uranates of the Na 2 U 2 O 7 type (“yellow uranyl”) are used as pigments for ceramic glazes and enamels (colored yellow, green and black, depending on the degree of oxidation). Na 2 U 2 O 7 also used as yellow paint in painting. Some uranium compounds are photosensitive. At the beginning of the twentieth century, uranyl nitrate was widely used as a vibrating agent to enhance negatives and produce tinted photographic prints (coloring positives brown or brown). Uranyl acetate UO 2 (H 3 COOH) 2 used in analytical chemistry - it forms an insoluble salt with sodium. Phosphorus fertilizers contain fairly large amounts of uranium. Uranium metal is used as a target in an X-ray tube designed to generate high-energy X-rays.

Some uranium salts are used as catalysts in chemical reactions, such as the oxidation of aromatic hydrocarbons, dehydration of vegetable oils, etc. Carbide 235 U alloyed with niobium carbide and zirconium carbide is used as fuel for nuclear jet engines(working fluid - hydrogen + hexane). Alloys of iron and depleted uranium ( 238 U) are used as powerful magnetostrictive materials.

In the national economy, depleted uranium is used in the manufacture of aircraft counterweights and anti-radiation screens for medical radiotherapy equipment. Depleted uranium is used to make transport containers for transporting radioactive cargo and nuclear waste, as well as products for reliable biological protection (for example, protective screens). In terms of absorption of γ-radiation, uranium is five times more effective than lead, which allows for a significant reduction in thickness protective screens and reduce the volume of containers intended for transporting radionuclides. Concrete based on depleted uranium oxide is used instead of gravel to create dry storage facilities for radioactive waste.

Depleted uranium is half as radioactive as natural uranium, mainly due to the removal of 234 U. It is used for alloying armor steel, in particular, to improve the armor-piercing characteristics of projectiles. When alloyed with 2% Mo or 0.75% Ti and heat treatment (rapid quenching of metal heated to 850°C in water or oil, further holding at 450° for 5 hours), uranium metal becomes harder and stronger than steel (tensile strength more than 1600 MPa, despite the fact that for pure uranium it is 450 MPa). Combined with its high density, this makes the hardened uranium ingot an extremely effective armor piercer, similar in effectiveness to the more expensive tungsten. The heavy uranium tip also changes the mass distribution of the projectile, improving its aerodynamic stability. When such a projectile (for example, an alloy of uranium with titanium) hits the armor, it does not break, but seems to sharpen itself, which achieves greater penetration. The process of armor destruction is accompanied by the grinding of a uranium pig into dust and its ignition in air inside the tank. Depleted uranium is used in modern tank armor.

Adding small amounts of uranium to steel increases its hardness without making it brittle and increases its resistance to acids. Particularly acid-resistant, even in relation to aqua regia, is an alloy of uranium and nickel (66% uranium and 33% nickel) with a melting point of 1200 O . Depleted uranium is also used as ballast in aerospace applications such as aircraft control surfaces. This material is used in high-speed gyroscope rotors, large flywheels, as ballast in space landers and racing yachts, and in oil drilling.

As already mentioned, uranium atomic bombs are not manufactured in our time. However, in modern plutonium bombs 238 U (including depleted uranium) is still used. It forms the shell of the charge, reflecting neutrons and adding inertia to the compression of the plutonium charge in an implosive detonation scheme. This significantly increases the weapon's effectiveness and reduces the critical mass (i.e., reduces the amount of plutonium needed to create a fission chain reaction). Depleted uranium is also used in hydrogen bombs, packing a thermonuclear charge with it, directing a strong flow of ultrafast neutrons to nuclear fission and thereby increasing the energy output of the weapon. Such a bomb is called a fission-fusion-fission weapon, after the three stages of explosion. Most of the energy output from the explosion of such a weapon comes from fission 238 U, producing significant amounts of radioactive products. For example, 77% of the energy during the explosion of a hydrogen bomb in the Ivy Mike test (1952) with a power of 10.4 megatons came from fission processes in the uranium shell. Since depleted uranium does not have a critical mass, it can be added to a bomb in unlimited quantities. In the Soviet hydrogen bomb (Tsar Bomba - Kuzkina's mother), exploded on Novaya Zemlya in 1961 with a yield of “only” 50 megatons, 90% of the yield was due to the thermonuclear fusion reaction, since the shell was made of 238 U was replaced by lead at the final stage of the explosion. If the shell were made (as it was assembled at the beginning) from 238 U, then the power of the explosion exceeded 100 megatons and the radioactive fallout amounted to 1/3 of the total of all world nuclear weapons tests.

Natural isotopes of uranium are used in geochronology to measure the absolute age of rocks and minerals. Back in 1904, Ernest Rutherford drew attention to the fact that the age of the Earth and the oldest minerals is of the same order of magnitude as the half-life of uranium. At the same time, he proposed to determine its age by the amount of helium and uranium contained in dense rock. But the drawback of the method soon became clear: extremely mobile helium atoms easily diffuse even in dense rocks. They penetrate into the surrounding minerals, and near the parent uranium nuclei there remains significantly less helium than follows according to the laws of radioactive decay. Therefore, the age of rocks is calculated by the ratio of uranium and radiogenic lead - the final product of the decay of uranium nuclei. The age of some objects, for example, micas, is even easier to determine: the age of the material is proportional to the number of uranium atoms that decayed in it, which is determined by the number of traces - tracks left by fragments in the substance. Based on the ratio of uranium concentration to track concentration, the age of any ancient treasure (vases, jewelry, etc.) can be calculated. In geology, a special term “uranium clock” was even invented. The uranium watch is a very versatile instrument. Isotopes of uranium are found in many rocks. The concentration of uranium in the earth's crust is on average three parts per million. This is enough to measure the ratio of uranium and lead, and then, using radioactive decay formulas, calculate the time that has passed since the crystallization of the mineral. Using the uranium-lead method, it was possible to measure the age of the oldest minerals, and using the age of meteorites, they determined the date of birth of the planet Earth. The age of the lunar soil is also known. The youngest pieces of lunar soil are older than the oldest terrestrial minerals.

The huge video panels installed in the Manege to announce Vladimir Putin's message to the Federal Assembly seemed unnecessary while they flashed slides with graphs of possible future GDP growth and life expectancy. But everything fell into place, and it became clear why Manezh, and why screens, when a movie with animation about the latest nuclear superweapon began. Putin himself acted as a television commentator and explained to the public in the country and in the world that everything shown and said should “sober up any potential aggressor.” Putin suggested that other countries “sooner or later” will also have modern weapons, but Russia already has them, and will become even better while the United States and others catch up. The next day, he explained that it was the United States that started the arms race when it withdrew from the ABM Treaty in 2002, and invited America to admit strategic defeat. “Russia could not be contained,” despite sanctions and NATO expansion, the president emphasized, noting that “fantastic” weapons are “not a bluff” and that it is necessary to negotiate on the basis of equality on a new world order.

Dmitry Peskov explained that “Russia will not be drawn into the arms race” and will not “symmetrically” respond to the deployment of missile defense by America, but will respond “asymmetrically” - deploying strike systems to overcome any missile defense system, “which is disproportionately cheaper to develop and serial production" It seems that they forgot to tell Peskov: the Ministry of Defense has already officially announced that next year it will begin the deployment of its own Russian missile defense system based on the S-500 Prometheus system, which should surpass the American one in all respects and eventually cover the entire territory of the Russian Federation.

The nuclear missile arms race is really unfolding - in all directions. Like half a century ago, both sides will forge both a missile defense shield and a rocket sword.

American diplomats, already demoralized by the rule of Donald Trump, were further upset by the message from Manege. Now, it seems, is not the time for meaningful diplomacy when the enemy is at the gates. But in the Pentagon the atmosphere is businesslike - they promise to protect the American people in any circumstances. Additional appropriations and weapons programs are now inevitable on both sides of the Atlantic.

The world is rapidly returning to the situation of the toughest confrontation of the Cold War in the mid-eighties, when the USSR was stuck in Afghanistan, American Pershing-2 missiles and ground-based Tomahawks were deployed in Europe, President Ronald Reagan announced a global missile defense program - the Strategic Defense Initiative (SDI , in the Russian version - SOI), and in Moscow, as now, an “asymmetric response” was announced, which, supposedly, is cheaper. It did not help -

The USSR lost in Afghanistan, lost the arms race, went bankrupt and burst. But many of the superweapons that Putin presented came from there - these are developments for overcoming SDI.

"Planning" combat unit (complex "Vanguard" from Putin’s presentation), which maneuvers at hypersonic speed when entering dense layers of the atmosphere, has been developed and studied for a long time on both sides of the Atlantic. Such a block can be installed on almost any launch vehicle, but the problem has always been that it does not collapse from overloads and, most importantly, is able to accurately home in on the target. The Americans were the first to develop and then deploy a revolutionary maneuvering homing ballistic combat unit 50 years ago on the Pershing 2 missile, which increased the accuracy of the hit to ten meters. The Soviet leadership was then so alarmed that it urgently agreed to sign the Intermediate-Range Nuclear Forces (INF) Treaty, just to get rid of the Pershings with their ultra-precision and flight time to Moscow in a few minutes.

Putin is now proud of the Avangard, which is supposed to be installed on the newest Yars ground-based mobile ICBMs. But it is completely unclear why: a capable American missile defense system does not exist in nature, and it is not known when, in how many decades, such a system may actually appear, and most importantly, what it will look like.

Avangard overcomes missile defense forces. Still from a video presentation. shown in Manege

Investing enormous amounts of money today in the deployment of programs to counter and overcome the current American missile defense system, designed solely to intercept a couple of primitive Korean or Iranian missiles, is a senseless waste.

Of course, Russian generals write completely different reports to the leadership, like their predecessors during the times of Reagan, Gorbachev and SDI. The General Staff then intimidated the political leadership of the USSR with a non-existent threat, and the country spent monstrous resources on an “asymmetric response.” The current bosses have forgotten nothing and learned nothing.

While Russia is spending effort and money on creating the Avangard, which will rush at wild speed across the sky, trying to “break through” the non-existent American missile defense system, the United States has already developed and can, in the context of a new arms race, deploy maneuvering homing ballistic warheads that do not only they will be able to break through the promising Russian missile defense system based on the S-500, but also seek out and hit moving strategic targets like the Yars ICBM, which was made mobile for the sake of invulnerability, and now may turn out to be defenseless (together with the Avangard) under the attack of ultra-precise and ultra-smart American ballistic and cruise missiles.

Putin also announced a successful test cruise missile with a “nuclear power plant” and a potentially unlimited flight range, which can fly to the United States, return and fly overseas again and, approaching from an unknown direction, “deceive” the American defense. Many experts rightly argue that it is impossible to place a nuclear reactor in a cruise missile - there are none so small, but even if it were possible, we would get a flock of flying potential Chernobyls.

Cruise missile "with a nuclear power plant." Screenshot of the broadcast “Russia 1”

A cruise missile is a small, expendable jet designed to crash into a target and explode. How then to test it, if even without a warhead (warhead), if hit, the onboard nuclear reactor could collapse, and then radioactive contamination of the area would occur?

But, of course, there is no “reactor” on board. A controlled nuclear chain reaction in a reactor is called that because it must be controlled, but this is impossible on an unmanned cruise missile. We are obviously talking about a so-called “atomic battery” or radioisotope source, in which energy is released due to nuclear decay without a chain reaction. “Atomic batteries” have been produced for a very long time in the USA, in the Russian Federation, and in other countries. For example, for spacecraft. And in the USSR they were also produced for autonomous lighthouses in the Far North.

But now, obviously, in Russia there are “nuclear batteries” that are an order of magnitude more powerful than before. Most likely, we are talking about the isotope uranium-232, which was produced from thorium in a fast neutron reactor. It appears that the same "innovative nuclear power plant" has been tested to create an "intercontinental underwater unmanned vehicle." Putin did not explain what it was, but said that the installation “with a volume one hundred times less than that of the installations of modern nuclear submarines, has a O more power and 200 times less time to reach maximum power.”

It is clear that this is nothing more than the same “atomic battery”, in which nuclear decay is constantly at maximum (which the Supreme Commander-in-Chief may not have been told about), but at the same time it is possible to regulate the engine power of the device by removing and dissipating part decay energy.

Pyotr Sarukhanov / Novaya Gazeta.

Uranium-232 has long been considered as the main, if not the only, radioisotope candidate for creating a “nuclear battery” of increased power for underwater and other drones and, by the way, for nuclear pumping of laser guns. It seems,

at least three of the six announced by Putin the latest developments- a cruise missile, an underwater drone and a combat laser with a mobile power plant - are essentially tied to a new type of “atomic battery”.

There is actually no big secret here - it is impossible to classify the periodic table. Uranium-232, its synthesis and decay, are well studied. Uranium-232 is relatively stable, with a half-life of 68.9 years. The high energy intensity of the decay of uranium-232 is due, among other things, to a cascade of relatively fast successive transmutations (up to lead), some of which produce penetrating gamma radiation. As a result, uranium-232 is not only expensive to produce, but extremely dangerous both for the personnel who work with it and for the environment.

It is unthinkable to use such an “innovative nuclear power plant” for civilian purposes. In general, making and testing an aircraft with a deadly radioactive core is criminal madness, possible only where people, land, water and air are ready to do anything for the sake of confrontation with the United States, hiding under the heading of the highest secrecy. By the way, according to Russian law, it is prohibited to classify anything related to the threat of radioactive contamination.

A radioactive “eternal” cruise missile is meaningless from a military point of view - the Americans can easily track it, including because it will “glow” brightly with gamma radiation: the aircraft cannot be made of cast lead. This device poses a greater threat to Russia itself than to America; it will be prohibitively expensive to produce, maintain, and dispose of.

The Americans, if they want, can deploy 10-20 thousand cruise missiles of various types, non-radioactive, high-precision and stealth, in response, and then what?

A laser gun with a nuclear filling, as one can judge, is a mobile Chernobyl on wheels, which moves through densely populated areas of the country and threatens disaster not at all for America.

Underwater nuclear drone from the same presentation

Underwater nuclear drone - “fundamentally the new kind strategic weapons, equipped with high-power nuclear munitions,” is, obviously, a self-propelled super torpedo “Status-6” developed by OJSC Central Design Bureau MT “Rubin”, seemingly accidentally declassified in November 2015, which can go underwater at a depth of up to 1 km , at a speed of up to 95 km/h for a range of up to 10 thousand km. The warhead of the product is up to 100 megatons.

The intention of the developers and the customer is that 10 or more of these “torpedoes” could explode underwater off the Pacific and Atlantic coasts of the United States, as well as in the Gulf of Mexico.

An explosion of enormous power would raise a monstrous artificial tsunami that could destroy the most populous and economically developed regions of America with a population of 150 to 200 million people.

In zones of extensive radioactive contamination, people and other warm-blooded creatures will not be able to exist for a hundred years or more. To do this, the developers will probably add all sorts of crap, such as cobalt, to a 100-megaton nuclear unit to create “dirty” explosions that guarantee maximum long-term radiation contamination.

To launch such drones, two special-purpose nuclear submarines “Belgorod” and “Khabarovsk” have already been completed, which are no longer suitable for anything. Special ships and ground infrastructure must also be built for the maintenance, operation and use of Status-6. The super torpedoes themselves, judging by the characteristics, must be made entirely of titanium alloy. All this will cost very much, and the fact that such “weapons” are absolutely immoral does not seem to worry at all, neither the leaders of the Russian military-industrial complex, nor the military, nor the political leadership.

Apparently, the President was told, and he repeated in the Manege, that autonomous super-torpedoes are practically invulnerable, since they are faster than any submarines and ships, and that in the whole world there are no means “that can resist them,” which, of course, is not true. “Status-6” has long been known to the potential enemy; it is even described in the new American nuclear doctrine (NPR-2018), published a few weeks ago.

American anti-submarine aircraft fly much faster than a nuclear drone floats, and there are Western torpedoes that surpass it in speed, and it will take several days to reach America, and it will even be impossible to recall it if something happens.

Weapons designed exclusively for untargeted mass destruction of civilians, based on maximum power explosion, monstrously expensive and immoral, is an echo of the fifties and sixties. It is inappropriate to brag about something like this and call it “fantasy.”

In 1815, the famous Swedish chemist Jens Jakob Berzelius announced the discovery of a new element, which he named thorium in honor of Thor, the thunder god and son of the supreme Scandinavian god Odin. However, in 1825 it was discovered that this discovery was a mistake. Nevertheless, the name was useful - Berzelius gave it to a new element, which he discovered in 1828 in one of the Norwegian minerals (now this mineral is called thorite). This element may have a great future ahead of it, where it will be able to play a role in nuclear energy that is not inferior in importance to the main nuclear fuel - uranium.

	Advantages and disadvantages
+	There is several times more thorium on Earth than uranium
+	No need to separate isotopes
+	Radioactive contamination during thorium mining is significantly less (due to shorter-lived radon)
+	Can use existing thermal reactors
+	Thorium has better thermomechanical properties than uranium
+	Thorium is less toxic than uranium
+	When using thorium, minor actinides (long-lived radioactive isotopes) are not formed.
-	During the irradiation of thorium, gamma-emitting isotopes are formed, which creates difficulties in fuel reprocessing

Distant relatives of the bomb

Nuclear energy, on which so much hope is now pinned, is a side branch of military programs, the main goals of which were the creation of atomic weapons (and a little later, reactors for submarines). As a nuclear material for making bombs, one could choose from three possible options: uranium-235, plutonium-239 or uranium-233.

This is what the thorium nuclear cycle looks like, illustrating the transformation of thorium into highly efficient nuclear fuel - uranium-233.

Uranium-235 is found in natural uranium in very small quantities - only 0.7% (the remaining 99.3% is isotope 238), and it must be isolated, which is an expensive and complex process. Plutonium-239 does not exist in nature; it must be produced by irradiating uranium-238 with neutrons in a reactor, and then separating it from the irradiated uranium. In the same way, uranium-233 can be obtained by irradiating thorium-232 with neutrons.

In the 1960s, it was planned to close the nuclear cycle for uranium and plutonium using approximately 50% of nuclear power plants using thermal reactors and 50% using fast reactors. But the development of fast reactors has caused difficulties, so that currently only one such reactor is in operation - the BN-600 at the Beloyarsk NPP (and another one has been built - the BN-800). Therefore, a balanced system can be created from thorium thermal reactors and approximately 10% of fast reactors, which will make up for the missing fuel for thermal ones.

The first two methods were implemented in the 1940s, but physicists decided not to bother with the third. The fact is that in the process of irradiation of thorium-232, in addition to the useful uranium-233, a harmful impurity is also formed - uranium-232 with a half-life of 74 years, the decay chain of which leads to the appearance of thallium-208. This isotope emits high-energy (hard) gamma rays, which require thick lead plates to protect against. In addition, hard gamma radiation disables control electronic circuits, which are impossible to do without in the design of weapons.

Thorium cycle

However, thorium has not been completely forgotten. Back in the 1940s, Enrico Fermi proposed producing plutonium in fast neutron reactors (more efficient than thermal ones), which led to the creation of the EBR-1 and EBR-2 reactors. In these reactors, uranium-235 or plutonium-239 is the source of neutrons that convert uranium-238 to plutonium-239. In this case, more plutonium can be formed than is “burned” (1.3-1.4 times), which is why such reactors are called “breeders”.

Another scientific group led by Eugene Wigner proposed its own breeder reactor design, but not with fast neutrons, but with thermal neutrons, with thorium-232 as the irradiated material. The reproduction rate decreased, but the design was safer. However, there was one problem. The thorium fuel cycle looks like this. By absorbing a neutron, thorium-232 turns into thorium-233, which quickly turns into protactinium-233, and it spontaneously decays into uranium-233 with a half-life of 27 days. And during this month, protactinium will absorb neutrons, interfering with the production process. To solve this problem, it would be good to remove protactinium from the reactor, but how to do this? After all, constant loading and unloading of fuel reduces operating efficiency to almost zero. Wigner proposed a very ingenious solution - a reactor with liquid fuel in the form of an aqueous solution of uranium salts. In 1952, a prototype of such a reactor, the Homogeneous Reactor Experiment (HRE-1), was built at Oak Ridge National Laboratory under the direction of Wigner's student, Alvin Weinberg. And soon an even more interesting concept appeared, ideal for working with thorium: a molten-salt reactor experiment. The fuel, in the form of uranium fluoride, was dissolved in a melt of lithium, beryllium and zirconium fluorides. MSRE operated from 1965 to 1969, and although thorium was not used there, the concept itself turned out to be quite workable: the use of liquid fuel increases operating efficiency and allows harmful decay products to be removed from the core.

A liquid salt reactor allows for much more flexible control of the fuel cycle than conventional thermal plants and uses fuel with the greatest efficiency, removing harmful decay products from the core and adding new fuel as needed.

Path of least resistance

Nevertheless, molten salt reactors (MSR) have not become widespread, since conventional thermal reactors using uranium turned out to be cheaper. The world's nuclear energy industry has taken the simplest and cheapest route, using proven pressurized water-water reactors (VVER), descendants of those designed for submarines, as a basis, as well as boiling water-cooled water reactors. Graphite-moderated reactors such as the RBMK represent another branch of the family tree - they descend from plutonium production reactors. “The main fuel for these reactors is uranium-235, but its reserves, although quite significant, are nevertheless limited,” Stanislav Subbotin, head of the systemic strategic research department of the Kurchatov Institute Research Center, explains to Popular Mechanics. — This issue began to be considered back in the 1960s, and then the planned solution to this problem was considered to be the introduction of waste uranium-238 into the nuclear fuel cycle, the reserves of which are almost 200 times greater. To do this, it was planned to build many fast neutron reactors that would produce plutonium with a breeding factor of 1.3-1.4, so that the excess could be used to power thermal reactors. The BN-600 fast reactor was launched at the Beloyarsk NPP - although not in breeder mode. Recently, another one was built there - BN-800. But to build an effective nuclear energy ecosystem, approximately 50% of such reactors are needed.”

All radioactive isotopes that occur naturally in nature belong to one of three families (radioactive series). Each such row is a chain of nuclei connected by sequential radioactive decay. The ancestors of the radioactive series are the long-lived isotopes uranium-238 (half-life 4.47 billion years), uranium-235 (704 million years) and thorium-232 (14.1 billion years). The chains end with stable isotopes of lead. There is another series starting with neptunium-237, but its half-life is too short - only 2.14 million years - so it does not occur in nature.

Mighty Thorium

This is where thorium comes into play. “Thorium is often called an alternative to uranium-235, but this is completely wrong,” says Stanislav Subbotin. — Thorium itself, like uranium-238, is not a nuclear fuel at all. However, by placing it in a neutron field in the most ordinary pressurized water reactor, you can obtain excellent fuel - uranium-233, which can then be used for the same reactor. That is, no alterations, no major changes to the existing infrastructure are needed. Another advantage of thorium is its abundance in nature: its reserves are at least three times greater than those of uranium. In addition, there is no need for isotope separation, since during associated mining only thorium-232 is found along with rare earth elements. Again, during uranium mining, the surrounding area is polluted by relatively long-lived (half-life 3.8 days) radon-222 (in the thorium series, radon-220 is short-lived, 55 seconds, and does not have time to spread). In addition, thorium has excellent thermomechanical properties: it is refractory, less prone to cracking and emits less radioactive gases when the fuel rod cladding is damaged. The production of uranium-233 from thorium in thermal reactors is approximately three times more efficient than plutonium from uranium-235, so the presence of at least half of such reactors in the nuclear energy ecosystem will close the cycle on uranium and plutonium. True, fast reactors will still be needed, since the breeding factor for thorium reactors does not exceed one.”

To produce 1 GW over the course of a year, it is required: 250 tons of natural uranium (containing 1.75 tons of uranium-235) is required to be mined; 215 tons of depleted uranium (including 0.6 tons of uranium-235) go into dumps; 35 tons of enriched uranium (of which 1.15 tons are uranium-235) are loaded into the reactor; spent fuel contains 33.4 tons of uranium-238, 0.3 tons of uranium-235, 0.3 tons of plutonium-239, 1 ton of decay products. 1 ton of thorium-232, when loaded into a molten salt reactor, is completely converted into 1 ton of uranium-233; 1 ton of decay products, of which 83% are short-lived isotopes (decay to stable ones in about ten years).

However, thorium also has one rather serious disadvantage. When thorium is irradiated with neutrons, uranium-233 becomes contaminated with uranium-232, which undergoes a decay chain leading to the hard gamma-emitting isotope thallium-208. “This greatly complicates the work on fuel processing,” explains Stanislav Subbotin. “But on the other hand, it makes it easier to detect such material, reducing the risk of theft. Moreover, in a closed nuclear cycle and with automated fuel processing, this does not matter much.”

Thermonuclear ignition

Experiments on the use of thorium fuel rods in thermal reactors are being conducted in Russia and other countries - Norway, China, India, and the USA. “Now is the time to return to the idea of ​​molten salt reactors,” says Stanislav Subbotin. — The chemistry of fluorides and fluoride melts is well studied thanks to the production of aluminum. For thorium, molten salt reactors are much more efficient than conventional water-water reactors, since they allow flexible loading and removal of decay products from the reactor core. Moreover, with their help it is possible to implement hybrid approaches, using not nuclear fuel as a source of neutrons, but thermonuclear installations - at least the same tokamaks. In addition, a molten salt reactor allows us to solve the problem with minor actinides - long-lived isotopes of americium, curium and neptunium (which are formed in irradiated fuel) by “afterburning” them in a garbage reactor. So, in the next few decades, we cannot do without thorium in nuclear energy.”

Plan:

Introduction

• 1 Formation and decay
• 2 Receipt
• 3 Application
Notes

Introduction

Uran-232(English) uranium-232) - radioactive nuclide chemical element uranium with atomic number 92 and mass number 232. Due to its long decay chain and higher specific energy release than most other isotopes, uranium-232 is a promising nuclide for use in radioisotope energy sources.

The activity of one gram of this nuclide is approximately 827.38 GBq.

1. Formation and decay

Uranium-232 is formed as a result of the following decays:

• β + -decay of nuclide 232 Np (half-life is 14.7(3) min):

• β − -decay of the nuclide 232 Pa (half-life is 1.31(2) days):

• α-decay of the nuclide 236 Pu (half-life is 2.858(8) years):

The decay of uranium-232 occurs in the following directions:

• α-decay in 228 Th (100% probability, decay energy 5,413.63(9) keV):

the energy of emitted α-particles is 5,263.36 keV (in 31.55% of cases) and 5,320.12 keV (in 68.15% of cases).

• Spontaneous fission (probability less than 1×10−12%);
• Cluster decay with the formation of nuclide 28 Mg (decay probability less than 5×10 −12%):

• Cluster decay with the formation of the nuclide 24 Ne (decay probability 8.9(7)×10 −10%):

2. Receipt

Uranium-232 is formed as a by-product during the production of uranium-233 by bombarding thorium-232 with neutrons. Along with the reaction of formation of uranium-233, the following side reactions occur in irradiated thorium fuel:

Due to the fact that the effective cross section for reactions (n, 2n) for thermal neutrons is small, the yield of uranium-232 depends on the presence of a significant number of fast neutrons (with an energy of at least 6 MeV).

If the nuclide thorium-230 is present in significant quantities in thorium fuel, then the formation of uranium-232 is supplemented by the following reaction, which occurs with thermal neutrons:

Since the presence of uranium-232 in irradiated fuel makes it difficult to safely work with it (see section “Application”), to reduce the formation of uranium-232 it is necessary to use thorium fuel with a minimum concentration of thorium-230.

3. Application

Uranium-232 is the founder of a long decay chain, which includes nuclides emitters of hard gamma rays:

232 U (α; 68.9 years) 228 Th (α; 1.9 years) 224 Ra (α; 3.6 days; emits a 0.24 MeV γ-quantum in 4.10% of decay cases) 220 Rn (α ; 56 s; γ 0.55 MeV, 0.114%) 216 Po (α; 0.15 s) 212 Pb (β−; 10.64 hours) 212 Bi (α; 61 s; γ 0.73 MeV, 6, 67%; γ 1.62 MeV, 1.47%) 208 Tl (β−; 3 min; γ 2.6 MeV, 99.16%; γ 0.58 MeV, 84.5%) 208 Pb (stable)

The rapid sequence of decays starting with radium-224 is accompanied by a significant amount of gamma radiation, with about 85% of the total gamma-ray energy produced by the decay of thallium-208, which emits predominantly 2.6 MeV gamma rays. This feature leads to the fact that the presence of uranium-232 as an impurity to uranium-233 is extremely undesirable, complicating the safety of working with it.

On the other hand, the high specific energy release makes this nuclide extremely promising for use in radioisotope energy sources.

Notes

1. 1 2 3 4 5 G. Audi, A.H. Wapstra, and C. Thibault (2003). “The AME2003 atomic mass evaluation (II). Tables, graphs, and references. - www.nndc.bnl.gov/amdc/masstables/Ame2003/Ame2003b.pdf.” Nuclear Physics A 729 : 337-676. DOI:10.1016/j.nuclphysa.2003.11.003 - dx.doi.org/10.1016/j.nuclphysa.2003.11.003.
2. 1 2 3 4 5 6 7 8 9 G. Audi, O. Bersillon, J. Blachot and A. H. Wapstra (2003). “The NUBASE evaluation of nuclear and decay properties - www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.” Nuclear Physics A 729 : 3–128. DOI:10.1016/j.nuclphysa.2003.11.001 - dx.doi.org/10.1016/j.nuclphysa.2003.11.001.
3. Properties of 232 U on the IAEA (International Atomic Energy Agency) website - www-nds.iaea.org/relnsd/tablenucsENSDF.jsp?query=3447
4. 1 2 Carey Sublette Nuclear Weapons Frequently Asked Questions - nuclearweaponarchive.org/Nwfaq/Nfaq6.html (English). nuclearweaponarchive.org.
5. Table of nuclides on the IAEA website - www-nds.iaea.org/relnsd/vchart/index.html

Transcript

1 92. URANIUM In addition to the three natural isotopes of uranium, ROSFOND includes data for uranium-233, uranium-236 and two much shorter-lived isotopes - uranium-232 and uranium Uranium-232 Radioactive. (T 1/2 =68.9 d). The decay chain of uranium-232 leads to the formation of thallium-208, which emits hard gamma radiation (2.7 MeV) during beta decay, which significantly complicates the radiation situation during operations with spent fuel. Modern libraries contain the following data estimates for uranium-232. FUND-2.2 score T.Ohsawa, T.Nakagawa, ENDF/B-VII.b2- score M. Chadwick, P.Young, 2005 JENDL-3.3 score T.Ohsawa, T Nakagawa, 1987 JEFF-3.1 score T.Mutsunobu, T. Kawano, Comparison of resonant integrals and thermal sections. Source σ s (eV) RI c σ f (eV) RI f ENDF/B-VII.b JENDL JEFF Muhabhab ± ± ± ±30 Large discrepancies in the estimates of resonance capture integrals are due to the lack of direct experimental data. Conclusion Despite the later date of the ENDF/B-VII.b2 estimate, its advantages over the JEFF-3.1 estimate, if any, are not obvious. In particular, JEFF-3.1 uses the 1994 Derrien estimate in the resonance region, while ENDF/B-VII.b2 uses the Muhabhab resonance parameters estimated a decade earlier. ROSFOND recommends accepting the assessment from JEFF-3.1. The spectra of 8-group delayed neutrons are replaced by the corresponding spectra for uranium-235. The group outputs are, of course, aligned with JEFF-3.1. The file also includes data on fission product yields from ENDF/B-VII.b2 1 (other libraries do not contain data on fission product yields for uranium-232). In the future, it would be desirable to perform a new assessment of the neutron data. The author of the conclusion is Nikolaev M.N. Contents of the ROSFOND file for 92-U-232 Replace!! MF = 1 General and special information about nuclide 1 T.R.England, B.F.Rider, ENDF-349,

2 MT = 451 header section MT = 452 total average fission neutrons MT = 455 delayed fission neutrons MT = 456 average prompt fission neutrons MF = 2 Resonance parameters MT = 151 resonance parameters section MF = 3 Neutron cross sections MT = 1 total MT cross section = 2 elastic scattering MT = 4 total inelastic scattering cross section MT = 16 reaction (n,2n) 92- U-231 MT = 17 reaction (n,3n) 92- U-230 MT = 18 all fission processes MT = inelastic scattering with excitation of discrete levels MT = 91 inelastic scattering with excitation of a continuum of levels MT = 102 radiative capture: reaction (n,gamma) 92- U-233 MT = 251 average cosine of the angle of elastic scattering in the laboratory. coordinate system MF = 4 Angular distributions of secondary neutrons MT = 2 elastic scattering MT = 16 reaction (n,2n) 92-U-231 MT = 17 reaction (n,3n) 92-U-230 MT = 18 all fission processes MT = inelastic scattering with excitation of discrete levels MT = 91 inelastic scattering with excitation of a continuum of levels MF = 5 Energy distributions of secondary neutrons 2

3 MT = 16 reaction (n,2n) 92- U-231 MT = 17 reaction (n,3n) 92- U-230 MT = 18 MT = 91 all fission processes inelastic scattering with excitation of a continuum of levels Uranium-233 Radioactive. (T 1/2 =1.592*10 5 years). Alpha decays into thorium-229 (T 1/2 = 7880 years). It is a promising nuclear fuel (the basis of the uranium-thorium fuel cycle). Modern libraries contain the following data estimates for uranium-233. FOND-2.2 and BROND-2 assessment by Sukhoruchkin and Klepatsky, ENDF/B-VII.b2 - assessment by Young, Hadwick, Talou, Leal, Derrien, JENDL-3.3 and JEFF-3.1 assessment by T. Mutsunobu, T. Kawano, In addition A recent (2005) assessment by V. Maslov is available. 1. The region of thermal neutrons and the region of allowed resonances. Table 1 shows the estimated thermal cross sections and resonant capture and fission integrals, as well as the number of prompt fission neutrons, in comparison with estimates of experimental data by Muhabhab and Tellier, as well as with a consensus estimate of thermal cross sections made by the international standards group in 2005. 2 In the latter The assessment takes into account all differences in the reference values ​​used to obtain the final results. Table 1. Thermal cross sections and resonance integrals. Source σ с (RI c σ f (eV) RI f ν t eV) FUND ENDF/B-VII.b JENDL Maslov Muhabhab ± ± ± ± ±0.004 Tellier ± ± ± ±17 Standards ± ± ± As we see, there are discrepancies in the accepted The estimated data on cross sections and resonance integrals do not go beyond the estimated errors of the totality of experimental data. Descriptions of the region of allowed resonances differ significantly. In the estimate of Sukhoruchkin and Klepatsky, this region extends to 100 eV, contains 178 resonances, the energy of the last eV. In the future, this assessment will not be considered as clearly outdated. 2 Data reported by members of the international group from Russia V. Pronyaev, S. Badikov and E. Gai 3

4 In the estimate of Mitsunobi and Kawano, the boundary of the region of allowed resonances is -150 eV. The parameters of 190 resonances with a maximum energy eV are given. In the estimate adopted in ENDF/B-VII.b2, the boundary of the region of allowed resonances is 600 eV; in this region the parameters of 738 resonances are given. In addition, the parameters of 16 bound states and 16 resonances lying above this region are specified. This assessment was also accepted by Maslov. The resonance parameters were assessed taking into account new measurements of the total cross section and fission cross section, carried out with very high resolution at the ORELA accelerator in using the well-known SUMMY program, which describes a set of experimental data using the least squares method based on the R-matrix formalism 3. Fig. 1 shows the increasing sum of the number of resonances, and Fig. 2 the increasing sum of the reduced neutron widths. Thin lines show linear approximations to the initial sections (up to 400 eV) of these curves. From Fig. 2 we can conclude that there is practically no missing resonance in the region under consideration. Figure 2 shows that in the eV range there is a shortage of reduced neutron widths, and then, above 500 eV, the same rate of increase in the sum of widths remains the same. The lack of resonances with large widths, of course, is not evidence of level skipping, but it casts doubt on the correctness of determining the resonance parameters in the specified interval. Despite this, the estimate of resonance parameters from ENDF/B-VII.b2 is, of course, the most complete and reliable, and ROSFOND should accept this estimate. Number of resonances Energy, eV ENDF/B-V II Fig.1. Increasing sum of the number of resonances 3 L. C. Leal, H. Derrien, J. A. Harvey, K. H. Guber, N. M. Larson and R. R. Spencer, R-Matrix Resonance Analysis and Statistical Properties of the Resonance Parameters of U-233 in the Neutron Energy Range from Thermal to 600 ev , ORNL/TM-2000/372, March

5 C ummah<Гn0>"Energy, eV Fig. 2. Sum of the reduced neutron widths. 2. Region of unresolved resonances. ENDF/B-VII In ENDF/B-VII.b2, the region of unresolved resonances extends to 40 keV; the structure of the cross sections is described by the parameters s-, p- and d-waves; the file of average resonance parameters is recommended only to take into account the resonant self-shielding of cross sections, the average cross sections themselves are specified in the file MF = 3. In JENDL-3.3 (and therefore in JEFF-3.1), the region of unresolved resonances extends only to 30 keV; parameters are specified only s- and p-waves, but these parameters are recommended for calculating not only self-shielding factors, but also average cross sections. In Maslov’s estimate, the region of unresolved resonances extends to the threshold of inelastic scattering keV. The parameters of s-, p- and d-waves are given, with with the help of which the average cross sections are also described. This is an obvious advantage of Maslov's estimate, however, it is necessary to consider how the calculated or given average cross sections are consistent with the available experimental data. In Fig. 3, the estimated data for the total cross section are compared with the experimental data. In JENDL-3.3, the experimentally established gross U-233 Total URR+Fast Region Cross section, barn ENDF/B JENDL=JEFF MASLOV Fulwood57 Stupegia62 Pattenden E+02 1.E+03 1.E+04 1.E+05 Energy, ev Fig.3. Total cross section in the region of unresolved resonances 5

6, the structure of the total cross section is reproduced by varying the average parameters of the distances between resonances and neutron widths (for all values ​​of J and parity). Oils do not introduce these artificial variations and therefore no structure of the middle section appeared in him. In general, the average cross section in this estimate is approximately one barn (~5%) lower than in the previous two, which, however, does not go beyond the scatter of experimental data. Let us now consider the data on partial sections. In Fig. Figure 4 compares the estimated fission cross sections with experimental data Cross section, barn U-233 Fission URR ENDF/B JENDL=JEFF MASLOV Guber2001 Nizamuddin E+02 Energy, ev 1.E+03 Fig. 4a. Fission cross section in the region of unresolved resonances 15.0 Cross section, barn U-233 Fission URR JENDL=JEFF Guber2001 Nizamuddin74 ENDF/B MASLOV E+03 Energy, ev 1.E+04 Fig. 4b. Fission cross section in the region of unresolved resonances 5.0 U-233 Fission URR+Fast Region Cross section, barn JENDL=JEFF Guber2001 Nizamuddin74 MASLOV ENDF/B E+04 Energy, ev 1.E+05 Fig. 4c. Fission cross section in the region of unresolved resonances 6

7 The presentation of data in the cited works is too detailed: the scatter of points does not reflect either the detailed resonance structure (the resolution is insufficient for this) or the gross structure. In Fig. 4d the estimated data are compared with the experimental ones in a narrow range from 600 to 800 eV. The experimental data were averaged over subintervals and the averaging results are presented in histograms. As can be seen, the gross structure of the fission cross section, displayed in the estimates ENDF/B-VII.b2 and JENDL-3.3, only qualitatively reflects the results of measurements that do not agree with each other in detail. This casts doubt on the appropriateness of describing the structure of the fission cross section in this energy range Cross section, barn ENDF/B JENDL=JEFF MASLOV 5.0 Guber2001 Nizamuddin74 Guber2001 Nizamuddin E+02 7.E+02 8.E+02 Energy, ev Fig. 4d. Fission cross section in the region of unresolved resonances In Fig. 5, estimates of the capture cross section are compared with Weston's data, the only ones available in EXFOR in the region of unresolved resonances. The estimate adopted in ENDF/B-VII.b2 clearly overestimates the capture cross section. The file description contains no references to any additional experimental data in this area. In connection with all of the above, it seems appropriate to include in ROSFOND Maslov’s assessment of data in the region of unresolved resonances U-233 Capture URR+Fast Region ENDF/B JENDL=JEFF MASLOV Cross section, barn Weston E E E E+03 Energy, ev Fig.5. Capture cross section in the region of unresolved resonances 7

8 3. Sections outside the resonant region In Fig. 6. Estimates of the total cross section are compared with the available experimental data. The discrepancies between the estimates are significantly less than the scatter of experimental data, so we can state that they are all equally good. Cross section, barn ENDF/B MASLOV Green73a Poenitz83 Poenitz78 JENDL=JEFF Foster Jr71 Green73b Poenitz E E E E E+06 Energy, ev 10.0 Fig. 6a. Full section. 9.0 Cross section, barn ENDF/B JENDL=JEFF 5.0 MASLOV Green73a Foster Jr71 Green73b 4.0 Poenitz83 1.E+06 1.E+07 Energy, ev Fig.6b. Full section. In Fig.7. Estimates of the fission cross section are compared with experimental data. Here the situation is not so good: the spread of experimental data 8

9 Cross section, barn JENDL=JEFF Tovesson2004c Guber2001 Shcherbakov2001 MASLOV ENDF/B Meadows74 Poenitz E+05 1.E+06 1.E+07 Energy, ev Fig. 7a. Fission cross section 9

10 Cross section, barn JENDL=JEFF Tovesson2004c Guber2001 Shcherbakov2001 MASLOV ENDF/B Meadows74 Poenitz E+05 1.E+06 1.E+07 Energy, ev 2.8 Fig. 7b. Fission cross section Cross section, barn JENDL=JEFF MASLOV Shcherbakov2001 ENDF/B Pankratov63 Medous Zasadny-84 Arlt-81 Alkhazov-83 Adamov E E E E E E+07 Energy, ev Fig. 7c. Division section. Far exceeds the errors attributed to them. As a result, the discrepancy between the estimated data and the experimental data reaches ±5% in the vicinity of 1 MeV and 8 MeV. Below 175 keV, Maslov's estimate is in better agreement with experimental data; above that, the ENDF/B-VII.b2 estimate has an advantage. Note, by the way, that when performing this assessment, the results of numerous measurements of the ratios of the fission cross sections of uranium-233 and uranium-235 were normalized to the standard fission cross section of uranium-235, adopted in 2005 (and included in ROSFOND). In Fig. 8. The estimation results are compared with the only experimental data from Hopkins. The ENDF/B-VII.b2 data goes straight to the experimental points; the other two estimates differ from them by an amount of the order of error. There are no experimental data on inelastic neutron scattering from uranium-233. Figure 9 compares the results of the discussed estimates. Near the threshold, the differences between them are quite large. The minimum in the total inelastic scattering cross section in the ENDF/B-VII.b2 estimate lies at 700 keV, i.e. precisely at the threshold of inelastic scattering with excitation of a continuous spectrum of levels adopted in this estimate. In two other estimates, this threshold is 100 keV lower. To clarify the situation in Fig. Figure 8 shows the total inelastic scattering cross section from the uranium-233 file from ENDF/B-VI. It's 10

11 is significantly lower than modern estimates, but like them, no peak is observed at the threshold. 1.E+00 Cross section, barn 1.E-01 1.E-02 ENDF/B JENDL=JEFF MASLOV Hopkins62 1.E-03 1.E+04 1.E+05 1.E+06 1.E +07 Energy, ev Fig.8. Capture section 2.0 U-233 Inelastic 1.5 Cross section, barn E E E E+07 Energy, ev Fig.9. Total inelastic scattering cross section Cross section, barn ENDF/B-VII MT=3 ENDF/B-VII MT=2 JENDL-3.3 MT=2 Maslov MT=2 Maslov MT=3 U-235 MT= E E E E+07 Energy, ev Fig. 10. Elastic scattering cross sections (MT=2) and total inelastic interaction cross sections (MT=3) 11

12 In Fig. Figure 10 shows the estimated cross sections for elastic scattering and the total cross section for inelastic interactions. 4 It can be seen that the anomaly in the cross section for inelastic scattering was also reflected in the behavior of the total cross section for inelastic interactions, which differs significantly from Maslov’s estimate. The presence of this anomaly, which does not occur for uranium-235 (the cross section of inelastic interactions for which is also shown for comparison in Fig. 10), raises doubts about the correctness of the estimate adopted in ENDF/B-VII.b2. Figure 11 shows data on the reaction cross sections (n,2n) and (n,3n). Cross section, barn ENDF/B(n2n) JENDL(n2n) MASLOV(n2n) ENDF/B(n3n) JENDL(n3n) MASLOV(n3n) E E E E+07 Energy, ev Fig. 11. Reaction cross sections (n,2n) and (n,2n). There are no differential experimental data for these reactions. The discrepancies in estimates above 16 MeV are large. Indirectly in favor of the ENDF/B-VII.b2 assessment is the fact that it was carried out up to 30 MeV, where the role of reactions (n, xn) is very significant and, undoubtedly, the calculation of their cross sections required increased attention from the evaluators. Reaction (n.4n) about 19 MeV. Its cross section, even at 20 MeV, is a fraction of a millibarn. When neutrons interact with uranium-233, reactions (n,p) and (n,α) are possible at all energies. Due to the high Coulomb barrier, the cross sections of these reactions are small: even at 20 MeV, the cross section of the first of them, according to EAF-2003, is 70 millibarns; the second - 5 millibarns. Nevertheless, it seems appropriate to include the cross sections of these reactions in ROSFOND. Summarizing the above, we can conclude that ROSFOND should accept the neutron cross sections estimated by Maslov, which, as a rule, being close to the estimate from ENDF/B-VII.b2, do not have an anomalously high cross section for inelastic scattering in the region below 700 keV. 4. Numbers of secondary neutrons and their energy-angular distributions 4.1. Number of fission neutrons The estimated numbers of neutrons for fission of uranium-233 by thermal neutrons are given in Table 1. The value adopted in ENDF/B-VII.b2 exceeds the recommendation of the standards group (based on a joint assessment of all data depending on ν p (233 U)) by three standard deviations assigned to this value. 4 The MT=3 cross section is not specified in JENDL-3.3 and is not easy to obtain, since the components are specified on different energy grids. For the same reason, the Maslov cross section MT=3 is given only up to the reaction threshold (n,2n). 12

13 This difference is exactly equal to the delayed neutron contribution assumed in this assessment: ν d = Thus, when assessing the data for ENDF/B-VII.b2, the value recommended by the international standards group as ν t was considered as ν p. The JENDL-3.3 score is 2.6 standard deviations below the recommended value. Maslov's estimate is also lower, but only by 1 standard deviation. It seems appropriate to adopt in ROSFOND the value recommended by the international standards group, i.e. ν t = The number of delayed neutrons according to the ENDF/B-VII.b2 estimate at low energies is equal to; according to the JENDL estimate and almost the same amount according to Maslov. If we take ν d = 0.0068, then for ν р we obtain a “round” number. In Fig. Figure 12 shows the energy dependences of ν р according to various estimates in comparison with experimental data. All given experimental data are renormalized either to ν р (252 Cf) = 3.7606, or to ν р (233 U;0.0253 eV) = 2.490, depending on the monitor used NUbar ENDF/B JENDL 2.5 MASLOV Smirenkin-58 Nurpeisov-73 Nurpeisov- 75 Gwin-86 Kolosov-72 Standard E E E E E E E E E E E+06 Energy, ev Fig. 12a. Number of prompt fission neutrons. The broken course of ν p with energy, accepted by Maslov, is not justified by experimental data. In general, up to 1.5 MeV, ν р accepted in this estimate seems to be underestimated. At higher energies, the data are shown in Fig. 12b NUbar 4.0 ENDF/B JENDL 3.5 MASLOV Smirenkin Nurpeisov-73 Nurpeisov Gwin-86 Kolosov E E E E E E E E E E E+07 Energy, ev Fig. 12b. Number of prompt fission neutrons. 13

14 In this area, ENDF/B-VII.b2 seems to be the best estimate. It can also be accepted at lower energies if we replace the value of ν р in the thermal region with (see Fig. 12a). In Fig. Figure 13 shows the estimated energy dependences ν d. For comparison, those for uranium-235 and plutonium-239 are given. A comparison shows that the energy dependence ν d adopted in ENDF/B-VII.b2 is erroneous. There is no physical basis for her behavior like this. On the contrary, the decrease in ν d with energy, manifested in all other estimates, is explained by the appearance of additional chances of fission. In ROSFOND, it is advisable to accept the energy dependence ν d from JENDL-3.3, renormalizing it to the accepted value of ν d in the thermal region NUbar ENDF/B JENDL-3.3 Maslov U-235-ROSFOND Pu-239-ROSFOND E E E E E E E E E E E+07 Energy, ev Fig. 13. Energy dependence of the yield of delayed neutrons 4.2. Spectra of fission neutrons. The spectra of prompt fission neutrons in the estimates under consideration are described in significantly different ways. In ENDF/B-VII.b2 these spectra are given by the Watt form with parameters a(e) and b(e) depending on the energy of neutrons E causing fission: 2exp(-ab/4) χ (E) = exp(E / a)sh be πa 3 b The nature of this dependence can be seen from Fig. 14, which shows the dependence of the average energy of fission neutrons< E >= a(3/2 + ab/4) as a function of E. The header section states that the fission neutron spectra are assumed to be as estimated by JENDL-3.3. This is obviously not entirely correct, since in the JENDL-3.3 estimate the spectra of prompt fission neutrons are defined differently, namely by functions defined at 164 points at each of 7 initial energies. Fission spectra are determined similarly in Maslov's estimate, but the spectra are specified at 326 points at each of 22 initial energies in the range up to 20 MeV. 14

15 Average fission neutron energy 2.40 ENDF/B-VII, E E E E E+07 Energy, ev Fig. 14. Energy dependence of the average energy of fission neutrons The description of the JENDL-3.3 file does not say anything about how the spectra of prompt fission neutrons were obtained. The description of Maslov’s file says the following: “The spectra of prompt fission neutrons (SMNF) were calculated using the semi-empirical model 5. The spectra of neutrons emitted before fission in the (n, n f), (n, 2nf) and (n, 3nf) processes were calculated using the Hauser statistical model - Feshbach, taking into account pre-equilibrium processes. The quality of the description was checked on the basis of experimental data from Starostov-83, Starostov-85, Lajtai-85, and Miura-02. Calculations indicate a decrease in the average energy of fission neutrons when the reaction thresholds (n, n f), (n,2nf) and (n ,3nf). The spectra of neutrons emitted by fission fragments were calculated as a superposition of two Watt spectra corresponding to a light and heavy fragment, differing in parameters determining the average energy. In this case, the difference in the kinetic energies of the fragments and the dependence of these energies on the moment carried away by the neutrons emitted before fission were taken into account. It was this mechanism that caused the decrease in the average energy of fission neutrons when the thresholds of fission with preliminary neutron emission were exceeded.” The justification given is fully consistent with the modern understanding of the mechanisms of fission neutron emission, and the fact that the assessment made it possible to describe experimental data increases their reliability. True, almost all spectra were measured for fission by thermal neutrons, and only Muir’s data were obtained at an energy of 550 keV, which still lies significantly below the reaction threshold (n,n f). Be that as it may, the spectra given in Maslov's estimate seem to be the most reliable. Let us now discuss data on delayed neutrons. In the ROSFOND library, as in JEFF-3.1, a universal 8-group representation of data on delayed neutrons is adopted; the definition of groups is the same for all fissile nuclei: each of them includes a certain group of precursors with close half-lives. Due to this, the group decay constants do not depend on the fissile nucleus. The neutron spectra of each group of precursors do not depend on the fissile nucleus. However, the total yield of delayed neutrons and the fraction of groups, of course, depend both on the fissile nucleus and on the energy of the neutrons causing fission. As with other fissile nuclei, the 8-group rating from JEFF-3.1 is adopted for uranium-233, with the following exceptions, however. 5 Maslov V., Porodzinskij Yu., Baba M., Hasegawa A., Kornilov N., Kagalenko A., Tetereva N.A. INDC(BLR)-...,IAEA, Vienna 15

16 1. The number of delayed neutrons emitted during fission by thermal neutrons is assumed to be equal (in JEFF-3.1 it is equal; in ENDF/B-VII.b, in Maslov). The energy dependence of this number is the same as in the JEFF-3.1 estimate (see Fig. 13). 2. The spectra of groups of delayed neutrons are assumed to be the same as for uranium-235 (see paragraph below) and for all other fissile nuclei. However, the outputs of each of the 8 groups are assumed to be the same as in JEFF-3.1, i.e. based on the recommendations of the work Spectra and angular distributions of scattered neutrons and neutrons of reactions (n,xn) Figure 15 compares the estimated values ​​of the first three moments of the angular distributions of elastically scattered neutrons. The estimates are very close to each other. All of them were obtained by calculation. EXFORe contains the results of only one unpublished work, Haoaut-82, in which the angular distributions of neutrons with energies of 0.7 and 1.5 MeV were measured. At these energies, it is very difficult to distinguish elastically scattered neutrons from inelastically scattered neutrons at low levels. IN brief description, given in EXFORe, the procedure for separating these processes is not described; it is only said that the correction for inelastic scattering introduced by the author ranged from 5 to 35% at both 0.7 MeV and 1.5 MeV. Since there are no discrepancies in the estimates at the mentioned energies, and the experiment is not highly reliable, a rather labor-intensive comparison with it was considered unnecessary. It is advisable to include in ROSFOND the estimate from ENDF/B-VII.b2, which, as a rule, occupies an intermediate position. Angular momentum value ENDF/B-VII 0.1 JENFF-3.1 Maslov E E E E+07 Energy, eV Fig.15. Angular moments of distribution of elastically scattered neutrons: solid curves 1st moment (average cosine of the scattering angle), dashed curves 2nd moment, dotted curves 3rd moment. 6 Spriggs, Campbell and Piksaikin, Prg Nucl Eng 41,223(2002) 16

17 As for the spectra of inelastically scattered neutrons, below the threshold of excitation of the continuum of levels they are determined by the completeness of accounting for the excited levels of the target nucleus. In this regard, Maslov's estimate has a certain advantage over JENDL-3.3: it takes into account all the levels specified in the PCNUDAT 2 database, while in JENDL-3.3 the excitation of some levels with energies from 400 to 600 keV is not described. In both estimates, the excitation of the level continuum is described starting from 600 keV, i.e. directly following the region of discrete levels. We do not discuss the estimate adopted in ENDF/B-VII.b2 here because of the doubts it raises about the correctness of the description of the energy behavior of the total inelastic scattering cross section (see paragraph 3 above). Spectra of neutrons scattered with excitation of a continuum of levels Figure 16 shows the spectra of neutrons that have experienced inelastic scattering with excitation of a continuum of levels of the target nucleus. Data are given for initial energies of 6 MeV, 10 MeV and 14 MeV. At 6 MeV, i.e. below the reaction threshold (n,n f) Maslov's spectrum is significantly harsher than the others: obviously, the proportion of pre-equilibrium neutrons emitted in it is higher. At 10 MeV, estimates of the neutron spectra differ significantly. In the spectrum adopted in JENDL-3.3, neutrons with energies below 3.7 MeV are completely absent, i.e. it is assumed that the emission of such slow neutrons is always followed by fission. In the ENDF/B-VII.b2 estimate, a tail of relatively slow neutrons is present, and in the Maslov estimate, this tail also exhibits a maximum in the region of the order of 1 MeV. At 14 MeV, there are no neutrons with energies below 5 MeV in the JENDL-3.3 spectrum, but the probability of emitting neutrons with energies of 6-8 MeV is significantly higher than in the other two estimates. The ENDF/B-VII.b2 and Maslovsky spectra above 7 MeV are close, but the Maslovsky spectrum has a long tail of slow neutrons. For some reason, after the emission of slow neutrons, neither the (n,2n) reaction nor fission occurs. Probability/MeV 9.0E E E E E E E E E E E E E E E E E E E+00 Spectra (n,n") 0.0E E E E E E E E+07 Energy, eV ENDF/B-VII; 6 MeV ENDF/B-VII; 10 MeV ENDF/B-VII; 14 MeV JENDL-3.3 ; 6 MeV JENDL-3.3; 10 MeV JENDL-3.3; 14 MeV Maslov; 6 MeV Maslov; 10 MeV Maslov; 14 MeV Fig. 16. Comparison of the spectra of neutrons inelastically scattered with excitation of the level continuum. 17

18 In Fig. Figure 17 compares estimates of the neutron spectra of the (n,2n) reaction for two initial energies of 10 and 14 MeV. The differences in estimates are quite large, especially at 14 MeV. The discrepancies indicate an unfavorable state of affairs with the assessment of spectra, and, therefore, cross sections of processes occurring through different channels and in different ways (pre-equilibrium neutron emission and ordinary evaporation, fission after the emission of one or two neutrons in one way or another). Since there are no significant differences in the estimates of the total fission cross section, compensation occurs for differences in the assessment of the contributions of various reaction mechanisms. Spectra (n,2n) Prob/MeV 1.0E E E E E E E E E E E-07 ENDF/B-VII; 10 MeV ENDF/B-VII; 14 MeV JENDL-3.3; 10 MeV JENDL-3.3; 14 MeV Maslov; 10 MeV Maslov; 14 MeV 0.0E E E E E E E E E E+06 Energy, eV Fig.17. Comparison of neutron spectra from the (n,2n) reaction. From what has been considered, it is clear that the assessment of the spectra of continuum reactions in ENDF/B-VII.b2 is in some sense intermediate, and this gives rise to the temptation to choose it for ROSFOND. However, problems may arise when further validating a composite file in which cross sections are taken from one assessment and spectra from another. Since it was decided to take the cross sections from, then the spectra should be taken in accordance with this estimate. Note that the spectra data in ENDF/B-VII.b2 are presented (unlike the other two) in the MF=6 ​​file format, i.e. spectra are given taking into account correlations between energy and scattering angle. This correlation, however, is described in a simplified manner using the semi-empirical Kalbach-Mann taxonomy. In addition to the spectra of neutrons, the spectra of recoil nuclei are also described (for which there is no practical reason), but the spectra of photons emitted in continuum processes are not described. This is another evidence of a bad assessment, which should be eliminated later when revising the assessment. 5. Data on the production of photons in neutron reactions Neither the Maslov estimate nor the JENDL-3.3 estimate provides data on the production of photons. JEFF-3.1 includes photon production data taken from ENDF/B-VI (estimated by Stewart and Weston 1978). In ENDF/B-VII.b2 with revised data on gamma rays in radiative capture. So 18

19 There is practically no choice of assessments. Let's look at what the available estimated data is based on. Total inelastic scattering: MT=4. Since Stewart and Weston's estimate individually took into account the excitation of only the first four levels of the target nuclei, the photon spectrum describes transitions only between these four levels. The spectrum of photons produced upon excitation of the continuum is described by a continuous spectrum of photons, which is assumed to be the same as for plutonium. Above 1.09 MeV, the multiplicity for MT=4 is assumed to be zero. The possibility of a more correct description of photon spectra, which opened up in connection with the explicit description of a much larger number of levels (28 in ENDF/B-VII.b2, 25 in Maslov, 25 in JENDL-3.3) has not been implemented anywhere. Photons emitted during fission: multiplicity up to 1.09 MeV corresponds to the estimate of Hoffmann 8 ; The spectra themselves are taken to be the same as for plutonium. Above 1.09 MeV, the multiplicity is taken to be zero. The multiplicity of photon emission upon capture below 1.09 MeV is arbitrarily taken to be equal to The spectrum is taken to be the same as for plutonium-239, corrected for differences in reaction energies. Above 1.09 MeV, the cross section for the production of photons during inelastic interactions is given (file MF=13) and the normalized spectrum (in file MF=15) is the same as for plutonium. In ENDF/B-VII.b2, the multiplicity of photon emission during capture and their spectra are calculated using GNASH program. All other data is accepted as described above, i.e. from ENDF/B-VI.7. ROSFOND should include data on photon production from ENDF/B-VII.b2. With further revisions of the file and, especially, in the case of a decision to include the MF=6 ​​file, a more correct calculation of the photons produced in neutron reactions should be carried out. Conclusion Based on the above, it seems appropriate to create a combined file for ROSFOND as follows. 1. Take files MF=2 and MF=3 from Maslov’s estimate. In the region of allowed resonances, as noted, they coincide. 2. Take the energy dependence of fission neutrons in accordance with ENDF/B-VII.b2, replacing the value at thermal energy with i.e. so that the total number of fission neutrons coincides with the value recommended by the standards group Include data on reaction cross sections (n.p) and (n,alfa) from EAF Reduce the elastic scattering cross section accordingly, and in the region of allowed resonances introduce a total cross section equal to the sum of (n.p) and (n,alfa). 4. The number of delayed fission neutrons at the thermal point is assumed to be equal, and its energy dependence is in accordance with the JEFF estimate. Also, the 8-group description of delayed neutrons from JEFF is accepted. The spectra of delayed neutrons are assumed to be the same as for uranium-235, and the relative yields of the groups are in accordance with JEFF ENDF/B-VI. 7, MAT= D. C. Hoffmann and M. M. Hjffmann, Ann. Rev. Nucl. Sci. 24, 151 (1974) 19

20 6. Take the angular distributions of elastically scattered neutrons in accordance with the estimate ENDF/B-VII.b2, the remaining angular distributions in accordance with Maslov’s estimate. 7. Accept the spectra of prompt fission neutrons and continuum spectra of other reactions in accordance with Maslov’s assessment. 8. Include data on fission product yields as estimated by R. Mills (JEFF). 9. Accept data on the production of photons in neutron reactions in accordance with ENDF/B-VII.b2. Author of the recommendation Nikolaev M.N. File content 20

21 92.3. Uranium-234 Content in natural mixture % Radioactive. (T 1/2 =2.455*10 5 years). Alpha decays into thorium-230 (T 1/2 =7.54*10 4 years). Modern libraries contain the following data estimates for uranium-233. FOND-2.2 estimate T. Ohsawa, M. Inoue, T. Nfkagawa, 1987 ENDF/B-VII.b2 - estimate Young, Hadwick, JENDL-3.3 estimate T. Watanabe, 1987 JEFF-3.1 estimate Maslov, In estimates accepted in ENDF/B-VII. b2 and in JEFF-3.1 the boundary of the region of allowed resonances, containing 118 resonances and one bound state, is 1500 eV. The positions of the resonances coincide exactly. The widths of the resonances, however, differ. In ENDF/B-VII.b2 they correspond to the data of Muhabhab-84; Maslov uses a later estimate from JENDL-3.2. In Fig. 1 shows the increasing sum of the number of resonances, in Fig. 2 is the sum of the reduced neutron widths. From the graphs we can conclude that above 900 eV some of the resonances are missed, but the missed resonances have small widths and their omission should not significantly affect the calculated cross sections Number of resonances Energy, eV Fig. 1. Increasing sum of the number of resonances Sum<Гn0>" ENDF/B-VII Maslov Energy, eV Fig. 2. Sum of reduced neutron widths 21

22 From Fig. 2 it can be seen that in Maslov’s estimate the neutron widths are taken to be smaller than in ENDF/B-VII.b2 (by about 12%). Radiation widths, on the contrary, are larger, on average by 45%. The pitch widths are almost identical. Both estimates contain areas of unresolved resonances described by the s-, p- and d-wave parameters. In Maslov's estimate, these parameters change greatly with energy, describing the gross structure of the cross sections. The result is visible from Fig. 3 and 4, which compare the capture and fission cross sections above the region of allowed resonances. 1.00E E+00 Maslov, gripper ENDF/B-VII, gripper Muradyan-99 Section, barn 1.00E E E E E E E E E E+07 Energy, eV Fig.3. Capture section 1.00E E+00 Section, barn 1.00E E-02 James-77 Medous-78 Maslov, division 1.00E-03 ENDF/B-VII, division 1.00E E E E E+07 Energy, eV Fig.4. Division section. The increased capture cross section in Maslov’s estimate is justified by the only available result of Muradyan. The structure of subthreshold division reflected in Maslov's estimate reflects James's results. Conclusion ROSFOND recommends adopting Maslov’s assessment from JEFF-3.1. The spectra of 8 groups of delayed neutrons should be taken as the same as those of uranium-235. Exits 22

The 23 fission products of uranium-234 are contained in ENDF/B-VI (England and Reeder 1989) and JEFF-3.1 (Mills 2005). It is natural to accept the latter assessment. The cross sections of the main reactions on the integral spectra are given in the table below Total Elastic Inelastic (n,2n) (n,f) (n,γ) eV Resonance integral Fission spectrum 235 U MeV Author of the conclusion Nikolaev M.N. Contents of the ROSFOND file for 92-U-234 Remake!! MF = 1 General and special information about the nuclide MT = 451 header section MT = 452 total average number of fission neutrons MT = 458 fission energy release MF = 2 Resonance parameters MT = 151 resonance parameters section MF = 3 Neutron cross sections MT = 1 total cross section MT = 2 elastic scattering MT = 4 total inelastic scattering cross section MT = 16 reaction (n,2n) 92- U-233 MT = 17 reaction (n,3n) 92- U-232 MT = 18 all fission processes MT = 19 fission ( first chance) MT = 20 division (second chance) - reaction (n,nf) - U- MT = 21 division (third chance) - reaction (n,2nf) - U- MT = inelastic scattering with excitation of discrete levels MT = 91 inelastic scattering with excitation of a continuum of levels MT = 102 radiative capture: reaction (n,gamma) 92- U-235 MF = 4 Angular distributions of secondary neutrons MT = 2 elastic scattering MT = 16 reaction (n,2n) 92- U-233 MT = 17 reaction (n,3n) 92- U-232 MT = 18 all division processes MT = 20 division (second chance) - reaction (n,nf) - U- MT = 21 division (third chance) - reaction (n, 2nf) - U-MT = inelastic scattering with excitation of discrete levels 23

24 MT = 91 inelastic scattering with excitation of a continuum of levels MF = 5 Energy distributions of secondary neutrons MT = 16 reaction (n,2n) 92- U-233 MT = 17 reaction (n,3n) 92- U-232 MT = 18 all processes divisions MT = 19 division (first chance) MT = 20 division (second chance) - reaction (n,nf) - U- MT = 21 division (third chance) - reaction (n,2nf) - U- MT = 91 inelastic scattering with excitation of a continuum of levels MT=455 fractions of groups and spectra of delayed neutrons MF = 8 Yields and decay characteristics of the resulting radionuclides MT = 16 reaction (n,2n) 92-U-233 MT = 17 reaction (n,3n) 92-U-232 MT = 102 radiation capture: reaction (n,gamma) 92- U-235 MT = 457 radioactive decay data 24

25 92.4.URANIUM General characteristics 1.1. Z= A= ± Aw= ± Content in natural mixture: 0.72 at%; weight% 1.5. List of neutron reactions 9 MT Reaction Q, MeV E threshold, MeV Product nucleus *) 234 U 16 (n,2n) (n,3n) U 37 (n,4n) U 19 (n,f 1) FP+n +γ 20 (n,n f 2) FP+n+γ 21 (n,2nf 3) FP+n+γ 38 (n,3nf 4) FP+n+γ 102 (n,γ) U 103 (n,p ) Pa 107 (n,α) Th 1.6. Radioactivity: Half-life: 7.038*10 8 years. Probability of alpha decay: Probability of spontaneous fission: 2*10-8 Decay energy Q α =4.678 MeV; Q sf = Resonance region: (MF=2) 2.1. Region of allowed resonances General characteristics of the region of allowed resonances 9 In the energy region under consideration, other reactions with the release of charged particles are possible - (n,d), (n,t), (n, 3 He), etc. - including exoenergetic ones, -(n,2α), (n,nα), - the cross sections of which, however, are very small and are not given in the evaluated data file. 25

26 Spin and parity of the target nucleus: 7/2 - Scattering radius: R=0.9602* cm does not depend on energy. It is only used to calculate potential barrier permeabilities and scattering phases. Resonance formula: Reich-Moore. Calculation of scattering anisotropy using resonance parameters is not provided Number of orbital moments one (namely l=0, i.e. only s-resonances are considered) Number of systems of resonances with different spins J: two (J=3 and J=4) Boundaries of the region of allowed resonances : from 10-5 eV to 2250 eV The number of resonances considered is 3193; of these, 14 are below the neutron binding energy and 9 are above the boundary of the allowed resonance region. The number of resonances with J=3 is 1449; of which 1433 are in the region from 0 to 2250 eV. The number of resonances with J=4 is 1744; of which 1732 are in the region from 0 to 2250 eV Estimation details The following contains a translation of the description of the assessment of resonance parameters given in the header section of the data file for uranium-235 from the ENDF/B-VI revision 5 library. This assessment was performed at the Oak Ridge Laboratory L .Lil et al. in 1997, adopted in all estimated neutron data libraries for uranium-235 from ENDF/B-VI (Rev.5). It is also included in the ENDF/B-VII.b2 library. The resonance parameters were estimated using the least squares method, taking into account the results of both differential measurements of neutron cross sections and integral experiments. The thermal cross sections (fission, capture and elastic scattering) and Westcott g-factors from the neutron standards file ENDF/B-6 10 were used as input parameters, as well as the K1 factor estimated by Hardy 11. Table 1 shows the named parameters obtained as a result of the fitting only based on the results of differential experiments, and then taking into account integral data, are compared with the input data of the SAMMY program. The value of ν obtained as a result of fitting to the listed parameters was equal to ± In Table 2, the fission and capture cross sections obtained by the SAMMY program using the fitted resonance parameters are compared with the results of direct measurements 10 A. Carlson, W.P. Poenitz, G. M. Hale et al., "The ENDF/B-6 Neutron Cross Section Measurements Standards," National Institute of Standards and Technology report NISTIR (1993) 11 J. Hardy, Brookhaven National Laboratory, report BNL-NCS (1979) Sec. B.1. 26

27 Table 1. Thermal parameters. Parameter Input value Fit only by diff. data Fission cross section ± Capture cross section 98.96± Scattering cross section 15.46± g f ± g a ± g γ K ± Fit by diff. and integrat. data Table 2. Calculated and experimental values ​​of integrals of the fission cross section (barn * eV) Energy range, eV Calculation according to res. Experimental data from to parameters Shark88 Weston84 Weston Table 3. Calculated and experimental values ​​of integrals from the capture cross section (barn * eV) Energy range, eV Calculation by res. Experimental data from to parameters desaussure67 Perez The resonant division and capture integrals calculated from the estimated resonance parameters are equal to barn and barn, respectively, which leads to 27

28 alpha value equal to 0.509, which is in excellent agreement with the data of integral experiments. When estimating the resonance parameters, the data from the following differential experiments were taken into account. 1. Harvey88 transmission experiments at the ORELA accelerator on an 18-meter flyby with an atom/barn thick sample cooled to 77K (0.4 to 68 eV). 2. Harvey88 transmission experiments at the ORELA accelerator on an 80-meter flyby with an atom/barn thick sample cooled to 77K (4 to 2250 eV). 3. Harvey88 transmission experiments at the ORELA accelerator on an 80-meter flyby with an atom/barn thick sample cooled to 77K (4 to 2250 eV). 4. Measurements of the Schark88 fission cross section at the RPI accelerator at a flight path of 8.4 m (from 0.02 to 20 eV). 5. Measurements of the fission and capture cross section of desaussure67 at the ORELA accelerator at a flight path of 25.2 m (from 0.02 to 2250 eV). 6. Measurements of the fission and capture cross section of Perez73 at the ORELA accelerator at a flight path of 39 m (from 0.01 to 100 eV). 7. Measurements of the Gwin84 fission cross section at the ORELA accelerator at a flight path of 25.6 m (from 0.01 to 20 eV). 8. Spencer84 transmission experiments at the ORELA accelerator on an 18-meter flight base with a sample of atoms/barn thickness (from 0.01 to 1.0 eV). 9. Measurements of the Wagemans88 fission cross section at the GELINA accelerator on an 18-meter flight base (from up to 1.0 eV) 10. Measurements of the Gwin96 absorption and fission cross sections at the ORELA accelerator (from 0.01 to 4 eV). 11. Measurements of the Weston84 fission cross section at the ORELA accelerator at an 18.9-meter flight path (from 14 to 2250 eV). 12. Measurements of the value of η Wartena87 at an 8-meter span (from to 1.0 eV). 13. Measurements of the value of η Weigmann90 on a mechanical chopper (from up to 0.15 eV) 14. Measurements of the fission cross section of Weston92 on the ORELA accelerator at an 86.5-meter flight base (from 100 to 2000 eV). 15. Measurements of the Moxon92 fission cross section at the ORELA accelerator (from 0.01 to 50 eV) Links to the experimental works used. Index Link Harvey88 J.A. Harvey, N.W. Hill, F. G. Perey et al., Nuclear Data for Science and Technology, Proc. Int. Conf. May 30-June 3, 1988, Mito, Japan. (Saikon Publishing, 1988) p. 115 Shark88 R.A. Schrack, "Measurement of the 235U(n,f) Reaction from Thermal to 1 kev," Nuclear Data for Science and Technology, Proc. Int. Conf. May 30- June 3, Mito, Japan (Saikon Publishing, 1988) p. 101 desaussure67 G. de Saussure, R. Gwin, L.W. Weston, and R.W. Ingle,"Simultaneous Measurements of the Neutron Fission and Capture Сross Section for 235U for Incident Neutron Energy from 0. 04 ev to 3 kev," Oak Ridge National Laboratory report ORNL/TM-1804 (1967) Perez73 R.B. Perez, G. de Saussure, and E.G. Silver, Nucl.Sci. Eng. 52, 46 (1973) 28

29 Gwin84 R. Gwin, R.R. Spencer, R.W. Ingle, J.H. Todd, and S.W. Scoles, Nuc.Sci.Eng. 88, 37 (1984) Spencer84 R.R. Spencer, J.A. Harvey, N.W. Hill, and L. Weston, Nucl.Sci.Eng. 96, 318 (1987) Wagemans88 C. Wagemans, P. Schillebeeckx, A.J. Deruyter, and R. Barthelemy, "Subthermal Fission Cross Section Measurements for 233U and 239Pu," Nuclear Data for Science and Technology, Proc. Int. Conf. May 30-June 3, Mito, Japan (Saikon Publishing, 1988) p. 91 Gwin96 R. Gwin, To be published in Nuclear Science Engineering Weston84 L.W. Weston and J.H. Todd, Nucl.Sci.Eng. 88, 567 (1984) Wartena87 J.A. Wartena, H. Weigmann, and C. Burkholz, report IAEA Tecdoc 491 (1987) p.123 Weigmann90 H. Weigmann, P. Geltenbort, B. Keck, K. Shrenckenbach, and J.A. Wartena, The Physics of Reactors, Proc. Int. Conf., Marseille, 1990, Vol.1 (1990) p. 133 Weston92 L.W. Weston and J.H. Todd, Nucl.Sci.Eng. 111, 415 (1992) Moxon92 M.C. Moxon, J.A. Harvey, and N.W. Hill, private communication, Oak Ridge National Laboratory (1992) Discussion of the results of estimating the parameters of allowed resonances. Let us note, first of all, that in 1985, the same group of evaluators, based on the same experimental data, using the same SAMMY program, estimated the parameters of allowed resonances. There are 12 resonances of uranium-235 in the same energy region. However, at that time, due to limited computer capabilities, the energy region under consideration had to be divided into 5 intervals. The evaluation results were accepted into the ENDF/B-VI library. 2, to the FOND-2 library and to many other libraries of assessed data. In Fig. Table 1 compares multigroup cross sections calculated on the basis of estimates for 1985 and 1997. The graphs show the deviations of cross sections calculated using ENDF/B-VI(Rev.5) from cross sections calculated using ENDF/B-VI (Rev.2) as a percentage ENDF/B-VI (Rev.5/Rev.2) capture, % fission,% alfa,% ENDF/B-VI (Rev.5/Rev.2) capture,% fission,% alfa,% Discrepancy, % Discrepancy, % ,5 5.5 10.5 15.5 Energy, eV Fig. 1a Energy, eV Fig. 1b 12 N.M.Larson, ORNL/TM-9719/R1, (1985) 29

30 Discrepancy, % ENDF/B-VI (Rev.5/Rev.2) fission,% capture.% alfa,% Energy, EV ENDF/B-VI (Rev.5/Rev.2) fission,% capture.% alfa,% Energy, eV Discrepancies, % Fig. 1c Fig. 1 d. As can be seen, the effect of overestimation turned out to be very significant: the capture cross section and its ratio to the fission cross section increased significantly. It must be said that it was precisely this increase that sharply reduced the calculated and experimental discrepancies in the criticality of aqueous solutions of highly enriched uranium, reducing them to an insignificant level. The reason for such a large change in the assessed data was not explained by the assessment authors. In the header section of the data file from ENDF/B-VI(Rev.2), it is noted that above 110 eV not all resonances are allowed. The corresponding section from ENDF/B-VI(Rev.5) and later versions of the ENDF/B library does not contain such a clause (see section above). It is therefore of interest to consider how complete the set of resonances contained in the latest estimate is. In Fig. Figure 2 shows the energy dependence of the density of levels with J=3 and J=4. The level density is expressed in the number of resonances per 100 eV Number of resonances per 100 eV N (J=3) N (J=4) Energy, eV Fig. 2 Energy dependence of the level density As can be seen, with an increase in energy to 1000 eV the “observed” level density decreases monotonically, halving. This is followed by a jump upward by approximately a factor of one and a half, and is followed again by a monotonic decline to approximately the previous level at 2000 eV. At this energy, the level density again increases abruptly almost to its original value, after which another decrease follows, this time quite 30

98.CALIFORNIUM The main interest in the neutron cross sections of Californian isotopes was associated with the production of 5 Cf as a compact neutron source used in a wide variety of fields. In this case, the initial product

53.Iodine Note on data quality assessment for fission fragments Considering that heavy isotopes of iodine are important fission products, we will make general comments on data quality priorities. Most

32. GERMANIUM Natural germanium contains 5 isotopes: 70 Ge, 72 Ge, 73 Ge, 73 Ge and 76 Ge (the latter is weakly radioactive). In addition, there are three more long-lived radioisotopes: 78 Ge, 79 Ge and 71 Ge. For stable

12. MAGNESIUM Magnesium does not have long-lived radioactive isotopes. For three stable isotopes, there are estimates by V. Hatchya and T. Asoni (1987), adopted in FOND-2.2 from JENDL-3.2. In '21, Shibata added to these estimates

45.RHODIUM 45.1. Rhodium-99 Radioactive (T 1/2 = 16.1 days). Capturing an orbital electron turns into stable ruthenium-99. Can be formed in negligible quantities in reactors due to the reaction of 102Pd

14. SILICON General notes. Natural silicon contains three stable isotopes in the following atomic concentrations: 28 Si 92.23%; 29 Si 4.67%; 30 Si - 3.10%. In addition, there is a beta-active isotope

37.RUBIDIUM 37.1. Rubidium-83 Radioactive (T 1/2 =86.2 days). Capturing an orbital electron turns into stable krypton-83. Possible reactions for the formation of 85 Rb(n,3n); 85 Rb(n,2n) 84 Rb(n,2n); 84

55. CESIUM Consideration of the state of affairs on neutron data for all cesium isotopes was carried out by V.G. Pronyaev. They also issued recommendations on the inclusion of assessed data files in ROSFOND. Footnotes

35. BROMINE 35.1. Bromine-79 Content in the natural mixture is 50.69%. Output when dividing 235 U 2.5*10-7 ; when dividing 239 Pu 8.6*10-4. Modern score data libraries use two scores: score

30. ZINC FOND-2.2 contains a data file for natural zinc (Nikolaev, Zabrodskaya, 1989) for neutron transfer calculation problems. Data for all stable isotopes (Nikolaev, 1989) and Grudzevich data,

18. ARGON FOND-2.2 contained neutron cross-section data for stable and radioactive isotopes of argon from EAF-3, as well as a complete data set for natural argon (estimated by Howerton, 1983, from ENDL-84).

33. ARSENIC 33.1. Arsenic-71 is radioactive (T 1/2 =65.28 hours). Capturing an orbital electron, it turns into germanium-71, which decays in the same way (T 1/2 = 11.43 days) into stable gallium-71. In reactors

51. Antimony A review of the state of affairs on neutron data for all isotopes of antimony was carried out by V.G. Pronyaev. They also issued recommendations on the inclusion of assessed data files in ROSFOND. Footnotes

49.INDIUM 49.1. Indium-111 Radioactive (T 1/2 = 2.8047 days). Experiencing the capture of an orbital electron, it turns into stable cadmium-111. In reactors can be formed in negligible quantities due to

50. TIN With the magic number of protons (50), tin has the largest number of stable isotopes (10). Difficulties in the model description of cross sections at energies below several MeV are due to the low density

20. CALCIUM IN FUND-2.2 the complete set of data is contained only for natural calcium. For stable and radioactive isotopes, estimates of neutron cross sections from eaf-3 are accepted. ENDF/B-VII contains data only

5.FILE 5. ENERGY DISTRIBUTIONS OF SECONDARY NEUTRONS 1 5.1.GENERAL DESCRIPTION File 5 contains data for energy distributions of secondary neutrons, presented in the form of normalized distributions

9.POTASSIUM IN FUND-2.2 the complete data file is contained only for natural potassium (H.Nakamura, 987). For stable and long-lived isotopes, the EAF-3 estimate is adopted. ENDF/B-VII contains data for natural

9. FLUORINE Fluorine does not have long-lived radioactive isotopes. ROSFOND includes data for the only stable isotope 19 F. 9.1. Fluorine-19 The libraries -VIIb2, JEFF-3.1 and FOND-2.2 use the assessment

79. GOLD 79.1. Gold-194 Radioactive (T 1/2 =38.0 hours). Decays by capturing an orbital electron into stable platinum-194. Possible ways formation in the reactor - triple reaction 197 Au(n,2n)

75. RHENIUM 77.0 General Notes This section describes the isotopes of rhenium: two stable and seven radioactive isotopes with half-lives of more than a day. 75.1. Rhenium-182. Radioactive. Experiencing orbital capture

52. TELLURIUM 52.1. Tellurium-118 Half-life: (6±2) days. Decay modes: e - 100%. Ground state spin: 0 +. JEFF-3.1/A=EAF-2003 incomplete evaluation of the 2003 file for the activation library, based

16. SULFUR ROSFOND presents data for all 4 stable isotopes of sulfur and for radioactive sulfur-35 16.1. Sulfur-32 Content in the natural mixture is 92% - the main isotope. In all modern libraries

71.LUTETIUM 71.1. Lutetium-169 Radioactive (T 1/2 = 1.42 days). Experiencing the capture of an orbital electron, it turns into ytterbium-169, which, in turn, turns in the same way (T 1/2 = 32.026 days)

80. MERCURY 80.0. General remarks In the FOND-2.2 library, all neutron data for 13 stable and long-lived mercury isotopes were taken mainly from the EAF-3 library. Complete Neutron Data Files

76. OSMIUM ROSFOND should provide complete sets of neutron data for 7 stable isotopes of osmium and data on neutron reaction cross sections for 5 long-lived radioactive isotopes. Unfortunately,

Half-life: (2.43±0.05) days. Decay modes: e - 100%. Ground state spin: 0 +. 56.BARIUM 56.1. Barium-128 JEFF-3.1/A incomplete evaluation of the 2003 file for the activation library based on

34. SELENIUM 34.1. Selenium-72 is Radioactive (T 1/2 =8.4 days). Experiencing the capture of an orbital electron, it turns into arsenic-72, which emits a positron (T 1/2 =26 hours) into germanium-72. In insignificant amounts it may

67.HOLMIUM Natural holmium contains only one isotope - 165 Ho. In addition, there is one very long-lived neutron-deficient isotope - 165 Ho (4570 years) and one neutron-rich isotope - 165 Ho (26.8 hours),

4. BERYLLIUM The ROSFOND library contains data for three isotopes of beryllium: radioactive 7 Be (53.29 days), stable 9 Be and radioactive 10 Be. 4.1. Beryllium-7 Radioactive. T 1/2 =53.12 d. Capture

91. PROTACTINIUM Protactinium has five long-lived isotopes, data for which must be submitted to the ROSFOND library. 91.1. Protactinium-229 Radioactive (T 1/2 =1.5 days). Experiencing a grip

82. LEAD ROSFOND includes data for all 4 stable and 4 long-lived radioactive isotopes of lead. 82.1. Lead-202 Radioactive. (T 1/2 =5.25*10 4 years). By capturing an orbital electron

48. CADMIUM 48.0. General remarks For the ROSFOND library it was necessary to select neutron data for 8 stable and 4 long-lived isotopes of cadmium. Let's consider the results of data revaluation activities

1 3.FILE 3. REACTION SECTIONS 3.1.GENERAL DESCRIPTION File 3 provides cross sections and derivative values ​​as a function of energy E, where E is the energy of the incident particle (in eV) in the laboratory system. They represent

68. ERBIUM Natural erbium includes six isotopes. Table 1 lists the contribution of each isotope to the natural mixture. Table 1 Composition of natural erbium, % Isotope % Er-162 0.139 Er-164 1.601 Er-166 33.503

70. YTERBIUM Natural ytterbium has 7 stable isotopes: 168 Yb, 170 Yb, 171 Yb, 172 Yb, 173 Yb, 174 Yb, 176 Yb and three fairly long-lived radioactive isotopes: 166 Yb, 169 Yb, 175 Yb. Neither of

5. BOR 5.1. Boron-10 Content in natural mixture: 19.8±0.3%. Ground state spin: 3+. 1. Reaction files 10 B(n,α) (MT=107) and 10 B(n,αγ 1) (MT=801) are used as standards for measurement

27. COBALT FUND-2.2 includes the assessment of T. Aoki, T. Asami, 1982. For radionuclides, the EAF-3 rating is adopted. -VII adopts the estimate of A. Smith, G. DeSaussure, 1989. -3.3 contains the estimate of T. Watanabe, 1994. JEFF-3.1

88.RADIUM 88.0. General notes Element 88 was discovered by the Curies in 1898 in the mineral known as uranium pitch, pitchblende and pitchblende. Already during this very first work it became clear

62.SAMARIUM There are 11 known stable and long-lived isotopes of samarium, of which 7 are preserved in nature. Two radioactive isotopes (151 Sm and 153 Sm) are formed as a result of the fission of heavy nuclei. As

23. VANADIUM Natural vanadium contains two isotopes V-5 (a weakly radioactive isotope with a content of .25%) and V-51. Thus, natural vanadium consists almost entirely of one isotope. Two more radioisotopes

69.THULLIUM Thulium has only one stable isotope - 169 Tm and 6 radioactive isotopes with a half-life of more than a day: 3 neutron-deficient (165 Tm, 167 Tm, 168 Tm) and three neutron-rich (170 Tm,

72. HAFFNIUM 72.0. General notes Hafnium has 6 stable isotopes: 174 Hf, 176 Hf, 177 Hf, 178 Hf, 179 Hf, 180 Hf. Two of them have long-lived isomers (the second ones). This is 178 Hf n (T1/2=31g.) and 179

93. NEPTUNIUM There are three natural radioactive families of thorium-232, uranium-235 and uranium-238 and one artificial radioactive series, the neptunium-237 family. In addition to “artificiality”, this family is distinguished by

1 4. FILE 4. ANGULAR DISTRIBUTIONS OF SECONDARY NEUTRONS 4.1.GENERAL DESCRIPTION File 4 contains representations of the angular distributions of secondary neutrons. It is used only for neutron reactions, reactions

DYSPROSIUM.0 General remarks For the ROSFOND library it was necessary to select neutron data for 10 stable and long-lived isotopes of dysprosium. It also seemed appropriate to include data for

3. Hauser-Feshbach theory. Following Hauser and Feshbach, we express the cross sections of compound processes in terms of average widths. We will proceed from the Breit-Wigner formalism. For an S-matrix element in the presence of a direct

95. AMERICIUM 95.0. General remarks The classical scheme for obtaining americium looks like this: 239 94 Pu + 1 0n (γ) 240 94Pu + 1 0n (γ, β) 241 95Am. Americium is a silver-white metal, malleable and malleable.

6. CARBON General notes. Natural carbon contains two stable isotopes in the following atomic concentrations: 12 C 98.89%; 13 From 1.11%. There is also a very long-lived (T 1/2 = 5730 y) isotope 14C,

2. HELIUM 4 He. The ROSFOND library contains data for two isotopes of helium 3 He and 2.1. Helium-3 1. General notes Modern libraries contain three independent estimates of neutron data for helium-3,

54.XENON 54.0 General remarks There are 14 known stable and long-lived isotopes and isomers of samarium, of which 9 are preserved in nature. Of the remaining five, four are long-lived isomers. Very

64. GADOLINIUM 64.0 General remarks For the ROSFOND library it was necessary to select neutron data for 12 stable and long-lived isotopes of gadolinium. Data for all these isotopes are contained in the library

77. IRIDIUM 77.0 General Notes This section describes: two stable and seven radioactive isotopes of iridium with half-lives greater than 24 hours. 77.1. Iridium-188. Radioactive. Experiencing orbital capture

7. NITROGEN Data for two stable isotopes of nitrogen are entered into ROSFOND: N-14 (99.634%) and N-15 (0.366%). Nitrogen does not have long-lived radioactive isotopes. In the process of analyzing neutron data, we used

1 12. FILE 12. PHOTON PRODUCTION MULTIPLICITIES AND TRANSITION PROBABILITIES File 12 can be used to represent the energy dependences of photon production cross sections either through multiplicities,

Neutron nuclear reactions Neutron nuclear reactions A nuclear reaction is the process and result of the interaction of nuclei with various nuclear particles (alpha, beta particles, protons, neutrons, gamma quanta

36.KRYPTON 36.1. Krypton-78 Content in the natural mixture is 0.35%. 1982 assessment carried out by a team of specialists for ENDF/B-V. fission products. assessment for the international product data library

73. TANTALUM ROSFOND should provide neutron data for 2 natural and 4 long-lived radioactive isotopes of tantalum. Of the two natural isotopes of tantalum, only 181 Ta is stable.

89.ACTINIUM 89.0. General Notes There is only one reason why element 89 anemones is of interest to many today. This element, like lanthanum, turned out to be the ancestor of a large family of elements, including

13. ALUMINUM Natural aluminum contains one isotope 27 Al. There is also a long-lived isotope 26 Al, data for which should also be presented in the ROSFOND library. 13.1. Aluminum-26 Radioactive.