RU2379773C1 - Hydride fuel for nuclear reactor and method of producing said fuel - Google Patents

Abstract

FIELD: nuclear physics. ^ SUBSTANCE: invention relates to nuclear engineering and solves the problem of producing nuclear fuel which provides simultaneous flow of fission reactions and nuclear fusion and energy generation and fusion and fission neutrons in a nuclear reactor core. The hydride of a fissile element contains heavy isotopes of deuterium and tritium preferably in equal and maximum concentrations, for example UD1.5T1.5. The method of producing hydride fuel for a nuclear reactor involves placing fissile material in metallic state into a reaction volume, heating it and keeping it in a dynamic vacuum at temperature above the temperature at which the fission material and the hydrogenating component begin to react, carrying out the hydrogenation process by feeding a hydrogenating component into the reaction volume and holding at hydrogenation temperature of the fission material and controlling pressure, and subsequent cooling. The hydrogenating components used are deuterium and tritium, with deuterium and tritium fed successively, and the hydrogenation process carried out preferably until equal and maximum concentrations of hydrogenating components are achieved. ^ EFFECT: production of nuclear fuel reactor, use of which provides near-optimal conditions for simultaneous flow of nuclear fission and fusion reactions in nuclear reactor cores. ^ 10 cl, 1 dwg, 1 tbl

Description

The invention relates to the field of nuclear technology and solves the problem of creating nuclear fuel, ensuring the simultaneous occurrence in the active zone of a nuclear reactor of fission and fusion reactions and the generation of fission energy and neutrons and fusion.

Fuel and a Method for Its Production are Known (Merten U. E.A., The Preparation and Properties of Zirconium - Uranium - Hydrogen Alloys. In: Proceedings of the Second United Nations International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1958, vol. 6., p. 111, United Nations, NY, 1958), which consists in the fact that first, by the usual method of arc melting, an alloy of zirconium with 8 wt.% Of uranium is obtained, and then an article to be hydrogenated is manufactured by extrusion, which is placed in a ceramic pipe and heated in vacuo to a temperature usually above 750 ° C, after which hydrogen is slowly fed into the reaction space, previously passing through the first purification system to achieve the required its content in the alloy, then the tube is detached from the hydrogen supply system and slowly cooled until yet not react any remaining hydrogen in it, and after that hydrogenated sample furnace cooled to room temperature.

This method allows to obtain cores for fuel rods of nuclear fission reactors with a length of 355.6 mm and a diameter of 35.6 mm of the following composition: 91 wt.% Zirconium, 8 wt.% Uranium and 1 wt.% Hydrogen, while hydrogenation takes several hours, density of a ternary alloy is close to the density of metallic zirconium, and one core of a light hydrogen isotope accounts for one zirconium core in the alloy. Of the fuel rods with such a core, it is possible to compose an active zone that has a large negative temperature effect of reactivity and provides the ability to work both in stationary and in pulsed mode.

The disadvantage of this fuel and method is that they do not provide the introduction into the fuel crystal lattice of a nuclear reactor of fission of heavy hydrogen isotopes and, therefore, the possibility of sequential reactions of fission of uranium nuclei and the synthesis of nuclei of heavy hydrogen isotopes heated as a result of interaction with fast fission neutrons or fragments of separated uranium nuclei to a temperature exceeding the threshold for fusion reactions.

This drawback is due to the requirement to provide a high slowing down fuel for the fuel of the TRIGA reactor for which this fuel was developed, which decreases significantly with increasing temperature, which ensures quick quenching of the chain reaction of fission of uranium nuclei in such a transition process in the core due to the large negative temperature effect of reactivity, which does not can be ensured if the place of atoms of the light hydrogen isotope in the U-Zr-H alloy is occupied by atoms of heavy isotopes, due to differences in the properties of light nuclei and heavy hydrogen isotopes characterizing neutron scattering.

The closest analogue, which coincides with the claimed invention by the most significant features, is powdered and / or compact hydride fuel for a nuclear reactor and the method for its production, described in the monograph "Metal hydrides" edited by V. Muller, D. Blackledge and J. Libowitz . Translation from English edited by R.A. Andrievsky and K.G. Tkach. Moscow, Atomizdat, 1973, pp. 36-49. The starting material is a powder or an article of pure metallic uranium, and the method is to provide direct interaction of pure hydrogen and a powder or an article of metallic uranium placed in the reaction volume. The method includes calibrating a volume hydrogenation unit, heating (annealing) the initial metal powder or product and degassing it by holding it for 2-12 hours in a dynamic vacuum at a temperature slightly higher than the temperature at which the interaction of hydrogen and metal begins (200-250 ° C), the subsequent hydrogenation process by slow or portioned supply of purified hydrogen into the evacuated reaction volume with pressure control, holding the powder or product in a hydrogen atmosphere at a rate hydrogenation of fissile material for the time necessary for complete absorption of the calculated volume of hydrogen, ensuring hydride production with the required hydrogen content, slow, as a rule, together with the furnace, cooling the hydride powder or hydride product, and monitoring the hydrogen content in uranium, for example, by weighing the powder or product before and after hydrogenation.

The fuel obtained using this method is a fine powder or products from uranium hydride, for example rods or tablets, with a given hydrogen content, which can be used, for example, for the manufacture of fuel elements of a nuclear fission reactor with a compact active zone with a large negative reactivity temperature effect such as a TRIGA reactor, other research reactors or space reactors. TRIGA reactors can operate both in stationary and in pulsed mode due to the good characteristics of pulse self-quenching, achieved through the use of hydride fuel, which provides a large negative temperature coefficient of reactivity of the active zone.

The disadvantage of this solution is that it does not provide the ability to obtain hydride fuel for a nuclear fission reactor with an optimal ratio of the concentration of deuterium and tritium in uranium hydride or other element used as fuel for the nuclear fusion reaction to occur.

This disadvantage is due to the fact that in the described prototype the production of hydrides based on heavy hydrogen isotopes as fuel for nuclear fission reactors for the production of energy and / or neutrons of fusion is not provided, and the main field of use of such hydrides is indicated by neutron diffraction analysis by neutron scattering used to determine the position an atom of one of the isotopes of hydrogen in structures with respect to other atoms, including atoms of other isotopes of hydrogen.

The technical effect of the claimed invention consists in creating fuel for a nuclear reactor, the use of which provides close to optimal conditions for the simultaneous occurrence of nuclear fission and fusion reactions in the active zones of nuclear reactors, so that the former initiate the second and simultaneously produce fission and fusion neutrons and fusion due to the presence of fissile nuclides and nuclides in the fuel that can enter into the synthesis reaction with a minimum energy threshold, and, therefore, ensure AET conditions for testing in research reactors synthesis reactors materials close to operating modes.

This effect is achieved by the fact that in a hydride fuel for a nuclear reactor, the fission element hydride contains heavy hydrogen isotopes of deuterium and tritium, preferably in equal and maximum concentrations.

The hydride of the fissile element consists of particles ranging in size from 0.1 to 100 μm. Uranium was selected as the fissile element, and uranium hydride is a compound UD _1.5 T _1.5 .

In a method for producing hydride fuel for a nuclear reactor, comprising placing fissile material in a metallic state in a reaction volume, heating it with holding in a dynamic vacuum at a temperature higher than the temperature at which the fissile material and the hydrogenating component begin to interact, carrying out the hydrogenation process by supplying a hydrogenating component to the reaction volume with exposure to the hydrogenation temperature of fissile material and pressure control, subsequent cooling, as hydrogenation x of the components use deuterium and tritium, moreover, deuterium and tritium are supplied alternately, and the hydrogenation process is preferably carried out until equal and maximum concentrations of hydrogenating components are achieved.

Uranium metal particles with sizes from 0.1 to 100 μm are placed in the reaction volume and a compound of the type UD _1.5 T _{1.5 is} obtained.

Uranium metal products may be placed in the reaction volume, the dimensions of which correspond to the shape changes during hydrogenation of the sizes of the cores of the fuel elements of a nuclear reactor.

Deuterium and tritium are fed into the reaction volume alternately in portions in two or more stages. Hydrogenating components are fed into the reaction volume to a pressure of 0.2-0.25 MPa. Excerpt in the process of hydrogenation of metallic uranium is carried out at a temperature of 200-440 ° C.

Cooling in the process of hydrogenation of metal uranium products is carried out at a speed of not more than 1 ° C per minute.

The content of heavy hydrogen isotopes of deuterium and tritium in the fissile element hydride, preferably in equal and maximum concentrations, provides the conditions for the effective occurrence of the (D, T) -reaction of nuclear fusion. Obviously, a decrease in the concentration of at least one of the heavy hydrogen isotopes in the hydride, as well as the replacement of one of the isotopes by another, will lead to a decrease in the reaction rate of syntheses with a low energy threshold and a decrease in the rate of fusion neutron generation. From the same considerations, the enrichment of uranium with uranium-235 is chosen to be the maximum possible under the conditions of heat removal.

The particle size of the uranium metal placed in the reaction volume is determined from technological considerations. With particle sizes less than 0.1 microns in the presence of active ventilation, significant loss of valuable product will occur due to "dusting", and with sizes greater than 100 microns during operation of the fuel due to inhomogeneities, local bursts of energy release and undesirable overheating can occur.

Before starting the hydrogenation process, the calibration of the volume hydrogenation unit is carried out using a precision burette calibrated in volume through 0.1 cm ³ in the temperature range of interest and a mercury manometer measuring pressure in the range of 1-760 mm Hg. accurate to 0.5 mmHg The presence of the calibration operation ensures the consistent supply of the required volumes of deuterium and tritium to the reaction space of the hydrogenation unit with high accuracy. Heating (annealing) of a metal powder or metal product with a high content of fissile nuclides and degassing during aging in a dynamic vacuum at a temperature higher than the temperature at which the interaction of metal and hydrogen begin is carried out to form the initial metal structure and to purify the material to be hydrogenated from sorbed gases and moisture. Slow or portioned supply of purified deuterium into the evacuated reaction volume with pressure control ensures a uniform distribution of deuterium over the metal volume without introducing gas-polluting impurities and without the appearance of cracks associated with stresses in the material during uneven hydrogenation. Slow or portioned supply of purified tritium into the evacuated reaction volume with pressure control ensures uniform distribution of tritium over the metal volume without introducing gas-polluting impurities and without the appearance of cracks associated with stresses in the material during uneven hydrogenation.

The supply of hydrogenating components to the reaction volume to a pressure of less than 0.2 MPa does not provide the desired hydrogenation rate, and an increase in pressure of more than 0.25 MPa is impractical, since it will complicate and increase the cost of equipment.

The exposure of the powder or product in an atmosphere of deuterium, and then tritium for the time necessary to completely absorb the calculated volume of heavy and superheavy hydrogen, is carried out to obtain a hydride with the required content of deuterium and tritium.

Exposure to hydrogenation of uranium metal at a temperature of less than 200 ° C does not provide an acceptable hydrogenation rate, since a temperature of 200 ° C is the threshold temperature for the start of the hydrogenation process. It is not practical to maintain a temperature of more than 440 ° C, since at a temperature above 440 ° C, the process of dissociation of uranium hydride begins.

Slow, as a rule, together with the furnace, cooling of the hydride powder or hydride product is carried out so that the temperature gradients in the material are not large, and therefore the thermal stresses in it do not exceed the ultimate strength. Cooling during the hydrogenation of uranium metal products at a rate of more than 1 ° C per minute can lead to cracks in the material.

The compliance of the content of heavy hydrogen isotopes in uranium hydride with the technical requirements for stoichiometry (for example, UD _1,5 T _1,5 ) is controlled by weighing the powder or product before and after hydrogenation.

New significant features of the proposed solution in comparison with the prototype are the operations of sequentially saturating the fissile material in the metallic state with deuterium to a state corresponding, for example, UD _1,5 hydride, and then tritium to a state corresponding, for example, UD _1,5 T ₁ hydride _{, 5} . This allows us to conclude that the claimed solution has novelty. The technical literature describes methods for the hydrogenation of fissile materials in a metallic state using hydrogen gas containing one isotope: protium, deuterium, or tritium, which make it possible to use the specific properties of each of these isotopes with respect to neutron scattering. In this case, deuterium and tritium nuclei located at a distance from the fissile nucleus, as measured by the lattice spacing of the crystal, for example, uranium hydride (~ 6.6 A), which gives two fragments with fission energy greater than 80 MeV and about two and a half neutrons with energy ~ 1 MeV each, when interacting with each of these objects, they can acquire energy above the threshold of the (D, T) synthesis reaction of ~ 30 keV and enter into this reaction with the formation of a helium nucleus and a neutron with an energy of ~ 14.1 MeV:

Thus, the inventive fuel of a nuclear fission reactor obtained using the inventive method has not only the property common for such fuels to provide a self-sustaining chain reaction of fission of heavy nuclei by neutrons, but also a new property to provide a non-self-sustaining fusion reaction of light nuclei heated by interaction with neutrons and fission products of heavy nuclei, and, ultimately, simultaneously produce neutrons and fission and fusion energy. This allows us to conclude that the claimed solution is characterized by an inventive step. Nuclear fuel of the type UD _1.5 T _1.5 can be used in materials science research reactors to create irradiating devices for testing materials from fusion power reactors under conditions more close to operational than when using conventional fission fuel from nuclear fission reactors due to the contribution of neutrons with energy of 14.1 MeV in the process of damage to the tested materials, as well as in fission energy reactors for additional energy production due to the synthesis reaction.

The drawing shows a diagram of an installation for saturation of samples of metallic uranium with hydrogen of the required isotopic composition, where

1 - furnace No. 1 with a reservoir for sponge titanium,

2 - receiver

3 - furnace No. 2 with a retort (reaction volume) for loading samples,

4 - nitrogen trap,

5 - cylinders with deuterium (D ₂ ) and tritium (T ₂ ).

The invention is illustrated by the following example.

Uranium enriched in uranium-235 90% is selected as a fissile element in hydride fuel for a nuclear reactor, and uranium hydride is a compound UD _1.5 T _1.5 and consists of particles from 0.1 to 100 microns in size or is a material products, for example, a fuel rod core.

A method of producing hydride fuel for a nuclear reactor by hydrogenating a powder of metallic uranium 90% enrichment in uranium-235 to a structure of type UD _1.5 T _1.5 is implemented using the installation shown in the drawing.

Hydrogenated samples in molybdenum cups are placed in a hydrogenation retort (reaction volume), which is pumped out to a pressure of 10 ^-3 -10 ^-4 Pa before the process.

Uranium metal products may be placed in the reaction volume, the dimensions of which correspond to the shape changes during hydrogenation of the sizes of the cores of the fuel elements of a nuclear reactor.

The retort is cut off from the vacuum system, purged with protium for 15 minutes and pumped out to a pressure of 10 ^-3 -10 ^-4 Pa.

Then, to degass the samples and form the structure of the material, the retort is heated to 300 ° C using an electric heater “Furnace No. 2” (3). Samples are kept at this temperature for 2 hours. Next, the retort is heated to 400 ° C at a speed of 2-5 degrees per minute with constant pumping.

The hydrogen supply system to the reaction volume (retort) in the installation includes cylinders with deuterium and tritium (5), which allows the hydrogenation components to be fed into the retort in batches in two or more stages (cycle) and performing saturation of samples from metallic uranium with any isotope hydrogen, first, for example, deuterium, and then tritium or in the reverse order.

A reservoir with sponge titanium preliminarily saturated with deuterium and tritium sequentially serves as a hydrogen source. The tank with a titanium sponge is brought to a temperature of 500-700 ° C using an electric heater “Furnace No. 1” (1). In this case, the overpressure in it reaches 0.2-0.25 MPa. After that, through the receiver (2), deuterium (tritium in the second hydrogenation cycle) is supplied to the hydrogenation retort from the reservoir. The hydrogenation procedure includes the following steps:

- supply of deuterium (tritium in the second hydrogenation cycle) to the hydrogenation retort for 10 minutes to a pressure of ~ 2.5 MPa at a constant temperature of the samples;

- exposure of the samples for 2.5 hours at a temperature of 400 ° C at a given pressure of deuterium (tritium in the second hydrogenation cycle);

- cooling of the samples at a rate of 1 degree per minute to 200 ° C with a gradual decrease in pressure to 0.01 atm;

- homogenization-exposure for 12 hours in order to equalize the deuterium content (tritium in the second hydrogenation cycle) over the volume of the sample at specified pressure and temperature;

- cooling the samples to a temperature of 100 ° C at a rate of 1 degree per minute and then to room temperature with the oven turned off.

A nitrogen trap (4) serves to freeze moisture from the hydrogenating component.

Evaluation of the effectiveness of the proposed solution is made for the case of using the invention in the technological process of manufacturing fuel for experimental research nuclear reactors designed to form the energy spectrum of neutrons.

, осуществляемая в гидриде урана UD_1,5T_1,5. На один поглощенный ядром

тепловой нейтрон образуется два осколка этого ядра с суммарной энергией 166 МэВ, из которых на легкий осколок (А≈95,3) приходится в среднем 98 МэВ и на тяжелый осколок (А≈138,1) - 68 МэВ. Каждый из осколков способен передать нескольким легким ядрам (ядрам отдачи, в нашем случае дейтерия и трития) энергию выше порога реакции синтеза. Кроме того, высокоэнергетичные нейтроны деления также могут передать ядрам дейтерия и трития энергию выше порога реакции синтеза.In such devices, the fission reaction is used.

carried out in uranium hydride UD _1,5 T _1,5 . For one absorbed by the core

a thermal neutron produces two fragments of this nucleus with a total energy of 166 MeV, of which 98 MeV is a light fragment (A≈95.3) and 68 MeV is a heavy fragment (A≈138.1). Each of the fragments is able to transfer several light nuclei (recoil nuclei, in our case deuterium and tritium) energy above the threshold of the synthesis reaction. In addition, high-energy fission neutrons can also transfer energy to deuterium and tritium nuclei above the synthesis reaction threshold.

The average path of the recoil nucleus and the distribution of its energy E along the path length x was calculated using:

- Bethe-Bloch formulas with energy values above 1.5 MeV (the dependence of the specific energy loss - (dE / dx) on the velocity of the incident particle v is proportional to 1 / v ² );

- Bohr formulas obtained on the basis of the Thomas-Fermi atom model, with energy values from 1.5 to 0.55 MeV (- (dE / dx) is proportional to 1 / v);

- Fermi-Teller formulas at energies less than 0.55 MeV (- (dE / dx) is proportional to v).

(Principles and methods of registration of elementary particles. Edited by L.A. Artsimovich. Publishing House of Foreign Literature. M., 1963.

Experimental Nuclear Physics, Under. Ed. E. Segre. Publishing House of Foreign Literature. M., 1955.

S.V. Starodubtsev, A.M. Romanov. The passage of charged particles through matter. Publishing House of the Academy of Sciences of the Uzbek SSR. Tashkent, 1962).

-конвертера тепловых нейтронов в нейтроны с энергией 14,1 МэВ (Зуев Ю.Н. и др. Измерение эффективности

-конвертера тепловых нейтронов в нейтроны с энергией 14 МэВ в экспериментальном канале реактора ИВВ-2М. Атомная энергия, 2002 г., т.92, вып.3, с.226-233) с результатами расчетов этого коэффициента по описанной методике. По опубликованным данным величина коэффициента лежит в диапазоне (1,5-2,9)·10^-4, а расчетная величина составила 1,97·10^-4.The total probability of the fusion reaction of light nuclei was evaluated by integrating the probability distribution along their path. The methodology was tested by comparing the experimental results of the conversion rate estimation

converter of thermal neutrons into neutrons with an energy of 14.1 MeV (Zuev Yu.N. et al. Measurement of efficiency

converter of thermal neutrons into neutrons with an energy of 14 MeV in the experimental channel of the IVV-2M reactor. Atomic energy, 2002, vol. 92, issue 3, p. 226-233) with the results of calculations of this coefficient by the described method. According to published data, the coefficient value lies in the range (1.5-2.9) · 10 ^-4 , and the calculated value was 1.97 · 10 ^-4 .

The velocity distributions of the deuterium and tritium nuclei as a result of interaction with the fission products of the nuclei were calculated using the Rutherford formula (S.V. Starodubtsev, A.M. Romanov. Passage of charged particles through matter. Publishing House of the Academy of Sciences of the Uzbek SSR. Tashkent, 1962.) and as a result of interaction with fission neutrons - according to the MCU neutron-physical calculation program (MCU-RR program with the nuclear data library DLC / MCUDAT-2.1. Report of the RRC KI, inv. No. 36 / 16-2000. M., 2000).

The calculation results are given in table 1.

Table 1
The yield of fusion reactions of deuterium and tritium nuclei per nuclear fission

Kickback accelerator initiator Exit, 10 ^-5 Neutron fission 6.0 Light shard 4.6 Heavy Shard 7.2 In total 17.8

Thus, the conversion coefficient of thermal neutrons into high-energy synthesis neutrons for the proposed fuel material

, даже если консервативно принять, что при замедлении осколка деления ядра

в ядерных столкновениях он ускоряет только два ядра дейтерия или трития выше порога реакции синтеза. Так как способность повреждать материалы у термоядерных нейтронов существенно выше, чем у нейтронов деления, их вклад в скорость повреждения образцов в экспериментальных устройствах, использующих топливо UD_1.5T_1.5, будет достаточным, чтобы оценивать возможность использования новых материалов в ядерных реакторах синтеза лучше, чем в устройствах с другими конвертерами или без конвертеров.UD _1.5 T _1.5 will not be lower than the corresponding coefficient for a known converter based on

, even if it is conservatively accepted that while slowing down a fission fragment

in nuclear collisions, it accelerates only two nuclei of deuterium or tritium above the threshold of the synthesis reaction. Since the ability to damage materials of thermonuclear neutrons is significantly higher than that of fission neutrons, their contribution to the damage rate of samples in experimental devices using UD _1.5 T _1.5 fuel will be sufficient to assess the possibility of using new materials in nuclear fusion reactors better than in devices with or without other converters.

The contribution of fusion neutrons to the rate of damage to materials depends on the specific design of the device.

As a fissile element, uranium with a high enrichment in uranium-233 can be selected, and uranium hydride can be a compound of the type UD _1.5 T _1.5 or plutonium in compounds of the type PuDT or PuD _1.5 T _1.5 . The method for producing hydride fuel for a nuclear reactor in these cases is similar to that considered in the example. The modes of the process are selected in accordance with the properties of the fissile element and its hydrides.

Thus, the claimed solution allows to achieve this goal, since it creates the conditions for the simultaneous occurrence of nuclear fission and fusion reactions in nuclear fission reactors and for the production of fission and fusion energy and neutrons, and therefore the conditions for testing the materials of synthesis reactors in research reactors, close to operational.

Claims (10)

1. Hydride fuel for a nuclear reactor, including fission element hydride, characterized in that the fission element hydride contains heavy hydrogen isotopes of deuterium and tritium, preferably in equal and maximum concentrations. 2. Hydride fuel according to claim 1, characterized in that the hydride of the fissile element consists of particles ranging in size from 0.1 to 100 microns. 3. Hydride fuel according to claim 1, characterized in that uranium is selected as a fissile element, and uranium hydride is a compound UD _1.5 T _1.5 . 4. A method of producing hydride fuel for a nuclear reactor, including placing fissile material in a metallic state in a reaction volume, heating it with holding in a dynamic vacuum at a temperature higher than the temperature at which the fissile material and the hydrogenating component begin to interact, carrying out the hydrogenation process by feeding the hydrogenating component to the reaction volume with exposure at a hydrogenation temperature of fissile material and pressure control, subsequent cooling, characterized in that in deuterium and tritium are used as hydrogenating components, and deuterium and tritium are supplied alternately, and the hydrogenation process is preferably carried out until equal and maximum concentrations of hydrogenating components are achieved. 5. The method according to claim 4, characterized in that particles of metal uranium with sizes from 0.1 to 100 μm are placed in the reaction volume and a compound of the type UD _1.5 T _{1.5 is} obtained. 6. The method according to claim 4, characterized in that the reaction volume contains articles of metallic uranium, the dimensions of which correspond to the shape changes during hydrogenation of the sizes of the cores of the fuel elements of a nuclear reactor. 7. The method according to claim 4, characterized in that the deuterium and tritium in the reaction volume are served alternately in portions in two or more stages. 8. The method according to claim 4, characterized in that the hydrogenating components are fed into the reaction volume to a pressure of 0.2-0.25 MPa. 9. The method according to claim 4, characterized in that the exposure in the process of hydrogenation of metallic uranium is carried out at a temperature of 200-440 ° C. 10. The method according to claim 4, characterized in that in the process of hydrogenation of products from metallic uranium, cooling is carried out at a speed of not more than 1 ° C per minute.

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