Nuclear fuel cycle remixing

Abstract

The present invention relates to the field of nuclear technology, in particular to uranium-plutonium oxide nuclear fuel for nuclear power plants with thermal neutron reactors. The technical result of the present invention is the development of a REMIX-type fuel component that allows nuclear fissionable material recovered from spent nuclear fuel to enter the nuclear fuel cycle and simultaneously use enriched natural uranium, as well as ensuring that the problem of handling previously separated plutonium (including weapon-grade plutonium) is solved. By recycling the fissionable material in spent nuclear fuel during the life of a nuclear reactor, the amount of spent nuclear fuel is reduced (up to 5 times), natural uranium used for fuel manufacturing is saved, and thus the self-sufficiency of the nuclear fuel cycle is ensured. The present invention makes it possible to use REMIX-fuel to solve all the problems that may arise in a closed nuclear fuel cycle, while taking into account the number of reactors, the availability of natural uranium, and the accumulated amount of spent nuclear fuel.

Description

Technical Field

[0001] The invention belongs to the field of nuclear technology, in particular to uranium-plutonium oxide nuclear fuel for a nuclear power plant with a thermal neutron reactor. Background Art

[0002] Currently, Russia has accumulated about 22,500 tons of processed nuclear fuel, and the amount of processed nuclear fuel unloaded from reactors increases by 650-700 tons each year. The spent nuclear fuel management strategy envisions two options: reprocessing of spent nuclear fuel with the recovery of uranium and plutonium and conditioning of radioactive waste, or direct disposal of spent nuclear fuel in geological formations.

[0003] The most efficient way to dispose of spent nuclear fuel is to incorporate it into a closed nuclear fuel cycle, where the fissile material (uranium and plutonium) contained in the spent fuel is reprocessed and returned to the fuel cycle (recycling). Closed nuclear fuel cycles can be achieved using fast neutron and thermal reactors. In these cases, the fuel for fast reactors (MOX) is uranium-plutonium oxide fuel, which is made from depleted spent uranium and plutonium recovered from spent nuclear fuel.

[0004] A closed nuclear fuel cycle with thermal neutron reactors can be achieved by using REMIX fuel as nuclear power plant fuel, which consists of uranium and plutonium separated from spent nuclear fuel, enriching part of the regenerated uranium and adding enriched natural uranium to provide an energy potential equivalent to that of enriched natural uranium fuel (for use in water kinetic reactors).

[0005] A known fuel composition for water-cooled thermal neutron reactors in nuclear power plants (Patent No. RU 2537013, published on December 27, 2014) was selected as a prototype. It consists of a mixture of regenerated plutonium and enriched uranium in the form of oxides. The enriched regenerated uranium is used as the enriched uranium, with the composition ratio determined by its energy potential, which corresponds to the energy potential of freshly prepared nuclear power plant fuel with 100% of the reactor core load provided by enriched natural uranium.

[0006] Specifically for a typical WWR-1000 with a spent nuclear fuel burn rate of 50 GW*day / tonne, this composition contains recycled plutonium with an enrichment of up to 5.25% plutonium and 4.2-3.5% uranium-235, mixed with other isotopes, while providing the same energy potential as fresh natural uranium fuel with a 4.33% uranium-235 content. This composition may contain recycled plutonium and some uranium that has been recycled without enrichment.

[0007] The fuel composition is irradiated in a dedicated batch reactor in maximum burnup mode with an increased number of overloads, so that the spent nuclear fuel (or the entire spent nuclear fuel) is no longer interesting for recycling in a closed nuclear fuel cycle in terms of the amount of uranium-235 isotope.

[0008] After reprocessing spent nuclear fuel using the Purex process, plutonium is re-extracted in a mixture with partially recovered uranium. The uranium obtained in a subsequent stage is evaporated and denitrated, and the uranium oxide is fluorinated. The resulting uranium hexafluoride is enriched with uranium-235 to a content of 5-6%. This product is defluorinated, and the oxide is dissolved in the re-extracted product to achieve the calculated isotopic composition. The mixed product is denitrated, and the resulting solid solution of uranium and plutonium oxide mixture is used to manufacture fuel pellets and then fuel assemblies. A small amount (up to 10%) of enriched natural uranium may be added to the enriched regenerated uranium to adjust its energy potential.

[0009] Disadvantages of known fuel components include the need to use a separate technological route to enrich the regenerated uranium that is one of the fuel components. Summary of the Invention

[0010] The aim of the present invention is to develop a REMIX-type fuel composition having an energy potential equivalent to that of freshly prepared nuclear power plant fuel made from enriched natural uranium and providing 100% loading for thermal reactor cores.

[0011] The technical result of the present invention is the development of a REMIX-type fuel component that allows nuclear fissionable material recovered from spent nuclear fuel to enter the nuclear fuel cycle and simultaneously use enriched natural uranium, as well as solving the problems of disposing of previously separated plutonium (including weapons-grade), reducing spent nuclear fuel and recovering fissionable material from spent nuclear fuel during the aforementioned period.

[0012] To achieve this technology, the REMIX fuel of the nuclear fuel cycle consists of a mixture of recycled plutonium and enriched uranium in the form of oxides, providing the same energy potential as enriched natural uranium fuel and the possibility of 100% loading the reactor core with thermal neutrons. Therefore, in order to provide the same energy potential as enriched natural uranium fuel, REMIX fuel contains 1-2% by mass of uranium with an isotopic content of more than 51% plutonium-239 obtained from the reprocessing of spent nuclear fuel from WGPU-type reactors, 17-19% by mass of enriched natural uranium with an isotopic content of 19.75% uranium-235, and recycled uranium obtained from the reprocessing of spent nuclear fuel from WGPU-type reactors with a mass fraction of more than 80%.

[0013] The specific content of recycled uranium and plutonium in REMIX fuel makes it possible to use REMIX fuel to meet the full range of challenges posed by a closed nuclear fuel cycle, taking into account the number of reactors, the availability of natural uranium, and the accumulation of spent nuclear fuel.

[0014] The source recycled plutonium and uranium for REMIX fuel can be either separately obtained products or an unfractionated mixture of uranium and plutonium separated during the reprocessing of spent nuclear fuel.

[0015] At the Federal State Unitary Enterprise Mining and Chemical Combine's Experimental and Demonstration Center (Federal State Unitary Enterprise Mining and Chemical Combine), spent nuclear fuel from hydroelectric reactors undergoes radiochemical reprocessing (using the simplified Purex process) to produce a mixture of unfractionated uranium and plutonium. Partial enrichment of natural uranium, as well as the production of nuclear fuel pellets, fuel elements, and fuel assemblies, is carried out using known technologies.

[0016] The fuel assemblies are irradiated in a series of reactors of the water-cooled power reactor type (with a combustion capacity exceeding 50 GW*day / ton).

[0017] The plutonium content of the REMIX fuel composition is 1-2% by weight, which allows, after minor modifications (in terms of personnel radiation protection), to use nuclear fuel production lines for enriching natural uranium as efficiently as possible to produce REMIX fuel.

Claims

1. REMIX fuel for the nuclear fuel cycle, comprising a mixture of regenerated plutonium and enriched uranium in the form of oxides, providing the same energy potential as enriched natural uranium fuel and suitable for 100% loading of a thermal neutron reactor core, characterized in that REMIX FUEL CONTAINS: Plutonium obtained by processing spent nuclear fuel of the water-cooled power reactor type, with a mass fraction of 1-2% and a content of the isotope plutonium-239 exceeding 51%; Natural uranium enriched to 17-19% by mass and 19.75% uranium-235; and Regenerated uranium with a mass fraction of more than 80% from the reprocessing of spent nuclear fuel from hydropower reactors.