A review of simulated nuclear fuel cycles with mixed uranium-plutonium fuel (REMIX) was carried out. The concept of REMIX fuel is one of the options for closing the nuclear fuel cycle (NFC), which makes it possible to recycle uranium and plutonium in VVER-1000/1200 thermal reactors at a 100% core loading. The authors propose a new approach to the recycling of spent nuclear fuel (SNF) in thermal reactors. The approach implies a simplified fabrication of mixed fuel when plutonium is used in high concentration together with enriched natural uranium, while reprocessed uranium is supposed to be enriched and used separately. The share of standard enriched natural uranium fuel in this nuclear fuel cycle is more than 50%, the share of mixed natU+Pu fuel is 25%, the rest is fuel obtained from enriched reprocessed uranium. It is emphasized that the new approach has the maximum economic prospect and makes it possible to organize the fabrication of this fuel and nuclear material cross-cycling at the facilities available in the Russian Federation in the short term. This NFC option eliminates the accumulation of SNF in the form of spent fuel assemblies (SFA). SNF is always reprocessed with the aim of further using the primary reprocessed uranium and plutonium. Non-recyclable in thermal reactors, burnt, reprocessed uranium, the energy potential of which is comparable to natural uranium, as well as secondary plutonium intended for further use in fast reactors, are sent as reprocessing by-products to the storage area.
This work is devoted to the comparative analysis of various scenarios of transition to introduction of the closed nuclear fuel cycle and sodium fast reactors in nuclear power of Russia. The analysis of the permissible scale of introduction of water-water power reactors and fast sodium reactors into the Russian nuclear power system was carried out taking into account the estimated reserves of natural uranium, the expected volumes of spent nuclear fuel from both national and foreign nuclear power plants and the quantity of plutonium available for the introduction of fast sodium reactors. The rate of growth in the capacity of the nuclear power system is not yet high, the resources of natural uranium seem significant, the natural uranium mining facilities and the amount of depleted uranium have not yet been classified as encumbrances. In the current situation, the practical solution to the problems of closing the nuclear fuel cycle and transition to the trajectory of development of nuclear energy as a system that meets in the future the requirements of sustainable development and energy security can already be started with the use of mixed uranium-plutonium oxide fuel in combination with fuel from enriched regenerated uranium in existing water-water power reactors and in BN-800. This step is the most promising in terms of minimizing contradictions between the existing legal and institutional framework, allowing the development of closed fuel cycle technology and reducing the amount of spent nuclear fuel. Based on the assessment of the technical and economic characteristics of various scenarios for the long-term development of the two- component nuclear power system in Russia, several possibilities for reducing the cost of implementing the transition stage from open to closed nuclear fuel cycle.
The VVER-1000 thermal neutron reactor can operate on mixed uranium-plutonium fuel with a content of reactor-grade plutonium up to 5% with a 100% loaded core. In this case, plutonium burns up to 56% of odd isotopes. The energy potential of such plutonium is very low, and its further use in thermal reactors is impractical. However, such plutonium can be used in fast neutron reactors. The paper presents the results of investigating the possibility for such isotopic plutonium composition to be used in the BN-1200 thermal neutron reactor and its value be increased for the plutonium recycle in the reactor. For this purpose, a precision model of the BN-1200 reactor has been developed using the Serpent Monte Carlo code. The model has been verified against the reference values of the nuclear fuel burnup and breeding ratios. The study has shown that such plutonium can be used in the BN-1200 reactor MOX fuel. Maintaining the operating cycle length requires the plutonium fraction in the MOX fuel to be increased up to 2%. In the BN-1200 reactor, the isotopic composition has been found to improve for the further recycle of plutonium in the thermal reactor, i.e. odd plutonium isotopes increase. The fewer odd plutonium isotopes at the beginning of the BN-1200 operating cycle, the greater their increase. It can be seen as the result of the calculation that plutonium from VVER-1000 spent mixed fuel must be loaded into the BN-1200 reactor at least twice to increase the fraction of odd isotopes to the level of reactor-grade plutonium.
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