The results of calculations of the neutron-physical characteristics of three variants of the fuel load in a VVÉR-1000 core are presented: a load consisting completely of enriched natural uranium (standard fuel) or reprocessed uranium-plutonium fuel from the first and second recycles. The calculations were performed for a stationary load of the core with a four-year fuel run. The difference between the neutronphysical characteristics of a core with a full load of uranium and reprocessed uranium-plutonium fuel is discussed. An analysis of the neutron-physical characteristics did not show any fundamental limitations for a possible 100% load of reprocessed uranium-plutonium fuel in a VVÉR-1000 core.Recirculating reprocessed uranium and plutonium in thermal reactors could increase the utilization efficiency of nuclear fuel and expand the resource base of nuclear power [1]. At the present time, experience has been gained in using reprocessed uranium and plutonium separately in thermal reactors. In our country, the uranium separated from spent VVÉR-440 fuel is mixed with the uranium extracted from spent BN-600 fuel and then usud for fabricating RBMK-1000 fuel [2]. The same scheme is used to fabricate fuel for experimental-commercial operation of fuel elements with reprocessed uranium in VVÉR-440 and -1000 reactors [3]. Plutonium separated from spent PWR fuel is used abroad, mainly in France, as a component of mixed fuel (a mixture of reprocessed plutonium and depleted or natural uranium) which is loaded into 30% of the PWR core [4,5].It has been proposed that fuel made from uranium and plutonium which are separated from the spent fuel of thermal reactors be used in these reactors as fuel after other actinides and fission products are removed and enriched natural uranium is added, taking account of the compensation of the even isotopes of uranium and plutonium [6,7]. It was supposed that because the content of plutonium in the reprocessed uranium-plutonium fuel is relatively low such fuel can make up 100% of the load of a VVÉR-1000 core.To check this assumption, the neutron-physical characteristics of three variants of a stationary load of a four-year run of fuel in a VVÉR-1000 reactor were analyzed. In the first variant, the load consisted entirely of fuel enriched with natural ura-UDC 621.039.516

The results of a calculation of the neutron-physical characteristics of different variants of the fuel load of a VVER-1000 core are presented. The load completely consists of either enriched natural uranium (standard fuel) or recovered fuel, consisting of a uranium-plutonium mixture of recovered material, recovered plutonium, and highly enriched uranium. The mass fraction of plutonium isotopes in the recovered fuel ranged from 2 to 5%. All load variants examined have the same energy potential. The neutron-physical characteristics of a core with a full load of uranium are compared for a core with recovered uranium-plutonium fuel. Analysis of the neutron-physical characteristics did not show any fundamental limitations on the possibility of a VVER-1000 core load consisting entirely of recovered uranium-plutonium fuel.It is proposed in [1] that fuel based on recovered uranium-plutonium (an unseparated mixture of isotopes) which is separated from the spent fuel from thermal reactors and from which other actinides and fission products are removed and is mixed (taking account of the compensation and even isotopes of uranium and plutonium) with enriched natural uranium be used in thermal reactors. The specific consumption of natural uranium in the production of such fuel is approximately 20% lower than for fabrication of uranium fuel, and the specific separation work required to enrich the uranium part of the mixture remains almost unchanged [2]. The neutron-physical characteristics of a core with a 100% load of uranium and recovered uranium-plutonium fuel which affect the VVER-1000 operating safety differed negligibly, since the mass fraction of plutonium in the recovered fuel is approximately 1% [2].The required content of fissile nuclides in the fuel can be obtained by adding to the reprocessed uranium-plutonium and mixture, together with enriched natural uranium, the plutonium separated from spent VVER-440 fuel. Many years of European experience has validated the possibility of using in PWR plutonium mixed with uranium-plutonium fuel (mixture of recovered plutonium and depleted uranium) with mass fraction of plutonium fissile isotopes 4-6% [3].

One scenario for using excess Russian weapons plutonium is to load it into VVÉR-1000 reactors. It is proposed that up to 40% of the fuel assemblies with uranium fuel be replaced with structurally similar fuel assemblies with mixed uranium-plutonium fuel. The stationary regime for burning fuel has the following characteristics: the run time is about 300 or 450 eff. days, the yearly plutonium consumption reaches 450 kg, the neutron-physical characteristics are close to the corresponding regimes with uranium fuel. The nuclear safety criteria and the irradiation dose for workers handling fresh and spent mixed fuel remain within the limits of the normative values. The use of mixed fuel makes it necessary to upgrade certain systems at nuclear power plants. A substantial quantity of weapons plutonium can be loaded every year into VVÉR-1000 reactors, effectively using the energy potential of this plutonium.One currently considered scenario [1] envisions using excess weapons plutonium in mixed uranium-plutonium fuel for VVÉR-1000 reactors. When such fuel is adopted in operating power generating units, the following conditions must be satisfied:• adoption of the fuel should not decrease the production of electricity or lower the uranium fuel utilization efficiency; • the energy potential of weapons plutonium should be used effectively for electricity production;• the isotopic composition of the removed plutonium should be close to that of power plutonium. This article summarizes the results of investigations performed over the last five years [2][3][4][5]. The neutron-physical characteristics of a VVÉR-1000 core with a partial load of mixed uranium-plutonium fuel, the salient features of the irradiation of three experimental fuel assemblies, licensing of computational programs, the nuclear and radiation safety when handling such fuel, the required upgrading of the systems of a nuclear power plant, and other aspects are discussed.The results presented below were obtained within the framework of Russian-American and Russian-French intergovernmental agreements concerning the salvaging of weapons plutonium. Specialists from the Physics and Power Engineering Institute, OKB Gidropress, All-Russia Research Institute for Standardization in Machine Engineering, and the All-Russia Research Institute of Nuclear Power Plants participated at different stages of this work. A substantial fraction of the neutron-physical and thermohydraulic calculations was repeated using domestic computational tools or analyzed by specialists at Oak Ridge National Laboratory (USA), the Atomic Energy Commission and the firm Framatom (France), and previously the Society for Safety of Systems and Reactors, the Siemens Company (Germany).Characteristics of Mixed Uranium-Plutonium Fuel. Fuel made of weapons quality plutonium is expected to be fabricated according to the European technology MIMAS [6], based on mixing UO 2 and PuO 2 powders. Depleted uranium contains 0.1-0.2 mass% 235 U. The following isotopic composition of plutonium was assumed for computation...

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