The use of MOX fuel in BN-800 reactor

Abstract

In accordance with the strategy for the development of two-component nuclear energy with NFC closure adopted in the Russian Federation, fast neutron reactors must ensure the effective use of mixed uranium-plutonium fuel based on plutonium extracted from SNF of thermal reactors, and then from their own SNF. The first domestic BN reactors used fuel developed by that time based on enriched uranium dioxide. The development of mixed uranium-plutonium oxide (MOX) fuel began with the irradiation of experimental fuel assemblies (FAs) in the research reactor BOR-60, as well as in power reactors BN-350 and BN 600. The BN-800 design was already focused on the use of mixed uranium-plutonium fuel. Due to the delay in the launch of industrial production of MOX fuel created at the Mining and Chemical Combine, the BN-800 was launched (2016) with a hybrid core formed mainly from FAs with uranium fuel manufactured at MSZ JSC. The share of FAs with MOX fuel manufactured at the pilot production facilities of JSC SSC RIAR and the Production Association MAYAK was 16%. The hybrid core was operated until the eighth operation cycle. The transition of BN-800 core to a full loading with MOX fuel was completed by the beginning of the 13-th operation cycle (2023). For fabrication of MOX fuel, plutonium of various isotopic compositions is used, which is ensured by the method implemented at the production site for adjusting the mass fraction of plutonium in the fuel. Currently, the core is being transferred to FAs with fuel cladding from more radiation-resistant steel EK164-CW, which will subsequently allow starting work to increase fuel burnup. At that, compared with current core operation mode with the use of ChS68-CW steel for pin cladding, it is planned to increase fuel burnup from 9.5% h.a. up to 12% h.a. by the maximum value and from 66 MW·d/kg to 86 MW·d/kg by the average value. As part of the development of the technology for burning out minor actinides from the 14-th operation cycle (2024), three FAs have been irradiated in the reactor, which include four fuel elements each with the addition of americium (0.9%) and neptunium (0.6%).