Low Enrichment Nuclear Fuel Based on Uranium-Zirconium Carbonitride: Reactor Tests and Preparation for Studies at Critical Assemblies

Uranium-zirconium carbonitride has been developed at the Federal State Unitarian Enterprise Scientific Research Institute the Scientific Industrial Association "Luch " (LUCH FSUE) and is a high-density high-temperature fuel with high heat conductivity capable of being used in various types of reactors, including fast reactors. The main problem hindering wide application of this fuel is insufficient knowledge of its behavior under irradiation, especially at high burnup. In the USSR, HEU UZrCN (96% by U-235) fuel underwent reactor testing to a low burnup of approximately 1%. However, to confirm practical applicability of this fuel, the fuel needs to be reactor tested at a high burnup. In the framework of a joint Belarussian-American-Russian effort, LEU (19.75% by U-235) UZrCN fuel will undergo reactor testing to a burnup of approximately 40% in the SM-3 reactor at the Joint Stock Company "State Scientific Center Research Institute of Atomic Reactors " (JSC "SSC RIAR "). To conduct the prolonged reactor experiment, an irradiating device with an experimental capsule containing UZrCN pellets has been made, neutronic analysis and thermophysical analysis have been carried out and a programme of pre-irradiation experiments has been implemented. In June 2019 a methodical experiment was carried out in the SM-3 reactor at the JSC "SSC RIAR " in order to confirm operability of the irradiating device developed. Testing of the irradiating device and refinement of the prolonged irradiation experiment procedure were carried out at cell 11 of the reflector of the SM-3 reactor at the JSC "SSC RIAR ". The period of irradiation equaled 23.3 effective days. The mean power density in the tested pellets throughout the methodical reactor testing was 516 W/cm(3). Burnup achieved for the pellets studied was 0.63% FIFA. The "Giacint " and "Kristal ", critical facilities of the State Scientific Institution "The Joint Institute for Power and Nuclear Research -Sosny " (the Scientific Institution "JIPNR - Sosny ") will be used for studying neutronic characteristics of critical and subcritical fast assemblies simulating the physical particulars of the cores of advanced gas-or liquid metal cooled fast reactor systems and accelerator driven systems. This paper provides a detailed description of the results of preparatory works for conducting the reactor testing and the results of the methodical reactor experiment. Also the experimental programme and the descriptions of the design and composition of the fast critical assemblies with UZrCN fuel are presented.