Gradual transition from the IRT-2M fuel with 80 % U235 enrichment to the IRT-2M fuel with 36 % U235 enrichment. Supplement to the Operational Safety Report of the LVR-15 reactor

Since highly enriched fuel will no more be available for research reactors, the spent IRT-2M fuel elements with 80 % U-235 enrichment will be gradually replaced with elements having a 36 % U-235 enrichment. The process will be stepwise. The report concerns the first step, where 2 assemblies are to be replaced in this manner, and its aim was to prove that nuclear safety will be maintained. The topics treated were as follows: description and design of the new fuel, compatibility of the new fuel assembly materials with relevant materials of the reactor, analysis of the neutron physical properties of the 1st mixed zone, a steady-state thermohydraulic calculation of the configuration involving up to 2 new fuel assemblies, and compliance with the requirements specified by the Decree of the Czechoslovak Atomic Energy Commission No. 9/1985 for fuel with a lower degree of enrichment during normal operation, in abnormal operating conditions, and in accident conditions. It is concluded that the criteria prescribed by the fuel manufacturer are satisfied, the material of the fuel assemblies is compatible with the materials of the LVR-15 reactor, and the design and strength stability requirements put on the new fuel assemblies are met. (P.A.). 18 tabs., 43 figs