Evaluation of nuclear characteristics of minor actinide loaded core; An analysis of BFS-67 critical experiment

Hazama, Taira ; Sato, Wakaei*; Ishikawa, Makoto; Shono, Akira

Collaboration between Russian Institute of Physics and Power Engineering (IPPE) and Japan Nuclear Cycle Development Institute (JNC) named (Investigation of neutronic-physical characteristics and their change when introducing large quantity of neptunium (Np) at different BFS critical assemblies) is under progress. This is the first report of the collaboration to describe experimental information and JNC analysis results on BFS-67 critical experiment. In BFS-67 experiment, nuclear characteristics (criticality, control rod worth, sodium void reactivity, reaction ratio, etc) were measured in 4 different cores with various amounts of Np and location. JNC analysis was perfomed based on a JNC standard analysis scheme as in the analyses of BFS-62 critical experiments. (1)Sensitivity coefficients of Np capture cross section for the sodium void reactivity and control rod worth are large enough and comparable to those of U-238 and Pu-239. This indicates the experimental data can be used to improve design accuracy of Np loaded core. (2)C/E values for the criticality show high accuracy of 0.995 independent of core patterns, indicating accuracy of the calculation is high enough. (3)Calculated values for the sodium void reactivity agree with experimental values within 1cent and there is no influence of Np loading on calculation accuracy. (4)Calculated values for the control rod worth agree with experimental values within experimental errors for enriched B4C control rod. Those for naturaI B4C slightly overestimate. An influence of Np loading is not observed. (5)Calculated values for the reaction ratio agree with experimental values within 5% for fission reactions, whereas those for capture reactions show nearly 10% of differences. Positions of foils used in the measurement should be reflected.