PRELIMINARY EVALUATION OF SIMILARITY BETWEEN THE MODIFIED STACY CORE CONFIGURATIONS AND THE PSEUDO-FUEL DEBRIS MODELS

抄録

The Nuclear Regulation Authority (NRA) has tackled the experimental approach for determining the criticality of pseudo-fuel debris plausibly simulating actual fuel debris since 2014, collaborating with the Japan Atomic Energy Agency. To elucidate the characteristics of the pseudo-fuel debris, the Japan Atomic Energy Agency modified the STACY (STAtic experiment Critical facilitY) to conduct critical experiments simulating fuel debris. Thus, we proposed three types of modified STACY core configurations.

In critical experiments in the modified STACY core, it is important to judge whether the proposed modified STACY core configurations are representative of pseudo-molten core– concrete interaction debris or not. In this study, we built pseudo-fuel debris models considering a volume ratio of pseudo-fuel debris to moderation (V_m/V_f) and calculated uncertainty-based similarity values (C_k) between the modified STACY core configurations and pseudo-fuel debris models using Tools for Sensitivity and Uncertainty Analysis Methodology Implementation-Indices and Parameters (TSUNAMI-IP) in SCALE 6.2. Consequently, the modified STACY core configuration loading structure rods we proposed completely resulted in high similarity to the pseudo-fuel debris models through Vm/Vf values. The main contributions to C_k values were ²³⁵U nu-bar, ²³⁵U chi, and ⁵⁶Fe (n,γ), except for the pseudo-fuel debris model, including extremely high concrete components.