[1I01-04] Criticality Safety of Fuel Debris

[1I04] Radiolysis gas reactivity feedback effect on prompt supercritical transient analysis of fuel debris

*Kodai Fukuda¹, Jun Nishiyama², Toru Obara² (1. Graduate major in Nuclear Engineering, Tokyo Institute of Technology, 2. Laboratory for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology)

Keywords:Criticality safety, Prompt supercritical transient analysis, Radiolysis gas reactivity feedback effect, Fuel debris, Fukushima Daiichi NPS decommissioning

Transient analysis for possible prompt supercritical accidents of fuel debris is important. In such analysis, it is necessary to include reactivity feedback effects properly. In this study, an analysis was performed in order to reveal reactivity effect of radiolysis gas void on prompt supercritical transient analysis in fuel debris systems.

In the analysis, radiolysis gas calculation was conducted using power profile which was obtained by the MIK code with Doppler feedback effect. The reactivity effect of the gas was analyzed by comparing generation time of the gas void and peak-time of the power.

It was concluded that the reactivity feedback effect of the radiolysis gas void can be ignored for the prompt supercritical transient analysis in the fuel debris systems.