A Numerical simulation of the melt relocation behavior in a severe accident using the JUPITER code; Experimental analyses of XR2-1 and LEISAN

Yamashita, Susumu   ; Yoshida, Hiroyuki  

The JAEA has developed a detailed thermal-hydraulic analysis code JUPITER based on mechanistic fluid flow simulation methodology to obtain melt relocation behavior instead of fuel assembly melt experiments. JUPITER has not only the capability to mechanistically analyze the relocation behavior and heat transport of melts with free interfaces, but also a eutectic and an oxidation reaction model, which have a significant impact on the accident progression. Although simulations have been performed for each model, simulations under the composite condition of these phenomena have not yet been performed. In order to confirm the feasibility of JUPITER for the experimental analysis of the melt relocation behavior under the composite condition, we applied JUPITER to the experimental analyses: XR2-1 experiment in which the melt conditions inside the mock-up fuel assembly of the BWR were obtained, and the LEISAN experiment in which the melting behavior of control rods due to steam concentration was observed. In the XR2-1 experimental analysis, the stainless steel/boron carbide (BC) and the Zircaloy melts were poured into the mock-up fuel assembly from the top boundary. Then, as in the experiment, several discharge paths of their melts were confirmed. In addition, the failure to the fuel assembly due to contact with the melts was also confirmed. In the LEISAN experiment analysis, the stainless steel control rod blade including the BC absorber was heated. As a result, the control rod melted at a temperature lower than the melting point of the stainless steel/BC due to the eutectic reaction between them.