BWR RPV lower head penetration failure caused by eutectic reactions with Zr-rich simulated metal; ELSA-3 test

下村 健太 ; 山下 拓哉  

Shimomura, Kenta; Yamashita, Takuya

Internal investigations at the Fukushima Daiichi Nuclear Power Plant have been conducted by Tokyo Electric Power Company Holdings, however, the condition of the reactor pressure vessel (RPV) has not yet been confirmed. To clarify the RPV damage progression during the accident, a simulation test (ELSA-3) was conducted using the LEISAN test facility owned by JAEA, focusing on the interaction between a zirconium-containing liquid metal (Zr-rich materials) that discharged to the bottom of the RPV lower head and the lower head structural components, forming a liquid metal pool and potentially causing failure through eutectic reactions. The test results showed that at the lower head penetration region, the eutectic reaction between the simulated metal debris and the lower structural components (CRD housings and CRD stub tubes) caused melting of the structural components, allowing the simulated metal debris to flow into the CRD housings. This eutectic reaction temperature is below the melting point of the individual structural materials, indicating that failure can occur due to inter-material eutectic reactions even without reaching the melting point. These results suggest that for Zr-rich molten materials, damage may occur through eutectic reactions between materials even below their melting points.