LIVE-J1 experiment on debris melting behavior toward understanding late in-vessel accident progression of the Fukushima Daiichi Nuclear Power Station

福島第一原子力発電所における後期炉内事故進展の解明に資するデブリ溶融挙動に関するLIVE-J1試験

間所 寛  ; 山下 拓哉  ; 佐藤 一憲 ; Gaus-Liu, X.*; Cron, T.*; Fluhrer, B.*; Stngle, R.*; Wenz, T.*; Vervoortz, M.*; 溝上 伸也

Madokoro, Hiroshi; Yamashita, Takuya; Sato, Ikken; Gaus-Liu, X.*; Cron, T.*; Fluhrer, B.*; Stngle, R.*; Wenz, T.*; Vervoortz, M.*; Mizokami, Shinya

Debris and molten pool behavior in the reactor pressure vessel (RPV) lower plenum is a key factor to determine its failure mode, which affects the initial condition of ex-vessel accident progression and the debris characteristics. These are necessary information to accomplish safe decommissioning of the Fukushima Daiichi Nuclear Power Station. After dryout of the solidified debris in the lower plenum, metallic debris is expected to melt prior to the oxide debris due to its lower melting temperature. The lower head failure is likely be originated by the local thermal load attack of a melting debris bed. Numerous experiments have been conducted in the past decades to investigate the homogeneous molten pool behavior with external cooling. However, few experiments address the transient heat transfer of solid-liquid mixture without external cooling. In order to enrich the experimental database of melting and heat transfer process of debris bed consisted of materials with different melting temperatures, LIVE-J1 experiment was conducted using ceramic and nitrate particles as high melting and low melting temperature simulant materials, respectively. The test results showed that debris height decreased gradually as the nitrate particles melt, and molten zone and thermal load on vessel wall were shifted from bottom upwards. Both conductive and convective heat transfer could take place in a solid-liquid mixture pool. These results can support the information from the internal investigations of the primary containment vessel and deepen the understanding of the accident progression.