Irradiation experiments of simulated wastes of carbonate slurry

炭酸塩スラリー模擬廃棄物の照射実験

永石 隆二 ; 本岡 隆文; 山岸 功 

Nagaishi, Ryuji; Motooka, Takafumi; Yamagishi, Isao

多核種除去設備(ALPS)の高性能容器(HIC)中で起きた炭酸塩スラリーの液位上昇に伴うたまり水発生は、スラリー中のSr-90等からのベータ線による放射線分解に起因すると考えられるが、詳細は明らかにされておらず、その原因究明に関する実験的研究を東電、東芝、栗田工業と協力しながら段階的に進めてきた。実験では、水素が主要なガス生成物であり、海水成分のハロゲン化物イオンだけでなく凝集沈殿処理剤の炭酸イオンによってもその発生が促進されることがわかった。また、水素が溶存種から気泡に変わり高粘度のスラリーに保持されることで、スラリーの容積変化(膨張)が起こるとともに、照射下で特異に上澄み水が形成されることがわかった。

Overflow of water from waste storage tanks of High Integrity Containers (HIC) in the multi-nuclide removal equipment (ALPS) was discovered at Fukushima Daiichi NPS in April of last year. The mechanism of overflow was not understood very much at that time. To elucidate that for chemical safety in the waste storage, irradiation experiments of simulated carbonate slurry by Co-60 -rays have been conducted in CLADS, JAEA in cooperation with TEPCO, TOSHIBA and KURITA. Hydrogen molecule was the main radiolytic gas product in the slurry, and its amount was enhanced by dissolved species of not only halide ions as seawater components but also carbonate ion as an additive for co-precipitation at a basic condition. The bubbles of molecules were further formed and almost held in the slurry without stirred. These sequentially led to the expansion of slurry, and then to its separation into the shrunk one and supernatant water, which was little accumulated without irradiated.