Characterization of sludge generated from decontamination device in Fukushima Daiichi NPS

福島第一原子力発電所における除染装置の運転に伴い生成されるスラッジの性状調査

比内 浩; 佐藤 大輔; 柴田 淳広  ; 明道 栄人 ; 駒 義和  ; 野村 和則  

Hinai, Hiroshi; Sato, Daisuke; Shibata, Atsuhiro; Myodo, Masato; Koma, Yoshikazu; Nomura, Kazunori

福島第一原子力発電所で発生した汚染水と汚染水処理で発生した二次廃棄物の性状調査のため分析を行っている。汚染水処理システムの1つとして、除染装置が運転され、高線量率を有するスラッジが二次廃棄物として発生した。スラッジは地下コンクリートピットに貯蔵されており、別場所への移送と、さらなる貯蔵のための処理が求められ、このスラッジを移送・安定化処理するため、種々の性状を把握することが必要であった。このためスラッジを放射能, 粒度分布などについて分析を行った。

We have been analyzing and characterizing the contaminated water generated in Fukushima Daiichi Nuclear Power Station (NPS) and secondary waste of the contaminated water treatment system for investigation of their waste management. As one of the contaminated water treatment system, Decontamination Device was operated from June until September 2011. The operation of this device generated secondary waste of sludge that have a high dose rate. In this device, the contaminated water was mixed with several reagents to remove some radioactive nuclides. As the result, the sludge was generated as a complex of chemically stable substances. This sludge has been stored in a concrete pit and is required to transport to another place of the site and treat for further storage. For the purposes and upcoming disposal, a small amount of the sludge was analyzed for its radioactivity, particle size distribution and others. For radiochemical analysis, the sludge was successfully dissolved into solutions and was measured for its radioactivity composition; the main nuclides were Sr-90 and Cs-137. The concentration of Sr-90 (6.6E7 [Bq/cm]) was about 10 times higher than that of Cs-137 in the sludge. And small amount of Pu-238 as alpha-ray emitting nuclide was determined. The sludge mainly contained small particles of 10 micro meter or less in diameter. The rate of sedimentation and behavior of mixing also investigated.