浅地中環境下におけるウラン系列核種の分配係数測定, 1

Measurement of distribution coefficients for uranium series radionuclides under shallow land environment condition, 1

石井 友章*; 稲川 聡*; 軍司 康義*; 坂本 義昭 ; 武部 愼一; 小川 弘道; 佐々木 朋三*

Ishii, Tomoaki*; Inagawa, Satoshi*; Gunji, Yasuyoshi*; Sakamoto, Yoshiaki; Takebe, Shinichi; Ogawa, Hiromichi; Sasaki, Tomozo*

ウラン廃棄物の浅地中処分の安全評価に必要となるウラン系列核種(鉛,ラジウム,アクチニウム,トリウム,プロトアクチニウム,ウラン)の分配係数を通気層環境及び帯水層環境で求めた。通気層環境としてはローム等の4種類の土と雨水の組み合わせ、帯水層環境としては砂等の3種類の土・岩石と地下水の組み合わせで各元素の分配係数をバッチ法により測定した。通気層環境と帯水層環境での分配係数を比べると、アクチニウム以外の元素で通気層環境での分配係数が帯水層環境よりも10倍~100倍大きい値が得られた。また、土の代表的な物性値である陽イオン交換容量(CEC)及び比表面積と各元素の分配係数の関係を求めた結果、鉛,ラジウム,プロトアクチニウムについてはおおむねこれらの物性値と分配係数に相関が認められた。

Distribution coefficients of Uranium series nuclide(Pb,Ra,Ac,Th,Pa and U) were obtained under aerated zone environment and aquifer environment, for the safety evaluation of shallow underground disposal of uranium bearing waste. The distribution coefficients of them on 4 kinds of soil such as the loam in the rain water as for aerated zone environment and on 3 kinds of soil and rock such as the sand in groundwater as for aquifer environment have been measured by batch method. The distribution coefficients in aerated zone environment were one or two orders in magnitude higher than that in aquifer environment, except Ac. And, there was approximately the linear correlation on the relationship between cation exchange capacity and specific surface area, which are representative physical property of the soil, and distribution coefficient of lead, radium and protactinium.