福島第一原子力発電所での放射性核種の短/長期挙動の評価,7; CAMSデータからの逆解析によるS/C水中のセシウム量の評価

Evaluation of short and long-term behavior of radioactive nuclides distributed in Fukushima Daiichi NPP, 7; Evaluation of cesium amounts in the S/C water based on backward evaluation from CAMS data

内田 俊介; 逢坂 正彦  ; 唐澤 英年; 木野 千晶*

Uchida, Shunsuke; Osaka, Masahiko; Karasawa, Hidetoshi; Kino, Chiaki*

S/CおよびD/W主要部位に存在する主要核種からCAMS位置での線量率を求めるための線量率変換係数を求めた。この変換係数を用いた逆解析により、福島第一原子力発電所各号機のS/C水中のCs量を求めた。この解析により、以下の点が明らかにされた。(1)1号機ではS/CへのCsの移行率が3号機の2倍強と大である。(2)1号機では事故後S/C気相部壁面への移行が顕著で、長時間かけて水相に移行するが、3号機では気相部への移行は観測されない。上記(1)については、Csの化学形態の差異によるものと推定するが、(2)の気相への移行率の差異についてはまだ原因は同定できていない。

Dose rate conversion factors have been calculated to obtain the dose rate at CAMS detector locations from major FP species in the major partial zone of the D/W and S/C. Based on backward analysis with the conversion factors, the Cs amounts in the S/C were evaluated. From the evaluation, two points were concluded. (1) Transfer rate of cesium from the D/W to the S/C for Unit 1 was 2 times larger than that for Unit 3. (2) Transfer of cesium from the S/C water phase to gas phase, especially the S/C wall, was larger than that expected and the deposited cesium was transferred into water phase gradually. Transfer of cesium for Unit 3 was not observed. It was supposed that the differences in cesium transfers for both units might be mainly from cesium chemical forms, while differences in transfer rate from water phase to gas phase was not well explained yet.