[3G06-08] Behavior of Radioactive Nuclides & Fuel Debris 2

[3G08] Evaluation of Short and Long-Term Behavior of Radioactive Nuclides Distributed in Fukushima Daiichi NPP

8.Evaluation of cesium amounts in the D/W bottom region based on backward evaluation from CAMS data

*Shunsuke Uchida¹, Hidetoshi Karasawa¹, Chiaki Kino², Masahiko Ohsaka¹ (1. JAEA, 2. IAE)

Keywords:Fukushima Daiichi NPP, severe accident, cesium, CAMS

The cesium amounts in the major partial zone of the D/W and S/C of Units 1 – 3 have been evaluated by applying the backward evaluation procedure (BEP) with the previously reported dose rate conversion factors (#7). As a result of comparing the BEP results with those of the forward evaluation procedure (FEP) based on the SA analysis code, the conclusions are summarized as follows.
The measured dose rate for A and B detectors of D/W CAMS for Unit 1 showed the different patterns, which could be clearly explained by applying local wash-out effects. The Cs amounts in the D/W bottom regions for Units 1 – 3 could be evaluated by the BEP. The Cs amounts obtained with the BEP in the D/W bottom region and S/C for Unit 1 were consistent to those with the FEP. The Cs amounts obtained with the BEP in the D/W bottom regions for Units 2 and 3 were more than 10 times as large as those with the FEP. It was concluded that sufficient care should be put on the discrepancy while the FP distribution in the PCV for preparing the safe fuel debris removal was calculated with SA analysis code.