Keywords:Fukushima Daiichi NPP, severe accident, cesium, CAMS, dose rate
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 137Cs amounts in the S/C were evaluated. From the evaluation, two points were concluded. Transfer rate of cesium from the D/W to the S/C for Unit 1 was 5 times larger than that for Unit 3. 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.