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Uchida, Shunsuke; Karasawa, Hidetoshi; Kino, Chiaki*; Pellegrini, M.*; Naito, Masanori*; Osaka, Masahiko
Nuclear Engineering and Design, 380, p.111256_1 - 111256_19, 2021/08
Times Cited Count：6 Percentile：70.8(Nuclear Science & Technology)It is essential to grasp the long-term distributions of FP as well as fuel debris all over the Fukushima Daiichi Nuclear Power Plant (1F) for safe completion of its decommissioning projects. The fuel debris is going to be removed from the plant under the severe conditions of FP being scattered during major decommissioning work, and then, the decommissioning projects are going to be terminated by storing safely the removed debris as recovered fertile materials or as materials for final radioactive disposal. In order to determine the FP distribution in the plant for the long period from the accident occurrence to the termination of the plant decommissioning, procedures for analyzing multi-term FP behaviors were proposed. The proposed procedures should be improved by applying the FP data measured in the plant and validated based on the feedback data. Then, the accuracy-improved procedures should be applied to estimate FP distribution during each period of the decommissioning projects.
Uchida, Shunsuke; Pellegrini, M.*; Naito, Masanori*
Nuclear Engineering and Design, 380, p.111303_1 - 111303_11, 2021/08
Times Cited Count：1 Percentile：15.7(Nuclear Science & Technology)Multi-term FP analysis procedures were developed to determine FP distribution all over F1 not only for analyzing accident propagation but also for planning its decommissioning projects. They should be validated based on the measured FP data. One of the useful tools for their validation was application of the dose rate data monitored by the containment atmosphere monitoring system (CAMS). However, in order to compare the data with different characteristics and dimensional units, e.g., FP distribution (kg, Bq) and dose rate (Sv/h), application of the conversion factors bridging them would be effective and useful. In order to prepare speedy, easy-to-handle and tractable procedures to calculate radiation dose rates at the CAMS detector locations, dose rate conversion factors were determined for major source locations and major radionuclides. The dose rates could be easily calculated by multiplying FP amounts obtained with the multiterm FP analysis procedures by the conversion factors.
Karasawa, Hidetoshi*; Uchida, Shunsuke*; Kino, Chiaki*; Naito, Masanori*; Osaka, Masahiko
no journal, ,
FPs that can have impact on the fuel-debris retrieval are selected and amount and radioactivities are evaluated based on FP distribution inside containment predicted by SA analysis code.
Kino, Chiaki*; Karasawa, Hidetoshi*; Uchida, Shunsuke*; Naito, Masanori*; Osaka, Masahiko
no journal, ,
FP distribution in 1F was phenomenologically evaluated in views of accident scenario. Possible retention of chemisorbed Cs in the separator etc. was implied.
Uchida, Shunsuke; Osaka, Masahiko; Karasawa, Hidetoshi; Kino, Chiaki*
no journal, ,
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.
Uchida, Shunsuke; Osaka, Masahiko; Karasawa, Hidetoshi; Kino, Chiaki*
no journal, ,
The Cs amounts in the major partial zone of the D/W and S/C of Units 1-3 have been evaluated by applying the BEP with the previously reported dose rate conversion factors. As a result of comparing the BEP results with those of the 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.
Okumura, Keisuke
no journal, ,
no abstracts in English
