Research and development of digital technologies to explore radiation source distributions for exposure reduction; Development status based on evaluation tests inside 1F Unit 5

Suzuki, Masahiro ; Aoki, Yuto; Aoki, Kazuhisa; Yamada, Susumu  ; Kim, M. ; Yamaguchi, Takashi ; Machida, Masahiko  ; Okamoto, Koji

In the decommissioning of TEPCO's Fukushima Daiichi NP (1F), it is crucial to improve the environment of working spaces inside the reactor building (R/B) as the fuel debris removal works go into full-scale levels. Among various environmental issues, the most essential one is to reduce the exposure of workers as much as possible by utilizing advanced safety planning and designing tools. Thus, JAEA has so far developed a digital software tool revealing 3D distributions of air dose rates inside target working places. In the tool system, a core part is to inversely estimate radiation source distributions and their magnitudes even in limited monitoring results using a machine learning technique called LASSO. This report presents that the core scheme was quite successful in a test event performed inside 1F Unit 5. This result motivates us to further test the system in Unit 23 and reorganize the tool system to make it more useful inside 1F.