Establishment of 3-D dose dispersion forecasting method and development of in-structure survey using the transparency difference of each line gamma-ray (Contract research). FY2022 Nuclear Energy Science & Technology and Human Resource Development Project

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to 'the Project') in FY2022. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station (1F), Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2022, this report summarizes the research results of the 'Establishment of 3-D dose dispersion forecasting method and development of in-structure survey using the transparency difference of each line gamma-ray' conducted in FY2022. We realized an electron track detecting Compton camera (ETCC) that can measure γ-ray images (linear images) with the bijective projection. In the 'Quantitative analysis of radioactivity distribution by imaging of high radiation field environment using gamma-ray imaging spectroscopy' (hereinafter referred to as the previous project) adopted in FY2018, the 1 km square area including the reactor buildings was imaged at once. In FY2021, 3D dosimetry in the reactor building of the Institute for Integrated Radiation and Nuclear Science was carried out, and 3D imaging of γ- rays was successfully obtained. This project will build on the results of the previous project to develop a practical 3D contaminant dispersion detection and prediction system for sub-mSv/h environments. In addition, a 3D radiographic Cs distribution measurement method inside the reactor building using highly penetrating ¹³⁴Cs γ-rays will be developed. Furthermore, we will realize the operation of ETCC at several mSv/h and conduct the same measurements inside the reactor building, and carry out the imaging of debris γs by detecting higher energy γ-rays which penetrate the reactor wall than a few MeV, aiming to realize a complete understanding of the debris. (author)