Abstract
Comprehensive study to obtain necessary data for evaluation of airborne release behaviour during fuel debris retrieval of Fukushima Daiichi is underway by the authors with domestic and international collaborations since JFY2021 as subsidized projects of Decommissioning, Contaminated Water and Treated Water Management, titled “Development of Safety System (Acquisition of Dust Dispersion Data)”, funded by the Japanese Ministry of Economy, Trade and Industry.
As a huge number of experiments are necessary to obtain reliable data for five cutting methods against various operational parameters, this project was planned to proceed in several phases. Dust dispersion data for dry cutting with disk cutter, chisel, core-boring and laser were assessed during JFY2021 to JFY2022, while those for wet cutting with same methods and AWJ are under measurements since JFY2023. In addition, computational analysis to simulate airborne release and transport behaviour has been developed for future analysis of aerosols behaviour within PCV and reactor building.
The experimental setups for tests consisted of rectangular wind tunnel to cut samples under 0.1 m/s airflow to simulate inside PCV and samplers to collect particles to measure total weight and particle size distribution. Due to smaller aerosol generation than reliable detection limit, cutting tests with core- boring and chisel were carried out within small acryl box instead of wind tunnel. With a correction to same flow condition according to computational analysis, the measured data with different cutting methods were compared each other.
As the fuel debris simulants, non-radioactive materials were used to measure the dependency on cutting method and cutting parameters while materials containing uranium are served for the absolute measurements. The dust dispersion data for dry cutting with disk cutter, chisel, core-boring and laser have been measured for cold simulants while the data with simulated fuel debris containing uranium was measured for disk cutter.
