Conversion Factors Bridging Radiocative Fission Product Distributions In The Primary Containment Vessel Of Fukushima Daiichi Npp And Dose Rates Measured By The Containment Atmosphere Monitoring System

Multi-term fission product (FP) analysis procedures were developed to determine FP distribution all over the Fukushima Daiichi nuclear power plant (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 multi-term FP analysis procedures by the conversion factors. This paper introduces the procedures to calculate the conversion factors based on a point kernel integral shielding calculation code, QAD-CGGP2. Then, the determined conversion factors for the 460 MWe BWR (1F Unit 1) and for the 780 MWe BWR (Units 2 and 3) are listed and the differences in those due to the reactor sizes are discussed.