Effect evaluation of partial termination of local sampling system in Hot Laboratory at Oarai Nuclear Engineering Institute; Airflow analysis on diffusion of radioactive material

Fukui, Makoto; Chizuwa, Shingo*; Kikuchi, Norihiro  ; Tanaka, Masaaki  ; Hashimoto, Makoto  

Hot laboratory (HL) at Oarai Nuclear Engineering Institute is a facility that conducts post-irradiation testing of fuel samples and reactor materials in hot cells. A set of local sampling system (LSS) is installed as a radiation control equipment to monitor the concentration of radioactive materials in the air in work environment. The LSS of HL equipped 23 sampling points, which are called as local sampling ends (LSE). It was recognized that air sampling had not operated at some of the LSE, and the concentration of radioactive materials in the air was not measured as prescribed. In this report, we evaluated the effect of partial termination of the LSS and the resulting increase in sampling intervals on the control of radioactive material concentrations in the air using airflow analysis assuming the diffusion of radioactive materials from hot cells in the controlled area of HL. The Service Area of the HL, where 10 LSEs were set in a wide area, was selected as an evaluation area. Airflow analysis including the diffusion of virtual contaminant particles was conducted on the evaluation area. Diffusion of virtual contaminants from hot cells and sampling of virtual contaminants at LSEs are simulated in the case of LSS in fully working and LSS with termination of 4 LSEs. The evaluation results showed that the effect of the partial termination of LSS and the resulting increase in sampling intervals on the control of the concentration of radioactive materials in the air are small.