In a nuclear emergency, it is expected that the screening tests will be conducted on a large number of vehicles and residents. The NRA’s manual shows that workers should use a Geiger-Mueller (GM) survey meter and so on. However, in order to conduct the screening tests more efficiently, it is expected that vehicle monitors will be utilized.
In this study, we conducted a performance test of vehicle monitors owned by some local governments to simulate the screening test.
Sealed radiation sources were substituted for the contamination of Operational Intervention Level 4 (OIL4), the evaluation criteria to conduct simple decontamination in the contamination inspection. The radiation source was attached practically to a tire and around wipers of a vehicle, and the counting rate of γ-rays from the radiation sources was measured using the “Gamma Pole”, the portable radiation portal monitor for vehicles manufactured by the Chiyoda Technol Corporation.
It is important that the development of a simultaneous measurement method for the contamination of a tire and around wipers in order to make the screening tests more efficient*1. Therefore, we considered discrimination methods for counting rates from both the two contamination.*2 As a result, it was estimated that in the case of contamination deposited on a tire, when the vehicle passes through the portal monitor at 5km/h or less, it would be discriminated 29 out of 30 times accurately. Similarly, it was estimated that in case of the contamination deposited on around wipers, it would be discriminated 20 out of 30 times.
We will continue to research measurement and operation methods using the Gamma Pole, such as a method for simultaneous measurement and evaluation of both the two contamination, and then develop an effective utilization of radiation portal monitors in contamination inspection of vehicles in nuclear emergency.
*1:H. Hiraoka et al.,”Examinations of Performance for Utilization of Radiation Portal Monitors in Contamination Inspection for Motor Vehicles in Nuclear Emergency (Contract Research)”, JAEA-Technology 2022-003 (2022)
*2:H. Hiraoka et al., “Study on optimization method for contamination inspection of vehicles in nuclear emergency, 1; Quick measurement by existent portable radiation portal monitors for vehicles”, 2023 Annual Meeting of AESJ (2023).
