Examinations of performance for utilization of radiation portal monitors in contamination inspection for motor vehicles in nuclear emergency (Contract research)

Hiraoka, Hirokazu; Komatsuzaki, Joji*; Hanaka, Norihiko*; Okamoto, Akiko; Saito, Yoshihiko*; Munakata, Masahiro; Togawa, Orihiko

JAEA-Technology 2022-003, 70 Pages, 2022/07

JAEA-Technology-2022-003.pdf:2.53MB

In contamination inspections for public in nuclear emergency, it is assumed that a large number of motor vehicles and evacuees will be inspected. At present, first measurement points of vehicles are tires and around a wiper, and they are basically inspected by persons using portable radiation surface contamination meters such as GM survey meters. However, in order to efficiently inspect contamination of vehicles, utilization of portable radiation portal monitors is being considered for the inspection. In this study, examination of performance of the portal monitor was conducted in order to obtain basic data. In this examinations, sealed radiation sources, Ba, 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 the wipers of a vehicle, and the counting rate of -rays from the radiation sources was measured using the portal monitor. Three examinations were conducted: static examination with a vehicle stationary, moving examination to mock the actual inspection, and high back ground examination to investigate performance of the equipment in high back ground environment. The vehicle mainly used in the experiments was a sedan, which is generally used as standard vehicles. And, a van whose front body is like that of a bus was used at this experiment. In addition, the "Gamma Pole" manufactured by the Chiyoda Technol Corporation was used as the portal monitor. As the result, it was estimated that the case of contamination equivalent to 40,000 cpm, the default value of the OIL4, deposited on the tread on a vehicle tire, when the vehicle passes through the portal monitor at 10 km/h or less, the contamination would be detected with a probability of 99% or more. Similarly, when the contamination deposited on around the wipers and the vehicle speed is 5 km/h or less,

Study on optimization method for contamination inspection of vehicles in nuclear emergency, 1; Quick measurement by existent portable radiation portal monitors for vehicles

Hiraoka, Hirokazu; Kawasaki, Kohei*; Kimura, Masanori; Togawa, Orihiko; Saito, Shota; Ezaki, Iwao*

no journal, , 

When the nuclear emergency occurs, inhabitants take the contamination inspection to evacuate. A large number of vehicle will come to the inspection area and make there congested. To do the quick inspection, simultaneous measurement of tires and wipers using the portable radiation portal monitors for vehicles is a key point. Consequently, we attempted the count rates obtained from tires and wipers are discriminated. First, the vehicle was driven at 5 km/h and the -ray counts rate was measured by the monitor. Ba sources were attached around the tire or on the wiper and measurements were taken 30 times each. Next, discrimination conditions based on a linear function were applied to the normalized count rates, with the maximum count rate of the measured values (Net value) set to 1.0, to evaluate the discrimination accuracy between the tire and the wiper. The evaluation results showed that the pattern with the source attached around the tire correctly discriminated 29 out of 30 times, while the pattern with the source attached on the wiper correctly discriminated 20 out of 30 times. It was found that in order to improve the accuracy of discrimination, the measurement method must be improved so that there is a large difference between measured values of the tire and the wiper.

Study on optimization method for contamination inspection of vehicles in nuclear emergency, 3; Verification of discriminative ability for contamination by the new set-up for portable radiation portal monitors for vehicles

Hiraoka, Hirokazu; Kawasaki, Kohei*; Kimura, Masanori; Togawa, Orihiko; Saito, Shota; Ezaki, Iwao*

no journal, , 

In nuclear emergency, vehicles which evacuating inhabitants use be taken the contamination inspection. For the quick inspection, it seems that realization of simultaneous inspection of tires and wipers by portable radiation portal monitors for vehicles is necessary. In order to fulfill the simultaneous inspection, the authors develop the measuring method which is able to suitably distinguish and evaluate each contamination. Monte Carlo simulation showed ahead that the new set-up of detectors improves the discriminative ability for contamination. In this study, based on the simulation results, the authors attached radiation sources to a vehicle, and verified the ability by the new-setup. As a result, the ability improved compared to one of the usual method.