ゲートモニタによる原子力災害時の車両検査効率化,2; タイヤとワイパー部の同時検査の精度評価

Improving the efficiency of vehicle screening during a nuclear emergency using portable radiation portal monitors, 2; Accuracy estimate of simultaneous screening of tires and wiper area

平岡 大和 ; 川崎 晃平*; 木村 仁宣 ; 齊藤 将大 ; 江嵜 巌*; 亀田 周二*

Hiraoka, Hirokazu; Kawasaki, Kohei*; Kimura, Masanori; Saito, Shota; Ezaki, Iwao*; Kameda, Shuji*

現在の避難退域時検査計画では、車両のタイヤはゲートモニタで、ワイパー部は検査員が測定し、検査基準値以下であるかを判定することとなっているが、両箇所をゲートモニタで同時に検査できれば効率化に繋がる。本研究では、ゲートモニタで同時検査した場合の判定精度を車両走行試験で得られる計数により評価した。その結果、ゲートモニタによるタイヤ検査はワイパー部の汚染の影響を受けにくく、高い精度となることを示し、ワイパー部の検査は警報値を低く抑えることで偽陰性が生じる可能性を抑えられることがわかった。ただし、ワイパー部検査では偽陽性が生じる可能性が高いことから、ワイパー部が警報判定となった場合に限り検査員による再測定を行うことが望ましい。

In the current contamination screening plan, the vehicle's tires are measured using a portable radiation portal monitor, while wiper area is measured by an inspector using a survey meter. These two measurements confirm that contamination levels are below the screening thresholds. However, if both areas could simultaneously be screened using the portal monitor, it would improve the efficiency of the screening process. In this study, we estimated the accuracy of simultaneous screening using the portal monitor based on radiation counts obtained from examinations using a vehicle. As a result, it was shown that tire screening with the portal monitor is less affected by wiper area's contamination and achieves high accuracy. Furthermore, it was found that keeping the alarm threshold low in wiper area screening can reduce the likelihood of false negatives. However, since wiper area screening has a higher likelihood of false positives, it is recommended that an inspector re-measure wiper area only if an alarm is triggered.