[3D07-10] Evaluation of Contamination Distribution

[3D09] Development of dose evaluation method for confirmation of completion of decommissioning

(2)Identification of radiocesium origin using ¹³⁵Cs/¹³⁷Cs isotope ratio

*Asako Fujiwara Shimada¹, Takehiko Tsukahara², Masao Nomura², Min Soek Kim², Taro Shimada¹, Seiji Takeda¹, Tetsuji Yamaguchi¹ (1. JAEA, 2. Tokyo Tech)

Keywords:135Cs/137Cs isotope ratio, identification of origin, decommissioning, accident at the Fukushima Daiichi Nuclear Power Station

Radiocesium from the Fukushima Daiichi Nuclear Power Station (1F) accident can be treated as background radioactivity at completion of decommissioning, so determining the origin of radiocesium is essential. Therefore, we studied identification of radiocesium origin using ¹³⁵Cs/¹³⁷Cs isotope ratio. The ratio originated from 1F was 0.3628±0.0005. When the ratio originated from decommissioning facility was 0.05-0.2 larger than that originated from 1F, it is challenging to decrease the stand deviation less than 0.01 for 1 Bq/g of ¹³⁷Cs because precision was decreased as decreasing the ¹³⁷Cs concentration. If the ratio is able to be determined within the standard deviation of 0.0005 for 0.5 Bq/g of soil sample, the identification would be available.