Practice for reducing contamination of controlled area under the influence of Fukushima nuclear accident

Yoshitomi, Hiroshi   ; Tatebe, Yosuke; Kawai, Keiichi; Kowatari, Munehiko

The Facility of Radiation Standards of the Japan Atomic Energy Agency provides various radiation fields for calibration and testing. It is located about 120 km away from Fukushima Dai-ichi Nuclear Power Plant, and radioactive materials discharged by the Fukushima nuclear accident contaminated around the FRS, even inside the building including radiation controlled areas. One month after the accident, the maximum contamination level in the controlled areas was 3.8 Bq/cm. Cs, Cs, I, Te and I were detected by spectrometry using an HPGe detector. However, contamination in controlled areas under widely contaminated environment have not been discussed in detail. As for FRS, practices for reducing contamination in the controlled areas were necessary to avoid the influence of the contamination to the calibration works. These practices described that the following two approaches were effective: (1) decontamination of the controlled areas by wiping out with wet cloth or steam cleaners, and (2) to prevent the dust with radioactive materials from letting in the controlled areas. As a result, surface contaminates inside the controlled areas were reduced to be dozens of times lower as compared with outside.