Practice for reducing contamination of controlled area under the influence of Fukushima nuclear accident (The 12th International Conference on Radiation Shielding (ICRS-12) and the 17th Topical Meeting of the Radiation Protection and Shielding Division of ANS (RPSD-2012)) -- (Accident of Fukushima Nuclear Power Plant and Its Influence)

The Facility of Radiation Standards (FRS) of the Japan Atomic Energy Agency provides various radiation fields for calibration and testing. Radioactive materials discharged by the Fukushima nuclear accident contaminated around the FRS including inside radiation controlled areas, even though the FRS is located 120 km away from there. A month after the accident, the maximum contamination level in the controlled areas was 7.3 Bq/cm. Cs, Cs, I, Te and I were identified by γ-ray spectrometry. As for the FRS, practices for reducing contamination in the controlled areas were indispensable to keep the facility running under contaminated environment. The following two practices were found to be effective: 1) decontamination by wiping out with a wet cloth or steam cleaners, and 2) to prevent dust with contaminants from entering into the controlled areas. As a result, contamination inside the controlled areas decreased and was maintained to be dozens of times lower as compared with the outside.