Dose estimate in treatment and disposal of contaminated materials due to the accident at the Fukushima Nuclear Power Plant

Takeda, Seiji ; Sawaguchi, Takuma ; Kimura, Hideo

Some kinds of material in the environment due to the accident at the Fukushima Nuclear Plant have been contaminated by radioactive cesium, which are represented by dehydrated sludge, surface soil, disaster wastes generated by the 2011 off the Pacific coast of Tohoku Earthquake and so on. Treatment (transportation, temporary storage or incineration) and disposal of the contaminated materials should be carried out while ensuring the safety of radiation for the workers and the public. In this study, in order to provide the technical information for making the guideline, the dose estimate for scenarios on the treatment and disposal is conducted, based on the method used for driving the clearance levels in Japan. Minimum activity concentration in contaminated material is calculated from the dose results, corresponding to the effective dose criterions indicated by the Nuclear Safety Commission of Japan (June 3, 2011). From the calculation result, it is suggested that it is necessary to forbid reusing the disposal site as construction, resident and agriculture in which the calculated doses for the public are higher than those in the other exposure pathways. Minimum activity concentration of radioactive cesium is derived to be 8.9 Bq/g for exposure pathway in landfill work under the condition of limited reuse of the site. In the case of the activity concentration below 8.9 Bq/g, the calculated dose of the resident due to direct and sky-shine radiation from the temporary storage place is less than 1 mSv/y, irrespective of the distance from the storage place.