Full system decontamination at Fukushima-Daiichi Nuclear Power Station

In Unit No.3 of Fukushima Daiichi Nuclear Power Station, Full System Decontamination was performed for the reactor and reactor recirculation system. Total radioactivity of about 10 TBq as converted to Co-60 was dissolved and removed, while the average dose-equivalent rate of the reactor bottom in water was reduced from 4.07 mSv/h before decontamination to 0.11 mSv/h after decontamination. The target DF20 could therefore be achieved. It was also proved that such a large-scale Full System Decontamination could be completed in exactly one week. In the future, the experiences and data obtained in the course of this work will be disseminated to those concerned when similar large-scale improvement work is to be made with other units. (J.P.N.)