Full system chemical decontamination and countermeasures against recontamination of the Fugen Nuclear Power Station

In August 1989 and January 1991, the first campaigns of full system chemical decontamination were performed successfully in each loop of two independent core cooling systems of Fugen as an operating power generating nuclear power station in Japan. Dilute chelate reagent, KD-203 was used for the decontaminations of the loops at 120oC for 24 hours. Occupational radiation dose of 6.6 and 7.8 man-Sv were saved by the decontaminations. All fuel assemblies were unloaded before the decontaminations. In the decontamination in 1991, the ninety two fuel assemblies were cleaned by ultrasonic vibration before reloading to the relevant core. This fuel crud cleaning slightly lowered the recontamination rate after the decontamination of 1991 than of 1989 without the cleaning. For further countermeasure against recontamination, high-efficiency crud removal resins which reduce crud iron concentration in feedwater to less than 1 ppb are under evaluation in Fugen. (author)