Decontamination of the reactor coolant pump in Maanshan nuclear power plant

To reduce the radiation dose that accumulated on the reactor coolant pump, decontamination work was carried out at the Maanshan Nuclear Power Plant. A four-step alkaline permanganate (AP)-CanDecon process was applied to remove the activity on the turning vane diffuser and pump impeller. The first step consisted of 8 h of AP treatment and 7 h of decontamination. It was followed by 2.5 h of AP treatment and 5 h of decontamination. An average decontamination factor of 2.9 was obtained. To understand the corrosion of the decontaminating reagents on the materials, coupons were installed in the decontamination tank. These were as-received and sensitized 304SS, alloy 600, casting stainless steel (CF-8), stellite-6, and carbon steels (A508 and A533). The exposure rates (mR h⁻¹) of the carbon steels were approximately five times higher in magnitude than those of the other materials. The decontamination levels (dpm per 100 cm²) of the A508 and A533 carbon steels were 5432 and 3701 respectively, while most of the rest of the materials were below the low limit of detection. Apparently, the corrosion product on the materials was a major factor in sustaining the exposure rate and the contamination level. The corrosion rate of the materials was also examined and compared with published data. An examination of the surface morphology of the materials after decontamination showed intergranular attack on the 304 stainless steel.