Primary coolant technology in VVER/PWR units. Experience with preconditioning, decontamination and recontamination

For the latest Czech and Slovak stations commissioned (Temelin and Mochovce) a modified hot functional test (HFT) chemistry was developed in the NRI Rez. Chromium-rich surface layer formed due to modified HTF chemistry ensures lower corrosion rates and radiation field formation. Long-term operation experience from both nuclear power plants are discussed in this paper. Radiation field, occupational radiation exposure and corrosion layers evolution during the first ten years of operation are compared and presented. The operation experience from all above-mentioned units showed a low level of corrosion products in the primary system as well as low dose rates. Actual in-pile loop tests carried out at the Nuclear Research Institute (NRI) Rez are focused on the study of surface preconditioning - similar to HFT chemistry - after decontamination. (orig.)