Abstract: During the third cycle refueling overhaul of Unit 4 of a nuclear power plant, a large number of activated corrosion products (⁵⁸Co) was released in the primary coolant during the oxidation operation, which had a great impact on radiation protection and the duration of the overhaul. Taking into consideration with the operating conditions of the third fuel cycle of Unit 4, this paper carries out a systematic analysis from the aspects of corrosion, migration deposition, purification, activation and dissolution. This paper summarizes three reasons for the high peak value of ⁵⁸Co in oxidation operation during the third cycle refueling overhaul of Unit 4. At the same time, relevant suggestions are put forward to reduce the peak value of ⁵⁸Co in oxidation operation and reduce the overhaul period occupied by purification process.

Key words: oxidation operation, ⁵⁸Co peak, pH, corrosion