Abstract: In the process of oxygenation operation during cold shutdown, the ⁵⁸Co release peak in the primary circuit can reach the value of about hundreds GBq/t, which has a notably effect on the occupational exposure and the shutdown process. This paper introduces the PWR oxygenation shutdown. Several key factors affecting the ⁵⁸Co activity concentration in the primary coolant during oxygenation shutdown are analyzed, including the primary coolant chemistry, material composition of steam generation tubes, mid-cycle shutdowns, the purification of chemical and volume control system. Based on these factors, some proposals are proposed.

Key words: oxygenation shutdown, primary circuit coolant, ⁵⁸Co peak, coolant chemistry