Abstract: ⁵⁸Co is the key γ radiation source of activated corrosion products of PWR nuclear power plant.Influenced by pH value and temperature variation,the solubility of activated corrosion products containing ⁵⁸Co will change continuously.During a shutdown process in Fuqing NPP,the specific activity of ⁵⁸Co in primary coolant was found to increase continuously as the coolant temperature drops.Meanwhile after completing fuel unloading within an outage period,the water temperature raised,leading an increase of the ⁵⁸Co specific activity in the spent-fuel pool,of which the maximum surface γ dose rate was reaching about 10 times of the designed value.By analyzing the specific activity of ⁵⁸Co,γ dose rate level and temperature variation trend in the two cases,as well as the system operation records comparison,it can be confirmed that the increase of ⁵⁸Co specific activity for both cases is closely related to the solution temperature.Under acidic environment,the solubility of activated corrosion products containing ⁵⁸Co has a positive temperature coefficient within a certain temperature range,which means the solubility will increase with the temperature rise.After reaching the maximum value,the solubility,decreasing with the temperature raise,shows a negative temperature coefficient.According to the conclusion,the specific activity of ⁵⁸Co was successfully reduced by starting the spare cooling circuit for the spent-fuel pool,of which the tem-perature drops.Finally,the surface γ dose rate of the spent-fuel pool quickly returned to the normal level,avoiding additional radiation exposure for the subsequent fuel operators.This successful practice provided a new idea for inhibiting and removing ⁵⁸Co in the activated corrosion products of PWR nuclear power plants.

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