Dissolved Oxygen Content Control Strategy in Secondary Loop System of Pressurized Water Reactor Nuclear Power Plant

The effects of dissolved oxygen content and the content ratio of hydrazine to dissolved oxygen content on material flow accelerated corrosion (FAC) in the secondary loop system of pressurized water reactor nuclear power plant were studied by weight loss method and simulated corrosion test. Combined with empirical feedback, the control strategy of dissolved oxygen content in the secondary loop system was given. The results showed that in the range of 0-30 μg/kg dissolved oxygen, the dissolved oxygen content had little effect on the uniform corrosion of the condensate pipeline material P11 carbon steel, and FAC rate of the steel between the low pressure heater and the deaerator decreased with the increase of dissolved oxygen content. Due to the low dissolved oxygen content, the content ratio of hydrazine to dissolved oxygen content exceeded 8, so the increase of hydrazine content had little effect on the corrosion rate of P11 low alloy steel. Under the condition of low dissolved oxygen of 2 mg/kg, the crack growth rate (CGR) of 690TT alloy was lower, and the CGR of 690TT alloy was increased by 1.08-3.53 times under the condition of saturated dissolved oxygen. It was suggested that the dissolved oxygen content in secondary circuit system of PWR nuclear power plant should be controlled by subsection control. The mass fraction of dissolved oxygen between condensate water and deaerator should be increased to 5-30 μg/kg. The mass fraction of dissolved oxygen between deaerator and steam generator should be controlled below 5 μg/kg, and hydrazine should be added to maintain the content ratio of hydrazine to dissolved oxygen above 5-8.