가압경수로 원전 물-증기 순환영역에서 암모니아와 MPA의 완충세기

Abstract

Amines, ammonia or 3-methoxypropylamine (MPA), are used to maintain the optimized pH for the prevention of corrosion in the secondary side of Pressurized Water Reactors (PWRs). They are differently dissociated as a function of temperature which is not same in each location of the water-steam cycle. pH at the operation temperature depends on temperature of fluid and equilibrium constants of water and amines. Thus, every amine provides the different pH in the entire secondary side so that pH is not only the sufficient parameter in corrosion control. The secondary parameter, i.e., buffer intensity, is the ability to maintain a stable pH when H + are added or removed due to the ingress of impurities or the reaction of corrosion. The buffer intensity is necessary to provide the selection criteria for the best pH control agent for secondary side and the basic understanding of the reason why the flow-accelerated corrosion(FAC) rate may demonstrate the bell-shape curve over temperature. The buffer intensities of ammonia and MPA were reviewed over the entire operation temperature of PWRs. The sufficient buffer intensity is provided for the inhibition of corrosion by ammonia in low temperature (25~100℃) and by DMA in high temperature (150~250℃). In terms of buffer intensity, i) the best pH control agent is an amine with pKa(T) range of pH(T)- 1 ≤ pKa(T) ≤ pH(T) + 0.5 and ii) the amine solution should have sufficient buffer intensity, β to inhibit corrosion, and iii) FAC rate may be maximum at the temperature, where βB/β ratio is lowest.