(The) study of pH control agents in the secondary water systems of nuclear power plant

Abstract

This thesis deals with the pH control characteristics of ammonia derivatives, such as ammonia[$NH_3$], morpholine[$O(CH_2CH_2)_2NH$], and cyclohexylamine[$C_6H_11NH_2$], which control the corrosion of steam generating systems and steam circuits in the secondary side of nuclear power plant. These volatile amines control the pH of steam/wet systems moving with steam and control the corrosion of alloys in water media. The neutralizing ability of ammonia derivative is affected by the basicity, volatility and steam/water distribution ratio of amine which are a function of temperature. During operation, the chemical and physical properties of amine change with temperature. Therefore, the pH value may deviates from the expected value or the chemical specification. So, the temperature effects must be considered to evaluate the neutralizing capacity of amine. The pH of neutralizing amine at high temperature must theoretically be evaluated with the thermodynamics of chemical and physical equations and mass balance of base amine. From the theoretical calculation, it is confirmed that the pH control of morpholine with temperature and steam quality is effective in steam generator and steam circuits, and cyclohexylamine is effective in the far away steam generators. In addition, the effects of amine with condensate demineralizer must be evaluated because amines behave as impurity in ion exchange process. From the performance of ion exchanger with neutralizing amine and sodium ions, the effects of condensate polishing plants(CPP) in nuclear power plants may experimentally be evaluated. The following affinity order for ion exchange resin is obtained by experimental results; $H^+ < O(CH_2CH_2)_2NH_2^+ < Na^+ <NH_4^+ < C_5H_11NH_3^+$ The impurity($Na^+$) removal ability of CPP is proportional to the affinity. So, in operation of two bed polisher, morpholine cycle is more efficient than the others.