THERMODYNAMIC STUDY IN SUPPORT OF PRESSURIZED-WATER REACTOR SPECIFIC REACTOR WATER CHEMISTRY

A theoretical approach is discussed that regards the kinetically deter mined pressurized water reactor (PWR) primary system as a set of therm odynamically defined metastable states that the related high-temperatu re aqueous system containing a combination of possible oxide phases (N ixFe3-xO4, Fe3O4, and metallic nickel or NiO) and corresponding dissol ution products may undergo under specified initial conditions. The stu dy shows that stability zones of those metastable states, particularly M(1) (NixFe3-xO4) and M(3) [Ni(m) + NixFe3-xO4] cover practically the entire PWR operational range and depend on specific plant conditions and applied chemistry control. The thermodynamic analysis is predicate d on the belief that defining the stability transition boundary betwee n those states-found as a function of temperature, coolant pH, dissolv ed hydrogen (DH), and ferrite stoichiometry (x value)-is of primary im portance for corrosion product behavior. Such a stability change influ ences both the particulate and ionic levels and the related activity t ransport and should be regarded as an important factor in optimizing P WR primary chemistry. The study offers an original approach to reasses sing such important issues as thermodynamic data and the solubility of spinel oxides, the role of transport of particulates and soluble spec ies, ''optimum'' pH and DH, and the chemistry effect on crud burst.