Water technology experience for materials protection in light water and heavy water reactor systems

This paper contains a brief history of the corrosion effects of the water environment on the major components of nuclear steam supply systems and how this history led to the current water chemistry control philosophy. The current philosophy minimizes the transport of corrosion products from component and piping surfaces in the balance-of-plant to the secondary side of pressurized water reactor (PWR) and pressurized heavy water reactor (PHWR) steam generators and to the fuel cladding surfaces in boiling water reactors (BWRs). Descriptions are given of various typical component corrosion problems and the actions taken to mitigate them. In general, the emphasis on design has been to minimize areas of high quality (i.e., low flow regions) in two-phase steam/water mixtures and associated localized contaminant and chemistry addition concentrations through efforts to maintain water purity at the lowest achievable level of contamination by both dissolved and suspended solids. Additional research in BWRs has been directed at reducing the corrosion potential in BWRs to avoid stress-assisted intergranular cracking of recirculation piping. This is being accomplished by strict control of water purity and a reduction of oxidizing potential through the addition of hydrogen. At present, the hydrogen addition program is experimental. The operating PWR and PHWR environment is also being maintained at reducing conditions in both Alloy 600 and Alloy 800 steam tubed generators and in the circulating reactor water environment