Selection criteria for the best secondary water chemistry

This paper describes, for PWR plants, the approach for selecting the best chemistry-pH, amine, corrosion inhibitors-according to the secondary system characteristics, such as presence or not of copper alloys, steam generator tubing alloy, tube support plate design, sludge pile importance. The impact of condensate polisher, sludge lancing, chemical cleaning, as well as other ways of eliminating undesirable compounds or mitigating them are also discussed. For plants with simultaneous presence of carbon steel and copper alloys, alternate amines like morpholine, or new reagents such as ethanolamine (ETA), can be selected to manage erosion-corrosion of carbon steel and decrease corrosion transport, at a pH acceptable for copper alloys (9.2 at 25 C). In more recent units, with an all ferrous system, a high pH operation, with only hydrazine addition, the easiest way, or with combined hydrazine and morpholine or ETA will be of some benefit against steam generator corrosion. When Alloy 600 has been selected, inhibitors such as boric acid, or maybe titanium oxide or cerium in the future, needs to be added in steam generators in order to decrease intergranular corrosion progression. In addition, caustic and lead contaminations must be strictly avoided, while sludge and deposits will be eliminated by lancing and chemical cleaning, if necessary. (orig.)