10 - Hideout, hideout return and crevice chemistry in nuclear steam generators

Abstract

Localized corrosion originating on the outside surface of the steam generator (SG) tubes has been a major cause of SG incapability in the commercial nuclear power industry, with the predominant modes of attack being either stress corrosion cracking or intergranular attack caused by the accumulation of highly concentrated solutions. The solutions accumulate in flow-restricted regions on the secondary side of the SG, such as crevices formed at the intersections between the SG tubes and the tube sheet, the tube-support structure and deposits that have accumulated on the tube surface and on the tube sheet. Processes leading to the formation of concentrated solutions (hideout) in these flow-restricted regions are discussed, and key results from experimental investigations of hideout and hideout return from a heated, fouled crevice, tube deposit and sludge pile are summarized. Methods to estimate the chemistry conditions that develop within flow-restricted regions on the SG secondary side, including deterministic models to predict the chemistry of concentrated solutions at high temperature, direct sampling of the flow-restricted region, and inferences from other sources of operating and experimental data, are also thoroughly discussed. Practical guidance for performing hideout return studies at operating plants, including guidelines for sampling, data evaluation and analysis, along with case studies involving hideout return studies for SGs of pressurized heavy water reactors and pressurized water reactors, is also presented.