PWSCC susceptibility of mill annealed alloy 600 in reactor coolant system water during the high pH operation Original Research Article

For the reduction of the radiation source in the primary water system of a PWR, an elevated pH operation to the value of 7.4 at 300°C, by changing the boron/lithium concentration ration and/or by raising the lithium concentration of the reactor coolant system (RCS) water, is known to be effective. There is a need to verify the effect of an elevated pH operation on the materials integrity of a PWR primary circuit, and a research program is under way to study and verify the optimum pH and/or the Li concentration from the viewpoint of the radiation source reduction and the materials integrity. Constant extension rate testing (CERT) to investigate the PWSCC susceptibility for mill annealed Alloy 600 was performed under the various RCS water chemistry conditions, by changing the boron and lithium concentrations for 16 different conditions. In this article, PWSCC susceptibility of mill annealed Alloy 600 with the change of RCS water chemistry conditions, and the results of a long term verification test to confirm the materials integrity of PWR primary system are discussed.