PWSCC SUSCEPTIBILITY OF MILL ANNEALED ALLOY 600 IN-REACTOR COOLANT SYSTEM WATER DURING THE HIGH PH OPERATION

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 degrees C, by changing the boron/lithium concentration ratio 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 e levated pH operation on the materials integrity of a PWR primary circu it, and a research program is under way to study and verify the optimu m pH and/or the Li concentration from the viewpoint of the radiation s ource reduction and the materials integrity. Constant extension rate t esting (CERT) to investigate the PWSCC susceptibility for mill anneale d Alloy 600 was performed under the various RCS water chemistry condit ions, by changing the boron and lithium concentrations for 16 differen t conditions. In this article, PWSCC susceptibility of mill annealed A lloy 600 with the change of RCS water chemistry conditions, and the re sults of a long term verification test to confirm the materials integr ity of PWR primary system are discussed.