Effect of zinc addition to simulated PWR primary water on corrosion resistance of alloy 600

Primary water stress corrosion cracking (PWSCC) of Alloy 600 component materials has become a major concern for pressurized water reactor (PWR) plants in recent years. The domestic nuclear industry is currently focusing on short-term mitigation plans directed towards the reactor vessel head (RVH), and in at least one case, the Alloy 600 weld joint between the reactor vessel and hot leg piping. There are many additional locations within the reactor coolant pressure boundary (RCPB) that contain Alloy 600 base metal or weld metal that may be susceptible to PWSCC over time. Addition of zinc to the reactor coolant system of Angra 1 has been used as a means to effect radiation dose reductions. The effectiveness of zinc in contributing to reduced radiation fields in PWR is now well established, with positive results observed in PWR's. The purpose of the present investigation was evaluation the effect of addition of zinc on the corrosion resistance of mill annealed alloy 600. Potentiodynamic polarization techniques was used to investigated the corrosion process. The tests were conducted in beginning-of-cycle primary water conditions (1200 ppm B, 2.2 ppm Li, without O2) at room temperature and pressure. The alloy 600 plate used had no previous heat treatment. The zinc concentration in the test solutions was from 20 to 500 ppb. The solutions were prepared using demineralized water and analytical grade lithium hydroxide, boric acid and zinc acetate. Initial results showed a relationship between zinc addition in the water and corrosion susceptibility that has to be further evaluated. (author)