Preliminary Study of the Effect of Dissolved Zinc in PWR Coolant on in-Core Crud Deposits

Abstract

While zinc addition to the primary coolant is used to reduce radiation fields in Pressurized Water Reactors (PWRs), further investigations of its effects on in-core deposition are required to determine if crud-induced power shift is increased or lessened. In this work, PWR chemistry operating at high-temperature and high-pressure subcooled boiling condition is simulated to study the effects of pH and 10-ppb zinc addition on the deposition of corrosion product, non-stoichiometric nickel ferrite, onto Zircaloy-4 heated surfaces. Preliminary results revealed the deposit morphology of chimneys and thick deposit on the boiling surfaces, whereas very small amounts of deposit were observed on non-boiling surfaces. Without zinc, the deposit thickness is greater at the lower pH (10 and 1.3 µm at pH300°C of 6.8 and 7.0, respectively). With 10 ppb zinc at pH300°C of 7.0, the deposition increased by about 60%.