Impact of nuclear environment on hydrothermal corrosion and silica transport for CVD SiC in light water reactors

Abstract

• Corrosion rate of CVD SiC as a function of flow rate and roughness was measured. • Impact of ion irradiation on corrosion was shown to be substantial. • CRUD deposition significantly reduces the SiC dissolution for BWR water chemistry. • Gamma radiation accelerates CRUD deposition for CVD SiC and Zircaloy. • Silica deposition and cladding thickness loss is likely only of concern for BWRs. The development of comprehensive corrosion and silica transport models is essential to estimate the cladding thickness loss of SiC/SiC composites and the free silica content in the coolant under the hydrothermal radiation environment of light water reactors. In the present work, the hydrothermal corrosion behavior of high purity unirradiated and 5.1 MeV Si ion irradiated CVD SiC with different surface finish are examined in a high and a low flow high-pressure flow loops (15 MPa, 300 °C). Experiments carried on CVD surfaces with different surface finish indicated accelerated dissolution of cladding material with an increase in surface roughness and irradiation damage. Further, a first-of-its-kind analysis to understand the impact of CRUD deposition on the CVD SiC corrosion suggests that the SiC dissolution would reduce significantly as a stable CRUD layer grows on the SiC surface. The experimentally determined dissolution rates and the mass transfer mechanisms are implemented in Radiation Chemistry Analysis Loop (RADICAL) code. The spatial inventory of silica deposition is estimated at different components in a typical BWR and PWR primary loops using the updated RADICAL code. Lastly, an enhancement of CRUD growth under gamma radiation on SiC and Zircaloy surfaces was observed.