Long-Term Corrosion Behavior of CVD SiC in PWR-Simulating Water

SiC ceramics show an outstanding oxidation resistance and a low hydrogen liberation rate in hot steam compared with the current Zr alloys, which promise larger safety margins under severe accident conditions. Moreover, its high temperature strength and stability under high neutron doses also provide high burn-up capability. In spite of the potential benefits of the SiC composite cladding, there are a lot of technical issues that need to be clarified for the LWR application. Especially, the corrosion resistance in the PWR water is an important parameter to insure the cladding performance under normal operating condition. Generally, SiC ceramics are highly corrosion resistant by forming a protective SiO2 layer in an air atmosphere. Long-term corrosion behavior of CVD SiC was investigated under simulated PWR primary water conditions. The dissolved hydrogen of about 2.7 ppm dramatically reduced the corrosion rate of SiC at 360 .deg. C under 20 MPa. The corrosion weight loss of CVD SiC under the dissolved hydrogen-controlled condition was extremely small compared with the condition without controlling the dissolved hydrogen. The oxide layer on the SiC specimen was readily dissolved and the SiC bare surface was exposed at the initial stage of the corrosion test. After the dissolution of the oxide layer, however, further corrosion occurred in a very sluggish way