Radial-hydride embrittlement of high-burnup Zircaloy-4 fuel cladding

Prestorage drying operations of high-burnup fuel may make Zircaloy-4 (Zry-4) fuel cladding more susceptible to failure, especially during fuel handling, transport, and post-storage retrieval. In particular, hydride precipitates may reorient from the circumferential to the radial direction of the cladding during drying operations if a threshold level of hoop stress at or above a corresponding threshold temperature is exceeded. This study indicates that the threshold stress is approximately 75-80 MPa for both nonirradiated and high-burnup stress-relieved Zry-4 fuel cladding cooled from 400degC and, under ring compression at both room temperature and 150degC, that radial-hydride precipitation embrittles Zry-4. Specifically, the plastic tensile hoop strain needed to initiate unstable crack propagation along radial hydrides decreases dramatically from >8% to <1% as radial-hydride fraction increases. Lower hydrogen contents (≤300 wppm) appear to be more susceptible to radial-hydride embrittlement compared to higher contents (>600 wppm), like that found in high-burnup Zry-4. (author)