Zircaloy-sheathed UO2 fuel performance during in-reactor LOCA transients

Four in-reactor transient tests with maximum fuel sheath temperatures up to about 10000C have been performed at Chalk River Nuclear Laboratories (CRNL) to measure fission product releases and verify sheath deformation calculations in the transient fuel performance code ELOCA. The two Zircaloy-sheathed elements survived the test transients intact and post-irradiation sheath strain measurements compare favourably with code predictions using measured fuel sheath temperature and coolant pressure transients. Sweep gas measurements of activity release to the fuel-sheath gap during high temperature transients with stainless steel-sheath fuel rods indicated increased release rates during high temperature operation. However, the largest releases were associated with rapid heatup and rewet quench. (orig.)