Non-Destructive Post-irradiation Examination Results of the First Modern Fueled Experiments in TREAT

ABSTRACT A series of experiments were conducted in the Transient Reactor Test (TREAT) Facility as part of commissioning for nuclear fuel safety research to be continued over the next several decades. TREAT was first constructed in the late 1950s to support research on nuclear fuel specimens under extreme nuclear-heated conditions. Following a decades-long hiatus, reactor operations were resumed at TREAT in 2017 to support the reemerging field of fuel-safety research. The first fueled tests were performed on fresh light-water reactor (LWR)-type sub length specimens (4.9% enriched UO2 in zirconium-alloy cladding) in inert gas capsules with the primary objective to demonstrate new irradiation capabilities, including calculation of energy-coupling factor, and to provide a baseline reference for interpretation of future experiments on accident tolerant fuel designs and high burnup standard fuels. In parallel, several new nondestructive post-irradiation experimental systems and processes have been developed and were successfully demonstrated using these samples. Five capsules were irradiated with energy injections and peak cladding temperatures of ∼212 and ∼1312 J/gUO2 and ∼561–∼2113°C, respectively. These irradiations resulted in various degrees of fuel damage that were characterized using advanced non-destructive examinations. The post-irradiation examinations highlighted that, in the most-energetic transient, zirconium breakout, also referred to as ‘candling,’ was observed as gross cladding melting and relocation. Post-irradiation examinations also confirmed results inferred from in situ instrumentation during irradiation and are consistent with previous results from other studies.