Effects of oxide and hydrogen on the circumferential mechanical properties of Zircaloy-4 cladding

Abstract

Mechanical properties of Zircaloy-4 cladding were evaluated by the ring tension test to simulate the cladding behavior under the reactivity-initiated accident (RIA) in a high burnup environment. Zircaloy-4 cladding was controlled to have a hydrogen content up to 1000 ppm and a oxide thickness up to 100 μm, followed by a circumferential ring tension test with a strain rate in the range of 0.01 and 1/s. The results showed that both the ductility and toughness decreased as the hydrogen content and the oxide thickness increased. Hydride inside the cladding played an important role in the brittle failure mechanism by a decohesion between the hydride and the metal matrix as well as a preferential fracture of the brittle hydride. Surface oxide also affected the mechanical property such as a reduction of the load bearing area, stress relieving effect, and so on. Correlation between the in-reactor RIA parameters such as the fuel enthalpy and out-reactor mechanical toughness was postulated and it was concluded that the change of the mechanical toughness caused by the oxide was more significant than that by the hydrogen.