Contribution to the understanding of brittle fracture conditions of zirconium alloy fuel cladding tubes during LOCA transient
Résumé
This work addressed fracture mechanisms of nuclear fuel claddings in hypothetical Loss-Of-Coolant-Accident (LOCA) conditions. To this aim, laboratory-scale “semi-integral” thermal-mechanical testswere carried out, using an oxidation temperature of 1200 C, slow cooling down to 700 C and a finalquench by reflooding under an axial load.Two fracture mechanisms were observed. Fracture in the burst zone was due to oxide formation andsubsequent transformation of ductile b into brittle oxygen-enriched a(O). The second fracture mechanismaffected a region both enriched in oxygen and in hydrogen due to secondary hydriding.In the investigated conditions, fracture location was independent of burst morphology, oxidation timeand axial loading. A fracture scenario as a function of the reflooding transient was proposed. Physicalfracture mechanisms were elucidated with respect to microstructural evolution in these two regions.Based on the local distribution of chemical elements and phases, a fracture threshold function of thelocal, layered microstructure was suggested for each fracture location.
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