[hal-01057288] Mesures de champs de déformations et d'échauffements de gaines en Zircaloy-4 sollicitées en conditions représentatives d'un accident d'excursion de réactivité

The hypothetical scenario of a control rod ejection in a Pressurised Water Reactor leads to a Reactivity Initiated Accident (RIA) triggering rapid thermal expansion of the pellet. Theses conditions result in a strain-controlled loading on the cladding with large strain rate (about 1s- 1). Because the cladding does not have time to increase in temperature, its ductility is limited. Such strain rates are high enough to enhance adiabatic conditions, in which localized heating due to rapid plastic deformation could be significant enough to lead to material softening. Tensile tests at strain rates ranging from 0.1 s-1 to 10s-1 and temperatures ranging from 25°C to 480°C were performed on cold-worked Zircaloy-4 samples. All tests were monitored by either a high-speed infrared camera at frame rates up to 3600Hz or optical high speed camera at frames rates up to 12500hz. Some tests were performed monitored simultaneaously by theses two cameras. Three different tubular sample geometries were tested, allowing the study of cladding behaviour and failure in the axial and circumferential directions. An increase in temperature of up to 80°C was measured for strain rates of 5 /s and 10 /s , and its effects on mechanical response is under analysis by thermo-mechanical FEM calculations, where Taylor-Quinney coefficient would be taken into account.

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