Structural integrity of hydrided nuclear fuel cladding
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Structural integrity of hydrided nuclear fuel cladding Jesús Ruiz-Hervías1, F. Javier Gomez2, Miguel A. Martín-Rengel1 and Elena Torres3 Departamento de Ciencia de Materiales, UPM, E.T.S.I. Caminos, Canales y Puertos. Profesor Aranguren s/n, E-28040 Madrid, Spain 2 Advanced Material Simulation, S.L. Isabel Collbrand, 6. E-28050 Madrid, Spain 3 Consejo de Seguridad Nuclear (CSN). Justo Dorado 11, E-28040 Madrid, Spain 1
ABSTRACT The structural integrity of nuclear fuel cladding is affected by the precipitation of hydrides during operation, which may embrittle the cladding. The aim of this work is to obtain the mechanical and fracture properties of the cladding as a function of the hydrogen content and testing temperature. To this end, the embrittlement caused by circumferential hydrides was simulated on unirradiated fuel cladding samples in the laboratory. The structural integrity of the cladding was assessed at different temperatures (20, 135 and 300ºC), by using the ring compression test. The mechanical properties and the fracture energy were calculated from the experimental load vs. displacement curves, by means of a finite element model which incorporates the cohesive crack model. INTRODUCTION Assessing the cladding performance during transport, interim storage and final disposal is essential for guaranteeing the safe confinement of radionuclides. Several processes can degrade the structural integrity of cladding during operation in reactor, and that will compromise its performance in later stages. Among the most relevant in-reactor degradation processes, corrosion, and subsequently, hydriding must be pointed out. As a consequence of zirconium corrosion in a primary cooling circuit environment in a Nuclear Power Plant, hydrogen is absorbed in the cladding and due to the thermal gradients, will precipitate as platelets of zirconium hydrides if its concentration is high enough. It has been shown that the formation of hydrides will embrittle the cladding [1]. This phenomenon becomes a key issue in high-burn-up fuel. The aim of this work is to obtain the mechanical and fracture properties of the cladding as a function of the hydrogen content and testing temperature. To this end, the embrittlement caused by hydrides is simulated on unirradiated specimens. Samples with different hydrogen contents (from 0 to 1200 ppm) are tested at several temperatures (20, 135 and 300 ºC) by means of the ring compression test. The mechanical properties and the fracture energy are calculated from the experimental load vs. displacement curves. A finite element model incorporating the cohesive crack model is used to this purpose. The agreement between the simulations and the experimental results is excellent in all cases studied.
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EXPERIMENTAL DETAILS The material used for this work was unirradiated PWR cladding (ZIRLOTM alloy [2]) with 9.5 mm outer diameter and 0.57 mm wall thickness. The samples for the ring compression test (RCT) were obtained by cutting the cladding in 10 mm high samples. Hydriding was induced via cathodic char
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