Elastic-plastic deformation of a nuclear fuel cladding specimen under the internal pressure of a polymer pellet

Full text: During the operation of light water reactors, corrosion results into the development of an oxide layer, on the external surface of zirconium alloy fuel cladding, and the introduction of hydrogen into the metal (Zr+2H2O→ZrO2+2H2). Initially, hydrogen is in solid solution and diffuses towards regions of low hydrogen concentration, high hydrostatic stress and low temperature. However, with increasing time of reactor operation, the hydrogen concentration may exceed its terminal solid solubility and brittle zirconium hydrides may precipitate. Indeed hydrides are present in high burn-up fuel cladding, which is therefore more susceptible to failure, depending on hydride volume fraction and existing defects in the oxide layer. The expansion due to compression (EDC) test has been developed for the study of irradiated and hydrided cladding failure, under high hoop strain rates, which are expected during a reactivity initiated accident (RIA). During this test, a piece of cladding tube is circumferentially loaded in tension due to the expansion of a polymer pellet, axially compressed inside the tube. A finite element simulation of the EDC-test is discussed. The objective of the study is: (i) to understand the deformation of the cladding, during the experiment, including the effect of cladding material properties, and (ii) to provide information, necessary for the development of failure criteria. The distributions of important field quantities with respect to the damage of the cladding are derived together with the evolution of their maximum values, during loading. It is shown that, before cladding yielding as well as after substantial plastic deformation, the radial displacement, on the external surface, and the total energy per unit volume, when appropriately normalized, vary along the cladding axis according to specific distributions, which do not depend on the level of loading. This characteristic of cladding deformation is useful for the interpretation of experimental measurements and the development of failure criteria. The numerical results are compared with experimental measurements. (author)