b'Assessment of the mechanical properties of highburnup cladding is essential to establish a licensingcriteria for modern and advanced nuclear fuel designs in light-water reactors.Three different Zircaloy alloys were usedin the hoop direction through the in the experiments: a stress relievedgauge section of a ring tension sample annealed Zircaloy-4 cladding, a fullyover a wide range of plastic strains. recrystallized Zircaloy-2 cladding, and aTraditional loading with hemi-cold worked Zircaloy-2 cladding. For thespherical inserts and gauge region Zircaloy-4 sample, hydrogen chargingparallel to the applied load results in results were consistent with those seenstrong bending moments through the in literature with a uniform distributionthickness of the cladding. One remedy of circumferentially oriented hydridesfor this is the use of a central dog-appearing through the specimen wallbone shaped insert to counter the thickness. The hydride microstructurebending moment. However, this can of the recrystallized annealed Zircaloy-2result in non-uniform plastic strains resulted in radial hydrides formingat the edges of the gauge region. at the cladding outer surface. TheseAnother remedy is to load the sample samples were then subjected to anperpendicular to the applied load additional heat treatment in a boxon top of the hemispherical inserts. furnace at 500C for 2 hours. FollowingHowever, this arrangement can lead the heat treatment, the hydridesto non-uniform loads in the gauge reoriented in the circumferentialregion if the friction is too high or the direction with a somewhat highergauge region too long. Finite element concentration toward the claddingsimulations were conducted to design outer surface. The result of the hydrogena test that minimized these effects. charging and subsequent heat treatmentResults showed that a specimen with on the hydride morphology is shown ina gauge width of 1mm and length of Figure 2. Results of the hydriding runs4mm when loaded in the perpendic-with cold-worked Zircaloy-2 ular arrangement showed promising are forthcoming. results when the friction coefficient Assessing the strength of claddingbetween the sample and loading grip materials in the circumferential orwas kept below 0.05. Figure 3 shows hoop direction is a challenging butthis test arrangement next to finite necessary task for cladding mate- element contours of the plastic strain rials such as Zircaloy which exhibitdistribution in the sample. The results directional anisotropy. The challengeof forthcoming mechanical tests will is to maintain a uni-axial stress statebe compared to these finite element simulations to validate their results.2019|AFC ACCOMPLISHMENTS 141'