Study on hydride Re-orientation properties in zircaloy-4 cladding tube

Hydrides re-orientation characteristics and its effects on the mechanical properties of spent fuel claddings have been studied experimentally using un-irradiated Zircaloy-4 cladding tubes. Effective radial re-orientation factor (Fe) which means the ratio of precipitated hydrides in radial direction to dissolved hydrides at test temperature was estimated from the measured radial orientation factor (Fn) and hydrogen content in the test sample. Fe was correlated with the test temperature and the loaded hoop stress. It is shown that the higher the temperature, the greater the Fe at the same hoop stress. The threshold stress of re-orientation to radial direction is around 100MPa at 300degC. To examine the effect of radial re-orientation of hydrides on cladding mechanical properties, ring tensile tests and axial tensile tests have been performed on re-oriented samples at room temperature. The results show that radial hydrides have no clear effect on the axial and circumferential yield stress of Zircaloy-4 cladding tubes in the range of our test condition. From these results it is concluded that although some hydrides may precipitate in radial direction of cladding tubes during dry storage of PWR spent fuel, such hydride precipitates have no clear influence on the mechanical strength of cladding tubes. (author)