Microstructure and mechanical properties of hydride blisters formed on Zircaloy-4 claddings

To assess the microstructural and mechanical characteristics of hydride blisters formed on Zircaloy-4 tubes, we employ the electron backscatter diffraction (EBSD) analyses and micro-cantilever failure tests directly on the hydride blister (HB) area. In the HB area, more than 70% of the blister area is characterized to be delta-hydride, and the HB area does not favor the orientation relation ((10 (1) over bar1)(alpha)//(001)(delta), [1 (2) over bar 10](alpha)//[(1) over bar 10](delta)) that is otherwise well matched in the Zr matrix area. The geometrically necessary dislocation density is observed in the entire blister area, indicating a large amount of strain throughout the blister area. Also, the deformation strain is concentrated in both the hydride and alpha-Zr phases of HB areas; however, the hydride underwent intensive deformation in the Zr matrix. The average fracture toughness of the hydride blister area obtained through the micro-cantilever test is 1.81 MPa root m, indicating a brittle fracture that may threaten the integrity of spent nuclear fuel claddings.