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The susceptibility of fuel cladding to failure in the case of a postulated reactivity-initiated accident may be determined by crack initiation within a hydride blister or rim and subsequent crack growth through the thickness of the cladding. This study has determined the fracture toughness of hydrided coldworked stress relieved Zircaloy-4 sheet subject to through-thickness crack growth at both 25 and 300°C. The experimental approach utilizes a novel procedure in which a narrow linear strip of brittle hydride blister across the specimen width creates a well-defined precrack upon initial loading. The subsequent crack growth resistance is then characterized by four-point bending of the specimen and an elastic-plastic fracture mechanics analysis. At room temperature, the through-thickness fracture toughness ͑K q ͒ is sensitive to the orientation of the hydride platelets and K q Х25 MPaͱm for crack growth through a mixed in-plane/outof-plane hydride field. In contrast, K q is much higher ͑Х75 MPaͱm͒ when the hydride platelets are oriented predominantly in the plane of the sheet and therefore normal to both the crack plane and the crack growth direction. At 300°C, the material exhibits greater ductility as the hydride particles within the matrix resist fracture such that K q Х83 MPaͱm, despite the much lower flow stress of the material.

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The U.S. Nuclear Regulatory Commission staff has analyzed results from the weld residual stress round robin study, conducted in 2014. An uncertainty quantification scheme was applied to the dataset in order to compare and contrast results from independent analysts. The uncertainty quantification scheme provides a rigorous framework within which to make judgement calls about appropriate modeling guidelines and potential validation schemes. This paper will explore various options for guidelines and validation approaches, as informed by a statistical analysis of the dataset.