Unzipping of cladding

A maximum of 1% of SNF discharged from reactors could be defective. Volume expansion associated with the oxidation/hydration of the SNF matrix or zirconium may crack/unzip defective cladding (Cunnane et al., 2003). Figure 7.15 shows a schematic of this unzipping process (DOE, 2002). Unzipping was observed in the Argonne National Laboratory 1.5-year long tests, caused by stress generated by corrosion product accumulation in the gap of cladding and the fuel matrix from uniform corrosion of Zircaloy cladding at 175°C (347°F) (Cunnane et al., 2003).

Oxidation/hydration may occur with either residual moisture inside the intact canister or container, or from moisture that has intruded into the failed canister or container. This cladding failure may affect the magnitude of the radionuclide release fraction and challenge the retrievability of the SNF materials, and lead to configuration changes in internal structure that impact nuclear criticality.

Подпись: (a)Подпись: 7.12 Hydride reorientation from circumferential (a) to radial (b) direction to hoop stress (Yagnik et al., 2004); cladding thickness of -0.6 mm. Used with permission from American Nuclear Society (ANS).image121



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