The fracture of Zircaloy-2 plate and fuel cladding tubing in hydrogen gas

It has been shown that in a high pressure hydrogen gas environment at 325 degreesC, Zircaloy-2 can fracture rapidly by a fracture mechanism called HGC. HGC is a recently discovered fracture mechanism that occurs by rapid crack tip hydriding and fracture and can lead to crack propagation rates in Zircaloy-2 as high as 1 cm/s. It has been postulated that HGC requires crack tip deformation to accelerate H absorption and hydride layer formation. We compared the fracture behavior of thick plate and thin walled Zircaloy-2 nuclear fuel cladding using a split mandrel test in a high pressure H-2 environment and found that cladding and plate both fractured in brittle manner at 315 degreesC-325 degreesC. The cladding deformed but did not fracture in the same test in an inert environment. Specimen size or thickness was thus not an overriding factor in brittle HGC behavior. The depth of the residual fracture surface hydride layer of similar to 20-50 mum may represent the heavy deformation region of the plastic zone during HGC fracture.