Pellet-Cladding Interaction Stress Validation Measurements for Incremental Centre Hole Drilling in AGR Fuel

Long term interim storage until a deep geological dispocal facility becomes operational is currently the end of life solution for spent Advanced Gas-cooled Reactor (AGR) fuel. For this purpose, the fuel pins are currently being stored in the fuel ponds of the former reprocessing plant, THORP, at Sellafield. Under these wet conditions, Stress Corrosion Cracking (SCC) has been observed on the cladding of some fuel pins, jeopardizing the containment of radioactive material inside the cladding. Residual stress in the cladding, caused by Pellet-Cladding Interaction (PCI) is suspected to be the driving force behind the SCC. The nature and magnitude of these stresses, and the quantity of affected fuel pins are currently unknown. For this purpose, the Incremental Centre Hole Drilling (ICHD) technique is being adapted for application on AGR fuel. For this, specific calibration data, both from finite elements (FE), and diffraction experiments on samples with a known stress state is required.