UK Regulatory Approach With Adoption of Novel Methods for Fatigue and Fracture Assessments

Abstract The UK’s regulatory framework is generally goal-setting; the key requirement of UK law and the ONR regulatory approach is that licensees are responsible for the safe build, operation and decommissioning of nuclear sites by demonstrating that the risks are reduced so far as is reasonably practicable (SFAIRP) or as low as reasonably practicable (ALARP). ONR defines a set of components as of highest reliability, i.e., whose failures are deemed to be outside the design basis because of intolerable consequences. Consequently, their integrity demonstration requires measures additional to the standard nuclear design code, including, inter alia UK specific requirements for defect tolerance assessments. For the upcoming Hinkley Point C (HPC) PWR, the licensee, NNB GenCo has developed a UK specific defect tolerance methodology, which includes some novel approaches. Those include use of the French RSE-M’s fatigue crack initiation approach (FCI) and a bespoke methodology for combining design transients for fatigue assessments. This paper showcases ONR’s regulatory review of those novel approaches with potential implications for future reactor design proposals.