Fracture Toughness Testing Qualification Strategy of the Hinkley Point C UK EPR

Abstract The UK approach to regulatory compliance arrangements for nuclear safety classified pressure equipment is viewed as amongst the most stringent worldwide, comprising a set of interrelated regulations, regulatory expectations, and guidance. In addition to this, the UK European Pressurised Water Reactor (EPR) at Hinkley Point C (HPC) is the first civil nuclear power station to be constructed in the UK since Sizewell B in the 1980’s and is therefore considered to be a First-of-a-Kind civil nuclear construction programme in the UK. In the UK, components whose failure would result in intolerable radiological release or, would compromise the plant directly or from secondary consequences, would be considered High Integrity Components (HIC). For such components, gross failure must be discounted from the design basis, and the requirements and expectation go beyond those normally considered for Class 1 components. For HICs, the UK’s Office for Nuclear Regulation (ONR) does not accept the use of a nuclear design code alone and such components require the development of dedicated and specific structural integrity safety cases that go beyond a nuclear manufacturing code such as ASME or RCC-M. For HPC, the HICs are the two Reactor Pressure Vessels (RPVs), eight Steam Generators (SG’s), Pressurizers, Reactor Coolant Pump Flywheels, Main Coolant Line, Main Steam Line (MSL) and Main Steam Isolation Valves. These components are either low-alloy or austenitic stainless steel and, on top of acceptance mechanical testing such as tensile and Charpy impact testing, are subjected to extensive fracture mechanics tests to substantiate the structural integrity claims in the associated safety cases and provide the needed materials performance data of the parts used in fabrication. This 6+ year mechanical testing programme has so far seen the creation of a compendium of upper shelf J-Resistance (J-R) fracture toughness test data in accordance with ASTM E1820. Tests have been performed across multiple samples from the production forgings the HICs are made of, to understand ductile fracture initiation and tearing resistance at plant operating and fault conditions. The results obtained provide the evidence to the ONR that the materials performance has been assessed with sufficient rigor. This paper outlines the materials testing strategy, technical requirements, technical challenges, and quality arrangements associated with the fracture toughness assessment of HPC’s HICs, performed by Amentum, Framatome and EDF.