Investigation of the thermal ageing effects on WWER-1000 materials for up to 60 years of operation

Ensuring the reliable performance of Water-Water Energetic Reactors (WWER) and justifying their service life extension to 60 years and beyond requires a comprehensive understanding of thermal ageing in primary circuit materials. This study investigates the degradation of mechanical properties selected to represent both austenitic and ferritic steels used in safety-critical components, specifically 08Ch18N10T after 28 years of operation, 38KhN3MFA after 30 years, and unirradiated 10GN2MFA. To simulate a 60-year service life, accelerated thermal ageing is performed at 450 °C using the Arrhenius equation for duration calibration. The experimental programme uses conventional tensile and instrumented Charpy V-notch testing alongside miniature Small Punch Testing (SPT) and hardness measurements. To optimise material use, a specialised alignment and welding device is developed and manufactured for the Charpy specimen, followed by successful validation and approbation of the process. This approach ensures that the mechanical properties of specimens remain unaffected by the welding heat, allowing for an accurate assessment of impact toughness.