Nuclear power plants (NPP) constitute a reliable supply of emission-free energy, thus playing an important role in achieving the binding target to cut emissions in the EU by at least 40% below 1990 levels by 2030.
Most of the about 180 nuclear power plants currently feeding electricity into European grids are, however, in the second half of their designed lifetime and need to comply with increased safety standards as defined by the Nuclear Safety Directive. In order to ensure the needed electricity supply for the next decades, the EU is targeting lifetime extensions of existing plants, generating a need for advanced methods to verify their safe operation.
In most reflections on ageing management for NPP, reactor pressure vessel (RPV) ageing is ranked number one in the list of safety concerns, as:
- the RPV is the primary barrier against release of radioactive material into the environment
- failure of the vessel in normal and accidental scenario is excluded by design
- it cannot be replaced
- it suffers from hardening and toughness degradation in consequence of thermal ageing and radiation exposure.
One of the most limiting safety assessments for long-term operation is the integrity analysis of the RPV for pressurised thermal shock (PTS) regimes. In the EU, currently used PTS analyses are reaching their limits in demonstrating the safety for power plants facing long-term operation.