Irradiation embrittlement is a major ageing issue for the components close to the core of a nuclear power plant (NPP), especially embrittlement of the reactor pressure vessel (RPV) beltline. Thus, extensive research has been performed for the last decades in the context of the EU-funded research. Mostly PWR RPV base and weld materials with emphasis on Russian materials were subject of investigation. Irradiation embrittlement depends on the neutron fluence, certain accompanying and alloying elements (especially Cu, P, Ni are deleterious), and the irradiation temperature (decreasing embrittlement with increasing temperature).
In addition, extensive research has been performed on – mostly non-destructive – measurement techniques for embrittlement assessment to reduce the usage of surveillance specimens and to improve the evidence of measurements. Another focus of research was the accurate determination of irradiation temperature and – especially – neutron dose.
A semi-mechanistic model was set up to reproduce the observed phenomena which is under continuous development.
Annealing allows reducing irradiation embrittlement effects at least to a certain extent, but often nearly completely and is a well-established mitigation method for aged RPV in WWER 440 plants.
As a synthesis of fracture toughness measurements, the “Master Curve” concept was established. The Master Curve is a concept in which the fracture toughness median value for 1T-CT specimens (thickness 25 mm) is correlated to the temperature. The Master Curve can be used for structural integrity assessment aspects as well as an ageing assessment tool. The IAEA is going to implement the Master Curve method for irradiation embrittlement assessment guidelines [Gerard2003].