The shells of the PWR heavy components are made of quenched and tempered low alloy steel (type A508 cl.3). Slow thermal ageing of the steel may occur by inter-granular segregation of impurities, depending on the service temperature and the concentration of residual elements (mainly phosphorus) in the steel. This phenomenon may generate embrittlement (i.e. a shift of ductile to brittle transition temperature). The pressurizer service temperature is the highest of the primary loop (345°C), and this component may be affected by more important ageing effects than others. In order to support rules for embrittlement predictions and to anticipate the potential embrittlement of the pressure boundary of this component, AREVA launched a research program, on different materials (base materials, weld metals, and heat affected zones of welds) based on accelerated ageing (400°C up to 30,000 hours and 450°C up to 20,000 hours), and Charpy impact toughness measurements. The aim of this paper is to present available results and to analyze them in the light of the literature and the available models.

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