Structural Studies of 15H2NMFAA Steel and its Welds after Long Thermal Exposures and Irradiation at the Operating Temperature of Reactor Pressure Vessel
A complex of microstructural studies (TEM, SEM and Auger) of VVER-1000 surveillance samples of the temperature sets in the initial state, after long thermal exposures (up to 180 000 hours) and irradiation was conducted in this paper.
It was shown that in non-irradiated elements of RPV the critical brittleness temperature shift can be caused by the development of reversible temper brittleness. Herewith its contribution to the total embrittlement of the material increases with increasing of operation time and can be decisive at extending the lifetime of VVER-1000 RPV up to 60 years and more. The level of grain-boundary segregations in various states was established. It is experimentally shown that radiation-enhanced diffusion of phosphorus to grain boundaries is observed in RPV steels.