The Assessment of the Primary Piping Material States on LTO Safe Operation of VVER-Type NPP in the Framework of SAMO-LTO Project

Abstract The nuclear power plant operators have usually implemented the ageing management programmes for main systems, structures and components (SSCs) important to safety in order to ensure their integrity and functional capability throughout plant service life. The most common ageing mechanisms are embrittlement, fatigue, corrosion, swelling, stress corrosion cracking etc. In many cases the one of the dominant ageing mechanisms for these SSCs is thermal ageing. The study of the (long term operation) LTO effects in the framework of monitoring programs with laboratory exposition and limited duration presents a particular problem. Therefore, the assessment of the SSC material states with a similar operating history (e.g., material from decommissioning units nuclear power plant V1, Jaslovske Bohunice, Slovakia) represents a unique opportunity to obtain relevant information on the effect of LTO on material degradation. DELISA-LTO (within the Horizon-Euratom-2021-NRT-1 call) project members collect and verify their wide experience and knowledge from the degradation of primary circuit components in VVER type units. While the EC-Horizon Europe DELISA-LTO project is comprehensively focused on all VVER-type reactors, the new SAMO-LTO project builds on its results, but focuses primarily on VVER-440 type reactors with specifics for operating or completed units in Slovakia in the nuclear power plant Jaslovske Bohunice V2 and nuclear power plant Mochovce.