VVER reactor pressure vessel materials database and monitoring of ageing and lifetime evaluation

From the beginning Skoda has paid a special attention to the assurance of the manufactured pressure vessels integrity. These evaluations, closely related to safety and life time, are performed practically for all operated WWER 440 equipment made in Skoda, and life time assessment programs for WWER 1000 reactors are being prepared. Good knowledge of all needed material properties is very important for the analyses. In connection to a number of upgrading performed during the manufacture of reactor pressure vessels, the manufacture itself was preceded by a large scope qualification tests covering testing of various base materials and weld joints on ten thousand test specimens. Continuous monitoring of properties degradation for the whole life time is one of important elements of safety and reliability of nuclear units. Analyses of actual condition of material with the evaluation of residual life time are necessary to perform first of all for the reactor pressure vessel which is due to considerable radiation embrittlement one of the most critical components of the nuclear power plant. Surveillance programs of material specimens which are required in regulations and recommendations of national and international authorities for nuclear safety, serve for the monitoring of changes to RPV material properties during the operation. New solution was designed, approved and implemented for a surveillance program of type V-320 WWER 1000 reactor pressure vessels manufactured in Skoda Plzeo (RPV Belene and Temelin, units 1 and 2)