Lifetime Management of WWER Reactor Pressure Vessels

Reactor pressure vessels are the most important components of nuclear power plants from safety and economic point of view. Thus, special interest is given to their lifetime management that requires a precious and periodical evaluation of their conditions. In Czech Republic, special program has been prepared for reactor pressure vessels in both nuclear power stations — Dukovany NPP with 4 units of WWER-440 MW and Temelin with 2 units of WWER-1000 MW reactors. This program is based on the following activities: • detailed calculations of real and potential regimes, especially of pressurized thermal shock events, • determination of vessel properties on the basis of testing surveillance specimens from standard, modified and supplementary programs, • calculations of neutron fluences on vessel wall, • measurements of neutron fluences on surveillance specimens and in vessel cavity, • evaluation of all results, evaluation of fluence and material property trends, • recommendations for future reactor pressure vessel operation (potential mitigation measures). The paper describes in detail all these activities and gives examples of their results and final evaluations. Lifetime assessment is based on a “Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs (VERLIFE)” using “Master Curve” approach for vessel integrity evaluation [1].