WELDING REPAIR PROCEDURE OF DEFECTS IN WWER REACTOR PRESSURE VESSELS

摘要

Reactor pressure vessels are components that are practically not replaceable and thus they determine the lifetime of the whole NPP. The lifetime of reactor pressure vessels is determined by the level of he material degradation as well as by the existence of defects found during in-service inspection and their size and location. According to some codes, it is necessary to have a procedure for the repair of potential defects found during in-service inspection that can be non-acceptable from the point of view of assurance of required RPV lifetime. A wide experimental program was realized to propose, check and approve a procedure for repair of potential defects in the underclad region of WWER-440 (WWER = Water-Water-Energy-Reactor = PWR type) reactor pressure vessels during operation. The experimental program was realized on as-received materials as well as on materials subjected to simulated ageing to a level representing the expected material embrittlement after design reactor lifetime. The main requirements for this procedure were: the RPV will not be pre-heated during repair welding, and no post-weld heat treatment will be applied. The maximum repair depth will be 40 mm including austenitic cladding thickness (8 to 10 mm). The procedure was developed and checked by series of mechanical testing (hardness, fracture toughness, impact notch toughness as well as by detailed metallography studies).