PWR蒸気発生器入口管台における割れ事例と点検規定について
Cracking Events on PWR Steam Generator Nozzles and Its Relationship to Inspection Rules
著者:
堂﨑 浩二 Koji DOZAKI 中間 昌平 Shohei NAKAMA
発刊日:
公開日:
and Eddy Current TestDissimilar Metal WeldFitness-for-Service CodeInaccessible RegionPrimary Water Stress Corrosion CrackingSteam Generator NozzleUltrasonic Test
概要
Similar cracking events have been occurring on steam generator nozzles of Japanese PWR plants since the first case was found at Mihama-2 in September 2007. These cracks were found by eddy current test (ECT) prior to performing a kind of shot peening as a preventive measure on dissimilar metal weld (DMW), a nd were considered as primary water stress corrosion cracking (PWSCC) based on cause investigation. It was pointed out that surface finishing such as grinding or machining played an important role on crack initiation. Cause investigation on one of these cracking events, that is, Trusuga-2 case, is reported in this paper in detail. Another discussion point on inspection rules was raised through these cracking events. Ultrasonic test has been usually performed for this DMW to meet the requirement of in-service inspection rules in Fitness-for-Service (FFS) Code issued by Japan Society of Mechanical Engineers ( JSME). In practice, however, inaccessible region exists for this DMW due to geometric configuration. In JSME FFS Code, there has been prepared an exemption rule for such inaccessible region. These cracking events suggested that it might be necessary to limit application of the exemption rule for this DMW.
