A multibarrier safety concept for the reactor pressure vessel of the Stade Nuclear Power Plant

Abstract

Two specific problems within the safety case of Stade RPV have been analysed: brittle fracture initiation and arrest under strip type emergency core cooling conditions and safety margins against ductile failure from deep cracks as postulated by ASME- and German KTA-rules. For EOL material conditions exclusion of initiation is shown for cracks of more than twice the size which is safely detectable by NDE; for arbitrarily postulated large cracks it is demonstrated that they are arrested well within the allowed depth of 3 4 of the wall thickness; therefore no critical crack size exists for Stade RPV under strip cooling. Growth in depth of an assumed 3 4 t circumferential flaw in the girth weld embrittled at EOL could occur only at upper shelf temperatures and by loads higher than about twice the service pressure; leak before break was demonstrated in a constraint-modified J − R-curve crack-growth analysis. But neither a transient nor the plant itself would be able to provide the necessary high loads. The LEFM and EPFM proofs are summarized in a multibarrier safety scheme.