Predicting the arrest of a long axial internal crack in a reactor pressure vessel

Abstract

The pressurised thermal shock (PTS) issue has provided increased motivation for the search for a reasonably accurate crack arrest prediction methodology. This issue has assumed greater significance recently as a consequence of the imposition of Regulatory Guide 1.99 Revision 2 procedures for determining the effects of radiation embrittlement, in the context of the screening criteria in the PTS rule that is used by the United States Nuclear Regulatory Commission to assess the integrity of reactor pressure vessels. The currently accepted procedure for predicting crack arrest is the ASME Code procedure, which is based on static linear elastic fracture mechanics principles, with a crack being presumed to arrest when the crack tip stress intensity factor K ST I falls below a value K Ia. Prompted by the results from a recent coordinated analytical and experimental programme conducted by Combustion Engineering, and also results from earlier analyses of a simple simulation model, a model vessel analysis, based on the reflectionless stress intensity factor procedure, shows that the ASME Code procedure is overly conservative when it is applied to the arrest of a long and deep axial crack in the thickness of a reactor vessel during a hypothetical PTS event.