Predicting crack arrest in reactor pressure vessels

Abstract

Abstract The pressurized 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 so-called K Ia 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 I ST falls below a value K Ia . The present paper reviews recent EPRI sponsored research, which shows that the static procedure is overly conservative when it is applied to the first arrest of a deep crack in the thickness of a reactor vessel. This conclusion is clearly important when assessing the consequences of the imposition of the procedures of Regulatory Guide 1.99 Revision 2. A more accurate crack arrest prediction procedure, i.e. the Combustion Engineering constrained static procedure or the reflectionless stress intensity factor procedure which are very similar in concept and their arrest prediction, should be considered to assess the impact of its use in the context of the screening criteria limits in the PTS rule.