Effect of cladding on the stress intensity factors in the reactor pressurevessel

In general, reactor pressure vessels (RPV) are cladded with stainless steel to prevent corrosion and radiation embrittlement. The ASME Sec. XI specifi es that a subclad crack which may be found during the in-service inspection must be considered as a semi-elliptical surface crack when the thickness o f cladding is less than 40% of the crack depth. In order to refine the frac ture assessment procedures for such subclad cracks, three-dimensional finit e element analyses were applied for various subclad cracks embedded in the base metal. A total of 18 crack geometries were analyzed, and the results w ere compared with those for idealized semi-elliptical surface cracks for tw o different loading conditions, i.e. internal pressure and pressurized ther mal shock. The resulting stress intensity factors for subclad cracks were 5 0-70% less than those for idealized surface cracks. It has been proven that the condition specified on the ASME Sec. XI is overly conservative for sub clad cracks which are assumed to be surface cracks. (C) 2000 Elsevier Scien ce S.A. All rights reserved.