FRACTURE-MECHANICS ANALYSES INCLUDING CONSTRAINT INVESTIGATIONS ON REACTOR PRESSURE-VESSELS UNDER PRESSURIZED THERMAL-SHOCK LOADING

In the integrity assessment of reactor pressure vessels the emergency core cooling system injection is one of the main load cases to be anal ysed. For a more generic assessment, parametric analyses are done conc erning the load pattern, the postulated crack geometry and the materia l properties. With detailed axisymmetric and 3D-finite element (FE) mo dels of reactor pressure vessels, temperature distributions in the str uctures and the deformations are calculated by elastic-plastic FE anal yses for axisymmetric and asymmetric strip-like cooling assumptions. W ith it, boundary conditions for FE detail models with partly and 360 d egrees circumferential cracks are determined. Different material prope rties for the circumferential weld near the core mid-height, the cladd ing and the base metal with estimated influence of neutron irradiation are considered. Crack loading based on the J-integral is calculated f or different crack geometries, and different parameters describing the constraint on the crack ligament with proposals for a fracture assess ment concept are discussed. Furthermore, simplified methods based on a nalytical formulas to calculate the stress distribution in the wall an d the stress intensity factor are applied and compared with FE results .