Probabilistic integrity assessment of reactor pressure circuits

The authors discuss how probabilistic structural assessment methods can provide benefits for both the safe and economic performance of nuclear plant. Three areas of potential application are identified and discussed: as part of an overall plant safety analysis to substantiate a case for new plant or continued operation of old plant, as a guide to decisions on plant design or modification, and as a guide to economic deployment of resources on maintenance, inspection and repair. The main technical problems with probabilistic structural assessment techniques are the need for a knowledge of variability in loads, material properties, defect occurrence etc. and fast, efficient and flexible codes that can handle a variety of problems. The illustration described in this paper uses the specific example of components in a Magnox reactor top duct but the overall project was mainly concerned with the development of probabilistic methods that could be widely used in the CEGB. The two classes of components considered are straight duct sections and fabricated welded 90 degrees corner units (mitre bends). Both have an internal diameter of 2 m and wall thicknesses of between 28 and 50 mm