Treatment of the influence of irradiation in design and operation control of pressure vessels of pressurized- and boiling-water reactors

The report shows how the influence of neutron irradiation on material properties is treated in the safety calculations for pressure vessels of KWU pressurized- and boiling-water reactors. The material properties which are important with respect to irradiation and the methods of their measurement are described. These properties are the NDT (nil ducility transition) temperature, the reference temperature RTsub(NDT) and the fracture toughness. The modified Porse's diagram and the fracture mechanics diagram used for the safety calculations are based on these properties. The irradiation-induced shifts of NDT temperature or RTsub(NDT) or fracture toughness vs. temperature curves, respectively, usually are measured by charpy-V tests. Design curves for conservative prediction of those shifts as a function of neutron fluence and copper content are presented. These curves are derived from literature data based on the so-called 30 ft lb criterion. Methods of fluence calculations needed for the shift prediction are described elsewhere in this issue. The predictions are tested and perhaps corrected during reactor operation by examination of surveillance samples irradiated under accelerated neutron flux in the pressurized-water reactors. The standard surveillance program for KWU pressurized-water reactors is described, and as an example, the results of the surveillance program of the Karlsruhe power reactor MZFR are reported. In this special case of a heavy-water moderated reactor, damage-function calculations were applied to refer the near core irradiation results to the vessel wall. (orig.)