Flux Effects on Radiation Induced Aging Behaviour of Low Alloy Steel Weld Material with High Nickel and Manganese Content

Abstract

As part of an on-going effort to verify the long-term fitness for service of the PWR-plants at the Swedish Ringhals site, weld material relevant for the two most modern units has been irradiated in the OECD Halden Materials test reactor (MTR) for up to three cycles of operation. The dose level achieved for each cycle is approximately equivalent to 20 years of operation during Light Water Reactor (LWR) conditions. The purpose of the test was three-fold. The first objective was to study the effect of the dose rate, the flux, -level on these kind of materials in order to verify or to discard the use of MTR-irradiated materials as part of the model building to understand the evolution of the mechanical behaviour under LWR conditions. The second objective was to enhance the available database of post-irradiation mechanical properties for analyses purposes, such as reactor pressure-temperature limit curves and defect tolerance analyses. Finally, the third objective was to produce ample amount of relevant irradiated material, enabling a comprehensive microscopy analysis of the evolution of the structure in the material to establish the occurrence frequency and type of precipitates and agglomerates, and if possible to study the occurrence of late blooming phases in high Ni and Mn bearing materials. This study will concentrate on the two first objectives. From the study, it appears clear that with these materials, it is possible to enhance the flux to speed up the irradiation induced degradation and still produce results that fall well in line with data extracted from the normal surveillance programs of the reactors. The flux effect as analysed from the mechanical property data appears to be negligible, if any.