Existing trend curves do not account for previous and more recently observed test and power reactor flux-level, thermal neutron and γ-ray field-induced effects. Any agreement between measured data and trend curve predictions that does not adequately represent the important neutron environmental and temperature effects as well as the microstructural damage processes, therefore, could be fortuitous. Empirically derived end-of-life (EOL) and life-extension-range (LER) trend curves are presented and discussed in this paper for high temperature [∼288°C (550°F)] irradiation of two weld, two plate, and two forging pressure vessel (PV) steels and low-temperature [∼60°C (140°F)] irradiation of one support structure-type steel.

Preliminary results of a comprehensive study of the effects of environmental variables (neutron spectrum, exposure, exposure rate, and the thermal and γ-ray fluxes associated with surveillance capsules and PV through-wall gradients) were used to develop these trend curves.

Pressurized water reactor (PWR) and boiling water reactor (BWR) plant-specific results together with those of the Poolside Facility (PSF) of the Oak Ridge Research Reactor (ORR) at the Oak Ridge National Laboratory (ORNL) and other research reactor experiments support the existence of a significant material-dependent flux-level effect for PV and support structure steels; that is, a steel may show a decrease, an increase, or no change in the measured Charpy shift with changes in fluxlevel. Further, the actual behavior of a material can change significantly as a function of neutron exposure; also, thermal neutron and γ-ray effects can contribute to observed changes in property, especially near steel-water interface positions with high thermal-to-fast-neutron ratios.