A physically-based correlation of irradiation-induced transition temperature shifts for RPV steels

Abstract

Irradiation embrittlement of reactor pressure vessel beltline materials is currently evaluated using U.S. Nuclear Regulatory Commission Regulatory Guide 1.99 Revision 2 (RG1.99/2), which presents methods for estimating the shift in Charpy transition temperature at 30 ft-lb (TTS) and the drop in Charpy upper shelf energy (ΔUSE). The purpose of the work reported here is to improve on the TTS correlation in RG1.99/2 using the broader database now available and current understanding of embrittlement mechanisms.The key areas expanded in the current database are low-flux, low-copper, and long-time, high-fluence exposures, previously sparse areas. The model incorporates both physically motivated features and empirical calibration to the U.S. power reactor surveillance data. It contains two terms, corresponding to the best-understood radiation damage features, matrix damage and copper-rich precipitates. The new model includes the variables copper, nickel, and fluence that are in RG1.99/2, but also includes irradiation temperature, neutron flux, phosphorus, and manganese.

Nonlinear Ultrasonic Techniques to Monitor Radiation Damage in RPV and Internal Components

“…For example, a rapid increase, followed by saturation, followed by slow coarsening and a decrease in number density of precipitates was predicted by models and confirmed experimentally for 0.3% Cu RPV steels irradiated at low neutron flux and 290°C [13]. As another example, it has been shown that an increase in the nickel content in irradiated RPV material correlates to an increase in both average radius and number density of copper-rich precipitates [16]. Further, changes in the irradiation temperature particularly in the range of about 250-300°C, as well as the neutron flux has been shown to strongly affect how the microstructure evolves over increasing neutron fluence [13,17,18].…”

“…As another example, it has been shown that an increase in the nickel content in irradiated RPV material correlates to an increase in both average radius and number density of copper-rich precipitates [16]. Further, changes in the irradiation temperature particularly in the range of about 250-300°C, as well as the neutron flux has been shown to strongly affect how the microstructure evolves over increasing neutron fluence [13,17,18]. The following sections provide a discussion on other possible contributions of microstructural features to β, in terms of reported microstructural evolutions over the relevant irradiation conditions in the current study.…”

Radiation damage characterization in reactor pressure vessel steels with nonlinear ultrasound

“…It has been shown for a neutron flux above about 5x10 11 n/(cm 2 -s), the evolution of microstructural features is dependent on flux [6,22]. This effect can be approximated by the relation [22,23]: 2 1 r e t t (5) r is an arbitrary reference flux, and in this study was r = 2.8x10 12 n/(cm 2 -s). At the relatively high neutron fluxes of samples in this study, it has been shown that an increase in neutron flux produces an increase in the concentration of unstable matrix feature clusters [6,22].…”

Reaction kinetic analysis of reactor surveillance data

“…The number of reactors worldwide that have been in operation for about or more than 40 years is increasing. Surveillance data from these aged reactors indicate higher ductile brittle transition temperatures than those predicted by embrittlement correlation methods [1,2]. In particular, the precipitates are the main defect clusters, and only small quantities of loops were observed by transmission electron microscopy.…”