Relationship Between Irradiation Hardening and Embrittlement of Pressure Vessel Steels

Abstract

Based on a large body of test and power reactor data, empirical relationships between irradiation strengthening and embrittlement are derived. It is shown that the Charpy V-notch (Cv) 41-J indexed transition temperature increases and the upper-shelf energy decreases systematically with increases in the yield stress. The transition temperature shifts are related to two mechanisms: (1) increases in the maximum temperature of elastic-cleavage fracture, and (2) decreases in the slope of the Cv energy versus test temperature curve associated with reductions in the upper-shelf energy. The cleavage shift contribution, which is usually dominant, can be predicted from the initial temperature of fracture at general yield and the change in ambient temperature static yield stress. In developing this simplified cleavage fracture model, it is shown that: (a) yield stress changes are independent of temperature and strain rate; (b) the increase in yield stress with decreasing temperature is independent of the strain rate, irradiation, and metallurgical state; and (c) the microcleavage fracture stress is independent of irradiation and temperature. A semi-empirical procedure for estimating the shift contribution due to upper-shelf energy decreases and the total temperature shift at 41 J, based on the observation of an approximately constant temperature interval of the transition regime, is proposed, along with a method for forecasting the entire irradiated Cv curve.

Relationship Between Radiation Inducted Yield Strength Increment and Charpy Transition Temperature Shift in Reactor Pressure Vessel Steels of Korean Nuclear Power Plants

“…The relationships between ∆YS and changes in the Charpy test properties from the US irradiated pressure vessel steel database were reported by a previous investigation [11]. It is worth noting the results in order to analyze the relationship in Korean LWR materials.…”

“…However, Odette et al reported that no particular effect of T41J on the proportional coefficient between ∆YS and TTS was found in the EPRI database, whereas test reactors data appeared to show a rather systematic trend of higher values in the proportional coefficient with increasing initial T41J, as well as with increasing ∆YS [11]. For the data group with high initial transition temperatures (-5 to -20°C), the proportional coefficient was ~0.65, about 50% higher than the corresponding value (~0.43) for the data group with low initial transition temperatures (-70 to -40°C) [13][14][15][16][17].…”

“…Odette et al reported an empirical trend between the irradiation-induced changes in the yield strength (∆YS) and transition temperature shifts for the base metals (plate/forgings) and weld metals [11]. The data points in Fig.…”

“…Odette et al reported that parameter f in the US data appears to have a nonlinear relationship with ∆YS [11]. The f value initially increased in proportion to ∆YS, and the slope increased with ∆YS.…”

Roadmap for Nondestructive Evaluation of Reactor Pressure Vessel Research and Development by the Light Water Reactor Sustainability Program

“…The TTS implications of LBP and transformation of CRPs to Mn-Ni-Si dominated features are increasing TTS with increasing neutron fluence, results not predicted by models based on surveillance data at relatively low fluences. References [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] were used variously for much of the preceding discussion.…”