Models for embrittlement recovery due to annealing of reactor pressure vessel steels

Technical Report · Mon May 01 04:00:00 EDT 1995

DOI:https://doi.org/10.2172/61205· OSTI ID:61205

Eason, E D; Wright, J E; Nelson, E E ^[1]; Odette, G R; Mader, E V ^[2]

---

1. Modeling and Computing Services, Boulder, CO (United States)
2. California Univ., Santa Barbara, CA (United States)

The reactor pressure vessel (RPV) surrounding the core of a commercial nuclear power plant is subject to embrittlement due to exposure to high energy neutrons. The effects of irradiation embrittlement can be reduced by thermal annealing at temperatures higher than the normal operating conditions. However, a means of quantitatively assessing the effectiveness of annealing for embrittlement recovery is needed. The objective of this work was to analyze the pertinent data on this issue and develop quantitative models for estimating the recovery in 30 ft-lb (41 J) Charpy transition temperature and Charpy upper shelf energy due to annealing. Data were gathered from the Test Reactor Embrittlement Data Base and from various annealing reports. An analysis data base was developed, reviewed for completeness and accuracy, and documented as part of this work. Independent variables considered in the analysis included material chemistries, annealing time and temperature, irradiation time and temperature, fluence, and flux. To identify important variables and functional forms for predicting embrittlement recovery, advanced statistical techniques, including pattern recognition and transformation analysis, were applied together with current understanding of the mechanisms governing embrittlement and recovery. Models were calibrated using multivariable surface-fitting techniques. Several iterations of model calibration, evaluation with respect to mechanistic and statistical considerations, and comparison with the trends in hardness data produced correlation models for estimating Charpy upper shelf energy and transition temperature after irradiation and annealing. This work provides a clear demonstration that (1) microhardness recovery is generally a very good surrogate for shift recovery, and (2) there is a high level of consistency between the observed annealing trends and fundamental models of embrittlement and recovery processes.

• Research Organization: Nuclear Regulatory Commission, Washington, DC (United States). Div. of Engineering Technology; Modeling and Computing Services, Boulder, CO (United States); California Univ., Santa Barbara, CA (United States)
• Sponsoring Organization: Nuclear Regulatory Commission, Washington, DC (United States)
• OSTI ID: 61205
• Report Number(s): NUREG/CR--6327; MCS--950302; ON: TI95011539
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
36 MATERIALS SCIENCE
ANNEALING
DATA
DATA ANALYSIS
MATHEMATICAL MODELS
MULTIVARIATE ANALYSIS
PHYSICAL RADIATION EFFECTS
PRESSURE VESSELS
REACTOR MATERIALS
STEELS