Effective Approaches for Managing Aging Effects in BWR Reactor Coolant System Components for License Renewal

2003 ◽  
Author(s):  
Barry J. Elliot ◽  
Vikram N. Shah ◽  
Yung Y. Liu
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Aging Effects ◽  
Irradiation Embrittlement ◽  
Intergranular Stress Corrosion ◽  
Reactor Coolant ◽  
Extended Operation ◽  
License Renewal ◽  
Coolant System

This paper discusses management of aging effects for reactor coolant pressure boundary components in boiling water reactors (BWRs): loss of fracture toughness due to thermal aging and neutron irradiation embrittlement of vessel internals made of cast austenitic stainless steel; cracking of the top guide due to irradiation-assisted stress corrosion cracking; cracking of the core shroud and reactor coolant system piping due to intergranular stress corrosion cracking; cracking of the small bore piping due to high-cycle thermal fatigue; and loss of preload in the pressure boundary bolting. The applicants for license renewal of BWR plants have proposed different approaches for managing these aging effects such that the intended functions of the affected components will be maintained, consistent with the current licensing basis, for the period of extended operation. The NRC staff has performed safety evaluation of these approaches and found them acceptable for adequately managing the aging effects during the period of extended operation. The technical bases for the acceptance are presented in this paper.

Intergranular Stress Corrosion Cracking Damage Model: An Approach and Its Development for Alloy 600 in High-Purity Water

CORROSION ◽  
1986 ◽  
Vol 42 (2) ◽  
pp. 99-105 ◽  
Author(s):  
Y. S. Garud ◽  
A. R. McIlree
Keyword(s):  
Strain Rate ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
High Purity ◽  
Corrosion Cracking ◽  
Model Parameters ◽  
Alloy 600 ◽  
Intergranular Stress Corrosion ◽  
Film Rupture ◽  
Intergranular Stress Corrosion Cracking

Abstract A logical approach to quantitative modeling of intergranular stress corrosion cracking (IGSCC) is presented. The approach is based on the supposition (supported partly by experimental and field observations, and by a related plausible underlying mechanism) that strain rate is a key variable. The approach is illustrated for the specific case of NiCrFe Alloy 600 in high-purity water. Model parameters are determined based on the constant stress IGSCC data (between 290 and 365 C) assuming a power law relation between the damage and the nominal strain rate. The model may be interpreted in terms of a film rupture mechanism of the corrosion process. The related mechanistic considerations are examined for the specific case. Resulting calculations and stress as well as temperature dependence are shown to be in good agreement with the data. More data are needed for further verification under specific conditions of interest.

Effects of Weld Overlays on Leak-Before-Break Margins

2011 ◽  
Author(s):  
G. Angah Miessi ◽  
Peter C. Riccardella ◽  
Peihua Jing
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Operating Conditions ◽  
Intergranular Stress Corrosion ◽  
Pressurized Water ◽  
Weld Overlay ◽  
Water Reactors ◽  
Weld Overlays ◽  
Leak Before Break

Weld overlays have been used to remedy intergranular stress corrosion cracking (IGSCC) in boiling water reactors (BWRs) since the 1980s. Overlays have also been applied in the last few years in pressurized water reactors (PWRs) where primary water stress corrosion cracking (PWSCC) has developed. The weld overlay provides a structural reinforcement with SCC resistant material and favorable residual stresses at the ID of the overlaid component. Leak-before-break (LBB) had been applied to several piping systems in PWRs prior to recognizing the PWSCC susceptibility of Alloy 82/182 welds. The application of the weld overlay changes the geometric configuration of the component and as such, the original LBB evaluation is updated to reflect the new configuration at the susceptible weld. This paper describes a generic leak-before-break (LBB) analysis program which demonstrates that the application of weld overlays always improves LBB margins, relative to un-overlaid, PWSCC susceptible welds when all the other parameters or variables of the analyses (loads, geometry, operating conditions, analysis method, etc…) are kept equal. Analyses are performed using LBB methodology previously approved by the US NRC for weld overlaid components. The analyses are performed for a range of nozzle sizes (from 6″ to 34″) spanning the nominal pipe sizes to which LBB has been commonly applied, using associated representative loads and operating conditions. The analyses are performed for both overlaid and un-overlaid configurations of the same nozzles, and using both fatigue and PWSCC crack morphologies in the leakage rate calculations and the LBB margins are compared to show the benefit of the weld overlays.

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