NDLI: The Sensitivity of Risk-Informed Reactor Structural Integrity Analysis Results to Various Interpretations of Warm Pre-Stress

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Mark, T. Ericksonkirk Terry, L. Dickson
Copyright Year	2009
Abstract	Warm pre-stress, or WPS, is a phenomenon by which the apparent fracture toughness of ferritic steel can be elevated in the fracture mode transition if crack is first “pre-stressed” at an elevated temperature. Taking proper account of WPS is important to the accurate modeling of the postulated accident scenarios that, collectively, are referred to as pressurized thermal shock, and to the accurate modeling of routine cool-down transients. For both accident and routine cool-downs the transients begin at the reactor operating temperature (approximately 290°C for pressurized water reactors in the United States) and proceed to colder temperatures as time advances. The probabilistic fracture mechanics code FAVOR, which is being used by the NRC to provide the technical basis for risk-informed revisions of 10 CFR 50.61 and 10 CFR 50 Appendix G, adopts a model of WPS as part of its fracture driving force module. In this paper we assess the conservatism inherent to the FAVOR WPS model relative to a best-estimate WPS model constructed using data recently produced by the European Commission “SMILE” project and published by Moinereau and colleagues. Assessments of the conservatisms inherent to the so-called “conservative principle” WPS model, and also to a classic LEFM model that does not credit WPS are also made. The data presented herein demonstrate that, for an integrated analysis of PTS risk, the FAVOR and conservative principle WPS models both over-estimate the vessel failure risk by a factor of between 2 and 3× relative to the best estimate model. Our examination of the effect of WPS models on the predictions of individual transients reveals that for the severe transients that dominate risk there is little difference (usually less than 4×) between the conditional probabilities of crack initiation and of through wall cracking predicted by the different WPS models. There are considerable differences in the predictions of the various WPS and non-WPS models for low severity transients, however, the contribution of these transients to the total risk of vessel failure is small.
Sponsorship	Pressure Vessels and Piping
Starting Page	333
Ending Page	339
Page Count	7
File Format	PDF
ISBN	9780791843703
DOI	10.1115/PVP2009-77127
e-ISBN	9780791838549
Volume Number	Volume 7: Operations, Applications and Components
Conference Proceedings	ASME 2009 Pressure Vessels and Piping Conference
Language	English
Publisher Date	2009-07-26
Publisher Place	Prague, Czech Republic
Access Restriction	Subscribed
Subject Keyword	Temperature Fracture mechanics Vessels Probability Risk Fracture (materials) Steel Modeling Stress Transients (dynamics) Fracture toughness Fracture (process) Thermal shock Pressurized water reactors Failure Accidents Operating temperature
Content Type	Text
Resource Type	Article

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