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Research Papers

A Risk-Informed Methodology for ASME Section XI, Appendix G

[+] Author and Article Information
Ronald Gamble

 Sartrex Corporation, Rockville, MD 20852sartrex@aol.com

William Server

 ATI Consulting, Black Mountain, NC 28711WILLIAMSER@aol.com

Bruce Bishop

 Westinghouse Electric Company, Cranberry Township, PA 16066bishopba@westinghouse.com

Nathan Palm

 Westinghouse Electric Company, Cranberry Township, PA 16066Palmn@westinghouse.com

Carol Heinecke

 Westinghouse Electric Company, Cranberry Township, PA 16066heineccc@westinghouse.com

J. Pressure Vessel Technol 134(3), 031002 (May 18, 2012) (11 pages) doi:10.1115/1.4006580 History: Received January 05, 2011; Revised January 17, 2012; Published May 17, 2012; Online May 18, 2012

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code [1], Section XI, Appendix G provides a deterministic procedure for defining Service Level A and B pressure–temperature limits for ferritic components in the reactor coolant pressure boundary. An alternative risk-informed methodology has been developed for ASME Section XI, Appendix G. This alternative methodology provides easy to use procedures to define risk-informed pressure–temperature limits for Service Level A and B events, including leak testing and reactor start-up and shut-down. Risk-informed pressure–temperature limits provide more operational flexibility, particularly for reactor pressure vessels with relatively high irradiation levels and radiation sensitive materials. This work evaluated selected plants spanning the population of pressurized water reactors (PWRs) and boiling water reactors (BWRs). The evaluation included determining appropriate material properties, reviewing operating history and system operational constraints, and performing probabilistic fracture mechanics (PFM) analyses. The analysis results were used to define risk-informed pressure–temperature relationships that comply with safety goals defined by the United States (U.S.) Nuclear Regulatory Commission (NRC). This alternative methodology will provide greater operational flexibility, especially for Service Level A and B events that may adversely affect efficient and safe plant operation, such as low-temperature-over-pressurization for PWRs and system leak testing for BWRs. Overall, application of this methodology can result in increased plant efficiency and increased plant and personnel safety.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Comparison of conventional and risk-informed P–T limit curves for a PWR pressure vessel

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Figure 2

Illustration of PWR system constraint, and conventional and risk-informed P–T curves

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Figure 3

Illustration of narrow operating window for a highly irradiated PWR pressure vessel

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Figure 4

Illustration of BWR operational, conventional, and risk-informed P–T curves for heat-up, where RTNDT at the vessel inner surface is equal to 160 °F

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Figure 5

BWR leak test P–T conditions, where RTNDT at the vessel inner surface is equal to 160 °F

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Figure 6

Schematic representation of a vessel beltline model used in the PFM analysis

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Figure 7

Illustration of pressure and temperature time histories input into FAVOR, where RTNDT at the vessel inner surface is equal to 160 °F

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Figure 8

CPFL computational results from the sensitivity study for PWR cool-down. Fluence levels correspond to approximately one plant life extension.

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Figure 9

CPFL computational results for cool-down for the limiting PWR. Fluence level corresponds to approximately two plant life extensions.

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Figure 10

CPFL computational results for heat-up for the limiting PWR. Fluence level corresponds to approximately two plant life extensions.

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Figure 11

CPFL computational results for heat-up for the limiting BWR. Fluence level corresponds to approximately two plant life extensions.

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Figure 12

CPFL computational results for combined cool-down and heat-up for the limiting PWR. Fluence level corresponds to approximately two plant life extensions.

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Figure 13

CPFL computational results for heat-up to leak test temperature for the limiting BWR. Fluence level corresponds to approximately two plant life extensions. Conventional ASME Appendix G leak test temperature is equal to 224 °F

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