XI.M17 (NUREG-2191 R0)
XI.M17 FLOW-ACCELERATED CORROSION
Program Description
This program manages wall thinning caused by flow-accelerated corrosion (FAC), and may also be used to manage wall thinning due to erosion mechanisms, if present, that are not being managed by another program. The program is based on commitments made in response to the U.S. Nuclear Regulatory Commission (US NRC) Generic Letter (GL) 89-08, and relies on implementation of the Electric Power Research Institute (EPRI) guidelines in the Nuclear Safety Analysis Center (NSAC)-202L for an effective FAC program. The program includes (a) identifying all susceptible piping systems and components; (b) developing FAC predictive models to reflect component geometries, materials, and operating parameters; (c) performing analyses of FAC models and, with consideration of operating experience (OE), selecting a sample of components for inspections; (d) inspecting components; (e) evaluating inspection data to determine the need for inspection sample expansion, repairs, or replacements, and to schedule future inspections; and (f) incorporating inspection data to refine FAC models. The program includes the use of predictive analytical software, such as CHECWORKS™, that uses the implementation guidance of Nuclear Safety Analysis Center (NSAC)-202L. This program may also manage wall thinning caused by mechanisms other than FAC, in situations where periodic monitoring is used in lieu of eliminating the cause of various erosion mechanisms.
Evaluation and Technical Basis
- 1. Scope of Program: The FAC program, described by the EPRI guidelines in Nuclear Safety Analysis Center (NSAC)-202L, includes procedures or administrative controls to assure that structural integrity is maintained for carbon steel piping components containing single- and two-phase flow conditions. This program also includes the pressure retaining portions of pump and valve bodies within these systems. The FAC program was originally outlined in NUREG–1344 and was further described through the US NRC GL 89-08. The program may also include components that are subject to wall thinning due to erosion mechanisms such as cavitation, flashing, droplet impingement, or solid particle impingement in various water systems. Since there are no materials that are known to be totally resistant to wall thinning due to erosion mechanisms, susceptible components of any material may be included in the erosion portion of the program.
- 2. Preventive Actions: This is a condition monitoring program; no preventive action has been recommended in this program. However, it is noted that monitoring of water chemistry to control pH and dissolved oxygen content are effective in reducing FAC, and the selection of appropriate component material, geometry, and hydrodynamic conditions, can be effective in reducing both FAC and erosion mechanisms.
- 3. Parameters Monitored or Inspected: The aging management program (AMP) monitors the effects of wall thinning due to FAC and erosion mechanisms by measuring wall thicknesses. In addition, relevant changes in system operating parameters, (e.g., temperature, flow rate, water chemistry, operating time), that result from off-normal or reduced-power operations are considered for their effects on the FAC models. Also, opportunistic visual inspections of internal surfaces are conducted during routine maintenance activities to identify degradation.
- 4. Detection of Aging Effects: Degradation of piping and components occurs by wall thinning. For FAC, the inspection program delineated in NSAC-202L includes identification of susceptible locations, as indicated by operating conditions or special considerations. For periods of extended operation beyond 60 years, piping systems that have been excluded from wall thickness monitoring due to operation less than 2 percent of plant operating time (as allowed by NSAC-202L) will be reassessed to ensure adequate bases exist to justify this exclusion. If actual wall thickness information is not available for use in this assessment, a representative sampling approach can be used. This program specifies nondestructive examination methods, such as ultrasonic testing (UT) and/or radiographic testing, to quantify the extent of wall thinning. Opportunistic visual inspections of up-stream and down-stream piping and components are performed during periodic pump and valve maintenance or during pipe replacements to assess internal surface conditions. Wall thicknesses are also measured at locations of suspected wall thinning that are identified by internal visual inspections. A representative sample of components is selected based on the most susceptible locations for wall thickness measurements at a frequency in accordance with NSAC-202L guidelines to identify and mitigate degradation before the component integrity is challenged. Expansion of the inspection sample is described in NSAC-202L, following identification of unexpected or inconsistent inspection results in the initial sample. The extent and schedule of the inspections provide for the detection of wall thinning before the loss of intended function. Inspections are performed by personnel qualified in accordance with site procedures and programs to perform the specified task.
- For erosion mechanisms, the program includes the identification of susceptible locations based on the extent-of-condition reviews from corrective actions in response to plant-specific and industry OE. Components in this category may be treated in a manner similar to other “susceptible-not-modeled” lines discussed in NSAC-202L. EPRI 1011231(Archived) provides guidance for identifying potential damage locations. EPRI TR-112657(Archived) or NUREG/–CR6031 provides additional insights for cavitation.
- 5. Monitoring and Trending: For FAC, CHECWORKS™ or similar predictive software calculates component wear rates and remaining service life based on inspection data and changes in operating conditions (e.g., power uprate, water chemistry). Data from each component inspection are used to calibrate the wear rates calculated in the FAC model with the observed field data. The use of such predictive software to develop an inspection schedule provides reasonable assurance that structural integrity will be maintained between inspections. The program includes the evaluation of inspection results to determine if additional inspections are needed to provide reasonable assurance that the extent of wall thinning is adequately determined, that intended function will not be lost, and that corrective actions are adequately identified.
- For erosion mechanisms, the program includes trending of wall thickness measurements to adjust the monitoring frequency and to predict the remaining service life of the component for scheduling repairs or replacements. Inspection results are evaluated to determine if assumptions in the extent-of-condition review remain valid. If degradation is associated with infrequent operational alignments, such as surveillances or pump starts/stops, then trending activities may need to consider the number or duration of these occurrences. Periodic wall thickness measurements of replacement components may be required and should continue until the effectiveness of corrective actions has been confirmed.
- 6. Acceptance Criteria: Components are suitable for continued service if calculations determine that the predicted wall thickness at the next scheduled inspection will meet the minimum allowable wall thickness. The minimum allowable wall thickness is the thickness needed to satisfy the component’s design loads under the original code of construction, but additional code requirements may also need to be met. A conservative safety factor is applied to the predicted wear rate determination to account for uncertainties in the wear rate calculations and UT measurements. As discussed in NSAC-202L, the minimum safety factor for acceptable wall thickness and remaining service life should not be less than 1.1.
- 7. Corrective Actions: Results that do not meet the acceptance criteria are addressed in the applicant’s corrective action program under those specific portions of the quality assurance (QA) program that are used to meet Criterion XVI, “Corrective Action,” of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix B. Appendix A of the Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) Report describes how an applicant may apply its 10 CFR Part 50, Appendix B, QA program to fulfill the corrective actions element of this AMP for both safety-related and nonsafety-related structures and components (SCs) within the scope of this program.
- The program includes reevaluation, repair, or replacement of components for which the acceptance criteria are not satisfied, prior to their return to service. For FAC, long-term corrective actions could include adjusting operating parameters or replacing components with FAC-resistant materials. However, if the wear mechanism has not been identified, then the replaced components should remain in the inspection program because FAC-resistant materials do not protect against erosion mechanisms. Furthermore, when carbon steel piping components are replaced with FAC-resistant material, the susceptible components immediately downstream should be monitored to identify any increased wear due to the “entrance effect” as discussed in EPRI 1015072.
- For erosion mechanisms, long-term corrective actions to eliminate the cause could include adjusting operating parameters and/or changing components’ geometric designs; however, the effectiveness of these corrective actions should be verified. Periodic monitoring activities should continue for any component replaced with an alternate material, since a material that is completely resistant to erosion mechanisms is not available.
- 8. Confirmation Process: The confirmation process is addressed through those specific portions of the QA program that are used to meet Criterion XVI, “Corrective Action,” of 10 CFR Part 50, Appendix B. Appendix A of the GALL-SLR Report describes how an applicant may apply its 10 CFR Part 50, Appendix B, QA program to fulfill the confirmation process element of this AMP for both safety-related and nonsafety-related SCs within the scope of this program.
- 9. Administrative Controls: Administrative controls are addressed through the QA program that is used to meet the requirements of 10 CFR Part 50, Appendix B, associated with managing the effects of aging. Appendix A of the GALL-SLR Report describes how an applicant may apply its 10 CFR Part 50, Appendix B, QA program to fulfill the administrative controls element of this AMP for both safety-related and nonsafety-related SCs within the scope of this program.
- 10. Operating Experience: Wall-thinning problems in single-phase systems have occurred in feedwater and condensate systems (US NRC Bulletin 87-01; US NRC Information Notice (IN) 92-35, IN 95-11, IN 2006-08) and in two-phase piping in extraction steam lines (US NRC INs 89-53, IN 97-84) and moisture separation reheater and feedwater heater drains (US NRC INs 89-53, IN 91-18, IN 93-21, IN 97-84). Observed wall thinning may be due to mechanisms other than FAC or less commonly, due to a combination of mechanisms (US NRC IN 99-19, Licensee Event Report (LER) 483/1999-003, LER 499/2005-004, LER 277/2006-003, LER 237/2007-003, LER 254/2009-004, LER 374/2013-001, LER 374/2015-001.
- The program is informed and enhanced when necessary through the systematic and ongoing review of both plant-specific and industry OE including research and development such that the effectiveness of the AMP is evaluated consistent with the discussion in Appendix B of the GALL-SLR Report.
References
10 CFR Part 50, Appendix B, “Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants.” Washington, DC: U.S. Nuclear Regulatory Commission. 2016.
EPRI. EPRI 1011231(Archived), “Recommendations for Controlling Cavitation, Flashing, Liquid Droplet Impingement, and Solid Particle Erosion in Nuclear Power Plant Piping Systems.” Palo Alto, California: Electric Power Research Institute. November 2004.
_____. EPRI 1015072, “Flow-Accelerated Corrosion–The Entrance Effect.” Palo Alto, California: Electric Power Research Institute. November 2007.
_____. EPRI TR–112657(Archived), “Revised Risk-Informed Inservice Inspection Evaluation Procedure.” Revision B-A. Agencywide Documents Access and Management System (ADAMS) Accession No. ML013470102. Palo Alto, California: Electric Power Research Institute. December 1999.
Licensee Event Report 237/2007-003, “Dresden Unit 2, High Pressure Coolant Injection System Declared Inoperable.” ADAMS Accession No. ML072750663. https://lersearch.inl.gov/LERSearchCriteria.aspx. September 2007.
Licensee Event Report 254/2009-004, “Quad Cities Unit 1, Pinhole Leak in Core Spray Piping Results in Loss of Containment Integrity and Plant Shutdown for Repairs.” ADAMS Accession No. ML093170206. [1]. November 2009.
Licensee Event Report 277/2006-003, “Peach Bottom Unit 2, Elbow Leak on Piping Attached to Suppression Pool Results in Loss of Containment Integrity.” ADAMS Accession No. ML063420059. [2]. December 2006
Licensee Event Report 374/2013-001, “LaSalle Unit 2, Pin Hole Leaks Identified in High Pressure Core Spray Piping.” ADAMS Accession No. ML13168A576. [3]. June 2013.
Licensee Event Report 374/2015-001, “LaSalle Unit 2, High Pressure Core Spray Inoperable Due to Division 3 Diesel Generator Cooling Water Pump Casing Leak.” ADAMS Accession No. ML15058A462. [4]. February 2015.
Licensee Event Report 483/1999-003, “Callaway, Manual Reactor Trip due to Heater Drain System Pipe Rupture Caused by Flow Accelerated Corrosion.” ADAMS Accession No. ML003712775. [5]. May 2000.
Licensee Event Report 499/2005-004, “South Texas Project Unit 2, Inoperability of Essential Cooling Water 2A and 2B Trains.” ADAMS Accession No. ML053410155. [6]. November 2005.
US NRC. [https://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1987/bl87001.html Bulletin 87-01, “Thinning of Pipe Walls in Nuclear Power Plants.” ADAMS Accession No. ML031210862. Washington, DC: U.S. Nuclear Regulatory Commission. July 1987.
_____. Generic Letter 89-08, “Erosion/Corrosion-Induced Pipe Wall Thinning.” ADAMS Accession No. ML031200731. Washington, DC: U.S. Nuclear Regulatory Commission. May 1989.
_____. Information Notice 89-53, “Rupture of Extraction Steam Line on High Pressure Turbine.” ADAMS Accession No. ML031180660. Washington, DC: U.S. Nuclear Regulatory Commission. June 1989.
_____. Information Notice 91-18, “High-Energy Piping Failures Caused by Wall Thinning.” ADAMS Accession No. ML031190529. Washington, DC: U.S. Nuclear Regulatory Commission. March 1991.
_____. Information Notice 92-35, “Higher than Predicted Erosion/Corrosion in Unisolable Reactor Coolant Pressure Boundary Piping inside Containment at a Boiling Water Reactor.” ADAMS Accession No. ML031200365. Washington, DC: U.S. Nuclear Regulatory Commission. May 1992.
_____. Information Notice 93-21, “Summary of NRC Staff Observations Compiled During Engineering Audits or Inspections of Licensee Erosion/Corrosion Programs.” ADAMS Accession No. ML031080042. Washington, DC: U.S. Nuclear Regulatory Commission. March 1993.
_____. Information Notice 95-11, “Failure of Condensate Piping Because of Erosion/Corrosion at a Flow Straightening Device.” ADAMS Accession No. ML031060332. Washington, DC: U.S. Nuclear Regulatory Commission. February 1995.
_____. Information Notice 97-84, “Rupture in Extraction Steam Piping as a Result of Flow-Accelerated Corrosion.” ADAMS Accession No. ML031050037. Washington, DC: U.S. Nuclear Regulatory Commission. December 1997.
_____. Information Notice 99-19, “Rupture of the Shell Side of a Feedwater Heater at the Point Beach Nuclear Plant.” ADAMS Accession No. ML031040409. Washington, DC: U.S. Nuclear Regulatory Commission. June 1999.
_____. Information Notice 2006-08, “Secondary Piping Rupture at the Mihama Power Station in Japan.” ADAMS Accession No. ML052910008. Washington, DC: U.S. Nuclear Regulatory Commission. March 2006.
_____. License Renewal Interim Staff Guidance LR-ISG-2012-01, “Wall Thinning Due to Erosion Mechanisms.” ADAMS Accession No. ML12352A057. Washington, DC: U.S. Nuclear Regulatory Commission. April 2013.
_____. NUREG–1344, “Erosion/Corrosion-Induced Pipe Wall Thinning in U.S. Nuclear Power Plants.” Washington, DC: U.S. Nuclear Regulatory Commission. April 1989.
_____. NUREG/CR–6031, “Cavitation Guide for Control Valves.” Washington DC: U.S. Nuclear Regulatory Commission. April 1993.
NSAC. NSAC-202L-R2(Archived), “Recommendations for an Effective Flow-Accelerated Corrosion Program.” Palo Alto, California: Electric Power Research Institute, Nuclear Safety Analysis Center (NSAC). April 1999.
_____. NSAC-202L-R3(Archived), “Recommendations for an Effective Flow-Accelerated Corrosion Program (1011838).” Palo Alto, California: Electric Power Research Institute, Nuclear Safety Analysis Center (NSAC). May 2006.
_____. NSAC-202L-R4, “Recommendations for an Effective Flow-Accelerated Corrosion Program (3002000563).” Palo Alto, California: Electric Power Research Institute, Nuclear Safety Analysis Center (NSAC). November 2013.