2191 R0 XI.S3

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Xl.S3 ASME SECTION XI, SUBSECTION IWF

Program Description

Title 10 of the Code of Federal Regulations (10 CFR) 50.55a, imposes the inservice inspection (ISI) requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section XI, for Class 1, 2, 3, and metal containment (MC) piping and components and their associated supports. The ISI of supports for ASME piping and components is addressed in Section XI, Subsection IWF. This program supplements ASME Code, Section XI, Subsection IWF, which constitutes an existing mandated program applicable to managing aging of American Society of Mechanical Engineers (ASME) Class 1, 2, 3, and MC component supports for subsequent license renewal.

The scope of inspection for supports is based on sampling of the total support population. The sample size varies depending on the ASME Class. The largest sample size is specified for the most critical supports (ASME Class 1). The sample size decreases for the less critical supports (ASME Class 2 and 3). Discovery of support deficiencies during regularly scheduled inspections triggers an increase of the inspection scope. The primary inspection method employed is visual examination. Degradation that potentially compromises support function or load capacity is identified for evaluation. ASME Code Section XI, Subsection IWF specifies acceptance criteria and corrective actions. Supports requiring corrective actions are reexamined during the next inspection period.

The requirements of Subsection IWF are supplemented to include monitoring of high-strength bolting (actual measured yield strength greater than or equal to 150 kilo-pounds per square inch (ksi) [1,034 megapascals (MPa)] for cracking. This program emphasizes proper selection of bolting material, lubricants, and installation torque or tension to prevent or minimize loss of bolting preload and cracking of high-strength bolting. This program includes a one-time inspection of additional supports for each group of materials used and the environments to which they are exposed outside of the existing Subsection IWF sample population.

Evaluation and Technical Basis

1. Scope of Program: This program addresses ASME Class 1, 2, 3, and MC component supports. The scope of the program includes support members, structural bolting, high-strength structural bolting [actual measured yield strength greater than or equal to 150 ksi (1,034 MPa)], anchor bolts, welds, support anchorage to the building structure, accessible sliding surfaces, constant and variable load spring hangers, guides, stops, and vibration isolation elements. The acceptability of inaccessible areas (e.g., portions of supports encased in concrete, buried underground, or encapsulated by guard pipe) is evaluated when conditions exist in accessible areas that could indicate the presence of, or result in, degradation to such inaccessible areas.

2. Preventive Action: Operating experience and laboratory examinations show that the use of molybdenum disulfide (MoS2) as a lubricant is a potential contributor to stress corrosion cracking (SCC), especially when applied to high-strength bolting. Thus, molybdenum disulfide and other lubricants containing sulfur should not be used. Preventive measures also include using bolting material that has actual measured yield strength less than 150 ksi (1,034 MPa). Bolting replacement and maintenance activities include proper selection of bolting material and lubricants, and appropriate installation torque or tension, as recommended in Electric Power Research Institute (EPRI) documents (e.g., EPRI NP-5067(Archived) and EPRI TR–104213(Archived)), American Society for Testing and Materials (ASTM) standards, and American Institute of Steel Construction Specifications, as applicable. If bolting within the scope of the program consists of ASTM A325 and/or ASTM A490 bolts (including respective equivalent twist-off type ASTM F1852 and/or ASTM F2280 bolts), the preventive actions for storage, lubricant selection, and bolting and coating material selection discussed in Section 2 of Research Council for Structural Connections publication “Specification for Structural Joints Using High-Strength Bolts” need to be used.

3. Parameters Monitored or Inspected: The parameters monitored or inspected include corrosion; cracking, deformation; misalignment of supports; missing, detached, or loosened support items; general structural condition of weld joints and weld connections to building structure for loss of integrity; improper clearances of guides and stops; and improper hot or cold settings of spring supports and constant load supports. Accessible areas of sliding surfaces are monitored for debris, dirt, or indications of excessive loss of material due to wear that could prevent or restrict sliding as intended in the design basis of the support. Elastomeric or polymeric vibration isolation elements are monitored for cracking, loss of material, and hardening. Bolting is monitored for corrosion, loss of integrity of bolted connections due to self-loosening, and material conditions that can affect structural integrity. Concrete around anchor bolts is monitored for degradation under the Structures Monitoring Program. High strength bolting (actual measured yield strength greater than or equal to 150 ksi (1,034 MPa) in sizes greater than 1 inch nominal diameter (including ASTM A490 bolts and ASTM F2280 bolts), should be monitored for SCC.

4. Detection of Aging Effects: The program requires that a sample of ASME Class 1, 2, and 3 piping supports that are not exempt from examination and 100 percent of supports other than piping supports (Class 1, 2, 3, and MC), be examined as specified in Table IWF-2500-1. The sample size examined for ASME Class 1, 2, and 3 component supports is as specified in Table IWF-2500-1. The provisions of ASME Code Section XI, Subsection IWF are supplemented to include a one-time inspection of an additional 5 percent of the sample size specified in Table IWF-2500-1 for Class 1, 2, and 3 piping supports. The one-time inspection is conducted within 5 years prior to entering the subsequent period of extended operation. The additional supports are selected from the remaining population of IWF piping supports. However, the responsible engineer should ensure that the sample includes components that are most susceptible to age-related degradation (i.e., based on time in service, aggressive environment, etc.).

The extent, frequency, and examination methods are designed to detect, evaluate, or repair age-related degradation before there is a loss of component support intended function. The VT-3 examination method specified by the program can reveal loss of material due to corrosion and wear, cracks, verification of clearances, settings, physical displacements, loose or missing parts, debris or dirt in accessible areas of the sliding surfaces, or loss of integrity at bolted connections. The VT-3 examination can also detect loss of material and cracking of elastomeric or polymeric vibration isolation elements. Elastomeric or polymeric vibration isolation elements should be felt to detect hardening if the vibration isolation function is suspect. IWF-3200 specifies that visual examinations that detect surface flaws which exceed acceptance criteria may be supplemented by either surface or volumetric examinations to determine the character of the flaw.

For all high-strength bolting [actual measured yield strength greater than or equal to 150 ksi (1,034 MPa)] in sizes greater than 1 inch nominal diameter (including ASTM A490 and equivalent ASTM F2280), volumetric examination comparable to that of ASME Code Section XI, Table IWB-2500-1, Examination Category B-G-1 should be performed at least once per interval to detect cracking in addition to the VT-3 examination. The sample of high-strength bolts subject to volumetric examination should be determined on a plant-specific basis such that the program can provide reasonable assurance that SCC is not occurring for the entire population of high-strength bolts. This volumetric examination may be waived with plant-specific justification.

5. Monitoring and Trending: The ASME Class 1, 2, 3, and MC component supports are examined periodically, as specified in Table IWF-2500-1. As required by IWF-2420(a), the sequence of component support examinations established during the first inspection interval is repeated during each successive inspection interval, to the extent practical. Component supports whose examinations do not reveal unacceptable degradation are accepted for continued service. Verified changes of conditions from prior examination are recorded in accordance with IWA-6230. Component supports whose examinations reveal unacceptable conditions and are accepted for continued service by corrective measures or repair/replacement activity are reexamined during the next inspection period. When the reexamined component support no longer requires additional corrective measures during the next inspection period, the inspection schedule may revert to its regularly scheduled inspection. Examinations that reveal indications which exceed the acceptance standards and require corrective measures are extended to include additional examinations in accordance with IWF-2430. If a component support does not exceed the acceptance standards of IWF-3400 but is repaired to as-new condition, the sample is increased or modified to include another support that is representative of the remaining population of supports that were not repaired.

6. Acceptance Criteria: The acceptance standards for visual examination are specified in IWF-3400. IWF-3410(a) identifies the following conditions as unacceptable:

1. Deformations or structural degradations of fasteners, springs, clamps, or other support items;
2. Missing, detached, or loosened support items, including bolts and nuts;
3. Arc strikes, weld spatter, paint, scoring, roughness, or general corrosion on close tolerance machined or sliding surfaces;
4. Improper hot or cold positions of spring supports and constant load supports;
5. Misalignment of supports; and
6. Improper clearances of guides and stops.

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Other unacceptable conditions include:

1. Loss of material due to corrosion or wear;
2. Debris, dirt, or excessive wear that could prevent or restrict sliding of the sliding surfaces as intended in the design basis of the support;
3. Cracked or sheared bolts, including high-strength bolts, and anchors; and
4. Loss of material, cracking, and hardening of elastomeric or polymeric vibration isolation elements that could reduce the vibration isolation function;
5. Cracks.

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The above conditions may be accepted provided the technical basis for their acceptance is documented.

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 10 CFR 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 50, Appendix B, QA program to fulfill the corrective actions element of this aging management program (AMP) for both safety-related and nonsafety-related structures and components (SCs) within the scope of this program.

Identification of unacceptable conditions triggers an expansion of the inspection scope, in accordance with IWF-2430, and reexamination of the supports requiring corrective actions during the next inspection period, in accordance with IWF-2420(b). In accordance with IWF-3122, supports containing unacceptable conditions are evaluated or tested or corrected before returning to service. Corrective actions are delineated in IWF-3122.2. IWF-3122.3 provides an alternative for evaluation or testing to substantiate structural integrity and/or functionality.

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 50, Appendix B. Appendix A of the GALL-SLR Report describes how an applicant may apply its 10 CFR 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 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 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: Degradation of threaded bolting and fasteners has occurred from boric acid corrosion, SCC, and fatigue loading (U.S. Nuclear Regulatory Commission (US NRC) Inspection and Enforcement Bulletin (IEB) 82-02, “Degradation of Th[https://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1991/gl91017.html Generic Letter 91-17, “Generic Safety Issue 79, Bolting Degradation of Failure in Nuclear Power Plants”). SCC has occurred in high-strength bolts used for nuclear steam supply system component supports (EPRI NP-5769(Archived)). US NRC Information Notice 2009-04 describes deviations in the supporting forces of mechanical constant supports, from code allowable load deviation, due to age-related wear on the linkages and increased friction between the various moving parts and joints within the constant support, which can adversely affect the analyzed stresses of connected piping systems.

The program is informed and enhanced when necessary through the systematic and ongoing review of both plant-specific and industry operating experience 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.

10 CFR 50.55a, “Codes and Standards.” Washington, DC: U.S. Nuclear Regulatory Commission. 2016.

ASME. ASME Code Section XI, “Rules for Inservice Inspection of Nuclear Power Plant Components, Subsection IWB, Requirements for Class 1 Components of Light-Water Cooled Power Plants.” New York, New York: The American Society of Mechanical Engineers. 2008.

_____. ASME Code Section XI, “Rules for Inservice Inspection of Nuclear Power Plant Components, Subsection IWC, Requirements for Class 2 Components of Light-Water Cooled Power Plants.” New York, New York: The American Society of Mechanical Engineers. 2008.

_____. ASME Code Section XI, “Rules for Inservice Inspection of Nuclear Power Plant Components, Subsection IWD, Requirements for Class 3 Components of Light-Water Cooled Power Plants.” New York, New York: The American Society of Mechanical Engineers. 2008.

_____. ASME Code Section XI, “Rules for Inservice Inspection of Nuclear Power Plant Components, Subsection IWE, Requirements for Class MC and Metallic Liners of Class CC Components of Light-Water Cooled Power Plants.” New York, New York: The American Society of Mechanical Engineers. 2008.

_____. ASME Code Section XI, “Rules for Inservice Inspection of Nuclear Power Plant Components, Subsection IWF, Requirements for Class 1, 2, 3, and MC Component Supports of Light-Water Cooled Power Plants.” New York, New York: The American Society of Mechanical Engineers. 2008.

EPRI. EPRI NP-5067, “Good Bolting Practices, A Reference Manual for Nuclear Power Plant Maintenance Personnel.” Volume 1: Large Bolt Manual, 1987; Volume 2: Small Bolts and Threaded Fasteners. Palo Alto, California: Electric Power Research Institute. 1990.

_____. EPRI NP-5769(Archived), “Degradation and Failure of Bolting in Nuclear Power Plants.” Volumes 1 and 2. Palo Alto, California: Electric Power Research Institute. April 1988.

_____. EPRI TR–104213(Archived), “Bolted Joint Maintenance & Application Guide.” Palo Alto, California: Electric Power Research Institute. December 1995.

US NRC Generic Letter 91-17, “Generic Safety Issue 79, Bolting Degradation or Failure in Nuclear Power Plants.” Agencywide Documents Access and Management System (ADAMS) Accession No. ML031140534. Washington, DC: U.S. Nuclear Regulatory Commission. October 1991.

_____. IE Bulletin 82-02, “Degradation of Threaded Fasteners in the Reactor Coolant Pressure Boundary of PWR Plants.” ADAMS Accession No. ML03120720. Washington, DC: U.S. Nuclear Regulatory Commission. June 1982.

_____. Information Notice 2009-04, “Age-Related Constant Support Degradation.” ADAMS Accession No. ML090340754. Washington, DC: U.S. Nuclear Regulatory Commission. February 2009.

RCSC. “Specification for Structural Joints Using High-Strength Bolts.” Chicago, Illinois: Research Council on Structural Connections. August 2014.

American Society of Mechanical Engineers

Stress Corrosion Cracking

Electric Power Research Institute

Quality Assurance

Generic Aging Lessons Learned - The US NRC GALL Report is NUREG-1801. The US NRC Subsequent License Renewal GALL is NUREG-2191

Subsequent License Renewal - The extension of the original license from 40 years to 60 years is known as License Renewal. Extensions of the license beyond 60 years are known as Subsequent License Renewal.

Aging Management Program

United States of America

Nuclear Regulatory Commission - The US federal government agency that regulates nuclear power plants

Agency wide Documents Access and Management System - The official recordkeeping system, through which the U.S. Nuclear Regulatory Commission (US NRC) provides access to the "libraries" or collections of publicly available documents