2191 R0 XI.M18: Difference between revisions

Revision as of 19:12, 4 October 2024

XI.M18 BOLTING INTEGRITY

Program Description

The program manages aging of closure bolting for pressure retaining components. The program relies on recommendations for a comprehensive bolting integrity program, as delineated in the following documents:

NUREG–1339, “Resolution of Generic Safety Issue 29: Bolting Degradation or Failure in Nuclear Power Plants.”
Electric Power Research Institute (EPRI) NP-5769(Archived), “Degradation and Failure of Bolting in Nuclear Power Plants” (with the exceptions noted in NUREG-1339 for safety-related bolting).
EPRI Report 1015336(Archived), “Nuclear Maintenance Application Center: Bolted Joint Fundamentals.”
EPRI Report 1015337(Archived), “Nuclear Maintenance Applications Center: Assembling Gasketed, Flanged Bolted Joints.”

The program includes periodic visual inspection of closure bolting for indications of loss of preload, cracking, and loss of material due to general, pitting, and crevice corrosion, microbiologically influenced corrosion (MIC), and wear as evidenced by leakage. Closure bolting that is submerged or located in piping systems that contain air or gas for which leakage is difficult to detect, is inspected or tested by alternative means. The program also includes sampling-based volumetric examinations of high-strength closure bolting to detect indications of cracking. The program also includes preventive measures to preclude or minimize loss of preload and cracking.

Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) Report aging management program (AMP) XI.M1, “ASME Section XI Inservice Inspections, Subsections IWB, IWC, and IWD,” manages aging effects associated with closure bolting within the scope of American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Section XI and supplements this bolting integrity program. GALL-SLR Report AMPs XI.S1, “ASME Section XI, Subsection IWE,” XI.S3, “American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Section XI, Subsection IWF,” XI.S6, “Structures Monitoring,” XI.S7, “Inspection of Water-Control Structures Associated with Nuclear Power Plants,” XI.M23, “Inspection of Overhead Heavy Load and Light Load (Related to Refueling) Handling Systems,” manage aging effects associated with safety-related and nonsafety-related structural bolting, and GALL-SLR Report AMP XI.M36, “External Surfaces Monitoring of Mechanical Components,” manages aging effects associated with heating, ventilation, and air conditioning (HVAC) closure bolting.

Evaluation and Technical Basis

1. Scope of Program: This program manages the effects of aging of closure bolting for pressure retaining components (aging effects associated with HVAC closure bolting are managed by GALL-SLR Report AMP XI.M36) within the scope of license renewal. This program does not manage aging of reactor head closure stud bolting ( GALL-SLR Report AMP XI.M3) or structural bolting ( GALL-SLR Report AMPs XI.S1, XI.S3, XI.S6, XI.S7, and XI.M23).

2. Preventive Actions: Selection of bolting material and the use of lubricants and sealants is in accordance with the guidelines of EPRI Reports 1015336(Archived) and 1015337(Archived) and the additional recommendations of NUREG-1339 to prevent or mitigate stress corrosion cracking (SCC). Of particular note, use of molybdenum disulfide (MoS₂) as a lubricant has been shown to be a potential contributor to SCC and should not be used. Preventive measures also include using bolting material that has an actual measured yield strength less than 150 kilo-pounds per square inch (ksi) or 1,034 megapascals (MPa). Bolting replacement activities include proper torquing of the bolts and checking for uniformity of the gasket compression after assembly. Maintenance practices require the application of an appropriate preload based on guidance in EPRI documents, manufacturer recommendations, or engineering evaluation.

3. Parameters Monitored or Inspected: This program monitors the effects of aging on the intended function of closure bolting. Closure bolting is inspected for signs of leakage. Closure bolting that is submerged or where the piping systems contains air or gas for which leakage is difficult to detect are inspected or tested by alternative means. High strength closure bolting {with actual yield strength greater than or equal to 150 ksi (1,034 MPa), and bolting for which yield strength is unknown, is monitored for surface and subsurface discontinuities indicative of cracking.

4. Detection of Aging Effects: AMP XI.M1 implements inspection of Class 1, Class 2, and Class 3 pressure retaining bolting in accordance with requirements of ASME Code Section XI, Tables IWB-2500-1, IWC-2500-1, and IWD-2500-1. These include volumetric and visual (i.e., VT-1, VT-2) examinations, as appropriate.

Degradation of pressure boundary closure bolting due to crack initiation, loss of preload, or loss of material may result in leakage from the mating surfaces or joint connections of pressure boundary components. Periodic inspections of ASME Code class and non-ASME Code class bolted joints for signs of leakage are conducted at least once per refueling cycle. The inspections may be performed as part of ASME Code Section XI leakage tests or as part of other periodic inspection activities, such as system walkdowns or GALL-SLR Report AMP XI.M36 inspections. Bolted joints that are not readily visible during plant operations and refueling outages are inspected when they are made accessible and at such intervals that would provide reasonable assurance the components’ intended functions are maintained. Closure bolting inspections includes consideration of the guidance applicable for pressure boundary bolting in NUREG-1339 and in EPRI NP-5769(Archived).

High strength closure bolting [actual measured yield strength greater than or equal to 150 ksi (1,034 MPa)] may be subject to SCC. For all closure bolting greater than 2 inches in diameter (regardless of code classification) with actual yield strength greater than or equal to 150 ksi (1,034 MPa) and closure bolting for which yield strength is unknown, volumetric examination in accordance to that of ASME Code Section XI, Table IWB-2500-1, Examination Category B-G-1, is performed (e.g., acceptance standards, extent and frequency of examination). Specified bolting material properties (e.g., design and procurement specifications, fabrication and vendor drawings, material test reports) may be used to determine if the bolting exceeds the threshold to be classified as high strength.

Closure bolting in locations that preclude detection of joint leakage, such as in submerged environments or where the piping systems contains air or gas for which leakage is difficult to detect, is inspected as follows:

Submerged closure bolting is visually inspected for loss of material during maintenance activities. In this case, bolt heads are inspected when made accessible, and bolt threads are inspected when joints are disassembled. In each 10-year period during the subsequent period of extended operation a representative sample of bolt heads and threads is inspected. If opportunistic maintenance activities will not provide access to 20 percent of the population (for a material/environment combination) up to a maximum of 25 bolt heads and threads over a 10-year period, then the subsequent license renewal application (SLRA) states how integrity of the bolted joint will be demonstrated. For example: (a) periodic pump vibration measurements are taken and trended; or (b) sump pump operator walkdowns are performed demonstrating that the pumps are appropriately maintaining sump levels.
For closure bolting where the piping systems contains air or gas for which leakage is difficult to detect, the SLRA states how integrity of the bolted joint will be demonstrated. For example: (a) inspections are performed consistent with that of submerged closure bolting; (b) a visual inspection for discoloration is conducted when leakage of the environment inside the piping systems would discolor the external surfaces; (c) monitoring and trending of pressure decay is performed when the bolted connection is located within an isolated boundary; (d) soap bubble testing is performed; or (e) when the temperature of the fluid is higher than ambient conditions, thermography testing is performed.
For closure bolting for components that are not normally pressurized, the SLRA states how aging effects associated with the closure bolting will be managed (e.g., checking the torque to the extent that the closure bolting is not loose).

The inspection includes a representative sample of 20 percent of the population of bolt heads and threads (defined as bolts with the same material and environment combination) or a maximum of 25 bolts per population at each unit. For multi-unit sites where the sample size is not based on the percentage of the population, it is acceptable to reduce the total number of inspections at the site as follows. For two-unit sites, 19 bolt heads and threads are inspected per unit and for a three-unit site, 17 bolt heads and threads are inspected per unit. In order to conduct 17 or 19 inspections at a unit in lieu of 25, the applicant states in the SLRA the basis for why the operating conditions at each unit are similar enough (e.g., chemistry) to provide representative inspection results. The basis should include consideration of potential differences such as the following:

Are there any systems which have had an out-of-spec water chemistry condition for a longer period of time or out-of-spec conditions, which have occurred more frequently?
For lubricating or fuel oil systems, are there any components that were exposed to the more severe contamination levels?
For raw water systems, is the water source from different sources where one or the other is more susceptible to microbiologically influenced corrosion or other aging mechanisms?

Inspections are performed by personnel qualified in accordance with site procedures and programs to perform the specified task. Inspections within the scope of the ASME Code follow procedures consistent with the ASME Code. Non-ASME Code inspections follow site procedures that include inspection parameters for items such as lighting, distance, and offset, which provide an adequate examination.

5. Monitoring and Trending: Where practical, identified degradation is projected until the next scheduled inspection. Results are evaluated against acceptance criteria to confirm that the timing of subsequent inspections will maintain the components’ intended functions throughout the subsequent period of extended operation based on the projected rate of degradation. For sampling-based inspections, results are evaluated against acceptance criteria to confirm that the sampling bases (e.g., selection, size, frequency) will maintain the components’ intended functions throughout the subsequent period of extended operation based on the projected rate and extent of degradation.

6. Acceptance Criteria: Any indications of aging effects in ASME pressure retaining bolting are evaluated in accordance with Section XI of the ASME Code. Leaking joints do not meet acceptance criteria. Plant-specific acceptance criteria are established when alternative inspections or testing is conducted for submerged closure bolting or closure bolting where the piping systems contains air or gas for which leakage is difficult to detect.

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 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.

Replacement of ASME pressure retaining bolting is performed in accordance with the requirements of ASME Code Section XI, as subject to the additional guidelines and recommendations of EPRI Reports 1015336(Archived) and 1015337(Archived). Replacement of other pressure retaining closure bolting (i.e., non-ASME Code class closure bolting) is performed in accordance with the guidelines and recommendations of EPRI Reports 1015336(Archived) and 1015337(Archived).

If a bolted connection for pressure retaining components is reported to be leaking, follow-up periodic visual inspections are conducted in accordance with plant-specific procedures until the leak is corrected. If the leak rate is increasing, more frequent inspections are warranted. The effects of leakage from bolted connections that have an intended function identified in 10 CFR 54.4(a)(2) are evaluated for its impact on components with an intended function identified in 10 CFR 54.4(a)(1) and located within the vicinity of the leaking bolted connection.

For sampling-based inspections, if the cause of the aging effect for each applicable material and environment is not corrected by repair or replacement for all components constructed of the same material and exposed to the same environment, additional inspections are conducted if one of the inspections does not meet acceptance criteria. The number of increased inspections is determined in accordance with the site’s corrective action process; however, there are no fewer than five additional inspections for each inspection that did not meet acceptance criteria, or 20 percent of each applicable material, environment, and aging effect combination is inspected, whichever is less. If subsequent inspections do not meet acceptance criteria, an extent of condition and extent of cause analysis is conducted to determine the further extent of inspections. Additional samples are inspected for any recurring degradation to ensure corrective actions appropriately address the associated causes. At multi-unit sites, the additional inspections include inspections at all of the units with the same material, environment, and aging effect combination. The additional inspections are completed within the interval (e.g., refueling outage interval, 10-year inspection interval) in which the original inspection was conducted. If any projected inspection results will not meet acceptance criteria prior to the next scheduled inspection, sampling frequencies are adjusted as determined by the site’s corrective action program.

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: Degradation of threaded bolting and fasteners in closures for the reactor coolant pressure boundary has occurred from boric acid corrosion, SCC, and fatigue loading (U.S. Nuclear Regulatory Commission [NRC] IE Bulletin 82-02, US NRC Generic Letter 91-17). SCC has occurred in high strength bolts used for nuclear steam supply system component supports (EPRI NP-5769(Archived)). The bolting integrity program developed and implemented in accordance with the applicant’s docketed responses to the U.S. Nuclear Regulatory Commission (US NRC) communications on bolting events have provided an effective means of ensuring bolting reliability. These programs are documented in EPRI Reports NP-5769(Archived), 1015336(Archived), and 1015337(Archived) and represent industry consensus.

Degradation related failures have occurred in downcomer tee-quencher bolting in boiling water reactors (BWRs) designed with drywells (ADAMS Accession No. ML050730347). Leakage from bolted connections has been observed in reactor building closed cooling systems of BWRs (Licensee Event Report 341/2005-001).

SCC of A-286 stainless steel closure bolting has occurred when seal cap enclosures have been installed to mitigate gasket leakage at valve body-to-bonnet joints (US NRC Information Notice 2012-15). The enclosures surrounding the bolts filled with hot reactor coolant that had leaked from the joint and mixed with the oxygen-containing atmosphere trapped within the enclosure. The enclosures did not allow for inspections of the bolted joints.

The applicant is to evaluate applicable operating experience (OE) to support the conclusion that the effects of aging are adequately managed.

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.

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.” New York, New York: The American Society of Mechanical Engineers. 2008.

EPRI. EPRI 1015336(Archived), “Nuclear Maintenance Application Center: Bolted Joint Fundamentals.” Palo Alto, California: Electric Power Research Institute. December 2007.

_____. EPRI 1015337(Archived), “Nuclear Maintenance Applications Center: Assembling Gasketed, Flanged Bolted Joints.” Palo Alto, California: Electric Power Research Institute. December 2007.

_____. 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.

Licensee Event Report 341/2005-001, “Manual Reactor Shutdown Due to Containment Cooler Leak.” [1]. March 2005.

US NRC Generic Letter 91-17, “Generic Safety Issue 79, Bolting Degradation or Failure in Nuclear Power Plants.” 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.” Washington, DC: U.S. Nuclear Regulatory Commission. June 1982.

_____. Information Notice 2012-15, “Use of Seal Cap Enclosures to Mitigate Leakage From Joints That Use A-286 Bolts.” Washington, DC: U.S. Nuclear Regulatory Commission. August 2012.

_____. Morning Report, “Failure of Safety/Relief Valve Tee-Quencher Support Bolts.” Agencywide Documents Access and Management System (ADAMS) Accession No. ML050730347. Washington, DC: U.S. Nuclear Regulatory Commission. March 14, 2005.

_____. NUREG–1339, “Resolution of Generic Safety Issue 29: Bolting Degradation or Failure in Nuclear Power Plants.” Washington, DC: U.S. Nuclear Regulatory Commission. June 1990.

2191 R0 XI.M18: Difference between revisions

Revision as of 19:12, 4 October 2024

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