XI.M18 (NUREG-1801 R0)
XI.M18 BOLTING INTEGRITY
Program Description
The program relies on recommendations for a comprehensive bolting integrity program, as delineated in NUREG-1339, and industry recommendations, as delineated in the Electric Power Research Institute (EPRI) NP-5769(Archived), with the exceptions noted in NUREG-1339 for safety related bolting. The program relies on industry recommendations for a comprehensive bolting maintenance, as delineated in the EPRI TR-104213(Archived) for pressure retaining bolting and structural bolting. The program generally includes periodic inspection of closure bolting for indication of loss of preload, cracking, and loss of material due to corrosion, rust, etc.
Evaluation and Technical Basis
- 1. Scope of Program: The program covers all bolting within the scope of license renewal including safety-related bolting, bolting for NSSS component supports, bolting for other pressure retaining components, and structural bolting. The program covers both greater than and smaller than 2-in. diameter bolting. The U.S. Nuclear Regulatory Commission (US NRC) staff recommendations and guidelines for comprehensive bolting integrity programs that encompass all safety-related bolting are delineated in NUREG-1339. The industry's technical basis for the program for safety related bolting and guidelines for material selection and testing, bolting preload control, inservice inspection (ISI), plant operation and maintenance, and evaluation of the structural integrity of bolted joints, are outlined in EPRI NP-5769(Archived), with the exceptions noted in NUREG-1339. For other bolting, this information is set forth in EPRI TR-104213(Archived).
- 2. Preventive Actions: Selection of bolting material and the use of lubricants and sealants is in accordance with the guidelines of EPRI NP-5769(Archived) and the additional recommendations of NUREG-1339 to prevent or mitigate degradation and failure of safety-related bolting (see item 10, below). (NUREG-1339 takes exception to certain items in EPRI NP-5769(Archived), and recommends additional measures with regard to them.) Initial ISI of bolting for pressure retaining components includes a check of the bolt torque and uniformity of the gasket compression after assembly. It is noted that hot torquing of bolting is a leak preventive measure once the joint is brought to operating temperature and before or after it is pressurized. Hot torquing thus reestablishes preload before leak starts, but is ineffective in sealing a leak once it has begun.
- 3. Parameters Monitored/Inspected: The aging management program (AMP) monitors the effects of aging on the intended function of closure bolting, including loss of material, cracking, and loss of preload. High strength bolts (actual yield strength > 150 ksi) used in NSSS component supports are monitored for cracking. Bolting for pressure retaining components is inspected for signs of leakage. Structural bolting is inspected for indication of potential problems including loss of coating integrity and obvious signs of corrosion, rust, etc.
- 4. Detection of Aging Effects: Inspection requirements are in accordance with the American Society of Mechanical Engineers (ASME) Section XI, Table IWB 2500-1 or IWC 2500-1 (1995 edition through the 1996 addenda) and the recommendations of EPRI NP-5769(Archived). For Class 1 components, Table IWB 2500-1, examination category B-G-1, for bolting greater than 2 in. in diameter, specifies volumetric examination of studs and bolts and visual VT-1 examination of surfaces of nuts, washers, bushings, and flanges. All high strength bolting used in NSSS component supports are to be inspected also to the requirements for Class 1 components, examination category B-G-1. Examination category B-G-2, for bolting 2 in. or smaller requires only visual VT-1 examination of surfaces of bolts, studs, and nuts. For Class 2 components, Table IWC 2500-1, examination category B-D, for bolting greater than 2 in. in diameter, requires volumetric examination of studs and bolts. Examination categories B-P or C-H require visual examination (IWA-5240) during system leakage testing of all pressure-retaining Class 1 and 2 components, according to Tables IWB 2500-1 and IWC 2500-1, respectively. In addition, degradation of the closure bolting due to crack initiation, loss of prestress, or loss of material due to corrosion of the closure bolting would result in leakage. The extent and schedule of inspections, in accordance with IWB 2500-1 or IWC 2500-1, assure detection of aging degradation before the loss of the intended function of the closure bolting. Structural bolting both inside and outside containment is inspected by visual inspection. Degradation of this bolting may be detected and measured either by removing the bolt, proof test by tension or torquing, by in situ ultrasonic tests, or hammer test. If this bolting is found corroded, a closer inspection is performed to assess extent of corrosion.
- 5. Monitoring and Trending: The inspection schedules of ASME Section XI are effective and ensure timely detection of cracks and leakage. If bolting for pressure retaining components (not covered by ASME Section XI) is reported to be leaking, then it may be inspected daily. If the leak rate does not increase, the inspection frequency may be decreased to weekly or biweekly.
- 6. Acceptance Criteria: Any indications in closure bolting are evaluated in accordance with IWB-31 00 and acceptance standards of IWB-3400 and IWB-3500, or IWC-31 00 and acceptance standards of IWC-3400 and IWC-3500. Indications of cracking in component support bolting warrant immediate replacement of the cracked bolt. For other pressure retaining components, a leak from a joint is immediately repaired if it is a major leak and causes adverse effect such as corrosion or contamination.
- 7. Corrective Actions: Repair and replacement is in conformance with IWB-4000 and guidelines and recommendations of EPRI NP-5769(Archived). As discussed in the appendix to this report, the staff finds the requirements of 10 CFR Part 50, Appendix B, acceptable in addressing corrective actions. Repair and replacement of other bolting including structural bolting is in conformance with the guidelines and recommendations of EPRI TR-104213(Archived).
- 8. Confirmation Process: Site quality assurance (QA) procedures, review and approval processes, and administrative controls are implemented in accordance with the requirements of 10 CFR Part 50, Appendix B. As discussed in the appendix to this report, the staff finds the requirements of 10 CFR Part 50, Appendix B, acceptable in addressing the confirmation process and administrative controls.
- 9. Administrative Controls: See Item 8, above.
- 10. Operating Experience: Degradation of threaded fasteners in closures for the reactor coolant pressure boundary has occurred from boric acid corrosion, stress corrosion cracking, and fatigue loading (US NRC IE Bulletin 82-02, US NRC Generic Letter (GL) 91-17). Stress corrosion cracking has occurred in high strength bolts used for NSSS component supports. The bolting integrity programs developed and implemented in accordance with commitments made in response to US NRC communications on bolting events have provided an effective means of ensuring bolting reliability. These programs are documented in EPRI NP-5769(Archived) and TR-104213(Archived) and represent industry consensus.
References
10 CFR 50.55a, Codes and Standards, Office of the Federal Register, National Archives and Records Administration, 2000.
ASME Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, ASME Boiler and Pressure Vessel Code, 1995 edition through the 1996 addenda, American Society of Mechanical Engineers, New York, NY.
EPRI NP-5769(Archived), Degradation and Failure of Bolting in Nuclear Power Plants, Volumes 1 and 2, Electric Power Research Institute, Palo Alto, CA, April 1988.
EPRI TR-104213(Archived), Bolted Joint Maintenance & Application Guide, Electric Power Research Institute, Palo Alto, CA, December 1995.
US NRC Generic Letter 91-17, Generic Safety Issue 79, "Bolting Degradation or Failure in Nuclear Power Plants," U.S. Nuclear Regulatory Commission, October 17, 1991.
US NRC IE Bulletin No. 82-02, Degradation of Threaded Fasteners in the Reactor Coolant Pressure Boundary of PWR Plants, U.S. Nuclear Regulatory Commission, June 2, 1982.
NUREG-1339, Resolution of Generic Safety Issue 29: Bolting Degradation or Failure in Nuclear Power Plants, Richard E. Johnson, U.S. Nuclear Regulatory Commission, June 1990.