X.S1 (NUREG-2191 R0)
X.S1 CONCRETE CONTAINMENT UNBONDED TENDON PRESTRESS
Program Description
This time limited aging analysis (TLAA) aging management program (AMP) provides reasonable assurance of the adequacy of prestressing forces in unbonded tendons of prestressed concrete containments, during the subsequent period of extended operation, under Title 10 of the Code of Federal Regulations (10 CFR) 54.21(c)(1)(iii). The program consists of an assessment of measured tendon prestress forces from required examinations performed in accordance with Subsection IWL of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section XI, as incorporated by reference in 10 CFR 50.55a, and as further supplemented herein. The assessment related to the adequacy of the prestressing force for each tendon group based on type (i.e., hoop, vertical, dome, inverted-U, helical) and other considerations (e.g., geometric dimensions, whether affected by repair/replacement, etc.) establishes (a) acceptance criteria in accordance with ASME Code Section XI, Subsection IWL and (b) trend lines constructed based on the guidance provided in the U.S. Nuclear Regulatory Commission (US NRC) Information Notice (IN) 99-10, “Degradation of Prestressing Tendon Systems in Prestressed Concrete Containments.” The US NRC Regulatory Guide 1.35.1, “Determining Prestressing Forces for Inspection of Prestressed Concrete Containments,” may be used for guidance related to calculation of prestressing losses and predicted forces.
Evaluation and Technical Basis
- 1. Scope of Program: The program addresses the assessment of unbonded tendon prestressing forces measured in accordance with ASME Code Section XI, Subsection IWL, when an applicant performs the concrete containment prestressing force TLAA using 10 CFR 54.21(c)(1)(iii).
- 2. Preventive Actions: This is primarily a condition monitoring program, which periodically measures and evaluates tendon forces such that corrective action can be taken, if required, prior to tendon forces falling below minimum required values established in the design. Maintaining the prestressing above the minimum required value (MRV) [prestressing force], as described under the acceptance criteria below, provides reasonable assurance that the structural and functional adequacy of the concrete containment is maintained.
- 3. Parameters Monitored: The parameters monitored are the concrete containment tendon prestressing forces in accordance with ASME Code Section XI, Subsection IWL. The prestressing forces are measured on common (control) tendons and tendons selected by random sampling of each tendon group using lift-off or equivalent method.
- 4. Detection of Aging Effects: The loss of concrete containment tendon prestressing forces is detected by measuring tendon forces, and analyzing (predicting) tendon forces and trending the data obtained as part of ASME Code Section XI, Subsection IWL examinations.
- 5. Monitoring and Trending: In addition to Subsection IWL examination requirements, the estimated and all measured prestressing forces up to the current examination are plotted against time. The predicted lower limit (PLL) line, MRV, and trend line are developed for each tendon group examined for the subsequent period of extended operation. The trend line represents the general variation of prestressing forces with time based on the actual measured forces in individual tendons of the specific tendon group. The trend line for each tendon group is constructed by regression analysis of all measured prestressing forces in individual tendons of that group obtained from all previous examinations. The PLL line, MRV, and trend line for each tendon group are projected to the end of the subsequent period of extended operation. The trend lines are updated at each scheduled examination.
- 6. Acceptance Criteria: The prestressing force trend line (constructed as indicated in the Monitoring and Trending program element) for each tendon group must indicate that existing prestressing forces in the concrete containment tendon would not fall below the appropriate MRV prior to the next scheduled examination. If the trend line crosses the PLL line, its cause should be determined, evaluated and corrected. The trend line crossing the PLL line is an indication that the existing prestressing forces in concrete containment could fall below the MRV. Any indication in the trend line that the overall prestressing force in any tendon group(s) could potentially fall below the MRV during the subsequent period of extended operation is evaluated, the cause(s) is/are documented, and corrective action(s) is/are performed in a timely manner.
- 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.
- If acceptance criteria are not met then either systematic retensioning of tendons or a reanalysis of the concrete containment is warranted so that the design adequacy of the containment is demonstrated.
- 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: The program incorporates a review of the relevant operating experience (OE) that has occurred at the applicant’s plant as well as at other plants. NUREG/CR–7111, “A Summary of Aging Effects and their Management in Reactor Spent Fuel Pools, Refueling Cavities, Tori, and Safety-Related Concrete Structures,” summarizes observations on low prestress forces recorded in some plants. However, tendon OE may vary at different plants with prestressed concrete containments. The difference could be due to the prestressing system design (e.g., button- headed, wedge, or swaged anchorages), environment, and type of reactor (i.e., pressurized water reactor and boiling water reactor) and possible concrete containment modifications. Thus, the applicant’s plant-specific OE is reviewed and evaluated in detail for the subsequent period of extended operation. Applicable portions of the experience with prestressing systems described in US NRC IN 99-10 could be useful.
- If plant-specific OE indicates degradation and/or losses that may fall below minimum required values established in the design, additional examinations may be required to determine the condition of an expanded tendon group. Upward trending group prestress forces or tendon measurements shall be further assessed as part of the OE.
- 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.
10 CFR 54.21, “Contents of Application-Technical Information.” Washington, DC: U.S. Nuclear Regulatory Commission. 2016.
ASME. ASME Code Section XI, Subsection IWL, “Requirements for Class CC Concrete Components of Light-Water Cooled Plants.” New York, New York: American Society of Mechanical Engineers. 2008.
US NRC. Information Notice 99-10, “Degradation of Prestressing Tendon Systems in Prestressed Concrete Containments.” Agencywide Documents Access and Management System (ADAMS) Accession No. ML031500244. Washington, DC: U.S. Nuclear Regulatory Commission. April 1999.
_____. NUREG/CR–7111, “A Summary of Aging Effects and their Management in Reactor Spent Fuel Pools, Refueling Cavities, Tori, and Safety-Related Concrete Structures.” ADAMS Accession No. ML12047A184. Washington, DC: U.S. Nuclear Regulatory Commission. January 2012.
_____. Regulatory Guide 1.35.1, “Determining Prestressing Forces for Inspection of Prestressed Concrete Containments.” ADAMS Accession No. ML003740040. Washington, DC: U.S. Nuclear Regulatory Commission. July 1990.