2191 R0 XI.S2

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Xl.S2 ASME SECTION XI, SUBSECTION IWL

Program Description

Title 10 of the Code of Federal Regulations (10 CFR) 50.55a imposes the examination requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section XI, Subsection IWL, for reinforced and prestressed concrete containments (Class CC). The scope of IWL includes reinforced concrete and unbonded post-tensioning systems. ASME Code, Section XI, Subsection IWL and the additional requirements specified in 10 CFR 50.55a(b)(2) constitute an existing mandated program applicable to managing aging of containment reinforced concrete and unbonded post-tensioning systems, and supplemented herein, for subsequent license renewal. Containments with grouted tendons may require an additional plant-specific aging management program (AMP), based on the guidance in U.S. Nuclear Regulatory Commission (US NRC) Regulatory Guide (RG) 1.90, “Inservice Inspection of Prestressed Concrete Containment Structures with Grouted Tendons,” to address the adequacy of prestressing forces.

The primary inspection method specified in IWL-2500 is visual examination, supplemented by testing. For prestressed containments, tendon wires are tested for yield strength, ultimate tensile strength, and elongation. Tendon corrosion protection medium is analyzed for alkalinity, water content, and soluble ion concentrations. The quantity of free water contained in the anchorage end cap and any free water that drains from tendons during the examination is documented. Samples of free water are analyzed for pH. Prestressing forces are measured in selected sample tendons. IWL specifies acceptance criteria, corrective actions, and expansion of the inspection scope when degradation exceeding the acceptance criteria are found.

The Code specifies augmented examination requirements following post-tensioning system repair/replacement activities.

Evaluation and Technical Basis

1. Scope of Program: Subsection IWL-1000 specifies the components of concrete containments within its scope. The components within the scope of Subsection IWL are reinforced concrete and unbonded post-tensioning systems of Class CC containments, as defined by CC-1000. The program also includes testing of the tendon corrosion protection medium and the pH of free water. Subsection IWL exempts from examination portions of the concrete containment that are inaccessible (e.g., concrete covered by liner, foundation material, or backfill or obstructed by adjacent structures or other components).

10 CFR 50.55a(b)(2)(viii) and the 2009 and later editions/addenda of the ASME Code specify additional requirements for inaccessible areas. The Code states that the licensee is to evaluate the acceptability of concrete in inaccessible areas when conditions exist in accessible areas that could indicate the presence of or result in degradation to such inaccessible areas. Steel liners for concrete containments and their integral attachments are not within the scope of Subsection IWL but are included within the scope of Subsection IWE. Subsection IWE is evaluated in Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) Report AMP XI.S1, “ASME Section XI, Subsection IWE.”

2. Preventive Action: ASME Code Section XI, Subsection IWL is a condition monitoring program. However, the program includes actions to prevent or minimize corrosion of the prestressing tendons by maintaining corrosion protection medium chemistry within acceptable limits specified in Subsection IWL.

3. Parameters Monitored or Inspected: Table IWL-2500-1 specifies two categories for examination of concrete surfaces: (i) Category L-A for all accessible concrete surfaces and (ii) Category L-B for concrete surfaces surrounding anchorages of tendons selected for testing in accordance with IWL-2521. Both of these categories rely on visual examination methods. Concrete surfaces are examined for evidence of damage or degradation, such as concrete cracks. IWL-2510 specifies that concrete surfaces are examined for conditions indicative of degradation, such as those defined in American Concrete Institute (ACI) 201.1R and ACI 349.3R. Table IWL-2500-1 also specifies Category L-B for test and examination requirements for unbonded post tensioning systems. The number of tendons selected for examination is in accordance with Table IWL-2521-1. Additional augmented examination requirements for post-tensioning system repair/replacement activities are to be in accordance with Table IWL-2521-2. Tendon anchorage and wires or strands are visually examined for cracks, corrosion, and mechanical damage. Tendon wires or strands are also tested for yield strength, ultimate tensile strength, and elongation. The tendon corrosion protection medium is tested by analysis for alkalinity, water content, and soluble ion concentrations. The pH of free water samples is analyzed.

4. Detection of Aging Effects: The frequency and scope of examinations specified in 10 CFR 50.55a and Subsection IWL provide reasonable assurance that aging effects would be detected before they would compromise the design-basis requirements. The frequency of inspection is specified in IWL-2400. Concrete inspections are performed in accordance with Examination Category L-A. Under Subsection IWL, inservice inspection (ISI) of concrete and unbonded post-tensioning systems is required at 1, 3, and 5 years following the initial structural integrity test. Thereafter, inspections are performed at 5-year intervals. For sites with multiple plants, the schedule for ISI is provided in IWL-2421. In the case of tendons, only a sample of the tendons of each tendon type requires examination during each inspection.

The tendons to be examined during an inspection are selected on a random basis. Regarding detection methods for aging effects, all accessible concrete surfaces receive General Visual examination (as defined by the ASME Code). Selected areas, such as those that indicate suspect conditions and concrete surface areas surrounding tendon anchorages (Category L-B), receive a more rigorous Detailed Visual examination (as defined by the ASME Code). Prestressing forces in sample tendons are measured. In addition, one sample tendon of each type is detensioned. A single wire or strand is removed from each detensioned tendon for examination and testing. These visual examination methods and testing would identify the aging effects of accessible concrete components and prestressing systems in concrete containments. Examination of corrosion protection medium and free water is tested for each examined tendon as specified in Table IWL-2525-1.

5. Monitoring and Trending: Except in inaccessible areas, all concrete surfaces are monitored on a regular basis by virtue of the examination requirements. Inspection results are documented and compared to previous results to identify changes from prior inspections. Quantitative measurements and qualitative information are recorded and trended for findings exceeding the acceptance criteria described in Element 6 for all applicable parameters monitored or inspected. The use of photographs or surveys is recommended. Photography and its variations may be used to trend aging effects such as cracking, spalling, delamination, pop-outs, or other age-related concrete degradation as illustrated in ACI 201.1R. Photographic records may be used to document and trend the type, severity, extent and progression of degradation.

For prestressed containments, trending of prestressing forces in tendons is required in accordance with the acceptance by examination criteria in IWL-3220. In addition to the random sampling used for tendon examination, one tendon of each type is selected from the first-year inspection sample and designated as a common tendon. Each common tendon is then examined during each inspection. Corrosion protection medium chemistry and free water pH are monitored for each examined tendon. This procedure provides monitoring and trending information over the life of the plant. 10 CFR 50.55a and Subsection IWL also require that prestressing forces in all inspection sample tendons be measured by lift-off or equivalent tests and compared with acceptance standards based on the predicted force for that type of tendon over its life.

6. Acceptance Criteria: IWL-3000 provides acceptance standards for concrete containments. Quantitative acceptance criteria for concrete surfaces based on the “second-tier” evaluation criteria provided in Chapter 5 of ACI 349.3R are acceptable. Applicants who elect to use plant-specific criteria for concrete containment structures should describe the criteria and provide a technical basis for deviations from those in ACI 349.3R. Inspection results, based on the acceptance criteria selected, are evaluated by the Responsible Engineer to ensure that the corrective action is implemented before loss of intended functions.

The acceptance standards for the unbonded post-tensioning system are quantitative in nature. For the post-tensioning system, quantitative acceptance criteria are given for tendon force and elongation, tendon wire or strand samples, and corrosion protection medium. Free water in the tendon anchorage areas is not acceptable, as specified in IWL-3221.3. If free water is found, the recommendations in Table IWL-2525-1 are followed. 10 CFR 50.55a and Subsection IWL do not define the method for calculating predicted tendon prestressing forces for comparison to the measured tendon lift-off forces. The predicted tendon forces are calculated in accordance with RG 1.35.1, “Determining Prestressing Forces for Inspection of Prestressed Concrete Containments,” which provides an acceptable methodology for use through the subsequent period of extended operation.

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 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 AMP for both safety-related and nonsafety-related structures and components (SCs) within the scope of this program.

Subsection IWL specifies that items for which examination results do not meet the acceptance standards are to be evaluated in accordance with IWL-3300, “Evaluation,” and described in an engineering evaluation report. The report is to include an evaluation of whether the concrete containment is acceptable without repair of the item and, if repair is required, the extent, method, and completion date of the repair or replacement. The report also identifies the cause of the condition and the extent, nature, and frequency of additional examinations. Subsection IWL also provides repair procedures to follow in IWL-4000. This includes requirements for the concrete repair, repair of reinforcing steel, and repair of the post-tensioning system.

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.

IWA-1400 specifies the preparation of plans, schedules, and ISI summary reports. In addition, written examination instructions and procedures, verification of qualification level of personnel who perform the examinations, and documentation of a QA program are specified. IWA-6000 specifically covers the preparation, submittal, and retention of records and reports.

10. Operating Experience: ASME Code Section XI, Subsection IWL was incorporated into 10 CFR 50.55a in 1996. Prior to this time, the prestressing tendon inspections were performed in accordance with the guidance provided in RG 1.35, “Inservice Inspection of Ungrouted Tendons in Prestressed Concrete Containments.” Operating experience pertaining to degradation of reinforced concrete in concrete containments was gained through the inspections required by 10 CFR 50.55a(g)(4) (i.e., Subsection IWL), 10 CFR Part 50, Appendix J, and ad hoc inspections conducted by licensees and the US NRC. NUREG–1522, “Assessment of Inservice Condition of Safety-Related Nuclear Power Plant Structures,” described instances of cracked, spalled, and degraded concrete for reinforced and prestressed concrete containments. The NUREG also described cracked anchor heads for the prestressing tendons at three prestressed concrete containments. US NRC Information Notice (IN) 99-10, Revision 1, “Degradation of Prestressing Tendon Systems in Prestressed Concrete Containment,” described occurrences of degradation in prestressing systems. IN 2010-14, “Containment Concrete Surface Condition Examination Frequency and Acceptance Criteria,” describes issues concerning the containment concrete surface condition examination frequency and acceptance criteria. The program considers the degradation concerns described in these generic communications. Implementation of Subsection IWL, in accordance with 10 CFR 50.55a, is a necessary element of aging management for concrete containments through the subsequent period of extended operation.

US NRC Inspection Report 05000302/2009007 documents operating experience (OE) of an unprecedented delamination event that occurred during a major containment modification of a post-tensioned concrete containment. Although the event is not considered attributable to an aging mechanism, aging characteristics of prestressed concrete containments and lessons learned should be an important consideration for major containment modification repair/replacement activities, especially those involving significant detensioning and retensioning of tendons, during the subsequent period of extended operation.

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 Part 50, Appendix J, “Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors.” Washington, DC: U.S. Nuclear Regulatory Commission. 2016.

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

ACI. ACI Standard 201.1R-08, “Guide for Conducting a Visual Inspection of Concrete in Service.” Farmington Hills, Michigan: American Concrete Institute. 2008.

_____. ACI Standard 349.3R-02, “Evaluation of Existing Nuclear Safety-Related Concrete Structures.” Farmington Hills, Michigan: American Concrete Institute. 2002.

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

US NRC. Information Notice 99-10, Revision 1, “Degradation of Prestressing Tendon Systems in Prestressed Concrete Containment.” Revision 1. Agencywide Documents Access and Management System (ADAMS) Accession No. ML031500244. Washington DC: U.S. Nuclear Regulatory Commission. April 1999.

_____. Information Notice 2010-14, “Containment Concrete Surface Condition Examination Frequency and Acceptance Criteria.” ADAMS Accession No. ML101600151. Washington, DC: U.S. Nuclear Regulatory Commission. August 2010.

_____. Inspection Report, Crystal River Nuclear Plant – Special Inspection Report 05000302/2009007. ADAMS Accession No. ML102861026. Washington, DC: U.S. Nuclear Regulatory Commission. October 12, 2010.

_____. NUREG–1522, “Assessment of Inservice Condition of Safety-Related Nuclear Power Plant Structures.” Washington, DC: U.S. Nuclear Regulatory Commission. June 1995.

_____. 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.

_____. Regulatory Guide 1.90, “Inservice Inspection of Prestressed Concrete Containment Structures with Grouted Tendons.” ADAMS Accession No. ML11249A008. Washington, DC: U.S. Nuclear Regulatory Commission. November 2012.

American Society of Mechanical Engineers

Aging Management Program

United States of America

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

Quality Assurance

US NRC regulatory guide

Operating Experience

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