2191 R0 XI.M10

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XI.M10 BORIC ACID CORROSION

Program Description

The program relies, in part, on implementation of recommendations in the U.S. Nuclear Regulatory Commission (US NRC) Generic Letter (GL) 88-05 to identify, evaluate, and correct borated water leaks that could cause corrosion damage to reactor coolant pressure boundary components in pressurized water reactors. Potential improvements to boric acid corrosion programs have been identified because of operating experience (OE) with cracking of certain nickel alloy pressure boundary components (US NRC Regulatory Issue Summary 2003-013 and NUREG–1823).

Borated water leakage from piping and components that are outside the scope of the program established in response to US NRC GL 88-05 may affect structures and components (SCs) that are subject to aging management review (AMR). Therefore, the scope of the monitoring and inspections of this program includes all components subject to an AMR that may be adversely affected by some form of borated water leakage. The scope of the evaluations, assessments, and corrective actions include all observed leakage sources and the affected SCs.

Borated water leakage may be discovered through activities other than those established specifically to detect such leakage. Therefore, the program includes provisions for triggering evaluations and assessments when leakage is discovered by other activities. The effects of boric acid corrosion on reactor coolant pressure boundary materials in the vicinity of nickel alloy components are managed by Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) aging management program (AMP) XI.M11B, “Cracking of Nickel-Alloy Components and Loss of Material Due to Boric Acid-Induced Corrosion in Reactor Coolant Pressure Boundary Components (PWRs Only).”

The recommended approaches described in Section 7 of WCAP-15988-NP, Revision 2, “Generic Guidance for an Effective Boric Acid Inspection Program for Pressurized Water Reactors,” provide an acceptable means of fulfilling the activities of this program.

Evaluation and Technical Basis

1. Scope of Program: The program covers any SCs on which boric acid corrosion may occur (e.g., steel and copper alloy) and electrical components onto which borated reactor water may leak. The program includes provisions in response to the recommendations of US NRC GL 88-05. US NRC GL 88-05 elicits a program consisting of systematic measures to provide reasonable assurance that corrosion caused by leaking borated water does not lead to degradation of the leakage source or adjacent SCs, to provide assurance that the reactor coolant pressure boundary will have an extremely low probability of abnormal leakage, rapidly propagating failure, or gross rupture. Such a program provides for (a) determination of the principal location of leakage, (b) examinations and procedures for locating small leaks, and (c) engineering evaluations and corrective actions to provide reasonable assurance that boric acid corrosion does not lead to degradation of the leakage source or adjacent structures or components. Although US NRC GL 88-05 addresses boric acid corrosion of reactor coolant pressure boundary components, the recommendations in US NRC GL 88-05 are also effective in managing the aging of other in-scope components.

2. Preventive Actions: Minimizing borated water leakage by frequent monitoring of the locations where potential leakage could occur and timely cleaning and repair if leakage is detected prevents or mitigates boric acid corrosion. In addition, the use of corrosion-resistant materials and coatings minimizes the effects of boric acid exposure.

3. Parameters Monitored or Inspected: The AMP monitors the aging effects of loss of material due to boric acid corrosion on the intended function of an affected SC by detection of borated water leakage. Borated water leakage results in deposits of white boric acid crystals and the presence of moisture. Discolored boric acid crystals are an indication of corrosion. Boric acid deposits, borated water leakage, or the presence of moisture that could lead to the identification of loss of material can be monitored through visual examination.

In order to identify potential borated water leaks inside containment that have not been detected during walkdowns and maintenance, the program tracks airborne radioactivity monitors, humidity monitors, temperature monitors, reactor coolant system water inventory balancing, and containment air cooler thermal performance. The program also looks for evidence of boric acid deposits on control rod drive mechanism shroud fans, containment air recirculation fan coils, containment fan cooler units, and airborne filters.

4. Detection of Aging Effects: Degradation of the component due to boric acid corrosion cannot occur without leakage of borated water. Conditions leading to boric acid corrosion, such as crystal buildup and evidence of moisture, are readily detectable by visual inspection, though removal of insulation may be required in some cases. Obstructions to visual inspections are removed unless a technical justification is documented by the program owner. Criteria for removing insulation for bare-metal inspections include the safety significance of the location, evidence of leakage from under the insulation, bulging of the insulation, and OE. Discoloration, staining, boric acid residue, and other evidence of leakage on insulation surfaces and the surrounding area are given particular consideration as evidence of component leakage. The program delineated in US NRC GL 88-05 includes guidelines for locating small leaks, conducting examinations, and performing engineering evaluations. In addition, the program includes appropriate interfaces with other site programs and activities, such that borated water leakage that is encountered by means other than the monitoring and trending established by this program is evaluated and corrected.

5. Monitoring and Trending: The program provides monitoring and trending activities as delineated in US NRC GL 88-05, timely evaluation of evidence of borated water leakage identified by other means, and timely detection of leakage by observing boric acid crystals during normal plant walkdowns and maintenance. The program maintains a list of all active borated water leaks, excessive boric acid deposits, discoloration caused by corrosion, and affected targets susceptible to corrosion to track the condition of components in the vicinity of leaks and to identify locations with repeat leakage.

6. Acceptance Criteria: All indications of boric acid leakage are screened to determine if more detailed evaluations of the leaking component or associated targets are warranted. Any detected borated water leakage not meeting screening criteria (i.e., essentially zero potential for adverse effects on SCs), including white or discolored boric acid crystal buildup, or rust-colored deposits are evaluated to confirm the intended functions of affected SCs consistent with the design basis prior to continued service.

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 Title 10 of the Code of Federal Regulations (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 corrective actions element of this AMP for both safety-related and nonsafety-related SCs within the scope of this program.

Borated water leakage and areas of resulting boric acid corrosion are evaluated and corrected in accordance with the applicable provisions of US NRC GL 88-05 and the corrective action program. Any detected boric acid crystal buildup or deposits should be cleaned. US NRC GL 88-05 recommends that corrective actions to prevent recurrences of degradation caused by borated water leakage be included in the program implementation. These corrective actions include any modifications to be introduced in the present design or operating procedures of the plant that (a) reduce the probability of reactor coolant leaks at locations where they may cause corrosion damage and (b) entail the use of suitable corrosion resistant materials or the application of protective coatings or claddings. When corrective actions include the use of enclosures to contain borated water leakage, the impact of the leakage environment on the potential degradation mechanisms of enclosed components is evaluated (US NRC Information Notice (IN) 2012-15). Such modifications should allow for periodic inspections.

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: Boric acid corrosion has been observed in nuclear power plants (US NRC Information Notices (INs) 86-108 (and supplements 1 through 3), IN 2002-11, IN 2002-13, and 2003-02) and has resulted in significant impairment of component-intended functions in areas that are difficult to access/observe (US NRC Bulletin 2002-01). Boric acid leakage can become airborne and can cause corrosion in locations other than in the vicinity of the leak (Licensee Event Reports (LER) 250/2010-005, LER 346/2002-008). Corrosion rates may be inaccurately predicted due to the installation of a different type of material than indicated on the design documents (LER 346/1998-009) or galvanic corrosion caused by wet boric acid crystals bridging between dissimilar metals (Electric Power Research Institute (EPRI) 1000975)(Archived).

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.

EPRI. EPRI 1000975(Archived), “Boric Acid Corrosion Guidebook.” Revision 1. Palo Alto, California: Electric Power Research Institute. November 2001.

Licensee Event Report 250/2010-005, “Containment Liner Through Wall Defect Due to Corrosion.” Agencywide Documents Access and Management System (ADAMS) Accession No. ML103620112. [1]. December 2010.

Licensee Event Report 346/2002-008, “Containment Air Coolers Collective Significance of Degraded Conditions.” ADAMS Accession No. ML031330192. [2]. May 2003.

Licensee Event Report 346/1998-009, “Reactor Coolant System Pressurizer Spray Valve Degraded with Two of Eight Body-to-Bonnet Nuts Missing.” [3]. August 1999.

US NRC. Bulletin 2002-01, “Reactor Pressure Vessel Head Degradation and Reactor Coolant Pressure Boundary Integrity.” ADAMS Accession No. ML020770497. Washington, DC: U.S. Nuclear Regulatory Commission. March 2002.

_____. Generic Letter 88-05, “Boric Acid Corrosion of Carbon Steel Reactor Pressure Boundary Components in PWR Plants.” ADAMS Accession No. ML031130424. Washington, DC: U.S. Nuclear Regulatory Commission. March 1988.

_____. Information Notice 86-108, “Degradation of Reactor Coolant System Pressure Boundary Resulting from Boric Acid Corrosion.” ADAMS Accession Nos. ML031250360, ML031250366, ML053070387, ML053070388. December 1986. Washington, DC: U.S. Nuclear Regulatory Commission. Supplement 1, April 20, 1987; Supplement 2, November 19, 1987; and Supplement 3, January 5, 1995.

_____. Information Notice 2002-11, “Recent Experience with Degradation of Reactor Pressure Vessel Head.” ADAMS Accession No. ML020700556. Washington, DC: U.S. Nuclear Regulatory Commission. March 2002.

_____. Information Notice 2002-13, “Possible Indicators of Ongoing Reactor Pressure Vessel Head Degradation.” ADAMS Accession No. ML020930617. Washington, DC: U.S. Nuclear Regulatory Commission. April 2002.

_____. Information Notice 2003-02, “Recent Experience with Reactor Coolant System Leakage and Boric Acid Corrosion.” ADAMS Accession No. ML030160004. Washington, DC: U.S. Nuclear Regulatory Commission. January 2003.

_____. Information Notice 2012-15, “Use of Seal Cap Enclosures to Mitigate Leakage from Joints that Use A-286 Bolts.” ADAMS Accession No. ML121740012. Washington, DC: U.S. Nuclear Regulatory Commission. August 2012.

_____. NUREG–1823, “U.S. Plant Experience with Alloy 600 Cracking and Boric Acid Corrosion of Light-Water Reactor Pressure Vessel Materials.” Washington, DC: U.S. Nuclear Regulatory Commission. April 2005.

_____. Regulatory Issue Summary 2003-13, “NRC Review of Responses to Bulletin 2002-01, Reactor Pressure Vessel Head Degradation and Reactor Coolant Pressure Boundary Integrity.” ADAMS Accession No. ML032100653. Washington, DC: U.S. Nuclear Regulatory Commission. July 2003.

Westinghouse Non-Proprietary Class 3 Report No. WCAP-15988-NP, Revision 2, “Generic Guidance for an Effective Boric Acid Inspection Program for Pressurized Water Reactors.” Pittsburgh, Pennsylvania: Westinghouse Electric Company. June 2012.

United States of America

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

Operating Experience

Aging Management Review

Quality Assurance

Electric Power Research Institute

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