1801 R0 XI.M10

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XI.M10 BORIC ACID CORROSION

Program Description

The program relies on implementation of recommendations of Nuclear Regulatory Commission (US NRC) Generic Letter (GL) 88-05 to monitor the condition of the reactor coolant pressure boundary for borated water leakage. Periodic visual inspection of adjacent structures, components, and supports for evidence of leakage and corrosion is an element of the US NRC GL 88-05 monitoring program.

Evaluation and Technical Basis

1. Scope of Program: The program covers any carbon steel and low-alloy steel structures or components, and electrical components, on which borated reactor water may leak. The program includes recommendations of US NRC GL 88-05. The staff guidance of US NRC GL 88-05 provides a program consisting of systematic measures to ensure that corrosion caused by leaking borated coolant does not lead to degradation of the leakage source or adjacent structures and components, and provides 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) examination requirements and procedures for locating small leaks, and (c) engineering evaluations and corrective actions to ensure that boric acid corrosion does not lead to degradation of the leakage source or adjacent structures or components, which could cause the loss of intended function of the structures or components.

2. Preventive Actions: Minimizing reactor coolant leakage by frequent monitoring of the locations where potential leakage could occur, and timely repair if leakage is detected, prevents or mitigates boric acid corrosion. Preventive measures also include modifications in the design or operating procedures to reduce the probability of leaks at locations where they may cause corrosion damage and use of suitable corrosion resistant materials or the application of protective coatings.

3. Parameters Monitored/Inspected: The aging management program (AMP) monitors the effects of boric acid corrosion on the intended function of an affected structure and component by detection of coolant leakage. Coolant leakage results in deposits of white boric acid crystals and presence of moisture that can be observed by the naked eye.

4. Detection of Aging Effects: Degradation of the component due to boric acid corrosion cannot occur without leakage of coolant that contains boric acid. Conditions leading to boric acid corrosion, such as crystal buildup and evidence of moisture, are readily detectable by visual inspection. The program delineated in US NRC GL 88-05 includes guidelines for locating small leaks, conducting examinations, and performing engineering evaluations. Thus the use of the US NRC GL 88-05 program will assure detection of leakage before the loss of the intended function of the component.

5. Monitoring and Trending: The program delineated in US NRC GL 88-05 provides for timely detection of leakage by observance of boric acid crystals during normal plant walkdowns and maintenance.

6. Acceptance Criteria: Any detected leakage or crystal buildup requires corrective actions prior to continued service.

7. Corrective Actions: The leakage source and areas of general corrosion are located and corrective actions are implemented in conformance with the program proposed by US NRC GL 88-05. The v requires that corrective actions to prevent recurrences of degradation caused by boric acid 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 primary 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. 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.

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 confirmation process and administrative controls.

9. Administrative Controls: See Item 8, above.

10. Operating Experience: Boric acid corrosion observed in nuclear power plants (US NRC Information Notice (IN) 86-108 S3) may be classified into two types: (a) corrosion that increases the rate of leakage (e.g., corrosion of closure bolting or fasteners) and (b) corrosion that occurs some distance from the source of leakage. The guidance of US NRC GL 88-05 is effective in managing the effects of boric acid corrosion on the intended function of reactor components.

References

10 CFR 50.55a, Codes and Standards, Office of the Federal Register, National Archives and Records Administration, 2000.

US NRC Generic Letter 88-05, Boric Acid Corrosion of Carbon Steel Reactor Pressure Boundary Components in PWR Plants, U.S. Nuclear Regulatory Commission, March 17, 1988.

US NRC Information Notice 86-108 S3, Degradation of Reactor Coolant System Pressure Boundary Resulting from Boric Acid Corrosion, U.S. Nuclear Regulatory Commission, December 26, 1986; Supplement 1, April 20, 1987; Supplement 2, November 19, 1987; and Supplement 3, January 5, 1995.

United States of America

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

Aging Management Program

Quality Assurance