XI.M29 (NUREG-1801 R1)
XI.M29 ABOVEGROUND STEEL TANKS
Program Description
The program includes preventive measures to mitigate corrosion by protecting the external surface of steel tanks with paint or coatings in accordance with standard industry practice. The program also relies on periodic system walkdowns to monitor degradation of the protective paint or coating. However, for storage tanks supported on earthen or concrete foundations, corrosion may occur at inaccessible locations, such as the tank bottom. Accordingly, verification of the effectiveness of the program is to be performed to ensure that significant degradation in inaccessible locations is not occurring and the component intended function will be maintained during the extended period of operation. For reasons set forth below, an acceptable verification program consists of thickness measurement of the tank bottom surface.
Evaluation and Technical Basis
- 1. Scope of Program: The program consists of (a) preventive measures to mitigate corrosion by protecting the external surfaces of carbon steel tanks protected with paint or coatings and (b) periodic system walkdowns to manage the effects of corrosion on the intended function of these tanks. Plant walkdowns cover the entire outer surface of the tank up to its surface in contact with soil or concrete.
- 2. Preventive Actions: In accordance with industry practice, tanks are coated with protective paint or coating to mitigate corrosion by protecting the external surface of the tank from environmental exposure. Sealant or caulking at the interface edge between the tank and concrete or earthen foundation mitigates corrosion of the bottom surface of the tank by preventing water and moisture from penetrating the interface, which would lead to corrosion of the bottom surface.
- 3. Parameters Monitored/Inspected: The AMP utilizes periodic plant system walkdowns to monitor degradation of coatings, sealants, and caulking because it is a condition directly related to the potential loss of materials.
- 4. Detection of Aging Effects: Degradation of exterior carbon steel surfaces cannot occur without degradation of paint or coatings on the outer surface and of sealant and caulking at the interface between the component and concrete. Periodic system walkdowns to confirm that the paint, coating, sealant, and caulking are intact is an effective method to manage the effects of corrosion on the external surface of the component. However, corrosion may occur at inaccessible locations, such as the tank bottom surface, thus, thickness measurement of the tank bottom is to be taken to ensure that significant degradation is not occurring and the component intended function will be maintained during the extended period of operation.
- 5. Monitoring and Trending: The effects of corrosion of the aboveground external surface are detectable by visual techniques. Based on operating experience, plant system walkdowns during each outage provide for timely detection of aging effects. The effects of corrosion of the underground external surface are detectable by thickness measurement of the tank bottom and are monitored and trended if significant material loss is detected.
- 6. Acceptance Criteria: Any degradation of paint, coating, sealant, and caulking is reported and will require further evaluation. Degradation consists of cracking, flaking, or peeling of paint or coatings, and drying, cracking or missing sealant and caulking. Thickness measurements of the tank bottom are evaluated against the design thickness and corrosion allowance.
- 7. Corrective Actions: The site corrective actions program, quality assurance (QA) procedures, site review and approval process, and administrative controls are implemented in accordance with 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 to address the corrective actions, confirmation process, and administrative controls.
- 8. Confirmation Process: See Item 7, above.
- 9. Administrative Controls: See Item 7, above.
- 10. Operating Experience: Coating degradation, such as flaking and peeling, has occurred in safety-related systems and structures (U.S. Nuclear Regulatory Commission [US NRC] Generic Letter (GL) 98-04). Corrosion damage near the concrete-metal interface and sand-metal interface has been reported in metal containments (US NRC Information Notice (IN) 89-79, Supplement 1, and US NRC IN 86-99, Supplement 1).
References
10 CFR Part 50, Appendix B, Quality Assurance Criteria for Nuclear Power Plants, Office of the Federal Register, National Archives and Records Administration, 2005.
US NRC Generic Letter 98-04, Potential for Degradation of the Emergency Core Cooling System and the Containment Spray System after a Loss-of-Coolant Accident Because of Construction and Protective Coating Deficiencies and Foreign Material in Containment, U.S. Nuclear Regulatory Commission, July 14, 1998.
US NRC Information Notice 86-99, Degradation of Steel Containments, U.S. Nuclear Regulatory Commission, December 8, 1986.
US NRC Information Notice 86-99, Supplement 1, Degradation of Steel Containments, U.S. Nuclear Regulatory Commission, February 14, 1991.
US NRC Information Notice 89-79, Degraded Coatings and Corrosion of Steel Containment Vessel, U.S. Nuclear Regulatory Commission, December 1, 1989.
US NRC Information Notice 89-79, Supplement 1, Degraded Coatings and Corrosion of Steel Containment Vessel, U.S. Nuclear Regulatory Commission, June 29, 1990.