XI.M17 (NUREG-1801 R0)
XI.M17 FLOW-ACCELERATED CORROSION
Program Description
The program relies on implementation of the Electric Power Research Institute (EPRI) guidelines in the Nuclear Safety Analysis Center (NSAC)-202L-R2(Archived) for an effective flow-accelerated corrosion (FAC) program. The program includes performing (a) an analysis to determine critical locations, (b) limited baseline inspections to determine the extent of thinning at these locations, and (c) follow-up inspections to confirm the predictions, or repairing or replacing components as necessary.
Evaluation and Technical Basis
- 1. Scope of Program: The FAC program, described by the EPRI guidelines in NSAC-202L-R2(Archived), includes procedures or administrative controls to assure that the structural integrity of all carbon steel lines containing high-energy fluids (two phase as well as single phase) is maintained. Valve bodies retaining pressure in these high-energy systems are also covered by the program. The FAC program was originally outlined in NUREG-1344 and was further described through the U.S. Nuclear Regulatory Commission (US NRC) Generic Letter (GL) 89-08. A program implemented in accordance with the EPRI guidelines predicts, detects, and monitors FAC in plant piping and other components, such as valve bodies, elbows and expanders. Such a program includes the following recommendations: (a) conducting an analysis to determine critical locations; (b) performing limited baseline inspections to determine the extent of thinning at these locations; and (c) performing follow-up inspections to confirm the predictions, or repairing or replacing components as necessary. The NSAC-202L-R2(Archived) (April 1999) provides general guidelines for the FAC program. To ensure that all the aging effects caused by FAC are properly managed, the program includes the use of a predictive code, such as CHECWORKS, that uses the implementation guidance of NSAC-202L-R2(Archived) to satisfy the criteria specified in 10 CFR Part 50, Appendix B, criteria for development of procedures and control of special processes.
- 2. Preventive Actions: The FAC program is an analysis, inspection, and verification program; thus, there is no preventive action. However, it is noted that monitoring of water chemistry to control pH and dissolved oxygen content, and selection of appropriate piping material, geometry, and hydrodynamic conditions, are effective in reducing FAC.
- 3. Parameters Monitored/Inspected: The aging management program (AMP) monitors the effects of FAC on the intended function of piping and components by measuring wall thickness.
- 4. Detection of Aging Effects: Degradation of piping and components occurs by wall thinning. The inspection program delineated in NSAC-202L(Archived) consists of identification of susceptible locations as indicated by operating conditions or special considerations. Ultrasonic and radiographic testing is used to detect wall thinning. The extent and schedule of the inspections assure detection of wall thinning before the loss of intended function.
- 5. Monitoring and Trending: CHECWORKS or a similar predictive code is used to predict component degradation in the systems conducive to FAC, as indicated by specific plant data, including material, hydrodynamic, and operating conditions. CHECWORKS is acceptable because it provides a bounding analysis for FAC. CHECWORKS was developed and benchmarked by using data obtained from many plants. The inspection schedule developed by the licensee on the basis of the results of such a predictive code provides reasonable assurance that structural integrity will be maintained between inspections. If degradation is detected such that the wall thickness is less than the minimum predicted thickness, additional examinations are performed in adjacent areas to bound the thinning.
- 6. Acceptance Criteria: Inspection results are used as input to a predictive computer code, such as CHECWORKS, to calculate the number of refueling or operating cycles remaining before the component reaches the minimum allowable wall thickness. If calculations indicate that an area will reach the minimum allowed thickness before the next scheduled outage, the component is to be repaired, replaced, or reevaluated.
- 7. Corrective Actions: Prior to service, reevaluate, repair, or replace components for which the acceptance criteria are not satisfied. Longer term corrective actions could consist of adjustment of operating parameters or selection of materials resistant to FAC. 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 the confirmation process and administrative controls.
- 9. Administrative Controls: See Item 8, above.
- 10. Operating Experience: Wall-thinning problems in single-phase systems have occurred in feedwater and condensate systems (US NRC IE Bulletin No. 87-01; US NRC Information Notices (INs) 81-28, 92-35, 95-11) and in two-phase piping in extraction steam lines (US NRC INs 89-53, 97-84) and moisture separation reheater and feedwater heater drains (US NRC INs 89-53, 91-18, 93-21, 97-84). Operating experience shows that the present program, when properly implemented, is effective in managing FAC in high-energy carbon steel piping and components.
References
US NRC Generic Letter 89-08, Erosion/Corrosion-Induced Pipe Wall Thinning, U.S. Nuclear Regulatory Commission, May 2,1989.
US NRC IE Bulletin 87-01, Thinning of Pipe Walls in Nuclear Power Plants, U.S. Nuclear Regulatory Commission, July 9, 1987.
US NRC Information Notice 81-28, Failure of Rockwell-Edward Main Steam Isolation Valves, U.S. Nuclear Regulatory Commission, September 3, 1981.
US NRC Information Notice 89-53, Rupture of Extraction Steam Line on High Pressure Turbine, U.S. Nuclear Regulatory Commission, June 13, 1989.
US NRC Information Notice 91-18, High-Energy Piping Failures Caused by Wall Thinning, U.S. Nuclear Regulatory Commission, March 12, 1991.
US NRC Information Notice 91-18, Supplement 1, High-Energy Piping Failures Caused by Wall Thinning, U.S. Nuclear Regulatory Commission, December 18, 1991.
US NRC Information Notice 92-35, Higher than Predicted Erosion/Corrosion in Unisolable Reactor Coolant Pressure Boundary Piping inside Containment at a Boiling Water Reactor, U.S. Nuclear Regulatory Commission, May 6, 1992.
US NRC Information Notice 93-21, Summary of NRC Staff Observations Compiled during Engineering Audits or Inspections of Licensee Erosion/Corrosion Programs, U.S. Nuclear Regulatory Commission, March 25, 1993.
US NRC Information Notice 95-11, Failure of Condensate Piping Because of Erosion/Corrosion at a Flow Straightening Device, U.S. Nuclear Regulatory Commission, February 24, 1995.
US NRC Information Notice 97-84, Rupture in Extraction Steam Piping as a Result of Flow-Accelerated Corrosion, U.S. Nuclear Regulatory Commission, December 11, 1997.
NSAC-202L-R2(Archived), Recommendations for an Effective Flow Accelerated Corrosion Program, Electric Power Research Institute, Palo Alto, CA, April 8, 1999.
NUREG-1344, Erosion/Corrosion-Induced Pipe Wall Thinning in U.S. Nuclear Power Plants, P. C. Wu, U.S. Nuclear Regulatory Commission, April 1989.