XI.M21A (NUREG-2191 R0)
XI.M21A CLOSED TREATED WATER SYSTEMS
Program Description
Nuclear power plants contain many closed, treated water systems. These systems undergo water treatment to control water chemistry and prevent corrosion (i.e., treated water systems). These systems are also recirculating systems in which the rate of recirculation is much higher than the rate of addition of makeup water (i.e., closed systems). This is a mitigation program that also includes condition monitoring to verify the effectiveness of the mitigation activities. The program includes: (a) water treatment, including the use of corrosion inhibitors, to modify the chemical composition of the water such that the function of the equipment is maintained and such that the effects of corrosion are minimized; (b) chemical testing of the water to demonstrate that the water treatment program maintains the water chemistry within acceptable guidelines; and (c) inspections to determine the presence or extent of degradation. Depending on the water treatment program selected for use in association with this aging management program (AMP) and/or plant operating experience (OE), this program also may include corrosion monitoring (e.g., corrosion coupon testing) and microbiological testing.
The water used in systems covered by this AMP may be, but need not be, demineralized and receives chemical treatment, including corrosion inhibitors, unless the systems meet the industry guidance for pure water systems. Otherwise, untreated water systems are addressed using other AMPs, such as Inspection of Internal Surfaces in Miscellaneous Piping and Ducting Components (XI.M38). Examples of systems managed by this AMP include closed-cycle cooling water (CCCW) systems (as defined by the U.S. Nuclear Regulatory Commission (US NRC) Generic Letter (GL) 89-13); closed portions of heating, ventilation, and air conditioning systems; and diesel generator cooling water. Examples of systems not addressed by this AMP include those systems containing boiling water reactor (BWR) coolant, pressurized water reactor (PWR) primary and secondary water, and PWR/BWR condensate that does not contain corrosion inhibitors. Aging in these systems is managed by the water chemistry AMP (XI.M2) and the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section XI, Inservice Inspection, Subsections IWB, IWC, and IWD AMP (XI.M1). Treated fire water systems, if present, are also not included in this AMP.
Evaluation and Technical Basis
- 1. Scope of Program: This program manages the aging effects of loss of material due to corrosion, cracking due to stress corrosion cracking (SCC), and reduction of heat transfer due to fouling of the internal surfaces of piping, piping components, piping elements and heat exchanger components fabricated from any material and exposed to treated water.
- 2. Preventive Actions: This program mitigates the aging effects of loss of material, cracking, and reduction of heat transfer through water treatment. The water treatment program includes corrosion inhibitors and is designed to maintain the function of associated equipment and minimize the corrosivity of the water and the accumulation of corrosion products that can foul heat transfer surfaces.
- 3. Parameters Monitored or Inspected: This program monitors water chemistry parameters (preventive monitoring) and the condition of surfaces exposed to the water (condition monitoring). Depending on the water treatment program selected for use in association with this AMP and/or plant OE, this program may also include corrosion monitoring (e.g., corrosion coupon testing) and microbiological testing.
- Water chemistry parameters (such as the concentration of iron, copper, silica, oxygen, and hardness, alkalinity, specific conductivity, and pH) are monitored because maintenance of optimal water chemistry prevents loss of material and cracking due to corrosion and SCC. The specific water chemistry parameters monitored and the acceptable range of values for these parameters are in accordance with the Electric Power Research Institute (EPRI) 1007820(Archived) “Closed Cooling Water Chemistry Guideline,” which is used in its entirety for the water chemistry control or guidance.
- The visual appearance of surfaces is evaluated for evidence of loss of material. The results of surface or volumetric examinations are evaluated for surface discontinuities indicative of cracking. The heat transfer capability of heat exchanger surfaces is evaluated by either visual inspections to determine surface cleanliness, or functional testing to verify that design heat removal rates are maintained.
- 4. Detection of Aging Effects: In this program, aging effects are detected through water testing and periodic inspections. Water testing determines whether the water treatment program effectively maintains acceptable water chemistry. Water testing frequency is conducted in accordance with the selected water treatment program.
- Because the control of water chemistry may not be fully effective in mitigating the aging effects, inspections are conducted. Visual inspections of internal surfaces are conducted whenever the system boundary is opened. At a minimum, in each 10-year period during the subsequent period of extended operation, a representative sample of 20 percent of the population (defined as components having the same material, water treatment program, and aging effect combination) or a maximum of 25 components per population at each unit is inspected using techniques capable of detecting loss of material, cracking, and fouling, as appropriate. The 20 percent minimum is surface area inspected unless the component is measured in linear feet, such as piping. In that case, any combination of 1-foot length sections and components can be used to meet the recommended extent of 25 inspections. Technical justification for an alternative sampling methodology is included in the program’s documentation. For multi-unit sites where the sample size is not based on the percentage of the population, it is acceptable to reduce the total number of inspections at the site as follows. For two-unit sites, 19 components are inspected per unit and for a three-unit site, 17 components are inspected per unit. In order to conduct 17 or 19 inspections at a unit in lieu of 25, the subsequent license renewal application includes the basis for why the operating conditions at each unit are sufficiently similar (e.g., flowrate, chemistry, temperature, excursions) to provide representative inspection results. The basis should include consideration of potential differences such as the following:
- Have power uprates been performed and, if so, could more aging have occurred on one unit that has been in the uprate period for a longer time period?
- Are there any systems which have had an out-of-spec water chemistry condition for a longer period of time or out-of-spec conditions occur more frequently?
- If degradation is identified in the initial sample, additional samples are inspected to determine the extent of the condition.
- The ongoing opportunistic visual inspections are credited towards the representative samples for the loss of material and fouling; however, surface or volumetric examinations are used to detect cracking. The inspections focus on the components most susceptible to aging because of time in service and severity of operating conditions, including locations where local conditions may be significantly more severe than those in the bulk water (e.g., heat exchanger tube surfaces).
- Inspections and tests are performed by personnel qualified in accordance with site procedures and programs to perform the specified task. Inspections within the scope of the ASME Code should follow procedures consistent with the ASME Code. Non-ASME Code inspections follow site procedures that include requirements for items such as lighting, distance, offset, surface coverage, presence of protective coatings, and cleaning processes.
- 5. Monitoring and Trending: Water chemistry data are evaluated against the standards contained in the selected water treatment program. These data are trended, so corrective actions are taken, based on trends in water chemistry, prior to loss of intended function. Where practical, identified degradation is projected until the next scheduled inspection. Results are evaluated against acceptance criteria to confirm that the sampling bases (e.g., selection, size, frequency) will maintain the components’ intended functions throughout the subsequent period of extended operation based on the projected rate and extent of degradation.
- 6. Acceptance Criteria: Water chemistry concentrations are maintained within the limits specified in the selected industry standard documents. Due to the water chemistry controls, no age-related degradation is expected. Therefore, any detectable loss of material, cracking, or fouling is evaluated in the corrective action program.
- 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 Generic Aging Lessons Learned for Subsequent License Renewal (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 structures and components (SCs) within the scope of this program.
- Water chemistry concentrations that are not in accordance with the selected water treatment program should be returned to the normal operating range within the prescribed timeframe for each action level. If fouling is identified, the overall effect is evaluated for reduction of heat transfer, flow blockage, and loss of material.
- If the cause of the aging effect for each applicable material and environment is not corrected by repair or replacement for all components constructed of the same material and exposed to the same environment, additional inspections are conducted if one of the inspections does not meet acceptance criteria. The number of increased inspections is determined in accordance with the site’s corrective action process; however, there are no fewer than five additional inspections for each inspection that did not meet acceptance criteria, or 20 percent of each applicable material, environment, and aging effect combination is inspected, whichever is less. If subsequent inspections do not meet acceptance criteria, an extent of condition and extent of cause analysis is conducted to determine the further extent of inspections. Additional samples are inspected for any recurring degradation to ensure corrective actions appropriately address the associated causes. At multi-unit sites, the additional inspections include inspections at all of the units with the same material, environment, and aging effect combination. The additional inspections are completed within the interval (e.g., refueling outage interval, 10-year inspection interval) in which the original inspection was conducted.
- 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: Degradation of CCCW systems due to corrosion product buildup [Licensee Event Report (LER) 327/1993-029] or through-wall cracks in supply lines (LER 280/1991-019) has been observed in operating plants. In addition, SCC of stainless steel reactor recirculation pump seal heat exchanger coils has been attributed to localized boiling of the closed cooling water, concentrating water impurities on the coil surfaces (LER 263/2014-001). Accordingly, OE demonstrates the need for this program.
- 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 50.55a, “Codes and Standards.” Washington, DC: U.S. Nuclear Regulatory Commission. 2016.
ASME. ASME Code Section XI, “Rules for Inservice Inspection of Nuclear Power Plant Components.” New York, New York: The American Society of Mechanical Engineers. 2008.
EPRI. EPRI 1007820(Archived), “Closed Cooling Water Chemistry Guideline.” Palo Alto, California: Electric Power Research Institute. April 2004.
Flynn, Daniel. The Nalco Water Handbook. Nalco Company. 2009.
Licensee Event Report 263/2014-001, “Primary System Leakage Found in Recirculation Pump Upper Seal Heat Exchanger.” Agencywide Documents Access and Management System (ADAMS) Accession No. ML14073A599. https://lersearch.inl.gov/LERSearchCriteria.aspx. March 2014.
Licensee Event Report 280/1991-019, “Loss of Containment Integrity due to Crack in Component Cooling Water Piping.” https://lersearch.inl.gov/LERSearchCriteria.aspx. October 1991.
Licensee Event Report 327/1993-029, “Inoperable Check Valve in the Component Cooling System as a Result of a Build-Up of Corrosion Products between Valve Components.” https://lersearch.inl.gov/LERSearchCriteria.aspx. December 1993.
US NRC. Generic Letter 89-13, “Service Water System Problems Affecting Safety-Related Components.” Washington, DC: U.S. Nuclear Regulatory Commission. July 1989.
_____. Generic Letter 89-13, Supplement 1, “Service Water System Problems Affecting Safety-Related Components.” Washington, DC: U.S. Nuclear Regulatory Commission. April 1990.