1801 R2 XI.S7

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XI.S7 RG 1.127, INSPECTION OF WATER-CONTROL STRUCTURES ASSOCIATED WITH NUCLEAR POWER PLANTS

Program Description

U.S. Nuclear Regulatory Commission (US NRC) Regulatory Guide (RG) 1.127, Revision 1, "Inspection of Water-Control Structures Associated with Nuclear Power Plants," describes an acceptable basis for developing an inservice inspection and surveillance program for dams, slopes, canals, and other raw water-control structures associated with emergency cooling water systems or flood protection of nuclear power plants. The US NRC RG 1.127 program addresses age-related deterioration, degradation due to extreme environmental conditions, and the effects of natural phenomena that may affect water-control structures. The US NRC RG 1.127 program recognizes the importance of periodic monitoring and maintenance of water-control structures so that the consequences of age-related deterioration and degradation can be prevented or mitigated in a timely manner.

US NRC RG 1.127 provides detailed guidance for the licensee's inspection program for water-control structures, including guidance on engineering data compilation, inspection activities, technical evaluation, inspection frequency, and the content of inspection reports. US NRC RG 1.127 delineates current US NRC practice in evaluating inservice inspection programs for water-control structures.

For plants not committed to US NRC RG 1.127, Revision 1, aging management of water-control structures may be included in the “Structures Monitoring” ( AMP XI.S6). Even if a plant is committed to US NRC RG 1.127, Revision 1, aging management of certain structures and components may be included in the “Structures Monitoring” ( AMP XI.S6). However, details pertaining to water-control structures, as described herein, are incorporated in AMP XI.S6 program attributes.

US NRC RG 1.127 attributes evaluated below do not include inspection of dams. For dam inspection and maintenance, programs under the regulatory jurisdiction of the Federal Energy Regulatory Commission (FERC) or the U.S. Army Corps of Engineers, continued through the period of extended operation, are adequate for the purpose of aging management. For programs not falling under the regulatory jurisdiction of FERC or the U.S. Army Corps of Engineers, the staff evaluates the effectiveness of the aging management program (AMP) based on compatibility to the common practices of the FERC and Corps programs.

Evaluation and Technical Basis

1. Scope of Program: US NRC RG 1.127 applies to raw water-control structures associated with emergency cooling water systems or flood protection of nuclear power plants. The water-control structures included in the RG 1.127 program are concrete structures, embankment structures, spillway structures and outlet works, reservoirs, cooling water channels and canals, and intake and discharge structures. The scope of the program also includes structural steel and structural bolting associated with water-control structures, steel or wood piles and sheeting required for the stability of embankments and channel slopes, and miscellaneous steel, such as sluice gates and trash racks.

2. Preventive Action: US NRC RG 1.127 is a condition monitoring program. This program is augmented to incorporate preventive measures recommended in NUREG-1339, Electric Power Research Institute (EPRI) TR-104213(Archived), EPRI NP-5067(Archived), and EPRI NP-5769(Archived) to ensure structural bolting integrity, if applicable. The documents provide guidelines for selection of replacement bolting material, approved thread lubricants, and appropriate torque and preload to be used for installation of bolting. If the structural bolting consists of ASTM A325, ASTM F1852, and/or ASTM A490 bolts, the preventive actions for storage, lubricants, and stress corrosion cracking potential discussed in Section 2 of RCSC (Research Council for Structural Connections) publication “Specification for Structural Joints Using ASTM A325 or A490 Bolts” need to be used.

3. Parameters Monitored or Inspected: US NRC RG 1.127 identifies the parameters to be monitored and inspected for water-control structures. The parameters vary depending on the particular structure.

Parameters to be monitored and inspected for concrete structures are those described in American Concrete Institute (ACI) 201.1 and ACI-349-3R. These include cracking, movements (e.g., settlement, heaving, deflection), conditions at junctions with abutments and embankments, loss of material, increase in porosity and permeability, seepage, and leakage.

Parameters to be monitored and inspected for earthen embankment structures include settlement, depressions, sink holes, slope stability (e.g., irregularities in alignment and variances from originally constructed slopes), seepage, proper functioning of drainage systems, and degradation of slope protection features. Steel components are monitored for loss of material due to corrosion. Parameters monitored for channels and canals include erosion or degradations that may impose constraints on the function of the cooling system and present a potential hazard to the safety of the plant. Submerged emergency canals (e.g., artificially dredged canals at the river bed or the bottom of the reservoir) should be monitored for sedimentation, debris, or instability of slopes that may impair the function of the canals under extreme low flow conditions.

Further details of parameters to be monitored and inspected for these and other water-control structures are specified in Section C.2 of US NRC RG 1.127. The program is augmented to require monitoring of bolted connections for loss of material and loose bolts and nuts and other conditions indicative of loss of preload. High strength (actual measured yield strength ≥ 150 ksi or 1,034 MPa) structural bolts greater than 1 inch (25 mm) in diameter are monitored for stress corrosion cracking, if applicable. Other structural bolting (ASTM A-325, ASTM F1852, and ASTM A490 bolts) and anchor bolts are monitored for loss of material, loose or missing nuts, and cracking of concrete around the anchor bolts. Accessible sliding surfaces are monitored for indication of significant loss of material due to wear or corrosion, debris, or dirt. The program also is augmented to require monitoring of wooden components for loss of material and change in material properties.

4. Detection of Aging Effects: US NRC RG 1.127 specifies that inspection of water-control structures should be conducted under the direction of qualified engineers experienced in the investigation, design, construction, and operation of these types of facilities. Visual inspections are primarily used to detect degradation of water-control structures. In some cases, instruments have been installed to measure the behavior of water-control structures. US NRC RG 1.127 indicates that the available records and readings of installed instruments are to be reviewed to detect any unusual performance or distress that may be indicative of degradation. US NRC RG 1.127 describes periodic inspections to be performed at least once every 5 years. This interval has been shown to be adequate to detect degradation of water-control structures before a loss of an intended function. The program should include provisions for increased inspection frequency if the extent of the degradation is such that the structure or component may not meet its design basis if allowed to continue uncorrected until the next normally scheduled inspection. US NRC RG 1.127 also describes special inspections immediately following the occurrence of significant natural phenomena, such as large floods, earthquakes, hurricanes, tornadoes, and intense local rainfalls.

The program should address detection of aging affects for inaccessible, below-grade, and submerged concrete structural elements. For plants with non-aggressive raw water and groundwater/soil (pH > 5.5, chlorides < 500 parts per million [ppm], or sulfates < 1500 ppm), the program should require (a) evaluation of the acceptability of inaccessible areas when conditions exist in accessible areas that could indicate the presence of, or result in, degradation to such inaccessible areas and (b) examination of representative samples of the exposed portions of the below-grade concrete when excavated for any reason. Submerged concrete structures should be inspected during periods of low tide or when dewatered and accessible.

For plants with aggressive environment raw water (pH < 5.5, chlorides > 500 ppm, or sulfates > 1500 ppm) or ground water/soil and/or where the concrete structural elements have experienced degradation, a plant-specific AMP accounting for the extent of the degradation experienced should be implemented to manage the concrete aging during the period of extended operation.

5. Monitoring and Trending: Water-control structures are monitored by periodic inspection, as described in US NRC RG 1.127. Changes of degraded conditions from prior inspection, such as growth of an active crack or extent of corrosion, should be trended until it is evident that the change is no longer occurring or until corrective actions are implemented in accordance with 10 CFR 50.65 and RG 1.160, Rev. 2.

6. Acceptance Criteria: Quantitative acceptance criteria to evaluate the need for corrective actions are not specified in US NRC RG 1.127. However, the “Evaluation Criteria” provided in Chapter 5 of ACI 349.3R provide acceptance criteria (including quantitative criteria) for determining the adequacy of observed aging effects and specifies criteria for further evaluation. Although not required, plant-specific acceptance criteria based on Chapter 5 of ACI 349.3R are acceptable. Acceptance criteria for earthen structures, such as canals and embankments, are consistent with programs falling within the regulatory jurisdiction of the FERC or the U.S. Army Corps of Engineers. Loose bolts and nuts, cracked high strength bolts, and degradation of piles and sheeting are accepted by engineering evaluation or subject to corrective actions. Engineering evaluation should be documented and based on codes, specifications, and standards such as AISC specifications, SEI/ASCE 11, and those referenced in the plant’s current licensing basis.

7. Corrective Actions: US NRC RG 1.127 recommends that when inspection findings indicate that significant changes have occurred, the conditions are to be evaluated. This includes a technical assessment of the causes of distress or abnormal conditions, an evaluation of the behavior or movement of the structure, and recommendations for remedial or mitigating measures. As discussed in the Appendix for GALL, the staff finds the requirements of 10 CFR 50, Appendix B, acceptable to address the corrective actions.

8. Confirmation Process: As discussed in the Appendix for GALL, the staff finds the requirements of 10 CFR 50, Appendix B, acceptable to address the confirmation process.

9. Administrative Controls: As discussed in the Appendix for GALL, the staff finds the requirements of 10 CFR 50, Appendix B, acceptable to address the administrative controls.

10. Operating Experience: Degradation of water-control structures has been detected, through US NRC RG 1.127 programs, at a number of nuclear power plants, and, in some cases, it has required remedial action. US NRC NUREG-1522 described instances and corrective actions of severely degraded steel and concrete components at the intake structure and pumphouse of coastal plants. Other degradation described in the NUREG include appreciable leakage from the spillway gates, concrete cracking, corrosion of spillway bridge beam seats of a plant dam and cooling canal, and appreciable differential settlement of the outfall structure of another. No loss of intended functions has resulted from these occurrences. Therefore, it can be concluded that the inspections implemented in accordance with the guidance in US NRC RG 1.127 have been successful in detecting significant degradation before loss of intended function occurs.

References

10 CFR Part 50, Appendix B, Quality Assurance Criteria for Nuclear Power Plants, Office of the Federal Register, National Archives and Records Administration, 2009.

ACI Standard 201.1R, Guide for Making a Condition Survey of Concrete in Service, American Concrete Institute, 1992.

ACI Standard 349.3R, Evaluation of Existing Nuclear Safety-Related Concrete Structures, American Concrete Institute, 2002.

EPRI NP-5067(Archived), Good Bolting Practices, A Reference Manual for Nuclear Power Plant Maintenance Personnel, Volume 1: Large Bolt Manual, 1987; Volume 2: Small Bolts and Threaded Fasteners, Electric Power Research Institute, 1990.

EPRI NP-5769(Archived), Degradation and Failure of Bolting in Nuclear Power Plants, Volumes 1 and 2, Electric Power Research Institute, April 1988.

EPRI TR-104213(Archived), Bolted Joint Maintenance & Application Guide, Electric Power Research Institute, December 1995.

US NRC Regulatory Guide 1.127, Inspection of Water-Control Structures Associated with Nuclear Power Plants, Revision 1, U.S. Nuclear Regulatory Commission, March 1978.

US NRC Regulatory Guide 1.160, Rev. 2, Monitoring the Effectiveness of Maintenance at Nuclear Power Plants, U.S. Nuclear Regulatory Commission, March 1997.

NUREG-1339, Resolution of Generic Safety Issue 29: Bolting Degradation or Failure in Nuclear Power Plants, U.S. Nuclear Regulatory Commission, June 1990.

NUREG-1522, Assessment of Inservice Conditions of Safety-Related Nuclear Plant Structures, U.S. Nuclear Regulatory Commission, June 1995.

RCSC (Research Council on Structural Connections), Specification for Structural Joints Using ASTM A325 or A490 Bolts, 2004.

United States of America

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

Aging Management Program

Electric Power Research Institute

US NRC regulatory guide