ML113000100
| ML113000100 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 11/09/2011 |
| From: | Chernoff H Plant Licensing Branch 1 |
| To: | Heacock D Dominion Nuclear Connecticut |
| Sandeers, Carleen, NRR/DORL, 415-1603 | |
| References | |
| TAC ME6886 | |
| Download: ML113000100 (13) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555"()001 November 9,2011 Mr. David A. Heacock President and Chief Nuclear Officer Dominion Nuclear Connecticut, Inc.
Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711
SUBJECT:
MILLSTONE POWER STATION, UNIT NO.2-ISSUANCE OF RELIEF REQUEST RR-04-12 REGARDING THE TEMPORARY NON-CODE COMPLIANT CONDITION OF THE CLASS 3 SERVICE WATER SYSTEM 10 INCH EMERGENCY DIESEL GENERATOR SUPPLY PIPING FLANGE (TAC NO. ME6886)
Dear Mr. Heacock:
By letter dated August 19, 2011,1 as supplemented by email dated August 20, 2011,2 and letter dated September 29, 2011, 3 Dominion Nuclear Connecticut, Inc (DNC or the licensee) requested relief from certain requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code) for Millstone Power Station, Unit No.2 (MPS2). The licensee proposed an alternative to performing repair/replacement activities as required by the ASME Code,Section XI, "Rules for Inservice Inspection (lSI) of Nuclear Power Plant Components," to a degraded flange on piping spool SK2952 in the 'A' Train 1O-inch service water (SW) supply line to the emergency diesel generator heat exchangers. Relief Request RR-04-12 proposes to perform periodic visual inspections, quantitative leakage monitoring, and periodic ultrasonic testing of the degraded flange. Relief Request RR-04-12, also places limits of the flange degradation, at which time the licensee would have to take predetermined actions, to ensure continued structural integrity of the flange.
The Nuclear Regulatory Commission (NRC) staff has reviewed the subject request and concludes, as set forth in the enclosed Safety Evaluation, that requiring an ASME Code repair/replacement of the degraded flange, at the time of discovery, would cause a hardship without a compensating increase in the level of quality and safety. The NRC staff's review also concludes that the proposed alternative in Relief Request RR-04-12 is acceptable because it provides reasonable assurance of structural integrity of the degraded flange.
Therefore, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.55a(a)(3)(ii), the NRC authorizes the use of Relief Request RR-04-12 until December 20, 2011, or until either a 1 gallon per minute (gpm) or greater leak rate occurs, a 1 Agencywide Documents Access and Management System (ADAMS) Accession No. ML11234A077 2 ADAMS Accession No. ML112340464 3 ADAMS Accession No. ML11279A036
D. Heacock - 2 minimum wall thickness of 0.04 inches is met, or a loss of 33% flange material has been reached, whichever occurs first.
On August 20, 2011, the NRC staff verbally authorized the use of Relief Request RR-04-12 during a teleconference with DNC. A summary of the teleconference, dated August 21, 2011, is publiclyavailable. 4 On September 3, 2011, the leak rate of the degraded flange exceeded the 1 gpm leak rate.
Accordingly, MPS2 entered the action statement of Technical Specification 3. 7.4.1, "Service Water System," and subsequently shutdown. The degraded flange was replaced and an extent of condition inspection was performed prior to plant start-up.
If you have any questions, please contact the Project Manager, Carleen Sanders, at 301-415-1603.
Sincerely, ffi~
Or Harold Chernoff, Chief Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-336
Enclosure:
As stated cc wI encl: Distribution via Listserv 4 ADAMS Accession No. ML112340505
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REQULATION RELIEF REQUEST RR-04-12 TEMPORARY NON-CODE COMPLIANT CONDITION EMERGENCY DIESEL GENERATOR SUPPLY PIPING IN THE SERVICE WATER SYSTEM MILLSTONE POWER STATION, UNIT NO.2 DOMINION NUCLEAR CONNECTICUT, INC DOCKET NO. 50-336
1.0 INTRODUCTION
By letter dated August 19, 2011,1 Dominion Nuclear Connecticut, Inc. (DNC or the licensee) requested relief from certain requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code) for Millstone Power Station, Unit No.2 (MPS2). The licensee proposed an alternative to performing repair/replacement activities as required by the ASME Code,Section XI, "Rules for Inservice Inspection (lSI) of Nuclear Power Plant Components," to a degraded flange on piping spool SK2952 in the 'A' Train 1O-inch service water (SW) supply line to the emergency diesel generator heat exchangers.
By email dated August 20, 2011, the licensee responded to the Nuclear Regulatory Commission (NRC) staff's request for additional information (RAI).2 In its response, the licensee revised the duration of the relief request and provided additional limits (acceptance criterion) on the flange and pipe wall thickness.
On August 20, 2011, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a(a)(3)(ii), the NRC staff verbally authorized the use of Relief Request RR-04-12.3 This safety evaluation documents the technical basis of the verbal authorization.
On September 3, 2011, the licensee shutdown MPS2 and replaced, in accordance with ASME Code, the degraded flange as a result of the leak rate exceeding the limit of 1 gallon per minute (gpm) as required in the relief request.
1 Agencywide Documents and Access Management System (ADAMS) Accession No. ML11234A077 2 ADAMS Accession No. ML112340464 3 ADAMS Accession Number ML112340505 Enclosure
- 2 8y letter dated September 29, 2011,4 the licensee submitted the results of the extent of condition inspections.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR SO.SSa(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components.
Section SO.SSa(a)(3) of 10 CFR states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Generic Letter (GL) 90-0S, "Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1,2, and 3 Piping," and NRC approved ASME Code Case N-S13-3, "Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping," are not applicable to the flange.
The code of record for the fourth lSI interval at MSP2 is the 2004 Edition, No Addenda, of ASME Section XI.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Component(s) Affected ASME Code Class 3 SW System 10-inch light weight slip-on flange (coated carbon steel) 3.2 Applicable Code Edition and Addenda MPS2 is currently in the fourth 10-year lSI interval, which began on April 1, 2010. The ASME Code,Section XI, 2004 Edition, No Addenda, applies to the lSI program, including repair/replacement activities. The SW system piping deSign code (Construction Code) is American National Standards Institute (ANSI) 831.1, 1967 Edition through the summer of 1973 Addendum.
3.3 Applicable Code Requirement ASME Code Section XI, 2004 Edition, No Addenda, Article IWA-4000, Repair/Replacement Activities.
4 ADAMS Accession Number ML11279A036
- 3 3.4 Proposed Alternative and Basis for Use On August 17, 2011, the licensee found a leak rate of 10 drops per minute coming from the outlet side flange on spool SK2952 of the "A" Train SW header to the "A" emergency diesel generator heat exchanger. The licensee performed ultrasonic testing (UT) and determined the area of degradation on the flange is localized and is contained in a radial alignment between two of the twelve flange bolts. In lieu of repairing or replacing the degraded flange, the licensee proposed to leave the degraded flange in service up to 4 months or until certain limits are reached, as discussed further in this Safety Evaluation.
The licensee's proposed alternative is based on demonstrating that the degraded flange will maintain its structural integrity during the continued operating period. The licensee presented the results of the flaw characterization, degradation mechanism assessment, stress analyses, flooding analysis, and assessments on spray and flow margin. In addition, the licensee proposed a compensatory monitoring plan with limits imposed on the leak rate and flange and pipe wall thickness to ensure the structural integrity of the degraded flange.
3.5 Duration of Proposed Alternative In the August 19, 2011, submittal, the licensee requested to operate with the degraded flange until the next refueling outage (fall 2012) or until the proposed limits are met. However, in the response to the NRC staff RAI dated August 20, 2011, the licensee shortened the duration of the proposed alternative to 4 months from the date of verbal authorization (Le., August 20, 2011) or until the limits are challenged, whichever occurs earlier.
3.6 Flaw Characterization The licensee stated that "based on the UT results of the current condition and experience from other similar lining failures discovered during normal inspection on carbon steel piping components in SW system piping, the flaw is characterized to be a localized area of corrosion rather than a crack~like flaw." The licensee inspects the coating on SW spool SK2952, including the degraded flange, every other refueling cycle to ensure that the pressure boundary of the SW pipe remains intact and that the tube sheets of safety-related heat exchangers for the diesel generator do not become clogged by coating material. This every other refueling outage inspection is based upon the inspection of one train of SW every outage. The licensee has implemented this inspection schedule for over 10 years and has detected and repaired many defects before through wall leaks have occurred. The licensee noted that there is no history of crack-like flaws in this piping system, and it is not considered credible that such a flaw exists in the small area. The NRC staff notes, it is more likely for carbon steel to corrode in a caustic environment (seawater) than develop cracks. The NRC staff finds that the licensee's flaw characterization is based on best-effort UT examinations and operating experience and, therefore, is acceptable.
3.7 Degradation Mechanism The licensee explained that the typical corrosion encountered in this carbon steel lined pipe comes from a break or perforation (holiday) in the coating or lining, resulting from mechanical assembly, disassembly or handling of the spool pieces. The flaws in the coating most often
- 4 occur in or around the inner diameter corners of the flanged joints. The licensee stated that the flanged connection under consideration joins piping composed of unlined (bare) AL6XN and epoxy-lined carbon steel. The licensee also stated that leaks from similar flanges had occurred in the past. Upon disassembly of these previous failures, the licensee discovered a small area of significant corrosion at the mouth of the lined carbon steel pipe which was roughly hemispherical in shape. The licensee believes that the initiating event for the subject corrosion is a chip in the epoxy lining of the flange which occurs during reassembly of the flange following inspection. This event is followed by galvanic corrosion between the exposed steel of the carbon steel pipe and the AL6XN pipe in a seawater environment. The NRC staff concurs that this analysis proposed by the licensee is reasonable and would result in corrosion damage similar to that observed in past events. The NRC staff also notes that the licensee appears to have attempted to avoid the occurrence of galvanic corrosion at the flange under consideration through the use of washers and gaskets, which appear to be electrically insulating in nature.
The NRC staff further notes that successful insulation of these joints is quite difficult. Finally, the licensee stated due to potential for corrosion in the epoxy-lined carbon steel pipe, it is in the process of replacing safety-related portions of the SW piping with AL6XN. The spool piece containing the flange under consideration (SK2952) is scheduled for replacement during the next refueling outage (fall 2012).
The licensee visually inspected the coating on the leaking flange during refueling outage 19, 2R19, in October 2009. The licensee did not find damage on the epoxy lining on the flange face and inside diameter of the pipe at that time. The licensee believes that the lining on the leaking flange may have been damaged when reinstalling the upstream spool. To derive a conservative corrosion rate, the licensee assumed that the lining defect initiated 11 months ago (one-half the duration since the last inspection in October 2009). Based upon UT measurements, at the time of discovery on August 17, 2011, the damaged area is about 3 inches long on the inside diameter of the flange (which is approximately 34 inches in circumference). The extent of the damage to this outlet flange is limited to the one area. UT measurements around the circumference of the flange did not identify any similar areas. Past experience has shown that the corrosion from this type of lining defect grows radially from a point on the inside diameter of the flange face. Hence, the 3 inches represents twice the actual growth. The licensee estimated a corrosion rate of 0.136 inches/month (1.5 inches/11 months). The NRC staff finds that the licensee has identified the degradation mechanism in the subject flange appropriately.
The NRC staff further finds that the estimated corrosion rate is conservative and that the licensee's proposed 30-day UT of the degraded flange will verify the appropriateness of the estimated corrosion rate of 0.136 inches/month.
3.8 Structural Integrity The licensee's structural integrity assessment of the degraded flange is documented in of the August 19, 2011, submittal. In the August 20, 2011, letter, the licensee noted that the flange face nominal thickness is 11/16 inches and the nominal flange hub thickness is 5/8 inches. The pipe stress analysis calculation used an operating temperature range of 33° Fahrenheit (F) to 80° F and a design pressure of 150 pounds per square inch (psig). The system design pressure is actually 100 psig at the defect location, but 150 psig was conservatively used for the pipe stress analysis qualification calculation. The NRC staff verified in the licensee's analysis that pipe stress levels for the adjoining pipe are less than 10% of the allowable in the ASME Code,Section III. The area of degradation is currently confined to an area radially aligned between two bolt holes on one carbon steel flange. The licensee
- 5 concludes that the flange will still be structurally acceptable with an area as large as 33% of the flange circumference completely missing (or the area between four bolt holes of a twelve-bolt hole pattern).
In RAI Question 6, the NRC staff asked the licensee to clarify the 33% limit on the flange inside circumference as part of the UT acceptance criterion. In the August 20, 2011, letter, the licensee noted that the flange inside circumference dimension is 33.77 inches and that the structural analysis assumed that 1!3 of the entire flange is lost. The licensee also noted that even a loss of a portion of the flange perimeter (not yet reaching the 33% degradation) would likely result in exceeding the leakage action level limit of 1 gpm and the flange would have to be repaired! replaced based on the limiting condition of 1 gpm.
In RAI Question 6(C), the NRC staff asked how the licensee would disposition the pipe portion of the flange joint if the pipe wall is also degraded. The licensee stated that it will evaluate the pipe in accordance with Code Case N-513-3 or other similar NRC-approved methodology. The licensee will also implement a limit on wall thickness reduction in accordance with Code Case N-513-3 or other similar NRC-approved methodology.
The NRC staff was concerned about the degradation of flange thickness and believes that it would be prudent to implement a limitation on the flange thickness, which if exceeded, would lead to the SW system being declared inoperable. In the August 20,2011, letter, the licensee proposed that an average wall thickness of less than 0.040 inches, as measured by the periodic UT between any two bolts (the accessible area), would require declaring the 'A' SW train inoperable. The minimum required wall thickness of 0.040 inches was derived based on the requirements of sub-article NC-3641.1 of the ASME Code,Section III, 1989 Edition.
The NRC staff finds that the licensee has demonstrated structural integrity of the degraded flange satisfactorily and has provided a minimum flange and pipe thickness of 0.04 inch to ensure that the structural integrity will not be challenged.
3.9 Augmented Inspections The licensee stated that it will monitor leakage by walkdowns (i.e., visual inspection) every 12- hour shift and perform UT on an approximate 30-day interval. In the August 20, 2011, letter, in response to RAI Question 5(H) regarding walkdown procedures, the licensee explained that although leak rate logs are typically taken at 12-hour intervals, the worst case postulated length of time would be 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> and is within the Technical Specification (TS) allowed outage time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This time is based on 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> shifts and the requirement for logs to be completed during the first half of the shift. The NRC staff finds the that inspection intervals for the visual and ultrasonic inspections are acceptable because it is consistent with ASME Code Case N 513-3.
3.10 Visual Inspection In letter dated August 20, 2011, in response to RAI Question Number 5(A), the licensee explained that scaffolding has been built allowing the operator direct access to the leak location.
Since the leak is on the east side of the flange between the piping and the wall, a mirror will be available to assist with inspection. The flange area will be without insulation until the flange is
-6 repaired or replaced, allowing bare metal visual examinations. The licensee has placed a catcher to collect the water that is leaking off of the flange. The leak will be locally measured with a graduated cylinder (currently a 25 milliliter cylinder) over a measured time period to determine the leak rate. The leak will be directed to the graduated cylinder via an installed hose between the catching device and the catch container. The licensee has calculated that if the 25 milliliter cylinder fills in 2.5 seconds, the leak rate is 1 gpm. The catch container is currently a 55 gallon drum placed on the floor level.
Initially, the monitoring will be directed by a Compensatory Actionsrremporary Logs sheet in accordance with station procedure. The Compensatory Actionsrremporary Log will then be incorporated into the plant equipment operator (PEO) shiftly rounds. When incorporated into the PEO rounds, the data is recorded on an electronic handheld device which is downloaded to the Local Area Network and can be trended readily. As stated in response to RAI question 5(J),
the licensee will record measured value and trend the leak rate daily.
The licensee stated that if the measured leak rate exceeds 0.25 gpm, the unit will enter the structural integrity action statement for Technical Requirements Manual (TRM) Technical Requirement 3.4.10. TRM 3.4.10 states that:
(a) With one or more ASME Code Class 1, 2 and 3 component(s) in a degraded or nonconforming condition(s), perform the following ACTIONS within 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />s:
(1) Determine that structural integrity is still maintained in the degraded or nonconforming condition or (2) Isolate the affected component(s) from service.
(b) If the above ACTION is not completed within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, immediately declare the affected component(s) nonfunctional.
Exceeding 0.25 gpm will also prompt increased monitoring and evaluation and may lead to entering the SW action statement for TS 3.7.4.1 which states that with one SW loop inoperable, restore the inoperable loop to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in COLD SHUTDOWN within the next 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Exceeding 1 gpm leak rate will lead directly to the TS 3.7.4.1 action statement being entered.
In the August 20, 2011, submittal, in response to RAI Question 7(C), the licensee clarified that the 1-gpm limit applies to the combined leak discharge from the pipe (not currently leaking) and the flange (currently leaking). If the combined leakage rate reaches 1 gpm, then the 'A' train SW system will be declared inoperable.
The NRC staff finds that the licensee has implemented a limit of 1 gpm leak rate beyond which the degraded flange will be repaired/replaced and an administrative control of 0.25 gpm beyond which the licensee will monitor the leakage more frequently. The NRC staff finds the acceptance criteria for the visual inspection are acceptable because these criteria will limit the potential for the degraded flange to challenge the structural integrity of the SW piping.
-7 3.11 Ultrasonic Inspection In its response to RAI Question NO.8 regarding the details of UT, the licensee explained that it will UT each of the 12 segments between the bolt holes around the circumference of the subject flange. Specific measurements will be recorded for each of the four dimensions depicted in of the relief request submittal dated August 19, 2011. The licensee will use the transducers as identified in Section 5.3 of Enclosure 2, Attachment 1 to the submittal.
Inspection results will be recorded on examination data sheets as depicted in Enclosure 1 of to the submittal. The NRC staff notes that because of the flange configuration, the ultrasonic examination is not capable of sizing the defect accurately. The licensee will be performing best-effort ultrasonic examinations which should be able to measure thickness and monitor degradation.
3.12 Operability Flow Margin The licensee stated that leakage from the degraded flange will not adversely affect the capability of the SW system to provide adequate cooling to the emergency diesel generator heat exchangers and to the other essential safety-related heat exchangers. The licensee applied a leakage limit of 1 gpm as the maximum acceptable leakage rate. The licensee's system hydraulic analysis demonstrates that a margin of at least 50 times is available (Le., > 50 gpm can be tolerated and all essential safety-related heat exchangers will still receive adequate SW flow for the limiting accident condition). The licensee noted that the flow rate through the pipe at the leaking flange location is dependent on conditions. During the summer months, with the diesel generator not running, there is normally no flow in this section of pipe. In the winter with low system flow demand and the diesel generator bypass valve open to provide extra system flow, there is approximately 1500 gpm flow in this section of pipe. At any time with the diesel running, there is approximately 800 gpm flow. The service water supply to the associated diesel generator heat exchangers is still considered operable with a leak rate of 50 gpm at the flange.
Therefore, the NRC staff finds that a limit of 1 gpm is acceptable because with a 1-gpm leak rate, the SW system will still be operable and will maintain a safety margin of about 50 before the system is declared inoperable.
3.13 Spray Concerns The licensee assessed the potential impact of the leakage spraying on other safety-related systems within an approximate 30 foot envelope of the current leak location. The licensee stated that based on its review, there are no spray concerns affecting any area components for the worst projected leak.
3.14 Flooding Analysis The licensee's flooding analysis assumed a 2-gpm leak rate which would result in a total leak volume of approximately 86,400 gallons based on a 30-day mission time. The 30-day mission time is based on the NRC's Generic Safety Issue (GSI)-191, "The Assessment of Debris Accumulation on PWR [pressurized water reactor] Sump Performance," containment emergency sump strainer design, that has a 30-day mission time. Cooling over the 30-day mission time is provided by SW. As a compensatory measure, leakage will be collected and directed to appropriate drains during normal plant operation, faCilitating the ability to monitor for degradation. The licensee stated that these drains may not be available/functional or credited
-8 following a design-basis accident. If the compensatory drain collection system is unavailable/nonfunctional, then operators will be alerted to any pooling of water in the auxiliary building basement by existing auxiliary building sump system indication. A water volume of approximately 120,000 gallons can be accommodated by the auxiliary building basement without impacting safety-related equipment. Therefore, the flooding for 30 days can be accommodated without operator action.
In the August 20, 2011, letter, in response to RAI Question No.3, the licensee clarified that the 2-gpm leak rate assumed in the flooding analysis allows for potential leakage increase from the action level of 1 gpm over the 30 day mission time for the SW system post accident. This assumes that the leakage increases to 1 gpm just prior to the limiting design-basis event occurring (large break loss-of-coolant accident) and that the leakage increases to an average of 2 gpm over the 30 day mission time. The NRC staff finds that as soon as the 1-gpm leak rate is detected, the licensee will perform corrective action and the total leak amount would most likely not reach the 86,400 gallons assumed in the flooding analysis. The NRC staff finds that the licensee's flooding analysis provides an acceptable technical basis of the 1-gpm limit.
3.15 Extent of Condition The licensee stated that no other SW system flange leaks are present in the MPS2 SW system.
During rounds and walkdowns, the operators will continue to identify future instances of this type of leakage in a timely manner. In response to RAI Question No.4, the licensee noted that MPS2 history has demonstrated that operator walkdowns are an effective method of detecting SW leaks. Since the operator rounds and walkdowns continue to be accomplished shiftly, no additional inspections were done. The licensee noted that the SW system on MPS3 uses corrosion resistant piping materials and does not utilize coated piping. Since the SW leak on MPS2 is believed to have been caused by damaged coating on the flange internals and MPS3 uses corrosion resistant piping materials, and does not use internal piping coatings, no inspections were performed at MPS3 for similar leaks.
8y letter dated September 29, 2011, the licensee submitted the results of the extent of condition inspections. The initial scope of the inspection is focused on flanges (carbon and stainless steel flanges mated with AL6XN stainless steel flanges) of the 'A' and '8' SW systems. After unit restart, the licensee will inspect other types of dissimilar metal joints (e.g., welds joining 300 series stainless steel to AL6XN stainless steel). The licensee performed ultrasonic and enhanced visual examinations (VT-2) which includes pipe insulation removal and close proximity inspection. The licensee detected a degraded flange at the outlet of the 'A' emergency diesel generator and a small through wall leak at a tap (flange) for a local pressure indicator in the supply line to the 'A' emergency diesel generator. The licensee has repaired both degraded flanges. The licensee did not detect deficiencies in the '8' train SW system. The NRC staff finds that the licensee's assessment of extent of condition is acceptable because the licensee has performed walkdowns of the MPS2 SW system piping and has examined the flanges in 'A' and '8' SW systems with ultrasonic and visual examinations. The licensee has corrected the deficiencies and will perform additional inspections of both 'A' and '8' SW systems after restart.
- 9 3.16 Hardship The licensee considered options for an ASME Code repair including shutting down to replace the piping flange or performing the same repair online. However, the licensee found that given the limited risk associated with the present condition, both of these options are considered a hardship without a compensating increase in the level of quality a(1d safety. An online repair would require SW temperature to be less than 58° F. As of the August 19, 2011, submittal, the SW temperature was 71 0 F and was expected to remain above 58 0 F well into October. Also, several configuration changes would have to be done to complete the repair online, such as aligning vital switchgear room coolers and chillers to the'S' train. The licensee contended that once these configuration changes are done, completion of the work activities for the spool replacement within the remaining 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of the action statement for one train of SW being unavailable would not be possible. Therefore, a transition to Mode 5 (a hardship) would be required to perform this repair. Further, there is no compensating increase in plant safety by performing the repair during the operating cycle.
In response to RAI Question No.1 0, the licensee expanded their description of the flange replacement, stating that U[t]he SW system cannot be isolated at the affected flange location.
The planned repair will replace the degraded 10-inch slip-on flange with a new 10-inch carbon steel weld neck flange. Since this portion of the SW system cannot be isolated, the Facility 1
['A' Train] SW header will be tagged out of service and drained by operations. Once the system is drained, an adjoining pipe elbow spool above the degraded flange will be unbolted, removed, and rigged to the floor. The affected flange will be cut off and the pipe end prepared for installing the new weld neck flange. The new carbon steel flange and exposed carbon steel piping will require coating after installation. The tagging, draining, and repair time is 6 shifts (72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />). An additional 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> is required for coating cure time. Therefore, the work activities required for flange replacement have a 5-day duration" which exceeds the 72-hour action statement for one train of SW being unavailable. Therefore, the ASME Code repair/replacement would require MPS2 to transition to MODE 5, which is a hardship.
In response to RAI Question No.9, the licensee stated that if MPS2 enters MODE 5 for some other reasons prior to the next refueling outage, the flange will be replaced. Additionally, the licensee requested relief for 4 months rather than to the next refueling outage (fall 2012). This will allow the licensee the opportunity to more accurately determine corrosion rates, prepare for flange repair, and explore other technologies for more accurate assessment of the boundaries of the degraded area.
The NRC staff finds that the licensee provided sufficient basis to support the argument that an ASME Code repair performed at this time would cause hardship without a compensating increase in the level of quality and safety.
3.17 Summary The NRC staff finds that: (a) the licensee has performed satisfactory stress analyses in accordance with the ASME Code,Section III, to demonstrate that with loss of 33% of the flange material (33% of the inside circumference), the surrounding pipe and flange will maintain the structural integrity of the SW piping; (b) the licensee will perform UT approximately every 30 days and implement limits (acceptance criteria) on the minimum wall thickness of 0.04 inches or 33% loss of the flange material, whichever occurs first; (c) the licensee will perform visual
- 10 inspections (walkdowns) every 12-hour shift to observe, measure, and record leakage at the degraded flange with acceptance criteria of less than 1 gpm and administrative control of 0.25 gpm; (d) the licensee has performed adequate flooding analyses, operability flow margin assessment, and extent of condition inspections and; (e) the licensee has provided a reasonable argument on hardship. The NRC staff concludes that the licensee has demonstrated that the proposed alternative will provide reasonable assurance of the structural integrity of 'A' Train SW system up to 4 months or until the limits of 1 gpm leak rate, minimum wall thickness of 0.04 inches, or loss of 33% flange material has been reached, whichever occurs first.
3.18 Flange Replacement On September 3, 2011, the degraded flange leak rate exceeded the 1 gpm limit specified in RR 04-12. Accordingly, MPS2 entered the action statement of TS 3.7.4.1 and subsequently shutdown. Disassembly of the degraded flange indentified that the insulation kit, designed to prevent accelerated galvanic corrosion of the coated carbon steel, was improperly installed and therefore was not effective. As a result of this through-wall leak, an extent of condition inspection was performed on the entire safety-related portion of the SW system. The results of the inspection were provided to the NRC in the September 29, 2011, letter.
4.0 CONCLUSION
S Based on the review presented above, the NRC staff concludes that requiring an ASME Code repair/replacement of the degraded flange, at the time of discovery, would cause a hardship without a compensating increase in the level of quality and safety. The NRC staff also concludes that the proposed alternative in Relief Request RR-04-12 is acceptable because it provides reasonable assurance of structural integrity of the degraded flange.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), the NRC staff authorizes the use of Relief Request RR-04-12 at MPS2 for the period of 4 months from the date of the verbal authorization, August 20, 2011, or until the limits of 1 gpm leak rate, minimum wall thickness of 0.04 inches, or loss of 33% flange material has been reached, whichever occurs first.
All other ASME Code,Section XI requirements for which relief have not been specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: J. Tsao Date: November 9, 2011
minimum wall thickness of 0.04 inches is met, or a loss of 33% flange material has been reached, whichever occurs first.
On August 20, 2011, the NRC staff verbally authorized the use of Relief Request RR-04-12 during a teleconference with DNC. A summary of the teleconference, dated August 21,2011, is publiclyavailable. 1 On September 3, 2011, the leak rate of the degraded flange exceeded the 1 gpm leak rate.
Accordingly MPS2 entered the action statement of Technical Specification 3.7.4.1, "Service Water System," and subsequently shutdown. The degraded flange was replaced and an extent of condition inspection was performed prior to plant start-up.
If you have any questions, please contact the Project Manager, Carleen Sanders, at 301-415-1603.
Sincerely, Ira! (REnnis for)
Harold Chernoff, Chief Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-336
Enclosure:
As stated cc wi encl: Distribution via Listserv Distribution:
PUBLIC Branch Reading RidsAcrsAcnw_MailCTR Resource RidsNrrDorlLpl1-2 Resource RidsNrrDeEpnbResource RidsNrrLAABaxter Resource RidsNrrPMMilistone Resource RidsOgcRp Resource RidsRgn1 MailCenter Resource LTrocine, EDO R-1 JTsao, NRR ADAMS A ccesslon N0.: ML113000100 *Bsy Memo Date d ** via
. emal
!oFFICE LPL 1-2/PM LPL 1-2/LA DE/EPNB LPL 1-2/BC I NAME CSanders ABaxter ** TLupold* HChernoff I
{REnnis for DATE 11/03/2011 11/03/2011 10/27/2011 11/09/2011 11/04/2011 I 1 ADAMS Accession No. ML112340505