ML20198H954

From kanterella
Jump to navigation Jump to search
Safety Evaluation Authorizing Proposed Alternative for Remainder of Second 10-yr Insp Interval for Plant
ML20198H954
Person / Time
Site: North Anna  Dominion icon.png
Issue date: 12/03/1998
From:
NRC (Affiliation Not Assigned)
To:
Shared Package
ML20198H900 List:
References
GL-90-05, GL-90-5, NUDOCS 9812300062
Download: ML20198H954 (11)
v • d • e


Text

- .- . . .. . ~ _. . . . .--.- - . . - .

y" $***%q}& UNITED STATES s- g NUCLEAR REGULATORY COMMISSION

$ 'C WASHINGTON, D.C. 20565 4001

          • )

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REVISION TO THE REQUEST FOR APPROVAL TO_ REPAIR FLAWS IN ACCORDANCE WITH GENERIC LETTER 90-05 )

FOR ASME CODE CLASS 3 SERVICE WATER PIPING VIRGINIA ELECTRIC AND POWER COMPANY UORTH ANNA POWER STATION. UNITS 1 AND 2 DOC'KET NOS.: 50-338 AND 50-339

1.0 INTRODUCTION

i j 10 CFR 50.55a(g) requires nuclear power facility piping and components to meet the applicable requirements of Section XI of the American Society of Mechanical Engineers (ASME) Boi!er and Pressure Vessel Code (hereafter referred to as the Code).Section XI of the Code specifies j Code-acceptable repair methods for flaws that exceed Code acceptance limits in piping that is in-service. A Code repair is required to restore the structuralintegrity of flawed Code piping, independent of the operational mode of the plant when the flaw is detected. Those repairs not in

compliance with Section XI of the Code are non-Code repairs. However, the implementation of l required Code (weld) repairs to ASME Code Class 1,2 or 3 systenis is often impractical for nuclear licensees since the repairs normally require an isolation of the system requiring the
repair, and often a shutdown of the nuclear power plant, i

Alternatives to Code requirements may be used by nuclear licensees when authorized by the Director of the Office of Nuclear Reactnr Regulation if the proposed alternatives to the

requirements are such that they are shown to provide an acceptable level of quality and safety in lieu of the Code requirements (10 CFR 50.55a(a)(3)(l)], or if compliance with the Code

, requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety (10 CFR 50.55a(a)(3)(ii)].

A licensee may also submit requests for relief from certain Code requirements when a licensee has determined that conformance with certain Code requirements is impractical for its facility (10 CFR 50.55a(g)(5)(iii)). Pursuant to 10 CFR 50.55a(g)(6)(l), the Commission will evaluate determinations of impracticality and may grant relief and may impose alternative requirements

, as it determines is authorized by law.

9812300062 981222 PDR ADOCK 05000338 n G PDR ,

~

Enclosure J

1 v e . . + . , -w ,-,-- - . m --

2 Generic Letter (GL) 90-05, " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1,2 and 3 Piping," dated June 15,1990, provides guidance for the staff in evaluating relief requests submitted by licensees for temporary non-Code repairs of Code Class 3 piping. For the purposes of the generic letter, impracticality is defined to exist if the flaw detected during plant operation is in a section of the Clans 3 piping that cannot be isolated for completing a code repair within the time period permitted by the limiting condition of operation of the affected system as specified in the plant TSs and performance of code repair necessitates a piant shutdown.

2.0 BACKGROUND

Virginia Electric and Power Company (hereafter referred to as the licensee) discovered at the North Anna Power Station, Units 1 and 2, various locations with evidence of possible previous leakage on severallines of the shared service water system (SWS). A repair plan was developed and implemented for all affected service water lines. In all cases, the licensee requested, pursuant to 10 CFR 50.55a(g)(6)(l), a relief frem the ASME Code,Section XI replacement lequirements. The licensee based its request for relief on the results of a "through-wall flaw" evaluation that was performed in accordance with the guidelines and acceptance criteria contained in GL 90-05. The NRC staff reviewed those requests and granted relief from the ASME Code requirements for each of the submitted reliefs. On February 24,1997, the licensee submitted a request for relief for certain stainless steellines of the SWS because the failure mechanism of the previously identified leaks was determined to be microbiologically induced corrosion (MIC). On August 8,1997, the licensee supplemented its relief request by identifying each and every line for which the relief would be applied. The purpose of the generic request was to avoid the submittal of a specific relief request to the NRC for each additional pin hole leak or location v.th possible evidence of previous leakage that may be identified during routine SWS piping walkdowns. The MIC monitoring program required walkdowns of the accessible portions of the stainless steel service water piping to identify, monitor and quantify leakage. When a leak or evidence of previous leakage was identified, structural analysis and increamd monitoring of the affected welds were implemented. Further, the program included provisions for evaluating continued system operability in accordance with GL 90-05 until appropriate Code repairs can be completed.

The NRC approved this relief on November 24,1997.

By its letter dated February 24,1998, as supplemented November 12,1998, the licensee submitted Revision 3 and Revision 4 to Revision 2 of relief request NDE-32, dated February 24,1997. This revislon contains several enhancements that could be made to the original program. The specific changes contained in this revision are:

1. Performance of a Code repair in 14 days after discovery of the MIC-induced leaks, in place of a structural analysis.
2. The use of an alternate non-destructive examination techn,que. The licensee submitted a report on the correlation between radiographic testing (RT) and ultrasonic testing (UT; examination techniques and the revised relief request would permit the use of either RT or UT to evaluate the MIC-affected locations in the SWS.

1 .

. 3 2 3. Minor program scope changes to correct discrepancies in the listing of the service water lines. -

j 3.0 LICENSEE'S RELIEF REQUEST j 3.1 Components for Which Relief is Recuested The following drawings containing the SWS line numbers for which a gen"iic relief was sought j were identified by the licensee.

3 DRAWING 11715-CBB-Q4Q_D-2. SHEET 1 i

1-1/4"-WS-G37-153A-Q3 3/4"-WS-F83-163 3/4"-WS-F82-163-Q3 1 4"-WS-G01-163-03 4"-WS-F99-163-Q3 l

l DRAWING 11715-CBB-040D-2. SHEET 2

+

j 1-1/4"-WS-H78-153A-Q3 1-1/4"-WS-H81-153A-Q3 i

, DRAWING 11715-CBM-078A-2. SHEET 1 3/4"-WS-G31-163-03 3/4"-WS-H77-163-Q3 4"-WS-H76-163-Q3

3/4"-WS-G30-163-03 3/4"-WS-339-163-Q3 3/4"-WS-G36-163-03
3/4"-WS-930-163-03  %"-WS-F61-163-Q3 2"-WS-D72-163-Q3

, 3/4"-WS-F78- 163-03 4"-WS-F63-163-Q3 3/4"-WS-F67-163-Q3 1

4"-WS-F64-163-Q3 3/4"-WS-F80-163-03 3/4"-WS-F68-163-03 E 4"-WS-F65-163-Q3 3/4"-WS-F69-163-03 8"-WS 93-163-Q3 l

8"-WS-94-163-Q3 4"-WS-F62-163-Q3 3/4"-WS-F66-163-Q3 )

3/4"-WS-F79-163-Q3 4"-WS-G35 163-Q3(*) 3/4"-WS-F81-163. Q3(*) j The two lines with (*) were added in Rev. 4.

DRAWING 11715-CBM-078A-2. SHEET 4 8"-WS-515-163-Q3 8"-WS-513-163-Q3 4"-WS-H43-163-Q3 3/4"-WS-H52-163-Q3 4'-WS-H50-163-Q3 3/4"-WS-H54-163-Q3 )

3/4"-WS-H67-163-Q3 3/4"-WS G32-163-Q3 8"-WS-115-163-03

8"-WS-113-163-Q3 4"-WS 103-Q3 3/4"-WS-H60-163-Q3 4

3/4"-WS-H62-163-Q3 4"-WS-56-163-Q3 8"-WS-114-163-Q3

, 8"-WS 516-163-Q3 8"-WS-514-163-Q3 3/4"-WS-F64-163-Q3

. 3/4"-WS-H53 i63-Q3 3/4"-WS-H66-163-Q3 4"-WS-H51-163-Q3 3/4"-WS-H55-163-03 3/4"-WS-G33-163-Q3 8"-WS-116-163-Q3 4"-WS-46-163-Q3 2"-WS-926-163-Q3 3/4"-WS-H61-163-Q3 3/4"-WS-H63-163-Q3 4"-WS-57-163-Q3 4"-WS-H49-163-Q3(*)

, 3/4"-WS-H65-163-Q3(*)

The two lines with (*) were added in Rev. 4. l 1

J

- ~ , - . -

4 DRAWING 11715-CBM-0708-2. SHEET 1 1 1/2"-WS-346-163-Q3 1"-WS-G06-163-Q3 1-1/2"-WS-348-163-Q3 1"-WS-G05-163-Q3 1-1/2"-WS-350-163-Q3 1"-WS-G04-163-Q3 J

1-1/2"-WS-352-163-Q3 1"-WS-G03-163-03 1"-WS-347-163-Q3 1-1/2"-WS-347-163-Q3 1"-WS-349-163-Q3 1-1/2"-WS-349-163-Q3 1"-WS-351-163-Q3 1 1/2"-WS-351-163-Q3 1"-WS-353-163-Q3 i

1-1/2"-WS-353-163-Q3 1

The following four lines that were in Rev. 2 were deleted in Rev. 4.

l 3/4"-WS-351-163-Q3 3/4"-WS-347-163-Q3 3/4"-WS-349-163-Q3 3/4"-WS-353-163-Q3 DRAWING 11715-CBM-0788-2. SHEET 3 1-1/2"-WS-724-163-Q3 1"-WS-933-163-Q3 1 1/2"-WS-726-163-Q3 1"-WS-934-163-Q3 1"-WS-729-163-Q3 1-1/2"-WS-729-163-Q3 1"-WS-731-163-Q3 1-1/2"-WS-731-163-Q3 1"-WS 725-163-Q3 1-1/2"-WS-725-163-Q3 1"-WS-727-163-Q3 1-1/2"-WS-728-163-Q3

, 1"-WS-935-163-Q3 1-1/2"-WS-730-163-03 1"-WS-936-163-Q3 1-1/2"-WS-727-163-Q3

{ The fcilowing four lines that were in Rev. 2 were deleted in Rev. 4.

i 4

3/4"-WS-725-163-Q3 3/4"-WS-729-163-Q3 )

. 3/4"-WS-725-163-Q3 3/4"-WS-731-163-Q3 DRAWING 11715-CBM-0780-2. SHEET 2 4"-WS-46-163-Q3 3/4"-WS-A47-163-03 1"-WS-81-163-Q3 1"-WS-77-163-Q3 1"-WS-477-163-Q3 1"-WS-481-163-Q3 j 3"-WS-73-163-03 4"-W3-47-163-Q3 3/4"-WS.-A49-163-Q3 1"-WS-82-163-Q3 1"-WS-78-163-Q3 1"-WS-478-163-Q3 1"-WS-482-163-Q3 3"-WS-74-163-Q3 4"-WS-56-163-Q3 3/4"-WS-A48-163-03 1"-WS-85-163-Q3 1"-WS-485-163-Q3 1' /3 487163 Q3 1"-WS-489-163-Q3 1"-WS-491-163-03 3" WS-75-163-Q3 3"-WS-76-163-Q3 3/4"-WS-79-163-Q3 3/4" WS-381-163-Q3 2"-WS-80-163-Q3 3/4"-WS-83-163-Q3  :

3/8"-WS-383-163-Q3 3/8"-WS-382-163-Q3 2"-WS-376- 133-Q3 3/8"-WS-397-163-Q3 3/8"-WS-398-163-Q3 1"-WS-90-163-Q3 3/4"-WS-C06-163-Q3 1"-WS-92-163-Q3 1"-WS-86-163-03 3/4"-WS-C01-163-Q3 1"-WS-488-163-03 3/4"-WS-913-163-Q3 ,

1"-WS-490-163-03 1"-WS-78-163-Q3 1"-WS-492-163-Q3 l 4"-WS-57-163-Q3 3/4"-WS-773-163-Q3 2"-WS-772-163-Q3 3/8"-WS-910-163-Q3 3/8"-WS-914-163-Q3 2"-WS-776-163-Q3 a a

l 5

3/8"-WS-916-163-Q3 2"-WS-777-163-03 1"-WS-486-163-03 2"-WS-377-163-Q3 3/8"-WS-C01-163-Q3 3/8"-WS-399-163-Q3 3/4"-WS-378-163-Q3 2"-WS-84-163-Q3 3/4"-WS-379-163-Q3 1"-WS-88-163-Q3 3/4"-WS-380-163-03 3/4"-WS-83-163-03 3/8"-WS-383-163-Q3 3/4" 'WS-A50-163-Q3 1"-WS-89-163-03 3/4"-WS-400-163-Q3 3/4"-WS-774-163-03 2"-WS-775-163-03 3/8"-WS-913-163-Q3 3/8"-WS-915-163-03 3/4"-WS-779-163-Q3 3/4"-WS-909-163-Q3 3/8"-WS-912-163-Q3 The following line that was in Rev. 2 was deleted its Rev. 4.

1"-WS-478-163-Q3 DRAWING 11715-CBM-078G-2. SHEET 1 2"-WS-D46-153A-03 1"-WS-D50-153A-Q3 3/4"-WS-D39-153A-Q3 1"-WS-D30-153A-Q3 3/4"-WS-D41-153A-Q3 3/8"-WS-D55-163-Q3 1"-WS-D31-153A-03 3/4"-WS. D43-153A-Q3 3"-WS-73-163-03 2"-WS-54-163-Q3 2"-WS-52-163-Q3 3/4"-WS-D67-163-03 2"-WS-50-163-Q3 3"-WS-74-163-Q3 2"-WS-55-163-Q3 3/4"-WS-D54-163-Q3 2"-WS-53-163-03 3/4"-WS-D68-163-Q3 2"-WS-51-163-03 2"-WS-C88-153A-03 2"-WS-C81-153A-Q3 2"-WS-C87-153A-Q3 2"-WS-63-163-03 3/4"-WS-D61-163-Q3 2"-WS-62-163-Q3 2"-WS-C80-153A-Q3 3/4"-WS-C67-153A-03 3/4"-WS-C73-153A-03 3/4"-WS-C76-153A-Q3 3/4"-WS-C70-153A-Q3 2"-WS-C86-153A-03 2"-WS-79-153A-Q3 2"-WS-C85-153A-Q3 3/4"-WS-D62-163-Q3 2"-WS-60-163-Q3 3"-WS-75-163-03 3/4"-WS-D69-163-03 2"-WS-61-163-Q3 3/4"-WS-D56-163-Q3 2"-WS-C83-153A-Q3 2"-WS-C89-153A-Q3 3/4"-WS-D60-163-Q3 2"-WS-64-163-Q3 2"-WS-65-163-Q3 2"-WS-C82-153A-Q3 3/4"-WS-C68-153A-Q3 3/4"-WS-C74-153A-03 3/4"-WS-C71-153A-Q3 3/4"-WS-D70-163-Q3 3"-WS-76-163-Q3 2"-WS-C78-153A-Q3 3/4"-WS-C66-153A-03 3/4"-WS-C72-153A-Q3 3/4"-WS-C75-153A-Q3 3/4"-WS-C69-153A-Q3 2"-WS-C84-153A-Q3 3/4"-WS-C77-153A-Q3 G 3 AWING 11715-CBM-078G-2. SHEET 2 2"-WS-D46-153A-Q3 3/4"-WS-D71-153A-Q3 1"-WS-D47-153A-Q3 3/4"-WS-D33-153A-Q3 3/4"-WS-D51-163-Q3 1"-WS-D48-153A-Q3 3/4"-WS-D35-153A-Q3 3/4"-WS-D52-163-03 1"-WS-D49-153A-Q3 3/4"-WS-D37-153A-Q3 3/4"-WS-D53-163-Q3 3"-WS-73-163-Q3 3/4"-WS-D63-163-Q3 3"-WS-74-163-Q3 2"-WS-454-163-Q3 2"-WS-455-163-Q3 2"-WS-452-163-Q3 2"-WS-453-163-03 2"-WS-450-163-Q3 2"-WS-451-163-Q3 2"-WS-949-153A-Q3 1-1/2"-WS-981-153A-Q3 1-1/2"-WS-965-153A-Q3 2"-WS-955-153A-Q3 3/4"-WS-D57- 163-Q3 2"-WS-464-163-Q3 2"-WS-465-163-Q3 3"-WS 75-163-03 3"-WS-76-163-03 3/4"-WS-D59-163-Q3

6 2"-WS-461-163-Q3 3/4"-WS-D65-163-Q3 3/4"-WS-D66-163-Q3 l 3/4"-WS-934-153A-Q3 2"-WS-948-153A-Q3 3/4"-WS-940-153A-Q3 l 1-1/2"-WS-976-153A-Q3 1-1/2"-WS-982-153A-Q3 3/4"-WS-943-153A-Q3 3/4"-WS-937-153A-03 2"-WS-954-153A-Q3 2"-WS-947-153A-Q3 1-1/2"-WS-977-153A-Q3 1-1/2"-WS-963-153A-Q3 2"-WS-953-153A-Q3 l 3/4"-WS-D58-163-03 2"-WS-462-163-Q3 2"-WS-463-163-03 l 2"-WS-946-153A-Q3 1-1/2"-WS-979-153A-Q3 1-1/2"-WS-978-153A-03 l 2"-WS-952-153A-Q3 2"-WS-945-153A-Q3 1-1/2"-WS-980-153A-Q3 l 1-1/2"-WS-961-153A-Q3 2"-WS-460-163-Q3 2"-WS-945-153A-03 l 2"-WS-944-153A-Q3 1-1/2"-WS-975-153A-Q3 1-1/2"-WS-971-153A-03 l 2"-WS-950-153A-Q3 2"-WS-951-153A-Q3(*)

This line with (*) was added in the Rev. 4.

l DRAWING 11715-CBM-078H-2. SHEET 1 i 1

1"-WS-9-163 3/4"-WS-E03-163 3/4"-WS-F44-163 I 1"-WS-G07-163 3/4"-WS-E08-163 1"-WS-947-163 1"-WS-G50-163 1"-WS-10-163 3/4"-WS-F45-163 2"-WS-E64-163  %"-WS-E68-163 1"-WS-D97-163 2"-WS-D91-163 1"-WS-H48-163 1"-WS-G 52-163(*)

This line with (*) was added in the Rev. 4.

The above listed piping lines are classified as ASME Code Class 3, moderate energy stainless steel piping of the SWS. The piping provides cooling water from the service water reservoir to safety-related equipment and returns service water back to return headers. Normal operating pressure is 100 psig. The design pressure is 150 psig and the design temperature is 150 F.

3.2 Section XI Edition for North Anna 1 and 2 North Anna Unit 1 - 1983 Edition of the ASME Code,Section XI including Summer 1983 Addenda.

North Anna Unit 2 - 1986 Edition of the ASME Code,Section XI.

3.3 ASME Section XI Code Reauirement

, The ASME Code Section XI requires that repairs or replacements of ASME Code Class components be performed in accordance with rules found in Articles IWA-4000 or IWA-7000, respectively. The intent of these rules serves to provide an acceptable means of restoring the structuralintegrity of a degraced Code Class system back to the original design requirements.

3.4 Content of the revision to the Relief Reauest The original Relief Request was sought from performing a repair or replacement of the service water piping per the requirernents of Article IWA-4000 or IWA-7000, respectively, and from

i

. . l 7

submitting to the NRC a relief request for each and every observation of evidence of pin hole leaks in the stainless steel piping pation of the SWS listed above. !t established a plan for contintred operat;or: with through-wall flaws in stainless steel piping in the SWS based upon the

.p dopo / y ov, r /3L 00 05. Relief was being sought because performing a Code repair muun th9 ims.g reaJitions of the SWS operation may be impracticable or impose undue '

Nden upon the licensee without a compensating increase in the level of quality and safety.

By its ietter dated February 24,1998, as supplemented November 12,1998, the licensee I submitted a revision to relief request NDE-32, dated February 24,1997. The specific changes l 1 contained in this revision are 1

1. Performance of a Code repair in 14 days after discovery of the MIC-induced leaks. in l place of a structural analysis.
2. The use of an alternate non-destructive examination technique. The licensee submitted a report on the correlation between RT and UT examination techniques and the revised relief request would permit the use of either RT or UT to evaluate the MIC-affected locations in the SWS.
3. Minor program scope changes to correct discrepancies in the listing of the service water i lines.

3.5 Basis for Relief l

The licensee has submitted a revision to the request for relief dated February 24,1997, as 1

. supplemented August 8,1997, and November 18,1997, and proposed alternatives to the Code requirement. The licensee has committed to evaluate any newly found flaw or indication of a flaw in accordance with the guidance provided in GL 90-05. Based upon the evaluation, it will j be established whether the discovered flaws satisfy the criteria for non-Code repair as described l in GL 90-05. The evaluation will also determine whether performing permanent repairs in j accordance with the ASME Code within the limits of the limiting conditions of the SWS would l constKute an undue burden (create undue hardship) upon the licensee since the repairs would necessitate the unnecessary isolation of portions of the SWS that are structurally sound and thus reduce the margins of safety of the SWS.

3.6 .LicJnsee's Altenative Proaram As an alternative to performing Code repairs in accordance with IWA-5250(a)(2) to through-wall flaws in the SWS, the flaws will be left as found. The through-wall flaw will be momtored for leakage and must meet the criteria for flooding and spraying consequences and for structural integrity as described in GL 90-05 to remain in service. All welds identified with through-wall flaws will be replaced within 18 months from the time of discovery. This alternative to the Code requirement will be followed for the remainder of the second 10-year inspection interval. The Unit 1 second 10-year interval will end on April 30,2000, and the Unit 2 second 10-year inten/al will end on April 30,2001. The structuralintegrity of the SWS will be monitored by the following methods until the repairs required by IWA-5250(a)(2) are completed.

8

  • Weekly visual monitoring of through-wall flaws from the time of identification until repair or completion of structuralintegrity analysis, if the welds are determined to be structurally acceptable, then the visual monitoring frequency will be decreased to once every six weeks.
  • All welds identified as having through-wall flaws and not repaired within 14 days of detection will be assessed for structural integrity within 14 days of detection. Butt we'ds will be examined by RT or UT methods, if accessible, to characterize the flaws. Socket welds and butt welds inaccessible to RT or UT will be assessed for structural integrity by assuming a conservative 3/4" diameter hole. Welds determined to be structurally adequate will be included in the above monitoring program. Identification of a structurally inadequate weld will result in the associated piping to be declared inoperable and the appropriate Technical Specification action statement to be taken.
  • Weekly visual monitoring of through-wall flaws in socket welds and butt welds inaccessible to RT or UT examination for a period of 2 months. If there is no significant change in the leakage rate, the monitoring frequency will be decreased to once every 6 weeks until the welds are repaired.
  • A significant change is defined as a 0.5 gpm increase in the leakage rate from the initial )

observed leakage condition for each weld. Should any location reach the threshold of significant change, the weld will be reassessed for structural integrity and flood / spraying j consequences. l

  • A walkdown every 6 weeks of the accessible stainless steel portions of the SWS will be performed. The frequency of walkdowns will be assessed after a year ano adjusted based on the results of the inspections.
  • A total leakage rate limit of 1.0 gpm for a single supply or return line for an individual component will be established. If this total leakage rate limit is exceeded, then an evaluation will be performed to determine if design service water flow is available to affected components. Inadequate service water supply will cause the associated service water lines and equipment to be declared inoperable and appropriate action will be taken according to the Technical Specifications.
  • An augmented inspection program will monitor a sample of 10 butt welds in the SWS using RT or UT examination methods. Examinatior3 will be performed every 3 months.

The frequency of examinations will be assessed after a year and may be adjusted for each location based on the results of the examinations.

4.0 STAFF EVALUATION AND CONCLUSIONS 4.1 Operability Determination. Root Cause Analysis and Structural Intearity Evaluation The licensee has proposed to use the guidance provided in GL 90-05 to assess newly discovered f!aws in certain stainless steellines of the SWS. The system was constructed in accordance with the requirements of ASME Code, Class o. A routine MIC monitoring program

l 9

i has been developed for the SWS. The program includes walkdowns to identify, monitor and l quantify leakage. The SWS has previously experienced MIC. Radiographic examination of the 1 welds having through-wallleakage revealed small voids surrounded by exfoliation, which is l typical of MIC. No other type of inservice defects were identified on the radiographs near the 1 areas with through-wallleaks. Additionally, a visual examination of a sample of piping segments l removed to repair leaking welds confirmed the presence of MIC. No through-wallleaks have  !

been identified involving the stainless steel lines associated with this relief. Flaw evaluation for newly discovered welds with through-wall leaks will be performed as follows. The flaws in butt i welds that can be characterized by radiography will be evaluated by three types of analysis: )

area reinforcement, limit load analysis, and fracture mechanics using the guidance from GL 90- l

05. The flaws in welds that cannot be characterized by radiography, i.e , socket welds and inaccessible butt welds, will be evaluated by the same analysis by assuming a 3/4-inch hole for i each pobt of leakage within a weld with through-wall leakage. Socket welds will be analyzed by treating the weld cross section as an equivalent pipe cross section.

l 4.2 Auamented Insoectio0 To assess the overall degradation of the SWS, an augmented inspection program has been developed. The augmented program is performed on a sample of 10 welds in the SWS using RT or UT and will be performed every 3 months. The frequency of testing will be assessed after a year and may be adjusted for each location based on the results.

4.3 hocosed Temporary Non-Code Repair and Monitorina Provisions As an alternative to performing Code repairs in accordance with IWA-5250(a)(2) for newly discovered through-wall flaws in the SWS, the flaws will be left as found. The through-wall flaw will be monitored for leakage and must meet the criteria for flooding and spraying consequences and for structural integrity as described in GL 90-05 to remain in service. All welds identified with through-wall flaws will be replaced within 18 months from the time of discovery. This alternative to the Code requirement will be followed for the remainder of the .ccond 10-year inspection interval. The Unit 1 second 10-year interval will end on December 24,1998, and the Unit 2 second 10-year interval will end on December 14,2000. The structuralintegrity of the SWS will be monitored by the visual and radiographic examinations as stated in paragraph 3.6 above until the repairs required by IWA 5250(a)(2) are completed.

4.4 Comparison of UT results with the RT/ destructive examination results The Mensee conducted a comprehensive study on RT and UT, comparing the flaw indication patten of the two testing programs and also did a destructive test / visual examination of the different test specimens and compared the results with the UT test results of those specimens.

The sarnple set consisted of 10 welds on three different 4" diameter service water lines.

Further, the sample set was selected to meet the fabrication conditions specified by Appendix Vill of the ASME Section XI for austenitic stainless steel piping welds. Five of the ten specimens selected for this program showed evidence of leakage in the field. For RT examination, a double-wall single viewing technique was used. For UT examination, since the form or structure of MIC does not present an optimum reflecting surface when using angle beam techniques, the test consisted of two examinations. One examination utilized a 2 MH7. dual element tandem

10 search unit and the second examination utilized a smaller 45 degree shear wave search unit.

The destructive examination consisted of cutting the specimens through the base metal, perpendicular to the pipe axis in each side of the weld, which resulted in coupon strips of 0.020 inch. Observations were made after each cut and the results were dccumented after every three cuts. The comparison of destructive and nondestructive examination (RT and UT) results showed that clusters of MIC shown by the destructive results agree with the RT/UT 'est indications (clusters of MIC are reported as a single indication in RT/UT).

The results achieved by this program provide the basis for the following observations:

  • The UT technique developed under this program is as effective as RT for detection of MIC.
  • The UT length sizing technique developed under this program is as effective as RT for length sizing of MIC indications when considering the totallength of a flawed weld.
  • The UT depth sizing technique developed is capable of measuring the depth of MIC indications within 0.060" and may be improved to 0.040"if sizing is limited to Mdications located on the accessible side when performing sizing on single access welds.

The licensee concluded that UT is a less intrusive examination technique compared to RT and is acceptable for monitoring MIC in stainless steel piping. The UT personnel should be qualified with adequate training for detection or sizing of MIC indications. For those cases where the MIC is located on the inaccessible side of single-sided access welds, the UT cannot be used for through-wall sizing. Finally, two or three welds examined by UT should be selected and examined by RT or a destructive examination technique on an annual basis.

4.5 Staff Conclusions The staff has determined that the licensee's proposed flaw evaluation has been consistent with the guidelines and acceptance criteria of GL 90-05. The staff finds the licensee's proposed UT examination technique to be used for the detection of MIC in the stainless steel service water piping is as effective as the currently followed RT examination technique. The staff finds the licensee's proposed approach acceptable to perform future structural integrity and operability assessments of the stainless steel piping as listed in paragraph 3.1 aboue. The licensee's revised alternative to postpone repairing through-wall leak discovered in certain stainless steel piping of the SWS in the future is reasonable because: (1) the licensee's flaw determination and monitoring program is consistent with the guidance of GL 90-05, as described above, up to the point of actually submitting a relief request to the NRC; (2) each occurrence of flaw detection is documented in the North Anna's corrective action system; and (3) ali relevant documentation is available for NRC staff review.

Furthermore, the staff finds that performance of an immedste Code repair after each and every newly discovered flaw caused by MIC would constitute an undue burden (create undue hardship) upon the licensee since the repair may exceed the time limits imposed by the governing Technical Specification and thus necessitate the isolation of portions of the SWS.

Isolating portions of the SWS to perform a Code repair is not in the best interest of plant safety,

l..

11 given the magnitude of the flaw and the assurance of structural integrity provided by licensee's alternative program. The staff, therefore, the alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(ii), in that compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. This alternative is authorized for the remainder of the second 10-year inspection interval for each unit.

Pri.1cipal Contributor: N. Kalyanam Date: December 3,1998

Retrieved from "https://kanterella.com/w/index.php?title=ML20198H954&oldid=3339177"