ML20217H908

Requests Relief of ASME Code Requirements,Paragraph IWA-5250(a)(2) & Paragraph IWA-5250(a)(3) for Period of 970909-25,when Last Weld Repaired

ML20217H908
Person / Time
Site:	North Anna
Issue date:	10/13/1997
From:	Saunders R VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
97-553, GL-90-05, GL-90-5, NUDOCS 9710170115
Download: ML20217H908 (13)

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huisi A EI.ECTRIC AND POWER CmWANY Ricnuoso, VII4GINI A 23261 October 13, 1997 United States Nucicar Regulatory Commission Serial No.97-553 Attention: Document Control Desk NL&OS/ETS R0 Washington, D.C. 20555 Docket Nos. 50-338 50-339 License Nos. NPF-4 NPF-7 Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPANY, blORTH ANNA POWER STATION UNITS 1 and 2 ASME SECTION XI RELIEF REQUESTS NDE-44 AND NDE-39 SERVICE WATER SYSTEM LEAKS On September 9,1997 during a system walkdown, ten locations with evidence of possible previous leakage i.e., stains, were identified in four ASME Class 3 Service Water lines in North Anna Units 1 and 2. In order to reduce the number of entries into action statements and service water manipulations, a repair plan was developed and implemented for the affected service water lines. Pursuant to 10 CFR 50.55a(3)(ii),

Virginia Electric and Power Company requests relief of ASME Code requirements, paragraph IWA-5250(a)(2) (Unit 1 - 1983 Edition with Summer 1983 Addenda) and paragraph IWA-5250(a)(3) (Unit 2 - 1986 Edition) for the period of September 9,1997 through September 25,1997, when the last weld was repaired. Relief Requests NDE-44 and NDE-39 for the leaking welds in Units 1 and 2, respectively, and the basis for the relief requests are provided in the attachment to this letter.

Where meaningful results could be obtained, the areas of leakage were examined by radiography and an evaluation was performed for continued operation in accordance with the Generic Letter 90-05, " Guidance for Performing Temporary Non Code Repair of ASME Code Class 1,2, and 3 Piping." The evaluation determined the operability and continued safe operation of the examined service water lines until the necessary ASME Code repairs could be made. The leaking locations were identified during a recurring system visual inspection which involves all of the stainless steel piping associated with the service water system. Additionally, in accordance with GL 90-05, radiographic assessment was performed on an additional sample of five welds. Each of these welds were found acceptable by radiography and structural integrity analysis. The indications of possible leakage were in the welds or the adjacent base material. Based on previous laboratory assessments of the repaired leaking indications the cause of leakage was determined to be microbiological influenced corrosion (MIC).

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, The condition of the Service Water System was monitored during the period corresponding to the relief request. The monitoring program included walkdowns of the affected welds to identify and quantify any leakage. No significant changes were noted in the condition of the affected piping during this period.

This relief request has been reviewed and approved by the Station Nuclear Safety and Operating Committee.

if you have any additional questions conceming this request, please contact us.

Very truly yours, I.

l R. F. Saunde@rs

! Vice President - Nuclear Engineering and Services Attachment

Commitments made in this letter

None.

3 cc: U. S. Nuclear Regulatory Commission Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85

! Atlanta, Georgia 30303 1

Mr. M. J. Morgan NRC Senior Resident inspector North Anna Power Station i

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1 ASME Section XI Rollef Requests NDE-44 and 39 North Anna Power Station Units 1 and 2 Virginia Electric and Power Company

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, Virginia Electric & Power Company North Anna Power Station Units 1 and 2

. -Second 10-Year Interval Request for Relief Number NDE-44 (Unit 1)

-Request for Relief Number NDE-39 (Unit 2)-

I. IDENTIFICATION OF COMPONENTS Mark / Weld # Line# Drawino# Joint

-14W- -2"-WS-775-163-Q3 11715-CBM 78C-2 SH. 2 SW=

12050-WS-2485E 53W 2" WS-776-163-Q3- 11715-CBM-78G-2 SH. 2 SW 12050-WS-2482C FW55 4" WS-F65-163-Q3 11715-CBM-78A-2 SH. 1 BW 11715-WS-2D89B FW67 4"-WS-47-163-Q3 11715-CBM 78C-2 SH. 2- BW 11715-WS-17F 3"-WS-75-163-Q3' FW83 11715-CBM-7BC-2 SH. 2 BW 11715-W3-1075A FW65 -4"-WS-56-163-Q3 11715-CBM-78C-2 SH. BW --

11715-WS-18E FW61 4"-WS-56-163-03 11715-CBM-78A-2 SH. 2 BW 11715-WS-18D FW66 4"-WS-56-163-Q3 11715-CBM-78A-2 SH. 2 BW 11715-WS-18D 8- 4"-WS-H48-163-Q3 11715-CBM-78A-2 SH. 4 BW 12050-WS-2H48A 11A 4"-WS-H48-163-Q3 11715 - CBM- 78A- 2 SH . 4 Inf

-12050-WS-2H48A-(a)' The above welds are Class 3, moderate energy. i piping in the Service Water (SW) system; (b) Line 2" WS-775-163-Q3 is1the cross-connection between instrument air ~ heat exchangers 2 IA-E-1B and 2-IA-E-1C. Line_2"-WS-776-163;Q3 is the cross-connection between instrument air.

heat exchangers 2-IA-E-1A and.2-IA-E-1B. Line 4*-WS-F65-163-Q3 is the return-from the Unit:1 air conditioning condenser. Line 4"-WS 163-Q3 provides cooling' water to the Unit:1

-charging pump _ lube _ oil coolers ^and-instrument air heat exchangers. Line 3"-WS-75-163-Q3'is the return line from the charging pump luba

' oil coolers.__Line 4"-WS-56-163-Q3 is the return from-the Unit 1 charging pump _ lube oil coolers and instrument air compressors. Line 4"-WS-H48-163-Q3 provides cooling water to the Unit 2 air conditioning condensers. The nomi-_ __

nal operating pressure and temperature is 75 psig and 95'F, respectively; and

' Relief Request NDE-44 Unit 1, NDE-39 Unit 2 Page 1 of 6

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, (c) Joint type - butt weld (BW), and socket weld (SW).

II. CODE REQUIREMENTS The above welds had external evidence of through-wall leak-age, i.e., active leaks or stains. Virginia Electric and Power Company decided to proceed under the assumption that each of the above Lelds contain through-wall flaws. Al-though this eviaence of leakage was not detected during the conduct of a system pressure test, it is being treated as such, and the requirements of IWA-5250 of the 1983 Edition and Summer 1983 Addenda are applicable to Unit 1. The re-quirements of IWA-5250 of the 1986 Edition are applicable to Unit 2.

"IWA 5250 Corrective Measures:

(a) The source of leakage detected during the conduct of a system pressure test shall be located and evaluated by the Owner for corrective measures as CC. lows:...

(2 or 3) repairs or replacements of .>mponents shall be performed in accordance '

5 IWA-4000 or IWA-7000, respectively."

Articles IWA-4000 and IWD-4000 of ASME Section XI Code repair requirements would require removal of the flaw and subsequent weld repair.

III. CODE REQUIREMENT FROM WHICH RELIEF IS REQUESTED Relief is requested from performing the above Code required

, repair of the above identified welds until the affected piping system can be taken out of service. The specific Code requirement for which relief is requested is the 1983 Edition and Summer 1983 Addenda, IWA- 5250 (a) (2) for Unit 1, and the 1986 Edition, IWA- 5250 (h) (3 ) for Unit 2.

IV. BASIS FOR RELIEF REQUEST This relief request is submitted in accordance with NRC Generic Letter 90-05 (GL 90-05), " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2,-and 3 Piping." The following information and justification are provided in accordance with the guidelines of Part B and C of Enclosure 1 to GL 90-05.

Scone. Limitations and Snecific Considerations 62992 The scope consists of the welds identified in Section I with evidence of possible through-wall leaks in the service water system for North Anna Power Station Units 1 and 2. The material of the piping is stainless steel ASME SA-312 type Relief Request NDE-44 Unit 1, NDE-39 Unit 2 Page 2 of 6

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316L.

LimitatiODE Based on radiographic examinations-and laboratory examina-tions of removed portions of piping from previous replace- .

ments, Microbiological-Influence Corrosion (MIC) was deter-mined to be the cause of the flaws. Radiographs of welds FW67, FW83, FW65, FW61, FW66, 8, and 11A chow indications of MIC. The MIC induced flaws originated on the inner diameter of the pipe and were detected during plant-operation. The intent of this request is to obtain relief for the period of operation from the identification of a through-wall flaw until repair was accomplished. To the extent practical, the

-repair-was accomplished in accordance with the guidance of NRC Generic Letter 90-05. This period extende from identi-fication of the first leaking weld on September 9, 1997 to when the repair of each weld (suspected of having through-wall flaws) was completed. All identified welds suspected of:having through-wall flaws were repaired by September 25, 1997.

Soecific Considerations System interactions, i.e., consequences of flooding and spray on equipment were evaluated. The identified flaws were located on the piping such that potential through-wall leakage would not affect plant equipment.

The structural integrity of the butt welds was evaluated based on radiographic examination results, the required design loading conditions, including dead weight, pressure, thermal expansion and seismic loads. The methods used in the-structural integrity analysis consisted of an area rein-forcement, fracture mechanics, and limit load analysis.

Each indication was considered to be through-wall due to the inability of either radiography or ultrasonics to determine

-indication depth. A summary of the-flaw evaluation is pr, vided in Attachment 1. All welds were analyzed and found

-acceptable, except welds FW65 and 8.

Radiography of socket weld 14W on line 2"-WS-775-163-Q3, and weld 53W on line 2"-WS-776-163-Q3 were not attempted because-radiographs of socket welds do not yield meaningful  :

results.- Additionally, flaws cannot be characterized for socket welds. Therefore, complete structural integrity analysis was not performed. Lines 2"-WS-775-163-03, and 2"-

WS-776-163-Q3 were removed from service and the socket welds were replaced by September 25, 1997, sixteen (16) days after the evidence of leakage was detected.

Because of the inability of both RT and UT to give reliable through-wall depth for MIC indications, all MIC indications Relief Request NDE-44 Unit 1, NDE-39 Unit 2 Page 3 of.6

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were considered-through-wall. This c 1servative assumption

-caused weld 8~on_line 4"-WS-H48-163-Q3_and. weld FW65 on line

,- 4"-WS 56-163-Q3 to fail'the assessment requirements of GL 90-05. Weld-8 was replaced on_ September 23, 1997 two (2) 1 days after the weld-waszradiographed and removed from ser -

! .vice. We:d 11A on line 4"-WS-H48-163-Q3.was replaced at the I

same-time as weld-8. Weld FW65 on line 4"-WS-56-163-Q3 was

[ replaced on September 16,-1997. Weld-FW55 on line 4"-WS-l F65-163-Q31did not show evidence of MIC on the radiographs.

L Therefore, no structural integrity analysis was performed on '

! weld FW55 = -However, weld'FW55 was replaced as a conserva-tive measure on September 23, 1997 two (2) days after the ~

weld was radiographed;and removed from service. . Welds FW67 s

.(on line 4" WS-47-163-Q3), FW83 (on line 3"-WS-75-163-Q3),

FW61 (on line 4"-WS 56-163-03), and FW66 ;(on line 4 "-WS-56-'

163-Q3) showed evidence of acceptable MIC as determined by i radiography and structural integrity analysis. However, j these welds were replaced as a conservative measure on l- September 16, 1997.

l The structural integrity for each weld identified with

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evidence of through-wall _ leakage (and remaining in service)

" was monitored weekly by. visual conitoring of through-wall flaws to determine any degradation of structural integrity.

Generic Letter 90-05 allows two options for temporary non-I code repairs of Class'3 piping in moderate energy systems,-

(1) non-welded repairs, and (2) leaving the piping as-is if

-there is no-leakage and the-flaw is'found acceptable by the

"through-wall flaw" approach discussed ~in Section C.3.a.

p The temporary non-code repair approach selected-was to leave the. welds as they were found,. subject to monitoring and i meeting the criteria for consequences and for structural

. integrity as described above until rep). aced.

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Evaluation g Flaw Detection Durina Plant Oceration and Imoracticality

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i petermination The subject welds-were identified as having evidence of througn-wall leakage during a rervice Water. System walkdown

[, conducted on September 9, 1997, eben both Units were operat-

-ing. During the past several months Virginia Electric and Power:CompLny has been-monitoring,- evaluating, and replacd79 l through-wall leaks in the Service Water System caused by MIC, Removing _ portions of the' Service-Water System, prior l -

to: performing a structural-integrity analysis, due to MIC can unnecessarily reduce the margin of safety by isolating

portions-of theiService-Water System that are structurally

j. sound and capable-of-performing their intended safety func-

!_ tion. Therefore,-performing Code repairs immediately was

-I Relief. Request NDE-44 Unit 1, NDE-39 Unit 2 Page 4 of 6 i

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e considered impractical.

Root Cause Determination and Flaw Characterization The Service Water System at North Anna Power Station has previously experienced MIC. The radiograph examinations of the service water welds with indications of through-wall leaks revealed small voids surrounded by exfoliation, which is typical of MIC. No otner type of operationally caused defects were identified by the radiographs.

Flaw Evaluation Flaw evaluation for the welds was performed as described in Attachment 1. The flaws were evaluated by three types of analyses, area reinforcement, limit load analysis, and fracture mechanics evaluation using the guidance from NRC Generic Letter 90-05. Because of the inability for either radiography or ultrasonie techniques to determine the extent of wall degradation, at the identified location, the struc-tural assessment considered each indication to be through-wall.

V. AUGMENTED INSPECTION To assess the overall degradation of the service water system augmented radiographic examinations were performed.

After the initial through-wall flaws were identified, five (5) additional locations on lines having the same function were examined using radiography. One (1) of the five (5) '

welds (weld FW74 on line 4"-WS-F65-163-Q3) had evidence of MIC, without showing evidence of through-wall leakage, i.e.

stains. Weld FW74 was found structurally acceptable by radiography and structural integrity evaluation, and not re-placed. Weld FW56 on line 4"-WS-F65-163-Q3 was replaced for ease of construction, i.e., it is on the same elbow as FW:5.

The remaining three welds which did not show evidence of MIC '

on the radiographs were not replaced, (welds FW59, FW60 and FW73 on line 4"-WS-F65-163-Q3).

VI. ALTERNATE PROVISIONS As an alternative to performing Code repairs in accordance with IWA-5250 (a) (2) for Unit 1 and IWA-5250 (a) (3) for Unit 2 on through-wall flaws in the Service Water System, it is proposed to allow the through-wall flaws to remain in ser-vice until a scheduled code repair, unless the structural integrity has been determined to be unacceptable. This alternate provision applies to the subject welds from iden-tification of the first leaking weld on September 9, 1997 to the repair of each weld suspected of having a through-wall flaw. All through-wall flaws had been repaired by Septem-Relief Request NDE-44 Unit 1, NDE-39 Unit 2 Pag; 5 of 6 l1

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ber 25, 1997.

The proposed alternative stated above ensures that the overall levels of plant quality and safety will not be

, compromised.

VII. IMPLEMENTATION SCHEDULE Repairs of tne ffected welds were completed by September 25, 1997. o

References:

1. USAS B31.1 Pown. Piping Code - 1967 Edition

2. EPRI Report NP 6301-D, " Ductile Fracture Handbook"

3. Nuclear Regular.ory Commission Generic Letter 90-05 " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2, and 3 Piping" N

Relief Request NDE-44 Unit 1, NDE-39 Unit 2 Page 6 of 6

Attachment 1 Flaw Evaluation Methods and Results Introductica Butt welds identified by radiography as having MIC were analyzed for structural integrity by three niethods, area reinforcement, limit load analysis, and linear clastic fracture mechanics evaluation.

Area Reinforcement Analvala The area reinforcement analysis is used to determine if adequate reinforcing exists such that ductile tearing would not occur. The guidelines of ANSI B31.1 paragraph 104.3.(d) 2 (reference 1) are used to determine the Code required reinforcing area. The actual reinforcing area is calculated and is checked against the required reinforc. ment area.

The Code required reinforcement area in square inches is defined as:

1. 07 (t.) (d )

i Where to is the code minimum wall, and d is the outside diameter i The Code required reinforcement area is provided by the available material around the flaw in the reinforcing zone.

t The results of this analysis determined that for the subject four inch (4") and three inch (3") pipes, a hele size of 2.2" and 1.7" respectively will be contained by the reinforcement provided by the excess material in the near vicinity.

Limit Load Analysis The structural integrity of the piping in the degraded condition was established by calculating the minimum margin of safety based upon a Limit Load Analysis. These methods are documented in EPRI report NP-6301-D (Ductile Fracture Handbook) (reference 2).

The limit load analysis of the postulated flawed sections were performed with a material flow stress representing the midpoint of the ultimate strength and yield point stress for the SA312-TP316L stainless steel material at the design temperature of 150'F.

Relief Request NDE-44 Unit 1, NDE-39 Unit 2 Page 1 of 4

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4 The flawed sections were subjected to deadweight, thermal, and

, seismic DBE loading.

The allowable limit load is given by, M. - 2 ' Or ' R[' t ' (2 cos (S) - sin (0) ) in-lbf or = flow stress = 0.5 ( S, + S.) , psi Sy = yield stress, psi S = ultimate stress, psi R. = mean radius of the pipe (inches)

L 11'(Rl'P) +F 2 4o(R;c R i

= internal radius of the pipe (inches)

P = pressure (psig)

F = axial load (lbs)

D = Outside diameter (inches) t = pipe thickness (inches) 0 - half angle of the crack (radians) = crack lenath 2'R, MR = Resultant Moment from the above mentioned loading conditions MR=OfY' +MZ ' + T*

MY = Bending Moment MZ = Bending Moment T = Torsion The calculated factor of safety is, FS = _M,_

(MR)

The minimum f actor of safety of 1.4 is required to be qualified for continued operation.

A summary of the results is listed in Table 1.

Fgacture Mechanics Evaluation s

A linear elastic fracture mechanics analysis was performed for circumferential through-wall crack using the guidance provided in NRC Generic Letter 90-05. The structural integrity of the piping in the degraded condition was established by calculating the stress intensity factor ratio based upon a Fracture Mechanics evaluation.

This method is documented in EPRI report NP-6301-D (Ductile Fracture Handbook) (reference 2).

Relief Request NDE-44 Unit 1, NDE-39 Unit 2 Page 2 of 4

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A through wall circumferential crack was postulated for every area containing MIC. The cracks were subjected to a design pressure loading of 150 psig in addition to the deadweight, normal operating thermal and seismic- DBE loadings. For the purpose of this evaluation a generic allowable stress intensity factor of K c - i 135 ksiVin was used for the material per NRC GL 90-05.

The applied stress intensity factor for bending, K 23, is found by:

Kg i =

ab- (x R

• 0) d *F3 The applied stress intensity factor for internal pressure, Ki p, is found by:

Kit = a,- ( n R. 0 ) F, The applied stress intensity f actor for axial tension, K r is found i by:

K r = at - ( n R. 0 ) #F i i The stress intensity factor for residual stresses, K a is found by:

i K th = S * ( x R. 0 ) #F t Total applied stress intensity factor Kr includes a 1.4 safety factor and is calculated by:

Kr = 1.4 - (Kra + i K p +i Kr) +Ka i The allowable stress intensity f actor is taken f rom Generic Letter 90-05.

4 Kat = 135 ksiVin for stainless steel.

Stress Intensity Factor Ratio is defined as:

SR = Er_

Kut The stress intensity factor ratio shall be less than 1.0 for continued operation.

A summary of the results are listed in Table 1.

1 Relief Request NDE-44 Unit 1, NDE-39 Unit 2 Page 3 of 4

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.a Table 1 --

SUMMARY

OF FLAW EVALUATION RESULTS FOR SERVICE WATER WELDS ,

Flaw .

Man. Max. Man. 'Attcwable Length Actual Max. . Max. Sending Berzfing Resutant ilmit Factor Applied- Allonsable

' Anatyred Flau Axial Torsion Moment Mcument Moment Load M. of E, Q- I Weld Nos. Line Nos. Lenoth in Leneth in Load Ibs 1 f t-lbs MT ft-tbs M2 ft-tbs MR ft-lbs it-tbf Safet/' ksi/in ksi/in FW65 4"-WS-56-163-03 2.12 3.25 mote 2 - - - - - - - -

8 4"-WS-N48-163-Q3 2.12 2.25 Note 2- - -- - - - - - -

FW67. 4"-WS-47-163-03 2.12 '1.936 117- 18 57 319 324.55 1.197m10* 36.8 62.24 135 FW83 3"-WS-75-163-03 1.65 0.937 122 7 62 189 =199.03 6.452m10' ~ 32.4 54.54 :135 FW61 4"-WS-56-163 2.12 0.437 151 152 140 454 498.82 1.196m10* 23.98 63.99 135-FW66 4"-WS-56-163-Q3 1.125 1.125 138 418 102 506 664.80 1.094x10*' 116.46 42.26 135' 11A 4"-WS-H43-163-Q3 2.12 1.125 293 674 240 666 977.46 1.1 W 10* 12.Z3 66.82 135 totes:

' 1. Limit load factor of sakty is Attowable Limit Load / Resultant Moment.

- 2. Weld FW65 and 8 failed the structural integrity evaluation because the actual teau tength was greater than the anatyred flew tength. The anatyred flees tength was bounded by the 15% circumferentist length as maxisun thru-welL flew tengths permitted by WRC Generic Letter GL 90-05.

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Relief" Request NDE-44 Unit 1, NDs-39 Unit 2 Page 4 of 4

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