ML20154F531

Safety Evaluation Re Util 880404 Request for Relief from ASME Boiler & Pressure Vessel Code Section XI Inservice Insp Requirements.Relief Acceptable Provided That Util Incorporates Three Listed Items in 880331 SER

ML20154F531
Person / Time
Site:	Sequoyah
Issue date:	05/11/1988
From:	NRC OFFICE OF SPECIAL PROJECTS
To:
Shared Package
ML20154F516	List: ML20154F513 ML20154F531
References
NUDOCS 8805230285
Download: ML20154F531 (15)

Text

• p NCg pf , 4 UNITED STATES y p, \

ef[k

'E g NUCLEAR REGULATORY COMMISSION W ASHINGTON, D. C. 20555 l

';'N'g/[e t 8 l g// '

SAFETY EVALUATION BY THE OFFICE OF SPECIAL PROJECTS RELATING TO RELIEF FROM THE BOILER AND PRESSURE VESSEL CODE, SECTION XI, "P.ULES FOR INSERVICE INSPECTION OF NUCLEAR POWER PLANT COMPONENTS - DIVISION 1" TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR POWER PLANT UNITS 1 AND 2 i DOCKET NOS. 50-327 AND 50-328

1.0 INTRODUCTION

Sequoyah has experienced microbiologically induced corrosion (MIC) in the butt welds of stainless (austenitic) steel piping in the essential raw cooling water (ERCW) system. The MIC attack initiated at the inside surface of the welds a'nd degradation occurred in the form of voids that became larger, and deeper, and eventually developed into a throughwall leak. The leakage was small and was characterized as drips er moist areas around the butt welds.

TVA developed a MIC program for Sequoyah based upon the data developed through inspection. The MIC program and the engineering (. valuation which fonned the basis for the program is described in TVA's letter dated January 20, 1987.

This program was reviewed and approved (with stated additions) in our Safety Evaluation Report forwarded by a letter dated March 31, 1988 (attached).

The Technical Specifications for the Sequoyah Nuclear Plant states that inservice examination for ASME Code Class 1, 2 and 3 components shall be performed in accordance with Section XI of the ASME Boiler and Pressure Yessel Code and applicable Addenda as required by 10 CFR 50.55a(g) except where specific written relief has been granted by the Conmission. Regulation 10 CFR 50.55a(g)(6)(i) authorizes the Comission to grant such relief and may impose such alternative requirements as it determines is authorized by law and will not endanger life or property or the comon defense and security and ,

is otherwise in the public interest giving due consideration to the burden '

upon the licensee that could result if the requirements were imposed on the j facility, i By 2 letters, both dated April 4, 1988, and in a clarification letter dated May 4,1988, TVA submitted a request for relief from the requirements of IWA-5250(a)(2) during the performance of their MIC program. These requirements were determined to be impractical to perform on Sequoyah Units 1 and 2 during power operation of the plants.

l l

8805230285 080511 1 PDR ADOCK 05000327 <

Q PDR l l

l

.. z.

2.0 EVALUATION In their submittal, TVA auested reliaf trom ASME Section XI, IWA-5250(a)(2) which requires, "The source of leakage detected during the conduct of a system

pressure test shall be located and evahated by the owner for corrective measures as follows

repairs or replacemnts of components shall be perfortred in accordance with IWA-4000 or IWA-7000, espectively." The basis for this relief is taken from TVA's submittal to NLC on the MIC Program dated January 20, 1988. This program does not require immediata repairs of leaking components as does the code.

The NRC contractor, Parameter. Inc... throJgn its consultant NOVETECH Corporation, has reviewed the TVA '41C program. The program includes: (1) a surveillance and inspection program to identify leakage, (2) allowable dearadation limits based on maintaining adequate margins against failure, (3)protectionfromleakageofnearbyequipmentimportanttosafeshutdown, (4) repair of leaking welds, and (5) planned implementation of a water treatment program to retard MIC activity.

The staff has reviewed the contractors tecnnical evaluation report (TER) and concurs with the essential findings in the TER. The program acceptance was documented in a safety evaluation report and forwarded by HRC/OSP letter dated March 31,1988 (attached). This letter discusses three additional program items required for NRC acceptance of TVA's MIC program. Additionally, the staff has reviewed the alternate examination recomended by TVA their relief request.

The licensee's submittals include a commitment that prior to initial entry into Mode 4, repair will be accomplished prior to a restart. Following initial entry into Mode 4, the MIC induced leakage will be evaluated by radiographic testing (RT) within 7 days of discovery and compared to established criteria.

If a weld is found with MIC damage that exceeds the screening criteria, that weld will receive further detailed seismic analysis within an additional 7 days. If the detailed seismic analysis determines a we.ld to be structually inadequate, appropriate ERCW Technical Specification (TS) actions will be taken. Sequoyah experience indicates that all welds will be within the screening criteria end, therefore, TS actions should not be required. If the weld is considered to be structurally sound, the leakage is insignificant, and the safe snutdown equipment 13 protected from the leakage, the leak will be scheduled for repair at the next available outage. Leekage rear safe shutd)wn equipment will be collected and drained. The licensee r' Mined the option to remove the system from service and x v ir the ~ecking jo,' . To satisfy this Code requirerrent without relief wet . require shutdown nf the facility and repair of the leaking pipe weldTer.t. This is an unnecessary cycle on the facility anc a burden nn the licensee.

I 3.0 CONCLUSICN Provided the licensee incorporates the three additional spScified items listad in the MIC SER dated March 31, 1988 the staff cnncludes that the licensee's request for relief from certain specific requi7ements of Section XI of the ASME

Code is acceptable. The propcsed alternatives with the three specified '

additional items, if properly implemented, will provide reasonable assurance that the ERCW system is capable of performing its intended safety function.

The staff has determined (1) that relief may be granted pursuant to paragraph 10 CFR 50.55a(g)(6)(1) based on our finding that certain requirements of Section XI of the Code are impractical to perform on Sequoyah Units 1 and 2 during power operetions of the plant, and (2) that granting such relief is authorized by law l and will not endanger life or property, or the common defense and security, and is otherwise in the public interest considering the burden that could result if they were imposed on the facility.

Principal Contributor: D. E. Smith, D. Loveless Dated: May 11, 1988 l

4 I

l

, . - - . - - - - - - - .,._-_.-.,-____-,,.-,,__.,.__,,..g. . , , - ,,,,._,,.-,--,__.-~,c., ,-, _-.v--.. -.--, ,-w,-wy.,r, -,ry

Attachment l

g. ,g UNITED STATES '

'f ,  %,

y '> v. t g NUCLEAR RECiULATORY COMMISSION s, j W ASHING TON, D. C. 20555

. ' ' , ' .* . March 31, 1988 Occket Nos. 50-327/328 Mr. S. A. White Manager of Nuclear Power Tennessee Valley Authority i 6N 38A Lookout Place 1101 Market Street Chattanooga, Tennessee 37402-2801

SUBJECT:

SAFETY EVALUATION OF MICR0 BIOLOGICALLY IHOUCED CORROSION (MIC) ,

PROGRAM Re: laquoyah Nuclear Plant, Units 1 and 2 Sequoyah Nuclear Plant has experienced MIC in pipe walls of carbon steel fire protection piping and in the butt welds of austenitic stainless steel in the essential raw cooling water (ERCW) system. By letter dated January 20, 1987, TVA submitted to the staff a progra'n for MIC control in the ERCW system.

The NRC staff and its contractor, Parameter Inc., hava reviewed the TVA MIC program. The staff concludes that TVA's inspection, evaluation and repair program for MIC of the ERCW system is capable of perfoming its intended safety function. TVA should note that, if leakage should occur in the ERCW piping, the requirements of ASME Code,Section XI shall apply and relief will be required for the interim period in accordance with 10 CP 50.55a.

A copy of the staff Safety Evaluation and the contractor Technical Evaluation Report is enclosed.

Sincerely, kct. eMey W Ck "P Gary G. Zech, Assistant Director for Projects TVA Projects Division Office of Special Projects

Enclosures:

1. Safety Evaluation

2. Technical Evaluation Report cc w/ enclosures:

See next page I

s u u- , t i L) 4 - t- O I2(g.

Mr. S. A. White Sequoyah Nuclear Plant Tennessee Valley Authority cc: Regional Administrator, Region !!

General Counsel U.S. Nuclear Regulatory Comission l Tennessee Valley Authority 101 Marietta Street, N.W.

400 West Sumit Hill Drive Atlanta, Georgia 30323 E11 833 i Knoxville, Tennessee 37902 Resident inspector /SeQuoyah NP i

Mr. R. L. Gridley c/o U.S. Nuclear Regulatory Comission l Tennessee Valley Authority 2600 Igou Ferry Road  ;

Soddy Daisy, Tennessee 37379 SN 157B Lookout Place Chattanooga, Tennessee 37402-2801 Mr. Richard King Mr. H. L. Abercre.mbie c/o U.S. GAO 1111 North Shore Drive j Tennessee Valley Authority Suite 225, Box 194 .

Sequoyah Nuclear Plant Krioxville, Tennessee 37919 ,

P.O. Box 2000  !

Soddy Daisy, Tennessee 37379 Tennessee Department of Health l and Environment  !

Mr. M. R. Harding Director, Bureau of Environtrent Tennessee Valley Authority ATTN:

Sequoyah Nuclear Plant T.E.R.R.A. Buildino, 1st Floor 150 9th Avenue North P.O. Box 2000 Nashville, Tennessee 37219-5404 l Soddy Daisy, Tennessee 37379 Mr. Michael H. Mobley, Director Mr. D. L. Williams Division of Padiological Health Tennessee Valley Authority 400 West Sumit Hill Drive T.E.R.R.A. Building, 6th Floor W10 885 150 9th Avenue North Knoxville, Tennessee 37902 Nashville, Tennessee 37219-5404 County Judge Cr. 'lenry Myers, Science Advisor Hamilton County Courthouse Comittee on Interior Chattanooga, Tennessee 37402 and Insular Affairs U.S. House of Representatives Washington, D.C. 20515

o anow

' (( 4 , Iog UNITED STATES NUCLEAR REGULATORY COMMISSION y w 3

j wassiNotoN. o. c. 2osss l V...../ ENCLOSURE 1 l

SAFETY EVALUATION BY THE OFFICE OF SPECIAL PROJECTS MICROB10 LOGICALLY INDUCED CORROSION (MIC) PROGRAM

TENNESSEE VALLEY AUTHORITY ,

SEQUOYAH NUCLEAR POWER PLANT, UNITS 1 AND 2 j

DOCKET NOS. 50-327 AND 50-328 l l ,

1.0 BACKGROUND

l Sequoyah has experienced microbiologically induced corrnsion (MIC) in the pipe walls of the carbon steel fire protection piping and in the butt welds of stain-less (austenitic) steel in the essential raw cooling water (ERCW1 system. Tt}e two known carbon steel MIC occurrences were in non-safety, stagnant portions * ,

of the fire protection system. TVA has not developed a progran to address  !

MIC for carbon steel piping in the fire system; however, leakage due to MIC in the system is not significant to date.

The stainless steel piping in the ERCW system had been in use for 9 years, i During the 9 years of service,!!!C had occurred at the butt welds in 6-inch I diameter piping. The MIC attack initiated at the inside surface of the welds ar,d degradation occurred in the form of voids that became larger, and deeper, and eventually developed into a throughwall leak. There can be several l fndividual sites on a given weld. The leakage was small and was characterized I as drips or moist areas arounti the butt welds.

l TVA detemined the extent of damage to the ERCW systein by visual inspection l for leaks and performed a sample radiographic inspection of 61 welds, which l

included the 28 leaks visually detected. TVA developed a MIC program for i Se,uoyah based upon the data developed through these inspections. The MIC program and the engineering which formed the basis for the program is I described in TVA's letter dated January 20, 1987. An ongoing investigation l is planned to monitor damage and verify the effectiveness of wate- treatment when the new water treatment program is implemented, j 2.0 TVA'S MIC MITIGATION PROGRAM The NRC contractor, Perameter, Inc., through its consultant NOVETECH Corpor-ation, has reviewed the TVA MIC program. The program include >: (1) a surveillance and inspection program to identify leakage, (2) allowable de radation limits based on maintaining adequate margins against failure, (3 protection from leakage of nearby equipment important to safe shutdown, (4 repair of leaking welds, and (5) planned implementation of a

• vater treatment progra:n to retard MIC activity.

l

-u c;o yVn uIIlln' ' ? Z y l(&;7.

'V

- - - . - - . ,, - - , . ~ . . - - ,, .,----n, . . - - - - - - . , . , , , . - - - - - - ,

a .

2-The contractor, in the attached Technical Evaluation Report (TER), has reached the following conclusions.

1. The screening criterion and associated analysis procedure developed to define allowable MIC degradation is acceptable.

2. The semiannual, weld-by-weld visual inspectien program is adequate te identify leaking welds. The radiographic test (RT) examination to detemine ths extent of MIC degradation in the weld volume subsecuent to leakage detection together with the screening criterion are adequate to assess the margin against failure for upset and postulated failed conditions.

3. Based on the review and evaluation of the licensee inspection, evaluation, and repair program, it is concluded that program implementation provides assurance that adequate safety margins will be maintained provided the program includes the following additional items: (1) at the same time leakage is detected, an assessment is made to ensure the acceptance criterion is net exceeded prior to the scheduled outhge or repair, (2) the frequency of direct visual i inspection of weld specific leaks is increased to monthly, and (3) the leakage fron a leaking weld does not exceed 0.5 gpm and the total leakage from all welds does not exceed 1 gpm.

4 Although the proposed program does not comply exactly with the licensing application of Section XI of the A.iME Code , it forms the basis for an adequate alternative to Code requirerents, and, when combined with the previously recomended additions, provides an I acceptable technical justification for implementation and relief from the exact Code requirements according to 10 CFR 50.55a. (

The staff has reviewed the TER and concurs with the essential findings in the TER. The staff emphasizes that a relief request from the repair requirements of the ASME Code,Section XI is necessary if TVA implements the proposed program in the event that leakage occurs in the ERCW piping. In the relief request, TVA should include the time frame for deviation from the pernar.ent Section XI repair, for example, an outage of sufficient duration to accomplish the repair but no later than the next refueling outage. The request should describe the hardship involved with perfoming an intnediate repair.

In the TER, the contractor states, "Based on a review of the Code, we agree with j the licensee that Section XI does not specifically address evaluation and repair j of defects that are detected at a time other than a regularly scheduled Section XI inservice inspection." When actual flaws are detected in an ASME  ;

Code class component in an operating reactor, the staff expects the licensee to 1 implement the requirements of ASME Section XI. When a throughwall flaw in ASME Class 1, 2, or 3 pressure retaining boundary is discovered by plant per onnel durinn maintenance, the Technical Specifications shall be folicwed and the rules of ASME Section XI should be used for repairs.

1 l

I J

~

TVA has stated it is developing some temporary repair methods for the ERCW stainless steel piping. The use of other than ASME Code repair method- l requires NRC review and approval prior to their implementation.

3.0 CONCLUSION

The staff concludes that TVA's inspection, t. valuation and repair prngram for l MIC for the ERCW austenitic stainless steel piping, if properly implemented, I provides reasonable assurance that the ERCW system is capable of performing its {

intended safety function. However, the staff position is that if leakage should '

occur in the ERCW piping, the requirements of ASME Code,Section XI apply and  ;

relief is required for the interim. period in accordance with 10 CFR 50.55a.  !

Principal Contributor: R. Hermann f Dated:

8 l

s

=- . ,

EN2LOSURE 2 )

= ,

1 .

' EVALUATION OF STRUCTURAL INTEGRITY ANALYSIS FOR  !

AUSTENITIC STEEL WELD 3 WITH MICROBIOLOGICALLY INDUCED CORRO3 ION i

l.0 BACKGROUND Degradation from microbiological 1y induced corrosion (MIC) has girth butt welds in 6-inch ,

been detected in austenitic steelcooling (ERCW) system at l piping of the essential raw water l Sequoyah Nuclear Plant (SQN). The MIC degradation initiates at the pipe inner surface and extends with timeat into the pipe wail.

selected regions I The degradation occurs in the form of voids

, in the weld and produces a porous structure that eventually may leak.

Visual inspection of 385 of the 405 welds in the ERCW system revealed 28 leaking welds that were subsequently repaired. The leakages from the welds were relativelyaround small the andMIC were character-penetration.

ized as dripping water or dampness Radiographic examinations also were performed on a sample of 67 welds (including the 28 leaking welds) to better assess the extent of MIC degradation in the pipe wall. The volumetrid examinations revealed varying degrees of MIC degradation in 61 of the 67 welds.

The licensee, Tennessee Valley Authority (TVA), has evaluated the MIC degradation in the ERCW piping, and has developed a program to ensure the degradation is monitored and controlled and that adequate margins against failure are maintained. This program was described in a January 20, 1988 letter (see Reference 1) and includes: (1) a surveillance and inspection program to identify i

on maintaining leakage, (2) allowable degradation limits based adequate margins against failure, (3) protection from leakage of nearby equipment important to safe shutdown, (4) repair of leaking welds, and (5) planned implementation of a water treat-ment program to retarc MIC activity.

. A description of the TVA program and a technical evaluation of j

that program are presented in Sections 2 and 3, respectively, i

2.0 ?ROGRAM

SUMMARY

, 2.1 Structural Analysis The ERCW piping is ASME Code Class allowable 3 piping.

MIC A structural degradation analysis was performed to define the and was based on maintaining the applied stress less than the Code allowable for Class 3 piping, or FIN: 02101-7-5, Parameter NOVETECH l l

i l .

1 l

, l

C app 5 FS Sh (1) l l

where capp is the applied stress, Sh is the code allowable stress, and i 2.4 for upset FS is the margin and is equal to 1.2 or or faulted conditions, respectively. ,

stress-is determined for the weld specific bending f The applied The degree of l of degradation.

moments, axial load, and levelreduce the pipe cross sectional area and degradation is used to tha computed section modulus, and consequently, to increase ,

applied stress, or (2) l C app * (M/Zr) + (p'Ai )/Ar where  !

capp is the applied stress, M is the resultant bending moment at any specified weld location, determined for any Z r is the reduced section modulus specified degraded weld, p is the pressure, Ai is the pipe flow area, (p.A1 ) is the axial force due to pressure, and ,

the cross sectional area of the pipe cetermined l

A is )

for the degraded weld.

Eq. 2 includes deadweight and primary The bending moment in bending is added for bending for upset conditions; seismic system temperatures are postulated faulted conditions. Because Axial seismic low, thermal stresses were considered negligible.

loads also are negligible and were not included in the applied stress computation.

properties, Zr and Ar , are determined by The reduced section projecting all the degradation regions in the weld onto a plane passing through the centerline of the circumferential weld.

2 NOVETECH

2.2 ' Allowable Degradation Screening criterion Eq. 2 and the results from the RT examination were used to establish a screening criterion to define allowable levels of MIC degradation. The criterion was developed by first computing the ratio SF.S h /C from Eq. 1 using sne stress computed from Eq. 2.

The stresses ah$recomputed using the reduced section properties and area for each of the 61 welds with MIC degradation and the loads associated with the location of maximum nominal stress in the ERCW tystem. This ratio was designated as the reserve factor and was plotted against the total circumferential length of MIC degradation for each associated weld. Allowable flaw lengths are those where the reserve factor is computed to be equal to or greater than 1.0.

The results indicate a linear relationship within a scatter band between reserve factor and total circumferential length of MIC degradation. This relationship indicates an allowable total circumferential flaw length for a reserve factor of 1.0 at the lower bound of the scatter band of about 8.5 to 9.0 inches for upset and faulted conditions, respectively.

2.3 Fracture Mechanics Analysis  !

A finite element fracture mechanics analysis also was performed to demonstrate that adequate margin against failure from MIC degradation exists in the ERCW piping (Ref. 3). The analysis was based on a comparison of the elastic plastic fracture mechanics crack driving force parameter, J-Integral, with the material res.4. stance to crack extension, J at initiation.

The analysis results indicate that a large postulate flaw would not extend at postulated faulted loads.

2.4 MIC Dete'etion During Service Inspection for MIC is based on visual leakage detection and consists of daily walkdowns of accessible areas to assess general plant conditions, and semi-annual, weld-by-weld inspections of the ERCW piping.

2.5 Plant Response to Leakage I Section XI of the ASME Code requires a pressure test at operating  !

pressure to detect defects in Class 3 piping; leaks found during the inspection are to be repaired. The licensee has stated that l Section XI of the Code does not address evaluation and repair of defects that are detected at a time other than a regularly scheduled Section XI inservice inspection (ISI), and has developed a repair program that may or may not require repair I

when leakage is detected.

f 3 l NOVETECH

4 by TVA includes the The response to leakage detection proposed following. If leakage from the ERCW pipe welds is detected If during Modes 5 and 6, repair will be made prior 4, to restart.

the following the leakage is detected during Modes 1,2,3, or action is planned: (1) perform radiographic of (RT) examination of leakage detection, (2) the leaking weld (s) within seven days if the examination exceeds the screening criterion, additional location specific analyses are to be performed and the integrity of the weld is to be reevaluated within seven days to determine adequate margin against failure, (3) if the reevaluation indi-cates the margins are not acceptable the appropriate action will taken according to the Technical, Specifications, (4) if the reevaluation shows acceptable marg!'nsnotand the leakage does not present a personnel hazard or will impact on safe shutdown equipment, the leak will be repaired at the next scheduled refueling.

2.6 Repair Method e

Currently, the planned repair is to replace the leaking weld with j a spool piece. Other options may be evaluated and implemented at a later time. i, -

2.7 MIC Retardation A water treatment program is planned to retard the MIC activity. )

Subsequent to program implementation, MIC degradation will be  ;

monitored to determine the effectiveness of the water treatment l in MIC retardation.

3.0 EVALUATION A review and evaluation of the information provided by TVA in References 1,2, and 3, and summarized in Section 2.0 has been performed; the results of this evaluation are presented in the remaining paragraphs of this section.

3.1 Analysis and screening Criterion The analysis procedure and assumptions used to develop the i screening criterion generally were found to be acceptable. The evaluation determined that use of the reduced section properties l properly account for the increase in applied stress that may i result from the MIC degradation. Although the assumed MIC spacing in Reference 2 was slightly less conservative than that implied by the fracture mechanics analysis in Referente 3, the flaw depth assumption in Reference 2 compensates for the flaw spacing, and, overall, the applied stress computational method is acceptably conservative.

4 NOVETECH

1 .  !

the screening criterion generally will be conser- l Application of  !

vative because it is based on the maximum stress location in the system and a degradation sample that is a reasonable representa-tion of the weld population. Computation of the reserve margin for weld specific loads when leaks are detected also was deter- i mined to be acceptable for defining the limiting condition i

(upset or faulted) and allowable weld specific degradation level.

i Because crack like defects may eventually form at MIC voids, a

fracture mechanics analysis was performed as part of this review 1

to determine the potential for unstable crack extension from MIC and verify the finite element results from Reference 3.

! The analysis was based on a comparison of the elastic plastic  ;

fracture mechanics crack driving force parameter, J-Integral (J), l with the material resistance to crack extension, J at initiation.

The procedures used to compute J follow those described in ,

Reference 4.

I The evaluation was performed assuming a 9-inch long circumferen-tial throughwall flaw and the faulted loads associated with the i

- maximum stress location. The crack length corresponds to a  !

j reserve margin of 1.0 determined from the screening criterion. l

This crack is larger than any likely to exist and was postulated as a very conservative bound (i.e. half of the pipe circumference). Conservative assumptions for material tensile l and toughness properties were used to model the base / weld metal i configuration.

The results from thg analysis indicate an applied J of approxi-mately 325 in-lb./in'. This compares tg material resistance to crack extension of about 500 in-lb./in , which is limiting for austenitic steel welds generally (see Ref. 5). These results and 7

i j the analysis assumptions demonstrate that large flaws will not

extend under postulated faulted loading and that the screening j criterion developed by the licensee is conservative.

j 3.2 Leakage Detection and Response i

The planned semi-annual, weld-by-weld visual inspection has been i evaluated and is judged acceptable based on the inspection frequency and inspection of individual welds where the insulation around the welds is removed and the welds will be visible during the inspection. Because the nature of the degradation is such that rapidly developing, significant leakage likely will not occur, and prior experience at SQN indicates small leaks can bo

detected, more frequent or additional inspection methods are not

required to determine piping integrity prior to leakage being j observed. Following leakage detection, the RT examination shoulc i be adequate to assess the degree of degradation in the weld volume, a

1 5

,i i NOVETECH l

, . ~ - - - - - - - - - . - - - . - - . - - - , . - - - - - . . - - - _ - . _ _ , , , , - - , _ - _._,,-..-_w,_,.-mnn-,.-,,.--n..

- ,--n-

ass d on c rovicw of the Codo wo agroo with Section XI does not specifically address evaluation tho licensee that defects that are detected at a time other and repair of scheduled Section XI inservice inspection. than a regularly application of the Code in the However, licensing that any Technical Specifications assumes inspection where degradation is detected is part of the approved ISI program and that Section XI evaluation and repair i requirements are acplicable. This application procedure  !

indicates that leakage from MIC degradation in the ERCW piping must be repaired to comply with the Code requirements.

However, our review i

indicates that the inspection, evaluation, and repair program developed by the licensee forms an adequate the basis for weld can remain alternative to code requirements, and in service subsequent to reevaluation provided that a leaking the following additional items are contained in the licensee's programt (1) at the time leakage is detected an assessment is made to ensure the acceptance criterion is not exceeded the scheduled outage or repair, (2) the frequency of theprior direct to visual inspection of weld and (3) the leakage from a leaking weld specific leaks is increased to monthly, and the total leakage does not exceed 0.5 gpm j from all welds does not exceed 1.0 gpm.  ;

This alternate program provides an acceptable technical basis for , I reitef frem exact Code requirements according to 10CFR50.55(a).

• 3.3 Repair Method Replacement  !

of leaking welds using spool pieces is generally accepted practice acceptable procedures and is preferred for this application, provided for welding austenitic steel are followed.

Other type repairs reviewed to ensure significant that may be considered in the future should be on the overall integrity of the ERCW system. numbers of repairs do not impact

4.0 CONCLUSION

S

1. The screening criterion and associated analysis procedure are acceptable.

developed to define allowable MIC degradation ,

l l

2. l The semi-annual, weld-by-weld visual inspection program is adequate to identify leaking welds. The RT examina-t' tion to determine the extent of MIC degradation in the weld volume subsequent to leakage detection together with the screening criterion are adequate to assess the  !

l margin conditions.

against failure fcr upset and postulated faulted l

6  !

NOVETECH l

l l

..'e

3. Based on the review and evaluation of the licensee inspection, evaluation, and repair program, it is concluded that program implementation provides assurance that adequate safety margins will be main-tained provided the program includes the following additional items: (1) at the time leakage is detected an assessment is made to ensure the acceptance criter-ion is not exceeded prior to the scheduled outage or repair, (2) the frequency of direct visual inspection of weld specific leaks is increased to monthly, and (3) the leakage from a leaking weld does not exceed 0.5 gpm and the total leakage from all welds does not exceed 1.0 gpm.

4. Although the proposed program does not comply exactly with the licensing application of Section XI, it forms the basis for an adequate alternative to Code require-ments, and, when combined with the previously recommended additions, provides an acceptable technical justification for implementation and relief from the exact code requirements according to 10CFR50.55(a).

5.0 REFERENCES

1. R. Gridley, Tennessee Valley Authority, "Sequoyah Nuclear Plant (SQN) Units 1 and 2 - Microbologically Induced corrosion (MIC) Program," January 20, 1988, Docket Nos. 50-327 & 32S

2. TVA-DNE Calculation CEB-CQS-355, RO, "Stress Evaluation of MIC Damage in ERCW 6-Inch Stainless Steel Girth Butt-Welds," December 15, 1987 (B41 871215 006).

1

3. TVA7 Westinghouse Presentation, "Fracture Mechanics ,

Evaluation of MIC Degraded Austenitic Steel Welds", i Bethesda MD, January 4, 1988.

4. A. Zahoor, "Evaluation of J-Integral Estimation Scheme for Thtoughwall Flawed Pipes," Nuclear Engineering and Design 100 (1987) pp 1-9, North Holland Publishing.

5.Section XI Task Group for Piping Flaw Evaluation, l "Evaluation of Flaws in Austenitic Steel Piping, Report l NP-4690-SR, Electric Power Research Institute, Palo l Alto, CA, July 1986.

7 NOVETECH i