ML20028H369

Forwards Request for Relief from ASME Section XI Requirements to Repair Noncode Class 2 Component, Specifically 3/4-inch Vent Line on Main Steam Line a Between Main Steam Trip Valve & Nonreturn Valve

ML20028H369
Person / Time
Site:	North Anna
Issue date:	12/21/1990
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
90-772, NUDOCS 9101020141
Download: ML20028H369 (10)

Text

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UHOINIA Ei.isCTHIC AND POWl:H COMI%NY H Wit M OND, YI HOINI A 20201 December 21,1990 U.S. Nuclear Regulatory Commission Serial No. 90 772 Attention: Document Control Desk NL&P/JBL:jbl R2 Washington, D.C. 20555 hkei No. 50 339 License No. NPF 7 Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNIT 2 ASME SECTION XI REllEF REQUEST TEMPORARY NON CODE REPAIR TO A CLASS 2 COMPONENI Pursuant to 10 CFR 50.55s(g)(5), relief is requested from certain Code requirements described in IWA 4000 and IWC 4000 of ASME Section XI,1983 Edition, Summer 1983 Addenda. The relief request is associated with a temporary non Code repair of a 4 3/4 inch vent line on the "A" main steam line between the. main steam trip valve and the non return valve outside of containment for North Anna Unit 2.

The temporary repair is an engineered, mechanical (bolted in place) enclosure filled ,'

-with a hardened liquid sealant. The mechanical enclosure is desigt.ed for the pressure / temperature rating of the main steam system. The enc!osure is fabricated

.from safety related materials and designed for the high temperature service to which it

is exposed.- The location of the flaw and the size of the pipe do not require an extensive, better than " leak stop' repair.

l A " Code" repair, in accordance with ASME Section XI, requires the removal of the flaw and _a subsequent weld repair. A Code repair is the practical procedure during a scheduled unit shutdown.- However, this flaw was detected during plant oporation and

-the plant would have to be shut down to perform a Code repair. Therefore, to avoid a plant shutdown and to limit the leakage from the p'n hole leak,- we used a temporary non Code (stop leak type) repair.

Pursuant to 10 CFR 50.55a(g)(G)(l), the Commission will evaluate determinations of

' impracticality, and may grant relief. We request that the temporary non Code repair described above-remain in place and the NRC grant specific relief from the Code requirements for this case. The engineered, temporary repair enclosure is intended to be utilized until the first opportunity for completion of a Code repair. The temporary e  ; repair will be removed and the flaw will be repaired in-accordance with the Code requirements during the next schedulad refueling outage 'or other outage of sufficient duration to effect the repair.

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In support of this request, a discussion of the background information, a description of the temporary repair, the specific relief request, and the measures being used to ennure structural integrity are provided in Attachment 1. Because the repair was parformed withcot prior NRC approval, a safety assessment and a discussion of the corrective measures necessary to prevent recurrence of this error are also provided (in Attachment 1). Reference sketches are provided in Attachment 2.

This repair is not considered an operations issue or a nuclear safety issue. Instead, due to the small size and location of the flaw, the repa r is considered more of an interim measure to prevent personnW injury.

This relief request for North Anna Unit 2 ics been reviewed and approved by the '

Station Nuclear Safety and Operating Committee.

Should you have any questions or require additional information, please contact us.

Very truly yours,

/ to , 'D M, L. Stewart Senior Vice President - Nuclear Attachments ec: U.S. Nuclear Regulatory Commission Region ll -

101 Marietta Street, N.W.

D11te 2900 Atlanta, Georgia 30323 Mr. M. S. Lesser NRC Senior Resident inspector North Anna Power Station I

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Attachment 1 2: ,

i ASME Ses cti.:7 XI Rellef Request Temporary ' Non Code Repair.-

to the Main Steam Piping Vent Line j .

North Anna Unit 2:

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4 ASME Section XI Relief Request j Temporary Non Code Repair

- to the Main- Steam Piping Vent Line North Anna Unit 2 l

Backaround InfoImhtlon Section XI of the ASME Boller and Pressure Vessel Code specifies the rules and requirements for insurvice inspection uf nuclear power plant components. These rules and requirements identify, in part, the areas subject to inspection, the examination methods and procedures to be used for the inspection, the inspection frequency, and the procedures for evaluation and disposition of the inspection results, in addition, the

, Code provides the rules and requirements for repairs and replacements.

Implementaticn ci ASME Section XI requires the preparation of an inspection plan.

Primarily, the Code required inspections, examinations, and repairs are performed in accordance with the inspection plans and are performed while the unit or system is shutdown, On June 15,1990, the NRC issued Generic. Letter 90 05, "Guldance for Performing Temporary Non Code Repair of ASME Code Class 1,2, and 3 Piping," This Generic Letter describes the NRC staff's position on temporary non Code repairs to ASME Code piping. -The Generic Letter states that _1) a Code repair is required to r" store the structural: Integrity of flawed ~ASME_ Code piping and 2) a Code repair D required independent of the operational mode of the plant when the flaw is detected. However, the required Code repair may be impractical for a flaw detected during plant operation 4

unisGs the facility is shut down.

The-Generic Letter also stated that, for Code Class 1 and 2 pipingi the licensee is required to perform Code _ repairs or reques'. NlC to grant relief for temocrary non-Code repairs'on a case by case basis regardless-of pipe size, Temporary non Code repairs of C_ ode Class 11 and 2 piping must heve load bearing capability similar to that provided by '_ engineered = weld overlays or engineered mechanical clamps. - The-Generic Letter further specifies that licensee requests based on repairs such as -

-encapsulation:of leaking pipes in cans using liquid sealants, clamps with rubber gaskcting, or non engineemd weid overlays (patches) will not be approved by'the

, staff.1

= NUNIARC has? identified several general concerns raised by the industry with respect to. Generic' Letter 90 05; One of these concerns and probably the most important concern is that the Generic Letter appears.to require a utility to prepare, submit, and -

1 receive NRC approval of regulatory relief under 10 CFR'50.55a(g), prior to undertaking

the' actual temporary leek repair, which could result in prolonged operation with the leaking condition.

With regard to this concern, the NRC determined a need to issue additional guidance u

which prcvides that " stopgap": measures may be used to-repair a leak while a utility

' goes through'th_e process of obtaining advance NRC aporoval for the temporary ;non-Code repair, Thb, guidance is in response to licensee fesdback-to NRC relative to the adverse = operational impacts of-delaying the-leak repair-whlle the NRC advance 5 -- , 3- * . y

approval is in process. The additional NRC guidance was provided in a letter of August 16,1990, from NRR to NRC Regional officiak. The " stopgap" measures outlined in the adoitional guidance apply to moderaS energy ASME Class 3 piping systems only. The measures must be reversibt and must not affect the structural integrity of the flawed piping. The additional guidance provides that, if the planned 1.'n-Code repair fits these criteria, it may be ampleted prior to NRC approval.

We are also aware of a draft ASME Codt case, currently in process under the Section XI Subcommittee, which would incorp) rate requirements similar to those of the Generic Letter into the ASME Code, but would obviate the need for NRC approval of a temporary repair. This draft Code case would have to be approved by ASME and subsequently accepted bv NRC prior to implementing it as part of a repair and replacement program.

Descriotion of the Tomocrarv Non Code Reoair On November 11,1990, we made a temporary non Code (stop leak type) repair to an ASME Section XI Code Class 2 component. Valve 2 MS 502 is a 3/4 inch vent valve on the "A" main steam line. The vent line is located between the main steam trip valve and the main steam non return valve. There is a " pin hole" leak in the pipe to-elbow weld at the inlet to the elbow located upstream of Valve 2-MS-502. The 3/4-inch pipe at the point of the flaw can not be isolated from the main steam line. A sketch of the location of the flaw is provided in Attachmont 2.

,,te tempt : y repair is an engineered, mechanical (bolted in-place) enclosure filled with a hananed ilquid sealant. The mechanical enclosure is designed for the pressure / temperature rating of the main steam system. The enclosure is fabricated from safety related ASTM materials and designed for the high temperature service to which it is exposed. The enclosure is designed and constructed to act as a pressure boundary only. An evaluation / calculation has been performed by engineering and it was concluded the seismic integrity-of the system is maintained with the enclosure installed, A sketch of the mechanical enclosure is provided in Attachment 2.

The location of the flaw and the size of the pipe do not require an extensive, better than " leak stop" repair, in-addition, engineered weld overlays are not a viable opt'on as a temporary repair because the main steam line can not be isolated.

Relief Reauest Pursuant to 10 CFR 50.55a(g)(5), relief is requested from certain Code requirements described in IWA 4000 and IWC-4000 of ASME Section XI,1983 Editic>n, Summer 1983 Addenda, associated with a tempora y non Code repair of a 3/4-inch vent line df the mair. steam line between the "A" main steam trip valve and the non-return valve outside of containment for North Anna Unit 2.

Article IWA-4000 of _Section XI of the ASME Code describes the Code repair precedures. A Code repair requires the removal of the flaw and a subsequent weld repair. The repair weld is subject to post repair nondestructive examination and a post epair pressure test may also be required. A Code repair is the practical procedure during a scheduled unit shutdown. However, this flaw was detected during plant operation and the plant would have to be shut down to perform a Code repair.

To avoid a plant shutdown and to limit the leakage from the pin-hole leak, we used a temporary non Code (stop leak type) repair by enclosing the leaking elbow in an engineared " box" and using a liquid sealant to fill the box. g Pursuant to 10 CFR 50.56a(g)(6)(l), the Commission mill evaluate determinations of impracticality, and may grant relief. We request that .ne temporary non Code repair described above remain in place and the NRC grant specific relief from the Code requirements. The engineered, temporary repair enclosure is intended to be utilized until the first opportunity for completion of a Code repair. The temporary repair will be j removed and the flaw will be repaired in accordance with the Code requirements  ;

during the next scheduled refueling outage or other outage of sufficient duration to effect the repair.

This repar is not considered an ope:ations issue or a nuclear safety issue. Instead, due to the small size and location of the flaw, the repair !s considered more of an interim measure to prevent personnel injury.

4 Measures to Ensure StructuralIntegrity Routine surveillance will ensure continued structural integrity of the engineered enclosure on the 3/4 inch une to verify that there is not excessive steam leakage or weeping.

Safety Assessment An evaluation of this temporary non Code repair has been performed with respect to the UFSAR safety analysis for a main steam line break outside containment. The s safety analysis assumes a much greater leakage path than would be created by the catastrophic failure of this 3/4 inch line or the failure of the mechanical enclosure. 5 Therefore, the safety analysis remains bounding.

Because this was a " pin hole" leak in the newly vselded joilt of a small diameter pipe, the unit should not be required to shut down to effect a Code repair. The pipe / elbow encicaure is adequately designed to serve as a temporary pressure boundary until the next scheduled refueling outage or other cutage of sufficient duration.

, - Corrective Measess The temporary non-Code repair to the ASME Section XI Class 2 pipe was performed on November 11,1990. On December 6,1990, the repair was identified as not having been-approved by the NRC prior to work being performed. When identified, a deviation report was submitted. As a corrective action to ensure this error does not reoccur, the station procedures are being revised to require that all temporary repair procedures on ASME' Code Class systems will be reviewed by station inservice inapt son personnel for applicable Code requirements.

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h Conclusion

-The temporary repair to the 3/4 inch pipe does not effect the performance of the main steam line or the valve (2-MS 502). It is our determination that the engineered, temporary repair is adequate as a pressure boundary in this application. Therefore, it is not necessary to shut ocwn the unit to effect a Code repair.

Although we were not timely ia requesting this relief, the temporary repair to the leak does provide the most reasonable solution to this problem during power operation.

This relief request for North Anna Unit 2 been reviewed and approved by the Station Nuclear Safety and Operating Comraittee.

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Attachment 2

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Sketches;of -the Temporary Non Code' Repair, to the Main Steam Piping Vent Line

North Anna Unit 2 -

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ra,3 Temporary Non Code Repair Location of Leak Valve 2-MS-502 3/4" Vent Line b

Insulation jl (5") i 12 1/2" 2"

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Location of Leak e 8"  ;

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, Temporary Non Code Repair Clamp (Bolted-lh place Enclosure)

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