ML20206B479

Requests Exemption from GDC 57 Re Reactor Containment - Closed Sys Isolation Valves,As Described in 10CFR,App a for Containment Penetrations M393 & M261.Detailed Technical Evaluation & Justification for Exemption Request,Encl

ML20206B479
Person / Time
Site:	Mcguire, McGuire
Issue date:	04/20/1999
From:	Barron H DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9904290258
Download: ML20206B479 (6)

Text

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., Duka Energy C:rpor:ti:n McGuire Nudear Station 12700 Hagers Ferry Road Huntersvale, NC 28078-9340

• " (704) 875-4800 OTHCE (704) 875-4809 MX April 20, 1999 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555-0001

Subject:

Duke Energy Corporation McGuire Nuclear Station, Unit 1 and Unit 2 Docket No. 50-369/50-370 Request for Exemption from 10 CFR 50, Appendix A, General Design Criteria 57 for Containment Penetrations M393 and M261 McGuire Nuclear Station requests exemption from General Design Criteria 57, Reactor Containment - Closed System Isolation Valves, as detailed in j 10 CFR 50 Appendix A for contatinment penetrations M393 and M261. This request is specific to two lines which branch off these main steam l piping penetrations and supply steam to the Turbine Driven Auxiliary I Feedwater Pump. Each of these lines contains isolation valves which do not meet the requirements of General Design Criteria 57. However, since special circumstances are present as defined in 10 CFR 50.12(a)(2), ,

McGuire believes that an exemption to the General Design Criteria 57 requirements is warranted to ensure these valves can fulfill their Engineered Safety Functions of providing auxiliary feedwater and //

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containment isolation.

Containment. penetrations M393 and M261 are main steam line containmen penetrations associated with Steam Generators "B" and "C" respectively.[j Outside containment and prior to their respective Main Steam Isolation Valve, a branch line from each of these main steam lines provides steam to the Turbine Driven Auxiliary Feedwater Pump through isolation valves SA-1 and SA-2 respectively. In addition, steam drain lines tie into these same branch lines through valves SA-77 and SA-78 respectively.

Since the main steam lines associated with penetrations M393 and M261 are not part of the reactor coolant pressure boundary nor connected  !

directly to the containment atmosphere, General Design Criteria 57

. requires that SA-1, SA-2, SA-77, and SA-78 be either automatic, or  ;

locked closed, or capable of remote manual operation. However, these '

valves do not satisfy the General Design Criteria 57 requirements since  !

they are locally operated, locked open, manual valves. The locked open feature ensures that the Auxiliary Feedwater System can perform its safety function of maintaining Steam Generator levels following certain Om 9904290258 990420 3 PDR ADOCK 05000369 PDR

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." l U.S. Nucicar Regulctory Commiccicn Document Centrol Desk April 20, 1999 Page 2 of 2 plant events. From a Probabilistic Risk AsscMament standpoint, providing this function is more risk significant than the safety function of containment isolation. The containment isolation function for SA-1, SA-2, SA-77, and SA-78 is satisfied by Emergency and Abnormal Operating Procedures which direct plant operators to close these valves when plant conditions warrant. Adding automatic or remote operation capabilities to these valves to ensure they perform their containment isolation function may introduce a new failure mode which could increase the consequences of an accident.

Based on the above, the requested exemption from the requirements of I General Design Criteria 57 will ensure the more safety significant function of auxiliary feedwater is provided while allowing for operator action to satisfy the containment isolation safety function. Upon NRC approval of this request, the McGuire UFSAR will be revised to identify SA-1, SA-2, SA-77, and SA-78 as containment isolation valves exempted from General Design Criteria 57. The NRC has reviewed a similar exemption request submitted on September 2, 1997 by the Catawba Nuclear Station. That request was approved by the NRC in a Safety Evaluation Report issued on December 29, 1998.

Attached is a detailed technical evaluation and justification for this exemption request. Please contact Julius Bryant at 704-875-4162 with any questions.

Very truly yours, H. B. Barron, Jr.

Attachment cc: L. A. Reyes .

U.S. Nuclear Regulatory Commission Region II Atlanta Federal Center 61 Forsyth St., SW, suite 23T85 Atlanta, GA 30323 F. Rinaldi U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Washington, D.C. 20555 S. Shaeffer NRC Resident Inspector McGuire Nuclear Station

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, Attachment Page 1 of 4 Technical Evaluation-and Justification for an Exemption to General Design Criteria (GDC) 57 GDC 57 Reauirements GDC 57, Reactor Containment - Closed System Isolation Valves, states that:

"Each line that penetrates primary reactor containment and is neither part of the reactor coolant pressure boundary nor connected directly to the containment atmosphere shall have at least one containment isolation valve which shall be either automatic, or locked closed, or

capable of remote manual operation. This valve shall be outside i

containment and located as close to the containment as practical. A simple check valve may not be used as the automatic isolation valve."

-General Description of Eauipment (Reference Attached Sketch) '

i Containment penetrations M393 and M261 are associated with the Main Steam (SM) lines for Steam Generators (SG) "C" and "B" respectively.

l These steam lines penetrate primary reactor containment and are not part of the reactor coolant pressure boundary nor connected directly.

to the containment atmosphere. Therefore, penetrations M393 and M261 meet the criteria for GDC 57 applicability. Outside of containment and prior to the respective Main Steam Isolation Valve (MSIV), a branch line comes off the SM line associated with.each of these 1 l penetrations. These branch lines form part of the Main Steam to l Auxiliary Equipment System (SA) used to supply steam to the Turbine I

Driven Auxiliary Feedwater (TDCA) Pump. Each-of these lines contains a manual isolation valve (SA-1 and SA-2), a drain valve (SA-77 and SA-78), and a check valve (SA-5 and SA-6). Downstream of these valves, the two SA lines join together prior to reaching the turbine for the TDCA Pump.

Valves SA-1, SA-2, SA-77, and SA-78 are locally operated, locked open, manual gate valves. Valves SA-5 and SA-6 are stop check valves. All of these valves are located in the Interior Doghouse which is a safety related building next to the Reactor Building. The piping and supports for SA-5 and SA-6 are procured and maintained to meet ASME Class II (Duke Class 3) standards. Therefore, they are of acceptable construction to extend.the respective penetration beyond valves SA-1 and SA-2 to include SA-5 and SA-6.

Valves SA-1, SA-2, SA-5, SA-6, SA-77, and SA-78 perform the safety related function of providing a high quality steam _ supply to the TDCA Pump turbine. Consequently, McGuire Technical Specification (TS)

'3.7.5, " Auxiliary Feedwater System", requires SA-1, SA-2, SA-77, and i SA-78 be open and'SA-5 and SA-6 be capable of opening for Engineered Safety Features (ESF) operation of the TDCA Pump. TDCA Pump operation can continue with one manual isolation valve (SA-1 and SA-2), or one drain valve (SA-77 and SA-78), or one stop check valve (SA-5 and SA-6) in the same SA line closed provided that high quality steam is available'to the TDCA Pump through the other SA line.

' Attachment Page 2 of 4 Valves SA-1, SA-2, SA-77, and SA-78 are not identified in any TS's or

,the McGuire UFSAR as Containment Isolation Valves. However, they perform the safety related function of containment isolation so the requirements of GDC 57 are applicable. Upon NRC approval of this exemption request, the McGuire UFSAR will be revised to identify SA-1, SA-2, SA-77, and SA-78 as containment isolation valves exempted from General Design Criteria 57.

Evaluation and Justification SA-1, SA-2, SA-77, and SA-78 do not meet the criteria of GDC 57 since they are locally operated, locked open, manual valves. The locked open feature ensures that the Auxiliary Feedwater (CA) System can perform its safety function. From a Probabilistic Risk Assessment (PRA) perspective, the TDCA Pump is one of the most risk significant safety system components. Consequently, SA-1, SA-2, SA-77, and SA-78 are administrati.vely locked open to ensure the reliability of CA.

The containment isolation function for SA-1, SA-2, SA-77, and SA-78 is satisfied by the use of station Operating Procedures (OP's), Emergency Operating Procedures (EP's) and Abnormal Operating Procedures (AP's).

OP's direct plant operators to close these valves when operation of the TDCA Pump is no longer necessary or desired. EP's and AP's provide for closure of SA-1, SA-2, SA-77, and SA-78 under accident conditions when isolation of one of the SA steam supply lines to the TDCA Pump is necessary.

The two UFSAR analyzed accident scenarios requiring the isolation of one SA steam supply are a Steam Generator Tube Rupture (SGTR) and a Main Steam Line Break. For the SGTR scenario, failure to isolate the steam supply to the TDCA Pump from the SG with a ruptured tube would allow a release of main steam to the atmosphere via the TDC1. Pump turbine exhaust. Consequently, depending on which SG has experienced the tube rupture, station procedures direct operators to close SA-1, SA-77, SA-2, and SA-78 as applicable. The time required for an operator to close the applicable SA valve has been estimated and factored into the accident analyses and dose calculations which show that the calculated off-site doses are within allowable values. In the case of a Main Steam Line Break, failure to isolate the steam supply to the TDCA Pump would divert steam flow from the intact steam line to the faulted piping effectively depressurizing a second SG.

This would render the TDCA Pump inoperable due to a loss of sceam supply and also affect the operation of the Motor Driven Auxiliary Feedwater Pumps. Therefore, depending on the break scenario, SA-5 and SA-6 (stop-check valves) are designed to automatically close to prevent a diversion of steam from the second SG to the faulted piping.

In addition, station procedures provide the option of closing SA-1, SA-2, SA-77, and SA-78 as applicable following a steam line break as a precaution in the event SA-5 and SA-6 fail to close.

Note that station procedures provide the option to manually close stop-check valves SA-5 or SA-6 to isolate one SA steam supply if closing SA-1, SA-2, SA-77, and SA-78 was unsuccessful. The use of SA-1, SA-2, SA-77, and SA-78 is preferred since they are closer to containment and can be closed in a shorter time than SA-5 and SA-6.

Based upon the above, the use of SA-1, SA-2, SA-77, and SA-78 in L .

1 o Attachment Page 3 of 4 satisfying the containment isolation function is preferred over SA-5

'and SA-6 cince they better meet the intent of GDC 57.

Conclusion Approval of this request for exemption to GDC a7 will not have an adverse impact on the health and safety of the public. This exemption will ensure the more safety significant function of auxiliary feedwater is provided while allowing for operator action to satisfy the containment isolation safety function. Note that adding automatic or remote operation capabilities to SA-1, SA-2, S A ",' 7 , and SA-78 to ensure they perform their containment isolation function may introduce a new failure mode which could increase the consequences of an accident.

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