ML20207A874

Draft Response to NRC Telcon Re Licensee Request for Approval of LBB Evaluation in Support of Elimination of Augmented Insp Program on RCS Loop Bypass Lines.Response Justifies Use of Less than One Gpm Detectable Leakage Rate

ML20207A874
Person / Time
Site:	North Anna
Issue date:	02/25/1999
From:	Christian D VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
99-103, NUDOCS 9903050291
Download: ML20207A874 (5)

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U.S. Nuclear Regulatory Commission Serial No.99-103 Attention: Document Control Desk NL&OS/ETS RO Washington, D.C. 20555 Docket Nos. 50-338 50-339 License Nos. NPF-4 NPF-7 Gentlemen:

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VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2.

REQUEST FOR ADDITIONAL INFORMATION - LEAKAGE INSTRUMENT SENSITIVITY FOR LEAK-BEFORE-BREAK APPLICATION -

REACTOR COOLANT LOOP BYPASS LINES In a June 23,1998 letter (Serial No.98-013), Virginia Electric and Power Company requested review and.appro"al of a leak-before-break evaluation in support of the elimination of the augmented inspection program on the Reactor Coolant System (RCS) loop bypass lines. The augmented inspections were required in lieu of modifications, which would have consisted of installed pipe whip restraints or barriers to prevent damage to surrounding equipment, should the reactor coolant piping fail.

During a recent teleconference'callwith the NRC Staff concerning the application of the 1

- leak-before-break (LBB) evaluation, the reviewer stated that in his opinion the required margin for crack stability was not justified for a 10 gpm crack assuming a one gpm RCS leakrate detection sensitivity. Therefore, the Staff requested additionalinformation to justify the use of a less than one gpm' detectable leakage rate to_ establish the required

'q margin for crack stability in the LBB analysis. The attachment to this letter provides the requested information ~and discusses our compensatory actions if the detection systems become unavailable.

The attachment establishes that North Anna's containment leakage monitoring systems have the ability to detect leakage in the 0.5 gpm threshold range. Therefore, LBB can be established by examining stability of a crack associated with 5 gpm leakage. Based on our evaluation submitted earlier for a crack associated with 10 gpm leakage and our i

ability _to detect 0.5 gpm, we believe that required margin exists for demonstration of i

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t LBB methodology. Thus, the demonstration of our ability to detect a for the augmented inspection program on the re A similar approach using increased RCS leakage monitoring sensitivity of less than a 1 gpm detectable leakage rate to establish the required m stability was used by Rochester Gas and Electric Corporation in letters da September 16,1998 and December 7,1998.

i If you need any additionalinformation, please contact us.

Very truly yours, l

D. A. Christian Vice President-Nuclear Operations Commitments made in this letter:

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There are no new commitments in this letter.

- Attachment U.S. Nuclear Regulatory Commission ec:

Region 11 Atlanta Federal Center 61 Forsyth Street, SW Suite 23T85 Atlanta, Georgia 30303 Mr. M. J. Morgan NRC Senior Resident inspector North Anna Power Station

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Attachment l

.l Requested information on Reactor Coolant System Leakage Detection System Sensitivity j

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Virginia Electric and Power Company North Anna Power Station Units 1 and 2 i

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L JEB:,-25'.99tTiiW10:49 VA POER-NLkP TEL:8042733582 P.005 Requested Information on Reactor Coolant System Leakage Detection System Sensitivity j

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Background

An evaluation of the Reactor Coolant System leakage detection capabilities has b i

L performed for North Anna. Past events were analyzed to determine the response the containment particulate monitors. These events, documented in LERs 50-339/91-011-00 8, 50-338/91-011-00, demonstrate that the. count rate'on the containment particulate radiation monitors (1-RM-RMS-159 and 2-RM-RMS-259) will roughly do with a 0.5 gpm leak. The containment gas radiation monitor responses (1-RM-RMS-160 and 2-RM-RMS-260) are also supplied for information.

North Anna Unit 2,11/3/91 (LER 50-339/91-011-00)- Packing Leak on 2-RH-MOV-2700.

The leakage was estimated at 24.9 gpm. 2-RM-RMS-259 increased from

' 4,000 cpm to 500,000 cpm. 2-RM-RMS-260 increased from 500 cpm to 2,500 cpm.

North Anna Unit 1, 5/11/91 (LER 50-338/91-011-00) - The RTD bypass manifold valves were leaking.

The leakage was estimated at 0.4gpm.

1-RM-RMS-159 increased from 4,000 cpm to 9,000 cpm.1-RM-RMS-160 increased from 300 cpm to 500 o

l epm. It should be noted that the unit later reduced power from 98% to 30%,

and the leakage increased to 0.7 gpm due to a failure of the B" cold leg loop stop valve disc pressurisation line.

Radiation Monitoring System Availability The containment airbome radiation monitors are required to be operable in modes 1 through 4 by Technical Specifications 3.3.3.1 and 3.4.6.1. Their performance is also tracked by the Maintenance Rule.

In addition to the containment radiation monite,rs, the containment sump level system i also capable of detecting smallleak rates. In the two RCS leakage events described above, the containment sump level was the parameter that first prompted operator action to investigate for increasing RCS leakage. The containment sump level system

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is calibrated and verified to be accurate for determining leak rates to < 0.15 gpm.

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Technical Specifications Operability Requirements I

Technical Specification (TS) 3.4.6.1 requires both the containment atmosphere particulate and gaseous radioactivity monitoring system, and the containment sump

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level and discharge flow measurement system to be OPERABLE w greater. than 200'F.

In addition, Technical Specification 3.3.3.1 Containment Particulate and Gaseous Radiation Monito requires the 1 through 4.

Per Te.chnical Specifications, with one of the leakage detection sys operation may continue for up to 30 days provided that a RCS leakrate c performed at least once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Otherwise, the plant is required t 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. If both systems were to become inop be required to shut down to HOT STANDBY in 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />.

Based on the ability of either RCS leakage detection systems to detec at -approximately 0.5 gpm, and the associated Technical Specifications statements, the existing instrumentation is adequate to ensure that a le system with adequate sensitivity will be operable when the plant is above 2 l

leakage monitoring systems are inoperable.Therefore, no a Conclusion The information supplied above demonstrates the ability of the North An containment leakage detection systems to detect leakage in the 0.5 gpm th range. Therefore, LBB can be established by examining stability of a crack as with 5 gpm leakage. Based on'our evaluation submitted earlier for a crac with 10 gpm leakage and our ability to detect 0.5 gpm, we believe th exists for demonstration of LBB methodology. Thus, the demonstratio

- detect a 0.5 gpm leak rate provides sufficient basis for approval of the

. reduce inspection requirements for the augmented inspection program on coolant loop bypass lines.

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