ML20209E762

Provides Addl Info to Justify Use of Less than One Gpm Detectable Leakage Rate to Establish Required Margin for Crack Stability in LBB Analysis,Per 980623 Application on Reactor Coolant Loop Bypass Lines

ML20209E762
Person / Time
Site:	North Anna
Issue date:	07/09/1999
From:	Christian D VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
99-331, NUDOCS 9907150144
Download: ML20209E762 (5)

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VIRGINIA EI.ECTRIC ANI) POWER CmWANY Ricaistmi), Vincisia 232r,i July 9, 1999 l

u U.S. Nuclear Regulatory Commission Serial No.99-331 Attention: Document Control Desk NL&OS/ETS R2 Washington, D.C. 20555 Docket Nos.

50-338 50-339 License Nos.

NPF-4 NPF-7 i

Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPANY l

NORTH ANNA POWER STATION UNITS 1 AND 2 REQUEST FOR ADDITIONAL INFORMATION LEAK DETECTION SYSTEM SENSITIVITY FOR LEAK-BEFORE-BREAK APPLICATION ON REACTOR COOLANT LOOP BYPASS LINES l

in a June 23,1998 letter (Serial No.98-013), Virginia Electric and Power Company requested review and approval 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 teleconference call with the NRC Staff concerning the application of the leak-before-break (LBB) evaluation, the reviewer stated that stability of a 10 gpm size crack could not be justified using standard NRC methodology. Consequently, a one gpm f

RCS leakrate detection sensitivity can not provide the required margin for LBB analysis.

The Staff requested additional information to justify the use of less than one gpm

' detectable leakage rate to establish the required margin for crack stability in the LBB analysis.

The attachment to this letter provides the requested information and discusses our compensatory actions if the containment leak detection systems become unavailable.

The attachment establishes that North Anna's containment leak detection monitoring system has the ability to detect leakage down to the 0.5 gpm within an hour threshold kO O range consistent with the assumptions for source term of Regulatory Guide 1.45.

Therefore, LBB can be established by examining stability of a crack associated with 5 gpm leakage. Based on the evaluation submitted earlier for a crack associated with 10 gpm leakage and the ability to detect 0.5 gpm leak within an hour, we believe that the required margin exists for demonstration of LBB methodology.

9907150144 990709 PDR ADOCK 05000338 P

PDR m

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i A similar approach using increased RCS leakage monitonng sensitivity to justify the use of less than a 1 gpm detectable leakage rate to establish the required margin for crack stability was used by Rochester Gas and Electric Corporation in letters dated September 16,1998 and December 7,1998.

If you need any additional information, please contact us.

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Very truly yours, i-

.e. ScCI i

i D. A. Christian i

Vice President - Nuclear Operations Commitments made in this letter:

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There are no new commitments in this letter.

Attachment cc:

U.S. Nuclear Regulatory Commission l

Region ll l

Atlanta Federal Center 61 Forsyth Street, SW l

Suite 23T85 Atlanta, Georgia 30303 Mr. M. J. Morgan i

NRC Senior Resident inspector l

North Anna Power Station I

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Attachment Requested Information on Reactor Coolant System Leakage Detection System Sensitivity Virginia Electric and Power Company North Anna Power Station Units 1 and 2

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Requested Information on Reactor Coolant System Leakage Detection System Sensitivity

Background

An engineering evaluation of the Reactor Coolant System leakage detection capabilities (containment particulate radiation monitors) has been performed for North Anna. That evaluation concluded that the Reactor Coolant System Leakage Detection System has the ability to detect leakage down to the 0.5 gpm within an hour threshold range consistent with the assumptions for source term (0.2% failed fuel) of Regulatory Guide 1.45.

In addition, past events were analyzed to determine the response of the containment particulate monitors. These events, documented in LERs 50-339/91-011-00 & 50-338/91-011-00, demonstrate that the count rate on the containment particulate

- radioactivity monitors (1-RM-RMS-159 and 2-RM-RMS-259) will roughly double with a 0.5 gpm leak. The containment gaseous radioactivity monitor responses (1-RM-RMS-160 and 2-RM-RMS-260) are also supplied for information. In both cases there was

. significantly less than 0.2% failed fuel in the core at the time of the event.

+ North Anna Unit 1, LER 50-338/91-011-00, dated 5/11/91, described a unit shutdown due to exceeding the Technical Specification limit for Reactor Coolant System (RCS) pressure boundary leakage. RCS pressure boundary leakage was identified due to a cracked weld on the 3/4-inch upper disc pressurization line for the "B" cold leg loop stop valve. The leakage was calculated at 0.7 gpm.

1-RM-RMS-159 increased from 4,000 cpm to 9,000 cpm.

1-RM-RMS-160 increased from 300 cpm to 500 cpm.

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+ North Anna Unit 2, LER 50-339/91-011-00, dated _11/3/91, described a plant shutdown required by Technical Specifications due to a packing leak on 2-RH-MOV-2700. The identified leakage to the Primary Drains Transfer Tank was calculated 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.

Radioactivity Monitoring System Availability The containment airborne radioactivity 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 radioactivity monitors, the containment sump level system is.also capable of detecting small leak rates. The containment sump level system is calibrated and verified to be accurate for determining leak rates to < 0.15 gpm.

Technical Specifications Operability Requirements

. T' chnical Specification (TS) 3.4.6.1 requires both the containment atmosphere e

particulate and gaseous radioactivity monitoring system and the containment sump level and discharge flow measurement system to be OPERABLE when the RCS is greater than 200 F.

In addition, Technical Specification 3.3.3.1 requires the containment particulate and gaseous radioactivity monitors to be OPERABLE in modes 1 through 4.

Per Technical Specifications, with one of the leakage detection systems inoperable, operation may continue for up to 30 days provided that a RCS leakrate calculation is 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 to be in at least HOT STANDBY'within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. If both leak detection systems were to become inoperable at the same time, the unit would 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 these limiting conditions for operation, no additional compensatory measures are necessary during times when the particulate and gaseous radioactivity monitoring system is inoperable.

Conclusion The information supplied above indicates that the North Anna containment leakage detection systems are capable of detecting leakage in the 0.5 gpm threshold range consistent with the assumptions for source term (0.2% failed fuel) of Regulatory Guide 1.45. 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 ability to detect 0.5 gpm leak within an hour, we believe that required margin exists for demonstration of LBB methodology.

The demonstration of our ability to detect a 0.5 gpm leak within an hour using the containment particulate radioactivity monitors provides sufficient basis for approval of l

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

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