ML20059E548

Forwards Supplemental Info Re Deletion of Pressurizer Safety Valve Requirement During Mode 5.Current Tech Spec Requiring One Operable Safety Valve in Mode 5 Unnecessary & May Be Deleted

ML20059E548
Person / Time
Site:	North Anna
Issue date:	08/31/1990
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
90-084A, 90-84A, NUDOCS 9009100230
Download: ML20059E548 (4)

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Y1HOINIA ELucTu!C AND POWEH COMPANY HICl!MONI),Y!nt01NIA 202 61 j August 31, 1990 U.S. Nuclear Regulatory Commission Serial No.: 90 084A [

Attention: Document Control Desk NL&P R1 .

Washington, D.C. 20555 Docket Nos.: 50 338  !

50 339 License Nos.: NPF 4 NPF 7 -

Gentlemen: l l VIRGINIA ELECTRIC AND POWER COMPANY  ;

NORTH ANNA POWER STATION UNITS 1 AND 2 DELETION OF PRESSURIZER SAFETY VALVE REQUIREMENT DURING MODE 5 - SUPPLEMENTAL INFORMATION ,

On May 16,1990, Virginia Electric and Power Company requested amendments, in the form of changes to the Technical Specifications, to Operating License Numbers .

NPF 4 and NPF-7 for North Anna Power Station Units 1 and 2, respectively. Those.

requested amendments supported the deletion of the operability requirement for one pressurizer safety valve in Mode 5 (cold shutdown) as currently specified in Technical Specification 3.4.2 " Safety Valves - Shutdown." The requirement to have one safety ,

valve operable in Mode 4 (hot shutdown)is unaffected.

A subsequent discussion between Virginia Electric and Power Company and the NRC i

l regarding this Technical Specification change request was conducted by telephone on August 30,1990. The NRC North Anna Project Manager requested that we provide 4 additional details regarding which design basis accidents described in the UFSAR were reviewed in light of the proposed change, and what the effects of the proposed

change were for each identified accident scenario. That information is provided in the I

I attachment.

If you have any questions or rs Julre additional Information please contact us '

immediately.

Very truly yours, b ed 1 b . L. Stewart nior Vice President Nuclear l Attachment I

900910023o 9ooest POR P

ADOCl o300o338 PDC y  ;

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4 oc: U.S. Nuclear Relpla'ory Commission Region it  ;

101 Marietta Street, N.W.

Suite 2900 Atlanta, Georgia 30323 l i

Mr. M. S. Lesser  :

NRC Senior Resident inspector Ncrth Anna Power Station Commissioner Department of Health Room 400 109 Governor Street Richmond, Virginia 23219  :

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ATTACHMENT I a

introduction The pressurizer code safety valves are designed to prevent the reactor coolant system

-(RCS) from being pressurized above the safety limit of 2735 psig. The relief capacity  ;

of the safety valves is adequate to relieve any overpressure condition which could 7 occur during power operations through hot shutdown (Modos 1 through 4). Although the current Technical Specification 3.4.2 requires that one safety valve be operable in the cold shutdown condition (Mode 5), the proposed Technical Specification change is intended to demonstrate why that Mode 5 requirement is unnecessary. .

Pronosed Technical Soecification Chance The proposed Technical Specification change would delete the current requirement in ,

Technical Specificatior. 3.4.2 " Safety Valves - Shutdown" for one operable pressurizer safety valve during Mode 5 (cold shutdown). In cold shutdown, primary system temperatures are less than or equal to 200 degrees Fahrenheit. This change would permit all three safety valves to be removed for inspection and maintenance at the same time. The requirement in specification 3.4.2 to have one safety valve operable in  :

Mode 4 (hot shutdown) is unaffected by this proposed change.

Desinn Basis Accidents Reviewed Those transients described in the North Anna UFSAR which experience pressures that challenge the pressurizer safety relief valves are: Loss of Normal Feedwater, Main Feedline Break, Locked Rotor, and Loss of Load transients. The limiting cases for these transients assume the reactor is initially operating at hot full power conditions, in Mode 5, the reactor is shutdown and decay heat removalis being accomplished by the Residual Heat Removal System.

l Loss of Normal Feedwater: Loss of Normal Feedwater increases the primary (RCS) side pressure and temperature when initiated from hot full power. Since the reactor is in cold shutdown with maximum temperatures equal or less than 200 degrees F, normal feedwater is not in service and this transient is not applicable to Mode 5 operation. In addition, the pressurizer safety valves are not usea in the rtimoval of heat from the RCS in Mode 5. Therefore, the effect of l removing the pressurizer safety valves during Mode 5 is inconsequential.

l Main Feedline Break: This tradient involves the interruption of feedwater to one or more steam generators. This would degrade or eliminate the transfer of heat from the primary to secondary side from hot full power conditions. In Mode 5 ,

operations, the reactor is in cold shutdown with maximum temperatures equal i or less than 200 degrees F, and the steam generators no longer function as the g heat sink. Therefore, this event is not credible in Mode 5.

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Locked Rotor: This event assumes that a locked rotor willinitiate a reactor trip -  !

during hot full power operation. Since the reactor is in a cold shutdown condition, this event is not credible in Mode 5.

Loss of Load transients: During Mode 5 the reactor is in a cold shutdown condition with no load on the system. Therefore, loss of load transients are not credible in Mode 5.

Safetv Issue Raised by the Removal of the Mode 5 Reauirement The safety issue of concern is whether or not appropriate overpressure protection is '

provided during cold shutdown (Mode 5). Mode 5 is defined as a reactor Keff less than 0.99 and an average RCS temperature of less than or equal to 200 degrees F. At this temperature, RCS overpressure protection is provided by the Low Temperature .

Overpressure Protection (LTOP) system.

There is a concern, while in cold shutdown, regarding overpressurization of the RCS in terms of reactor vessel materials considerations. This concern is addressed via the low temperature overpressure protection (LTOP) system. The LTOP system is addressed separately in Technical Specifications. Technical Specification 3.4.9.3 requires that two independent power operated relief vat /e (PORV) systems be operable in Mode 5 for the purpose of overpressure protection. Those systems are designed to ensure that pressure is maintained within the limits defined by reactor vessel materials embrittlement analyses. No credit is taken for the safety valves to provide this protection. If credit were taken for pressure relief via the safety valves, no protection is afforded because pressure greater than that permitted by the materials analyses would be achieved while in cold shutdown before pressure could be relieved .

by a safety valve. The LTOP setpoint is significantly lower than the safety valve setpoint and affords the necessary protection. ,

Conclusion .

Our analysis demonstratos that the identified design basis accidents described in the-UFSAR and overpressure protection for the RCS in cold shutdown are unaffected by -

having no prensurizer safety relief valve operat!e during cold shutdown. We conclude that the current Technical Specification requiring one operable safety valve in Mode 5 is unnecessary and may be deleted.

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