ML20112J581

Application for Amends to Licenses NPF-4 & NPF-7,revising Tech Spec 3.7.4.1 to Extend Allowable Time for Inoperability of Redundant Svc Water Headers Beyond 72 H to Facilitate Mod & Maint Activities.Fee Paid

ML20112J581
Person / Time
Site:	North Anna
Issue date:	03/29/1985
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Harold Denton, John Miller Office of Nuclear Reactor Regulation
Shared Package
ML20112J585	List: ML20112J581 ML20112J587 ML20112J592
References
85-167, NUDOCS 8504050229
Download: ML20112J581 (13)

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March 29, 1985 Mr. Harold R. Denton, Director Serial No.85-167 Office of Nuclear Reactor Regulation E&C/SAA:ceh Attn: Mr. James R. Miller, Chief Docket Nos. 50-338 Operating Reactors Branch No. 3 50-339 Division of Licensing License Nos. NPF-4 U. S. Nuclear Regulatory Commission NPF-7 Washington, D. C. 20555 Gentlemen:

AMENDMENT TO OPERATING LICENSES NPF-4 AND NPF-7 NORTH ANNA POWER STATION UNIT NOS. 1 AND 2 PROPOSED TECHNICAL SPECIFICATION CHANGE Pursuant to 10CFR50.90, Virginia Power requests an amendment, in the form of changes to the Technical Specifications, to Operating License Nos.

NPF-4 and NPF-7 for the North Anna Power Station Unit Nos.1 and 2.

As previously discussed with members of the NRC staff, Virginia Power is pursuing a program to upgrade the Service Water System at North Anna.

Currently planned modifications and maintenance activities include installation of new discharge headers and spray arrays and mechanical cleaning of the service water piping. In order to avoid an adverse impact on station operation during implementation of these and other modifications and maintenance activities which may be required in the future, it is desired to extend the time period that one of the redundant service water headers can be out of service. Technical Specification 3.7.4.1 currently limits the time period that one of the headers can be inoperable to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This submittal requests that Technical Specification 3.7.4.1 be revised to extend the allowable time that one of the redundant service water headers can be inoperable beyond 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> up to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> provided 3 out of.4 service water pumps and 1 out of 2 auxiliary service water pumps are operable during the LCO condition. If the specified number of service water pumps and auxiliary service water pumps are not operable, the current 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> action statement would still apply.

Enclosure 1 provides the safety evaluation justifying the extended Limiting Condition for Operation (LCO). The safety evaluation is based on a probabilistic safety assessment performed by IMPELL Corporation which is included as Enclosure 2. The proposed changes to the Technical Specifications for Units 1 and 2 are included in Enclosures 3 and 4, respectively. \

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The safety evaluation concludes that the probability of failure of the Service Water System to provide adequate flow during the extended LCO will be reduced below the failure probability during the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LCO allowed by the current Technical Specifications. This increased reliability will be achieved by increasing the number of service water pumps and auxiliary service water pumps required to be operable during the extended LCO.

i The proposed changes and the safety evaluation have been reviewed and approved by the Station Nuclear Safety and Operating Committee and the Safety Evaluation and Control staff. It has been determined that this request does not pose a significant hazard consideration as defined in 10CFR50.92 or an unreviewed safety question as defined in 10CFR50.59.

We have evaluated this request in accordance with the criteria in 10CFR170.12. Accordingly, a voucher check in the amount of $150.00 is enclosed as an application fee.

Inasmuch as the proposed changes will result in significant operational benefits and facilitate implementation of planned upgrades to the Service Water System, we solicit your expenditious review and approval by August 1, 1985. We are interested in meeting with you during the month of April

, to discuss the details of this proposed change and the supporting safety analysis.

Very truly yours, q

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W. L. Stewart

Enclosures:

(1) Safety Evaluation for Proposed Changes (2) Probabilistic Safety Assessment (3) Proposed Technical Specifications Changes - Unit 1 (4) Proposed Technical Specification Changes - Unit 2 (5) Voucher Check $150 d

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cc: Dr. J. Nelson Grace Regional Administrator Region II Mr. Leon B. Engle NRC Project Manager - North Anna Operating Reactors Branch No. 3  ?

Division of Licensing Mr. M. W. Branch NRC Resident Inspector North Anna Power Station Mr. Charles Price Department of Health 109 Governor Street Richmond, Virginia 23219

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CG000NWEALTR OF VIRGINIA )

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CITY OF RICIDIOND )

The foregoing document was acknowledged before me. in and for the City and Commonwealth aforesaid, today by W. L. stewart who is Vice President -

Nuclear Operations. of the Virginia Electric and Power Company. He is duly i

- authorized to esecute and file the foregoing document in behalf of that

! Company, and the statements in the document are true to the best of his i

knowledge and belief.

Acknowledged before as this "A % day of 'Mr..<1 19 f i .

My Commission espires: $ b. (o 19 2'h .

4 Ag ii Notary Public i

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Enclosure 1 SAFETY EVALUATION REQUEST TO CHANGE SERVICE WATER SYSTEM TECHNICAL SPECIFICATIONS NORTH ANNA UNITS 1 AND 2

1.0 Introduction The Service Water System (SWS) is a common system to both North Anna Units 1 and 2 and is designed for the removal of heat resulting from -

the simultaneous operation of various systems and components of the 'two reactor units. There are two independent sources of water that provide the ultimate heat sink for the North Anna units. These are the Service Water Reservoir and the North Anna Reservoir. The SWS is designed with redundant supply and return headers which are supplied by four service water pumps and two auxiliary service water pumps. Two pumps are required to provide adequate flow for both units during normal operation and design basis accident conditions. A complete description of the SWS design and function is contained in the North Anna Updated Final Safety Analysis Report. (Reference 1) ,

The current Technical Specifications allow one of the two redundant headers to be out of service for a maximum of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> before the units must begin shutting down. In order to facilitate implementation of modifications and maintenance of the Service Water System while avoiding any adverse impact on station operation, it is desired to revise the Technical Specifications to allow for operation of the SWS for a period of seven days (168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br />) with one of the redundant headers inoperable.

The purpose of this evaluation is to assess the impact on plant safety resulting from extending the time that one of the headers can be out of service during operation from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br />.

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2.0 Probabilistic Safety Assessment In order to evaluate the impact on plant safety resulting from operation of the Service Water System in an extended LC0 condition, a probabilistic safety assessment was performed. The study was performed by IMPELL Corporation under contract to Virginia Power (Reference 2).

! The analysis includes:

(1) A reliability study of the SWS in normal operation (i.e.

l two main headers operable);

(2) A reliability study of the SWS in an LC0 condition with 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> as the mission time; a

(3) A reliability study of the SWS in an LC0 condition with 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> as the mission time; and i (4) Several sensitivity studies to investigate the reliability

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of systems supported by service water and potential changes

! in system operation or maintenance to enhance service water I system reliability.

The analysis was based upon a qualitative and quantitative i probabilistic evaluation of the reliability of the Service Water System.

The qualitative system evaluation included the performance of a failure l'

modes and effects analysis which identified potential failure mechanisms and evaluated their consequences in terms of system performance. The quantitative system evaluation consisted of a fault tree analysis of the SWS and applicable support systems. The fault tree was analyzed by assigning probabilities to the basic events contained in the tree. These l were derived from system and component failure data and human error data and models. Industry data sources and North Anna plant-specific j operating experience were reviewed to develop the data base for this analysis, i

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The results of the quantitative analysis of the SWS (pumps and 1 major headers) indicate that the system failure probability increases from 3.2x10-5 to 4.0x10-5 when the time period for the LC0 is extended from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br />. This small increase in failure probability of the SWS- due tc extension of the LC0 condition would result in a negligible increase in overall plant risk. The results of sensitivity cases to investigate the reliability of service water. flow to selected systems supported oy service water also indicated an incr' ease in failure probability due to extension of the LC0 conditions. This increase in failure probability was also judged to be insignificant.

Based on the results of the reliability study, a significant contributor to SWS failures was determined to be pump unavailability due to maintenance. A sensitivity study was therefore performed to evaluate the impact of reducing the maintenance activity on the service water pumps during the extended LC0 condition. This pre-condition would limit maintenance activities such that 3 out of 4 service water pumps and 1 out of 2 auxiliary service water pumps are available at the beginning of the extended LC0 condition. The resul t of this action reduces the SWS I

failure probability for the extended LCO case from 4.0x10-5 to 2.0x10-5 ,

i The failure probability of the selected systems supported by service j water was also investigated for the reduced maintenance case. The result was that the failure probability for service water flow to the supported l'

systems wip also reduced for the extended LCO condition.

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d 3.0 Description of Proposed Change to the Technical Specifications The proposed change consists of adding a second action statement to Specification 3.7.4.1 which would extend the allowable time that one of the service water loops can be inoperable beyond 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> up to a maximum of 7 days (168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br />). Extension of the LC0 time period would be contingent on 3 out of 4 service water pumps and 1 out of 2 auxiliary service water pumps being operable since initial entry into the action statement. In the event that the required number of service water pumps and auxiliary service water pumps are not operable, the LC0 action statement would remain as currently specified, requiring the inoperable loop be returned to service within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.

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4.0 Conclusions Based on the results of the probabilistic safety assessment, it is concluded that extension of the LC0 time period would result in a negligible increase in risk. The probability of a service water system failure increases from 3.2x10-5 to 4.0x10-5 when the time period for the LCO is extended from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br />. Furthermore, since the proposed revision to the Technical Specifications requires that 3 out of 4 service water pumps and 1 out of 2 auxiliary service water pumps be operable during the extended header outage, the failure probability will be reduced from 4.0x10-5 to 2.0x10-5 . Therefore, the reliability of the Service Water System for the 168 hour0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> extended LC0 condition will be increased over that of the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LC0 condition as governed by the current Technical Specifications.

It is concluded that operation under the proposed Technical Specifications for the Service Water System will not create an unreviewed safety question as defined in 10CFR50.59 since:

(1) There will be no increase in the' probability or consequences of any accident previously analyzed. The reliability of the Service Water System for the extended ~

168 hour0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> LC0 condition will be increased over that of the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LC0 condition as allowed by the current Technical Specifications.

(2) The operation of the nuclear units under the extended LCO does not create the possibility of a new or different kind of accident not previously analyzed. The units are currently licensed to operate with only one header operable under current LC0 restrictions. This does not change as a result of extending the time period.

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(3) The margin of safety as defined in the bases to any technical specification will not be reduced. The probability of failure of the Service Water System during the extended LC0 has not been increased under the proposed -

change to the Technical Specifications.

In addition, it is concluded that the extension of the LC0 time period to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> under the proposed Technical Specifications will not pose a significant hazards consideration as defined in 10CFR50.92. As stated above, the change will not result in any increase .in the .

probability or consequences of a previously analyzed accident or reduce any safety margin.

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~5.0 References i

1. North Anna Power. Station Updated Final Safety Analysis Report.

2. IMPELL Corporation, Report No. 03-1250-1097.

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ENCLOSURE 2 PROBABILISTIC SAFETY ASSESSMENT a .

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