ML20247M878

Application for Amend to License DPR-46,removing Min Stroke Time Requirement for Reactor Recirculation Discharge Valves. Application Consists of Proposed Change 70

ML20247M878
Person / Time
Site:	Cooper
Issue date:	05/31/1989
From:	Kuncl L NEBRASKA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20247M881	List: ML20247M885 NLS8900105, Application for Amend to License DPR-46,removing Min Stroke Time Requirement for Reactor Recirculation Discharge Valves. Application Consists of Proposed Change 70
References
NLS8900105, NUDOCS 8906050183
Download: ML20247M878 (7)

Text

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\ GENERAL OFFICE

• 'x - -Nebraska Public Power District * * ""hE#0~@#fa^!sP'S ""

NLS89000105-May 31, 1989

~ U.S. Nticlear Regulatory Commission Document Control Desk Washington, D.C. 20555 Gentlemen:

Subject:

Proposed Change No. 70 to Technical- Specifications Reactor Recirculation Discharge Valves Minimum Stroke.

Time Cooper Nuclear Station

.NRC Docket No. 50-298, DPR-46 In accordance with the applicable provisions specified in 10 CFR 50, Nebraska Public Power Disurict requests that the Cooper Nuclear Station Technical ~ Specifications be revised to remove the

- minimum stroke time requirement ~ for the Reactor Recirculation Discharge valves.

The Attachment contains a description of the proposed change, the attendant 10 CFR 50.92 evaluation, and the Technical Specification page revised by the institution of this charge. - .This proposed

. change has been reviewed by.the necessary Safety Review Committees and incorporates' _ all amendments to the CNS Facility Operating License through Amendment 128 issued February 21, 1988.

In addition to the signed original, 37 copies are also submitted l- for your use. By- copy of this letter and attachment the

- appropriate State of Nebraska official is being notified in accordance with 10 CFR 50.91(b) (1) . Copies to the NRC Region IV Office and the' CNS Resident Inspector are also being sent in accordance with 10 ' CFR 50.4 (b) (2) .

Should you have any questions or require additional information',

please contact me.

Since ely, L. G. Eu cl

Nuclear Power Group Manager LGK/kcw:rh/1329 i Attachment ~

l cc: H. R. Borchert

-Department of Health StapeofNebraska L NRC-Regional Office , 00 Region IV. 'i Arlington, TX g\

' NRC Resident Inspector Office l: Cooper Nuclear Station 1

8906050163 890531 afdre Menex c5000298 _ _ _ _ _ _ _ _ _ _ _

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• P'ge a 2 May 31, 1989 STATE OF NEBRASKA )

) ss PLATTE COUNTY )

L. G. Kuncl, being first duly sworn, deposes and says that he is an authorized representative of the Nebraska Public Power District, a public corporation and political subdivision of the State of Nebraska; that he is duly authorized to submit this request on behalf of Nebraska Public Power District; and that the statements contained herein are true to the best of his knowledge and belief.

L. G. ~8uncl Subscribed in m resence and sworn to before me this 3/

day of an , 1989.

On00mnD 17). NIfct am mm.mEaw NOT RY PUB'L[C /' COLLEEN 88. KUTA arc =a w w ( m i

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I Attachment to NLS89000105

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Page 1 of 5 REVISED TECHNICAL SPECIFICATIONS TO REMOVE REACTOR RECIRCULATION DISCHARGE VALVES MINIMUM STROKE TIME Revised Page  !

115 I. INTRODUCTION This proposed change requests, that the minimum stroke time for the Reactor Recirculation Discharge Valves be removed from the applicable surveillance requirements section of the CNS Technical Specifications. Currently, the CNS Technical Specifications require testing the valves to verify a closure time between 20 and 26 seconds. The District proposes, and justifies in the following pages, removal of the minimum stroke time requirement for the Reactor Recirculation System Discharge Valves.

The Reactor Recirculation System at Cooper Nuclear Station (CNS) consists of two recirculation loops which provide the path for driving the flow of water to the reactor vessel jet pumps. Each loop contains one variable speed, motor-driven recirculation pump and two motor-operated gate valves, one on the suction side of the pump and the other on the discharge side.

The normal function of the Reactor Recirculation Pump Discharge Valves is to isolate the recirculation pump to facilitate pump maintenance. However, closure of the discharge valves is necessary during certain Loss-of-Coolant j Accident (LOCA) scenarios to ensure successful inj ection of the Low Pressure Coolant Injection (LPCI) mode of the Residual Heat Removal (RHR) '

System. The closure of the discharge valve would isolate the LPCI flow from possible pipe ruptures in the recirculation suction line and thereby  ;

ensure that the LPCI system would not discharge makeup water out through i the break.

To demonstrate operability of the discharge valves, Section 4.5.A.3.e of j the CNS Technical Specifications requires that they be tested during each  ;

refueling outage to verify that the valves stroke from full open to full closed in 20 s t s 26 seconds.' The discharge valves are motor-operated and the closing time is controlled by the characteristics of the operator  ;

input power, the motor and gearing design, and the valve characteristics

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(i .e. , packing friction, etc. ) . The maximum closure time (26 seconds) is used in the CNS LOCA Analysis as an input for LPCI injection time.

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'This requirement was instituted with Amendment No. 32 to the CNS Technical Specifications which authorized, among other things, modifications to the Low Pressure Coolant Injection (LPCI) System, i I

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• Attachment'to NLS89000105 Page 2 of 5 l

.The'specified minimum closure time is not an input.to the LOCA analysis,

'but was to ensure that the. valves will not L experience a differential pressure greater than.' their ' design differential pressure of 200-psig.

following a postulated' LOCA. The concern was that if . the 200 psig  !

differential pressure was exceeded, the valve's Lay fail to close which 1 would negate the validity.of the CNS ECCS analysis.'

'II. DESCRIPTION OF CHANGES This. proposed change removes the minimum stroke time requirement for the t

Reactor . .~ Recirculation Discharge Valves. CNS Technical Specifi- ]

cation 4.5.A.3.c requires the District to test each Recirculation Discharge

~ q Valve every refueling outage to verify its capability to stroke from full open to , full closed. in 20 $ t s 26 seconds. This proposed change will .,

remove ; the minimum stroke time require' ment, thus requiring stroke time j testing to demonstrate closing capability in s 26_ seconds. The surveillance frequency will remain unchanged, i

III. EVALUATION  !

An analysis has been performed by General Electric in support of this  !

request. ' There are _two potential LOCA related concerns regarding closure .  ;

of the ~. discharge - valve with stroke times less than the minimum time currently specified in the CNS Technical Specification. The first concern Dis the potential to incapacitate the valve before it closes. The second-  !

concern is whether fast valve closure would impair recirculation flow ,

coastdown. These concerns are addressed separately below.  !

I Imnact ot. Valve Closure l

The valve motor operator is designed to open and close the discharge valve )

against a 200 psi differential. If the valve.in'the broken loop attempts to close during a LOCA event when the pressure differential across the

. valve is greater than 200 psi, it is possible that the motor operator could malfunction and prevent the valve from closing. )

l To protect against this possibility, there is a low reactor pressure permissive which initiates valve closure. Per Table 3.2.B (Page 2) of the ]

CNS Technical Specification, this pressure permissive is  !

185 $ P $ 235 psig. For the double-ended maximum line break, the vessel depressurizes at an approximate rate of 20 psi /sec. Assuming the_ pressure permissive is set at the maximum allowed pressure of 235 psig, the pressure differential across the valve in the broken loop (which for this case is simply the vessel pressure minus the drywell pressure) is below 200 psi within. approximately 2 seconds of the pressure permissive signal, significantly less than the normal closure time.

The same condit Jans apply even for smaller breaks. The depressurization rate for a 1.0 f t break is approximately 10 psi /sec, and the' pressure )

differential across the valve in the broken loop is below 200 psi within

-4 seconds of the pressure permissive signal.

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Attachment to NLS89000105-Page 3 of 5 Very.small breaks depressurize the reactor slowly, and the vessel pressure may remain close.to 235 psig as the valve closes. However, for small breaks such as this, the pressure on the side of the valve disc closest to the break will be significantly greater than the drywell pressure.

Thus, the pressure differential across the valve for very small breaks would be less thun 200 psi. Therefore, the minimum requirement for valve stroke time has no impact on valve closure capability during any postulated LOCA scenario.

Imoact on Recirculation Flow Coastdown i The ECCS performance analysis takes credit for recirculation flow coastdown in the unbroken loop during the first few seconds following a LOCA. The decaying core flow due to the pump coastdown results in effective heat transfer during the initial phase of blowdown.

Typically, this heat transfer is sufficient to maintain nucleate boiling throughout che core for the first 5 to 10 seconds following the design basis accident (DBA) . Closure of the recirculation discharge valve, which j takes place only after the 235 psig pressure permissive is satisfied, would .

have no impact on recirculation flow coastdown because it takes a minimum of 20 seconds to reach this pressure. Therefore, the minimum requirement for valve closure stroke time has no impact on recirculation flow coastdown during a LOCA.

IV. SIGNIFICANT HAZARDS DETERMINATION 10 CFR 50.91(a)(1) requires that licensee requests for operating license amendments be accompanied by an evaluation of significant hazards posed l by the issuance of the amendment. This evaluation is to be performed with respect to the criteria given in 10 CFR 50.92(c) . The following analysis meets these requirements.

A. Evaluation of this Amendment with Respect to 10 CFR 50.92.

The enclosed Technical Specification change is judged to involve no significant hazards based on the following:

1. Does the proposed change involve a significant increase in the probability or consequences of an accident previously evaluated?

Evaluation: f The proposed change involves removal of the minimum stroke time requirement for the Recirculation Discharge Valves that are required to fully close following a Design Basis Loss of Coolant Accident (LOCA). Removal of the minimum valve stroke time requirement vill not affect the probability of occurrance of a LOCA.

The LOCA analysis that assures compliance with 10CFR50.46 does I not rely on the minimum valve closure time as an input. )

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Attachment to NLS8900010'5L Page.4 of 5'

• • Rather, ' the maximum valve closure time Lis used - as . a key parameter in the analysis. The maximum valve closure time is unaffected by this proposed change. The minimum valve closure

' time was originally incorporated into Technical Specifications to ensure.that the valves would stroke < slow enough and hence

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would not exceed their maximum design differential pressure following'a LOCA. If the differential pressure,is exceeded, the valve may fail to fully close, thus1 invalidating the LOCA analysis.

Analysis shows that'even with significantly faster valve' stroke -

-times, the valves will not be subjected to a greater than design --differential pressure due to the expected reactor l pressure decay rate following a LOCA along with the setpoints j specified. in Technical Specifications- for .the pressure permissive relays that actuate' valve closure.

The LOCA analysis also takes credit for core heat removal that takes place during recirculation flow coastdown in the unbroken I

' loop the first few seconds following a LOCA. The proposed

. change will not invalidate this assumption due to the expected 1 J

, . reactor pressure decay -rate and the pressure permissive setpoint.

Because the proposed change will not affect recirculation di scharge valve closure or recirculation flow coastdown, there is no significant increase in the consequences of an accident 'l previously evaluated.

The CNS LOCA Analysis does not rely on the minimum stroke time as an input. The two concerns identified with respect to fcst ,

closure ~of the Recirculation Discharge Valves (i.e., failure "

to close due to high differential pressure,. and impact of fast .

closure on Recirculation Pump coastdown) are' obviated by the  ;

CNS LOCA. characteristics and the CNS Recirculation Discharge i Valve pressure permissive control logic.

2. Does the proposed license amendment create the possibility for a new or different kind of accident from any accident previously evaluated?

Evaluation: ]

Removal of the minimum stroke time surveillance requirement for the Reactor Recirculation Discharge Valves will not allow any new mode of plant operation or create the possibility for a new or different kind of accident from any accident j previously evaluated. Removal ' of the minimum stroke time requirement for the Recirculation Discharge Valves does not  ;

create any new unanalyzed failure mode nor will it place the plant in an unanalyzed condition.

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( ' Attachment to NLS89000105 l' Page 5 of 5 i

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3. Does the proposed amendment involve a significant reduction in the margin of safety?

Evaluation:

This proposed change will remove a 20 second minimum stroke time' from the surveillance requirements for the Recirculation Discharge Valves. This value is not an input to the CNS LOCA analysis.

The maximum stroke time, 26 seconds, is an input to the CNS LOCA analysis, and will remain 'in the' 'CNS Technical Specifications. As explained above, removal of the minimum valve stroke time for the recirculation discharge valves will not invalidate any part of the CNS LOCA analysis. Therefore, the margin of safety with respect to the accidents analyzed for CNS will not be reduced, l

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