ML20059F124

Safety Evaluation Supporting Amends 38 to Licenses NPF-37 & NPF-66 & Amends 25 to Licenses NPF-72 & NPF-77

ML20059F124
Person / Time
Site:	Byron, Braidwood
Issue date:	08/31/1990
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20059F117	List: ML20059F114 ML20059F124
References
GL-88-17, NUDOCS 9009110099
Download: ML20059F124 (5)

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SAFETY EVALUATION'BY THE OFFICE OF; NUCLEAR REACTOR REGULATION o

L' RELA 1ED T0' AMENDMENT NO.-yg,TO FACILITY OPERAflNG LICENSE NO. NPF-37, AMENDMENT NO.

38 TO FACILITY OPERATING LICENSE NO. NPF-66,-

I AMENDMENTjN0.,,2,5,;Tp,-fACILJT,Y,pPERATip0JJCENEF NO. NPF-72,

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J AND AMENDMENT NO.- 25 TO FACILITY OPERATING LitaSE NO. NPF-77:

COMMO NW E A L.T.H..E.D.I.S.O.N..CO.M.P.A.N.Y.

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by(letterdatedJu.uary~31,1990, as supplenented August 30, 1990, Comonwealth 1 Ediscn' Company (Ceco) - the licensee, submitted proposed anendnent changes.to L

t the Technical-Specifications ~ (TS) and associated bases for Byron Station,.

Units 1 and 2, and Braidwood Station,. Units I and 2.

The preposal is a result ~

.of an engineering review performed to identify any changes that.might mitigate 4

or p nycnt the consequences cf e loss of decey heat renoval event.' The licensee vhas identified; in response to Generic Letter _88-17, three changes:

(1)-

. reduction \\of the Residual Heat Removal:(RHR) minimum flowrate during refueling operations;'(2) removal of the RHR auto closure'. interlock'on'the RHR system suction isolation valves; (3) allowance' for' one' safety injection (SI). pump -

to be available for injection during low temperature operatiori.

o Based onieur review of the licensee's subn.ittal,.We have found the revisions

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.to be acceptable.

h, 2.0 ' FJylpult,,RHR.FQWR*.Ti The required miniaum RHR flowrateLduring midloop operations is based on the-g

' ability of the RHR to' remove decay heat such that Reactor Coolant System b

(RCS)temperaturecanbecontrolledandthatthereactorcoolanttemperature

. rise through the core.does not exceed reactor vessil internals delta T limits.

Ji tThe flow rate ensures that there is sufficient coolant circulation maintained-through the core to minimize the effect of a boron dilution incident and

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prevent boron stratification, and that the pressure drop across the RHR bypass flow control valve does not result in cavitation.

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42-i Vortexing at thejunction'of? the RHR system suction line and the RCS may occur if the water level is too. low, a situation to be avoided since~this mayJintroduce: air into< the-RHR system pump suction. Vortex 1r.g can occur--

more easily when flow is high. The likelihood of vortex formation due to partial draining of the RCS can be offset by reducing the RHR flow-rate. As discussed in NUREG-1269,." Loss'of Residual Heat Removal System, Diablo Canyon, Unit 2 April 10, 1987,". reduced.RHR-system flow rate would provide e

a greater margin against vortexing and can help preclude an inadvertent loss' of decay heat removal (DHR) capability due to air entrainment and cavitation of. the RHR system pumps.

The-licensee has' revised Specif; cation 4.9.8.1 to reflect a reduction in flow rate from " greater.than or equal to 2800 gpm" to " greater than or equal.

t to 1000 gpo." -As long os one RHR pump is running,-even at flow rates as low e

L as 1000,gpm, there is enough mixing in the flow to ensure that no boron strati-l-

.fication occurs, as wel1~as-the uniform distribution of boron-to minimize-t 1.he effects' of.a boron dilution scenario. This reduction in flow rate will o

reduce;the susceptibility to vortexing, and is consistent with NUREG-1269.

However,;1000 gpm is. not always sufficient'to maintain the' RCS temperature

less. than or equal to 140 degrees F for example, shortly 'after shutdown.

l Hence,'the.changeproposedbythelIcenseewillincludetheadditionofa Surveillance Requirement which " verifies.that the RCS temperature-is being L-maintained at'less than or equal to 140 degrees F" while operating at the reduced flowrate. This is' consistent with Mode 6 operating requirements.

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. Since the proposed Technical ~ Specification will require an RHR.flowrate-that

'provides adeouate mixing and is sufficient to maintain RCS temperature less than 140 degrees F, the staff finds the proposed. Technical Specification

-modificatier s to be acceptable.

. 2.1 Removal of the Auto Closure Interlock r

' During normal and emergency conditions, the low ' pressure RHR system is

,t isolated from the high pressure RCS. This isolation is.necessary to avoid y

damages resulting from overpressurization, and minimize the potential for loss of integrity of the low pressure system and possible radioactive releases to the environment. The purpose of the Auto Closure' Interlock (ACI) is to preclude conditions that could lead to an interfacing system i

loss-of-coolant accident (LOCA)' by ensuring that both suction / isolation valves ~ in each RHR system train.are fully closed when the reactor coolant t

system is pressurized above-the RHR design pressure.

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4, 7 There is a; competing concern regarding ths ACI however, and that.is th.

potential for the ACI circuitry to cause. inadvertent RHR isolation during cold b

and-refueling ' operations. Westinghouseperformeda-genericevaluation(WCAP-11736) to study the impact of removing the ACI feature. The results of the.

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~ evaluation showed that removal of the RHR ACI combined with the' addition of

e' alarms and procedures improves the availability of the RHR system during short-term and long-tcrm cooldown and reduces the estimated core damage; g

frequency. The licensee.has, therefore,' proposed to remove the ACI at'the f'

- Byron and Braidwood Stations and substitute alternative features to )rotect H

L against RHR overpressurization. These changes are consistent.with tie staff'sLposition taken'on the removal of'the ACI. The changes consist of h

hardware and procedural enhancements that the staff believes.will produce a

- net safety benefit. The hardware changes: include the addition of an alarm j

- to each RHR suction valve. The setpoint for the alarm will be within the p

range of the open permissive.setpoint pressure and the RHR system design i

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pressure minus the RHR pimp head. The open permissive.that prevents these valves-from being opened will'be left in place and will not be disabled by.

the addition of the alarm and the removal of the ACI circuitry. The valve-j position. indicator to the alarm will not be affected by power lockout of the RHR suction valves and a method independent of the alarm for determining.

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. valve position:will be available in the control room following power lockout.

. of.the RHR suction valves. The licensee has committed to the hardware changes listed above and.has proposed two methods independent of the alarm for-H determining valve position:

(a)'Normalpositionindicationpoweredfromanindependent

. valve supply source; (b) Monitor Light Group 1, powered from an annunciator input m"

-cabinei: (an-independentpowersource)andlocatedon.the-control = room panel; 7

. The licensee has also committed to the following procedural modifications:

.-(1) The alarm response procedure used during plant startup.

will.be modified to reflect alarm recognition responses.

for the'added-alarm. The procedure will be revised to.

direct the' operator to take the. necessary actions to close the'openRHRsuctionvalve(s),if.they'areinotclosedfollowing.

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' alarm actuation.

If'this is not possible, the operator will be instructed to not pressurize further and to return to the 7,

safe shutdown mode of operation.

.(2) A surveillance procedure for the.RHR suction valve alarms is added to periodically verify that the alarms are operable.

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4 (3) - A method independent of the alarm will be used to verify a

that these valves are closed when the power to these valves is locked out.

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In a teleconference held July 24,1990, between the licensee and the NRC, the licensee also stated that an instrument surveillance procedure was in place to 1-i periodically verify operability of the alarms.

The staff has reviewed the Byron and Braidwood Stations submittal and has found the proposed hardware changes and procedural modifications are adequate alternatives to assure RHR system overpressure protection. Removal of the ACI is, therefore, acceptable.

2.2> Safety Injection Pump Availability The availability of a Safety Injection (SI) pump provides for the mitigation of the effects of a loss of decay heat removal event during mid-loop operations.

Operation of at least one SI pump is required in some cases to prevent core.

1 uncovery. The licensee proposes to have an SI pump available in Modes 5 and 6.

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-The potential for low. temperature overpressurization has been ' analyzed and accounted for in the Specification by requiring pressurizer level to be less-l than 5 percent if the $1 pump is available.

It is the licensee's entention i

that during RCS reduced inventory conditions, +,he safety injection pump motor

~ circuit breakers will be racked in and the pump secured by placing.the Control 1

Room handswitch in the Pull-to-Lock position. This will prevent the safety i

injection pump from bein; inadvertently started by a signal, but will allow e

the operators to start the pump from.the Control Room if needed to mitigate a j

loss of decay heat removal.

' This modification is consistent with Generic Letter 88-17~and is acceptable.

3.0 ENVIRONMENTAL CONSIDERATION

' These amendments involve a change to a requirement with' respect to the

' installation or use of the facility componehis located within.the restricted i

-areas as defined in 10 CFR Part 20 or a change.to a surveillance requirement.

^3 The' staff has determined that these amendments involve no significant increase i

Lin:the amounts, and no significant change in the types, of any effluents that may be released offsite and that there is no significant increase in individual

.t or cumulative occupational radiation exposure.

The Commission has previously i

issued a proposed finding that these ame.1dments involve no significant hazards consideration and there aas been no public comment on such finding.

'Accordingly, these amendments meet the eligibility criteria for categorihal exclusionsetforthin.10CFR51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environnental assessment need be prepared

'in connection with the issuance of these amendments.

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4.0 CONCLUSION

We have concluded, based on'the considerations 4:scussed above, that:

(1)there endangered by operation in the proposed manner.is reasonable assurance that the healt

? such activfties will be oftheseamendmentswill.notbeinimicaltothecommondefensea(3)theissuance conducted in compliance with the Commission's regalations and nd security or to the_ health and safety of the public.

Principal Contributors:

A. Massey Dated:

August 31, 1990

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