ML20150A977

Comments on Evaluation of Fire Protection Safe Shutdown Methods as Followup to 780925-28 Site Visit & Telcon

ML20150A977
Person / Time
Site:	Yankee Rowe
Issue date:	10/16/1978
From:	Moody D YANKEE ATOMIC ELECTRIC CO.
To:	Ziemann D Office of Nuclear Reactor Regulation
References
NUDOCS 7810200051
Download: ML20150A977 (13)

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Telephone 617 366-9011 TWX 710 390-0739 "5-YANKEE ATOMIC ELECTRIC COMPANY

. Y f&P 20 Turnpske Road Westborough, Massachusetts 01581

.' LN KEE

WYR 78-89 October 16, 1978 United States Nuclear Regulatory Commission Washington, D. C. 20555 Attention: Office of Nucicar Reactor Regulation Mr. Dennis L. Ziemann, Chief Operating Reactor Branch #2 Division of Operating Reactors

Reference:

(a) License No. DPR-3 (Docket No. 50-29)

Attachment:

(A) Safe Shutdown Methods (B) Shutdown Capability Improvement (C) Additional Shutdown Capability Improvement

Subject:

Fire Protection Evaluation Safe Shutdown Methods A site visit of the USNRC Fire Hazard Evaluation Team was held at the Yankee Rowe plant on September 25 through September 28, 1978.

At the exit interview, Yankee was requested to investigate various methods of plant shutdown independent of fires in certain specified areas. The results of that investigation were reported to the USNRC by telephone on Monday, October 2, 1978, and are submitted herewith as Attachment A. Yankee was also requested to provide additional information of the new ECCS modification and its improvement on shut-down capability. Information pertaining to this modification is provided in Attachment B.

Presently under design is an additional modification which will further guarantee shutdown capacity. This modification will be installed i

during the November, 1978, refueling outage. Details are described in Attachment C.

We trust this information is satisfactory to you; however, should you have any questions, please contact us.

Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY

.T-D. E. Moody Manager of Operations Oy 7P/o 2_o

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LDM/em Attachments

i Attachment (A) .

' Additional information has been requested concerning t.he availability ,

of methods for shutting down the plant which would be independent of the turbine building, switchgear room, control room, manhole #3, or 1

a single cabic run in the primary auxiliary building (PAB) f or charging and shutdown pumps. That information is provided in the following i

discussion.

DISCUSSION:

The results of an investigation confirm that such methods are availabic through the use of existing redundant equipment or systems.

In some inst ances temporary power supplies will be provided. The methods described include adequate time for temporary power to be connected or manual valve operation. The investigation utilized the premise, expressed in the Fire 11azards Analysis, that certain functions are required to safely shutdown the plant. Simply states those functions are:

A. Insert negative react.ivity B. Remove decay heat The ability to insert negative reactivity in the form of control rods is virtually guaranteed in all cases, First it is a fail safe system by design and construction. Secondly, the methods described below require that the rods be scrammed immediately upon recognition of a Shutdown Basis Fire before fire damage can affect the control circuitry. Boration to cold shutdown is provided in

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all methods described below. Subsequent investigation may reveal that.-

boration is not actually necessary to provide an acceptable shutdown ,

margin; however, the systems required are available.

The ability to remove decay heat is availabic in all cases via the steam generator safety valves but continuous availability requires a feed system. The availability of this heat removal path provides suf ficient time for manual valve lineup or temporary power supply cables t.o be installed for cooldown and long term cooling. The following discussion addresses shutdown methods which are independent of fire damage in npecific areas.:

The methods described are those which require a minimum of equipment i and manpower. If additional equipment remains available, its use could modify the methods of shutting dcwn.

Switchycar Room Fire in the switchgear room could ultimately result in loss of the offsite power supply to plant equipment because of suitchgear and 1

transforme r damage. In this case, heat removal for the short term  ;

l can be accomplished by venting steam through the steam generator safety valves and makeup water is provided by the steam driven feed pump.

When additional manpower is available, temporary power cable can be run from one of the emergency diesel generators to a charging pump, providing ir method for boration and primary system makeup.

4 In addition, as reactor coolant pressure decreases below 1500 psi,

- the ECCS pumps are capable of injecting borat ed water for makeup 2- ,

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-as'they are provided with power from the emergency diesel generators.

For long term cooling, temporary power lines will be run from the diesel generators to the shutdown cooling pumps. A hose interconnection between the fire system and sbi tdown cooling system heat exchanger completes the heat re.aval path. Fire system pressure would be.provided by a fire engine. .For the 'long term, a temporary transformer can.be provided and connected to one of many available overhead power lines.

t From this transforraer, power supply cables could be run to the fire pumps to. relieve the. fire engine.

Control Room The method described above for a switchgear room fire is applicable for a control room fire as well. A fire in tho' control room, which was confined to the control room, would leave much additional equipment available since generally only control circuitry would be subject to-damage. power supply switchgear and transformers should be undamaged and manual operation of switchgear possible. In this case, the steam generator / steam driven pump in available and i i addition charging pumps, shutdown cooling pumps, component cooling pumps, and service j l

uater pumps are available to provide a J ong term cooling capability.

Manhole No. 3 In this instance all f unctions are available. The offsite power supply is unaffected. The main condenser is available for heat removal and the main feed system provides water to the steam generator. One

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charging. pump power cable is- not routed through manhole. No. 3 and this pump ,ls available for boration' and makeup to the reactor coolant system.

I The ECCS pumps are available as described above under Switchgear Room.

Temporary power cables from the ' diesel generator or the Switchgear Room to the shutdown cooling pump can. restore'its function and similar cables to the component cooling system pumps provide a heat removal pathway to the undamaged service water system.

PAB Cable Run to Charging or Shutdown Pumps As explained above,.one charging pump power cable follows a different route than the other two so no single cable tray fire sould remove all charging capability. In this instance, heat removal is to.the condenser with makeup water from~ the feed system. . In the time available, routing

.of temporary cable around any fire damage would quickly provide shutdown cooling and component cooling. The service water system is unaffected by this situation and completes the heat removal path. >

Turbine Building The most difficult method is one which is independent of the turbine room since the feed line connections from the feed pumps, the emergency feed pump, and the charging pumps are located in the turbine building.

In addition, the main feed pumps are in the turbine building and the steam driven emergency feed pump is in the house heating boiler room adj a cent to the turbine hal] . A method of bringing the plant to a

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safe shutdown condition independent of the turbine building is described below. Since this is the'most difficult method, detailed' description

'of the ecluipment and the procedure is provided. ,

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.The timing of the loss of various components cannot be accurately predicted consequently conservative assumptions have been made and are clearly indicated in the following discussion.

The' plant is assumed to be operating at full power with a full operating shift of.five men available when the f' e la d.iscovered. The  !

.c Shif t Supervisor recognizes this as a Safe Shutdoun Fire and notifies the control room operators who initiate the following actions:

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1. The reactor is scrammed causing a turbine trip. During this

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period, decay heat removal continues as required - to the main .l condenser, and stean generator water is provided by the main feed system.

2. Doration to cold shutdown requirements is initiated using one or more of the three charging pumps taking suction directly from the boric acid mix tank which contains a 12% solution of boric acid. Pumps and valves can be controlled from the main control room. Injection of the required amount of boric acid is completed in approximately 15 minutes.

3. During and i:vaediately f ollowing the boration, plant cooldown at the maximum rate of 100 F/ hours is begun. This can be done ,

f rom the control room without requiring assistance from the fire

-fighting team. However, it should be recognized that any fire-requires notification of the Duty and Call Officer and that s .

additional assistance will be shortly available.

4. At 1/2 hour following discovery of the fire, all circulating ,

vater pumps are assumed to lose power and the main condenser is lost as a heat sink. lleat removal to atmosphere is initiated

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- via the steam generator cafety valves and the atmospheric-  ;

. exhaust valve. Until this occurs the net plant water inventory is assumed to remain constant. Atl hour, ' the main feed system is' assumed to lose power and be unavailable .

for steam generator makeup. At this time feed to the' steam generatorn is provided by the emergency feed pump. Feedwater is provided'from the demineralized. water tank ~and the primary water' storage-tank.

5. During the cooldown process the water ' level in one steam generator is maintained near the' upper' limit of the wide range.

level indicator. ..The remaining three generators are filled to the top and isolated. The non-return valves are closed and vents are opened. At 1 1/2 hours, use of the steam driven feed pump is assumed to be lost.

Conservative analysis indicates that .o 'iicient- heat removal' capability is available in the steam generators, without additional- ,

makeup to remove decay heat and cooldown to 330 F at which time i shutdown cooling can be initiated.

6. Power to the shutdown cooling pumps is restored by providing temporary cables betwcon one of the emergency diesel generators and a suitable point on the pump motor cable. Cooling to the heat.-

exchanger (normally by componer.t' cooling water) is provided through an existing emergency hose connection to the fire main. ,

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l Pressure is maintained on the fire system by a fire truck' taking t -'

suction f rom Sherman Pond and- discharging into one of several .

connections availabic at, or near, the screen well house.

Availability of this pump can be assumed since this mode of cooling need not begin' unt.11 approximately 12-18 hours ..

af ter the fire has been discovered.

Ultimately a. temporary power transformer and overhead cable  ;

connected to any of several available. power lines would-release the fire truck.

y Plant procedures directing this operationg have been provided .

! - and' are currently' l'n ef f ect. The location of the appropriate c - cabic termination has been determined end cable is available. -e p

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s Attachment (B) i= ,

Plant' Shutdown Capability Improvement as a Result of ECCS Modification 1

4 Additional inforraation has been requested concerning the modification-of 'the ECCS nystem and 'its coincidental irr.proveraent in safe shutdown capability. A description of the applicable portion of that improvement is given below.

The ECCS system presently consists of three trains of IIPSI pumps which take suction from the safety injection tank and discharge into each loop cold leg. In the event that additional injection pressure is required three trains of LPSI pumps are provided which take suction from the safety injection tank and discharge into the st tion of the HPSI pumps increasing the total injection pressure. In this mode'the ,

. HPSI pump suction.from the Safety Injection Tank is closed by a swing.

check valve operating from the increased pressure provided by the LFSI pumps. Each pair of HPSI/LPSI pumps are powered by its own diesel generator. Cranking power to start one diesel generator-is provided by a battery in the safety injection pump room. The remaining two l diesels are cranked by power from batterica in the switchgear room.

One aspect of the scheduled modification, shown near the bottom of Sketch A, is a provision for injection into #4 loop hot leg.

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l This is accomplished by an' interconnection between the HFSI dischargo-header and the normal charging line. This noJification has the added l benefit of providing three additional trains of pumps available for l

charging pump service to aid in shutting doun the reactor plant. These pumps with their associated diesel generator power supplies are independent ,

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of offsite power and can f unction despite damage to the suitchgear room, control room, turbine building, manhole //3, or any single cable' run to the charging or shutdotm cooling pumps. In the event of a switchgear room fire either the two diesels could'be started before the switchgear room batteries are damaged or temporary cables run from the surviving battery. In any event the diesels and their associated pumps remain undamaged.

An additional benefit is gained. The emergency piping connection >

from' the chargint; pump discharge header to the steam generator feed lines is now also connected to the discharge' of the HPS1 pumps. In thic configuration the larger capacity F.CCS pumps _ are available 'for emergency feed to the steam generator. This.makes additional methods and capacity available f or emergency steam generator f eed which is independent of the switchgear room, control room, manhole No. 3, or any single cable run to charging or shutdown pumps. The emergency feed line connection to the steam generator feed lines is located in the turbine building, however, and is not completely independent.

This modification is described in detail in Proposed Change Number 160 submitted June 6, 1978. No description of its use in fire or other damage situation is provioed in the proposed change. All the equipn.ent is safety grade, redundant and, where applicable, provided with emergency pcwcr supplies.

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' Attachment '(C)- Additional Modification to Improve Shutdown Capability During the site visit of the NRC Fire llazard Review Team in September, a . concern was expressed 'about the ability to safely shutdown :

the plant' independent of fires in certain'specified areas.

A shutdown method independent of the turbine building was of the greatest ' concern since several areas such as the control room, switchgear room, cmcrgency feed pump area and the feedwater control station area are either within 'the boundaries or adjacent to the turbine building.

Yanken Atomic Elect ric Company (YAEC) addressed this concern and snbsequently described the available inethods by .telecon a*.d in '

Attachment A.

'A modification to the ECCS cystem, to be installed during the ref ueling outage improvec the plant shutdown capability. The' benefits of this modification on shutdown capability are explained in Reference (b). ,

To further enhance the ability to safely shutdown, independent i of the turbine ' building, YAEC is installing an additional modification during the November refueling outage. This modification consists of a piping interconnection between the new hot leg injection line described in Attachment B and each steam generator blowdown line.

This new interconnection is shown on attached Sketch B. This .

' interconnection provides a incans of feeding the steam generators independent of the steam generator feed lines in the turbine building, the main feed

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pumpc , and' the emergency s team d riven . feed ' pump. It makes three  ;

charging pumps lavailable to feed the secam generators. -In addition the location of the. interconnection nakes the three trains of safety

~ injection. pumps available to feed the steam generator.. As described in' Reference (b), power for~ each train of safety injection pumps is provided by a separate emergency diesel generator ranking this system

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independent of. any equipment anywl.ere in t.bc turbine building complex.

Multiple locked valves provide assurance against interference with the normal functions of either the'ECCS or the charging system.

By providing a permanently installed steam generator-feed system completely independent of- the turbine building the availability of ,

the steam generator decay. heat removal system is considerably increased.

It is the opinion of YAEC that this modification significantly improves the shutdown capability of the plant by providing redundant, separated systemc.

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