ML17256B075

ECCS Switchover to Recirculation

ML17256B075
Person / Time
Site:	Ginna
Issue date:	06/30/1982
From:	Fleming R WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML17256B074	List: ML17256B073 ML17256B075
References
TASK-06-07.B, TASK-6-7.B, TASK-RR FSD-SS-M-2083, FSD-SS-M-2083-R01, FSD-SS-M-2083-R1, NUDOCS 8206290197
Download: ML17256B075 (38)

Text

FSD/SS-N-2083 GINNA NUCLEAR STATION ECCS SWITCHOVER TO RECIRCULATION R.

W.

FLEMING NAY 1982 C

Rev.

1 J UNE 1982 S.

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IIRJ KN-1000 WESTINGHOUSE ELECTRI C CORPORATION P.

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BOX 355 PITTSBURGH'A 15230

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Introduction The. Ginna.Nuclear Station Safety Injection System Design (see *Figure-1')

and -'Eme,rgency. In.struction E-1.2 have,.been reviewed specif'icaLly with respect to the post-LOCA switchover to recirculation.

These documents reflect the original design intent which allowed both Low head safety injection (LHSI/RHR)

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pumps, twohigh,head safety injection.,(HHSI), pumps and one containment, spray pump to continue to operate until the refueling water storage tank (RWST)

Level decreased to,a Level near the RWST outlet nozzles.

ALL the operating safeguards pumps were then stopped and the systems realigned for the recirculation mode before restarting the pumps.

Since the design resulted in a termination of aLL injection f Low whiLe

~ the system realignment to the recirculation mode was being completed the reactor coolant would continue to boiL away without makeup..

The totaL boiloff time period would be determined by the sum of the time increments required for the operator to accomplish severaL discrete actions to realign the pumps and valves in both 'the LHSI and HHSI parts of the system.

An improvement in the use of the installed safety injection

system, during a

Large LOCA~ would result if all inj ection f Low is not terminated during the switchover to recirculation.

Since the reactor coolant makeup will be greater than the boiloff rate from the reactor coolant

system, a net loss of system inventory will not occur during the switchover of the LHSI pumps.

Potent ia L Alternative Switchover Procedures Several alternative procedures have been suggested for other Westinghouse designed

plants, each intended to maintain some safety injection flow during the, switchover from the injection mode to the recircuLation mode of operation.

The folLowing is a

brief description of three of these alternatives.

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In those system designs which include check valves at the pump suction connections from both the RWST and the

sump, a "f'Lying""transfer-of- -the" pump "suction-source-can "be made without stopping erat'her the LHSI or HHSI pumps.

For the LHSI, the sump valves are opened while the pumps continue to draw from the RWST.

Then depending on the relative pressures on the Lines

caused, by the elevation of the RWST or the pressure in the containment the LHSI wiLL draw from one suction source while the check valves prevent backflow in the Line with the Lower source of pressure.

SubsequentLy the LHSI pump discharge isolation valves to the HHSI pump suction header would be opened while the HHSI pumps continue to draw f'rom the RWST.

Again, check valves prevent backf Low to the RWST as the HHSI,.pump suct ion pressure is increased by the discharge pr'essure f rom the LHSI pumps.

t Note that this flying transfer alternative is not possible on Ginna due to the absence of check vaLves in the pump suction Lines.

Another procedure which gives a partial "flying" transfer invoLves only the LHSI pumps.

In this alternative, the sump valves would be opened whi Le the LHSI pumps continue to draw from the RWST.

However, if the elevation of the water in the RWST provides a pressure at the pump suction greater than the pressure in the containment

sump, water would flow from the RWST into the sump untiL the LHSI pump suction isolation valves could be closed.

Note that if one of these isolation valves could not be closed, the RWST would continue to drain into the sump unti L the RWST emptied.

'This single failure can be accepted if the RWST has sufficient margin between the Level at which the transfer to 'recirculation begins and the empty Level, to allow the operators to complete aLL actions required

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to r ealign the:system for recirculation before the tank empties.

Since this alternative presents a potential concern regarding the extra volume margin required in the RWST~

it was not considered for Ginna.

.3.

The third alternative procedure is'a modification of the present procedure and involves simply transferring the LHSI and HHSI pumps suction from the injection mode to the recircuLation mode separately so that both sets of pumps are not inoperative at the same time.

The LHSI pumps are transferred first and during the realignment the HHSI pumps continue to inject into the RCS.

After the LHSI pumps have been reaLigned, and are operating in their recirculation

mode, the HHSI are realigned.

This aLternative maintains either the LHSI or HHSI pumps in operation at aLL times and prevents the complete termination of aLL injection f Low during the switchover to recirculation foLlowing a

Large LOCA.

This third alternative is the one selected for further evaLuation for the Ginna Station.

Summar Operatin Guidelines Attachment I presents a

summary required to effect a switchover to r

whi ch avoids terminat ing a L L saf ety RCS following a Large LOCA.

The obj is to switchover the LHSI pumps to th'e HHSI pumps continue to operate t

RWST of the operator actions t

ecirculation in a

way injection flow to the ective of the procedure he recirculation mode while aking their suction from the It should be noted that in these guidelines, the component cooling isolation valves for the residuaL heat exchangers are opened before the switchover procedure is begun.

This operation

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can be performed at a time in the procedure after the operator has verified the,,proper operation of the service water and'omponent--coo-l-ing-pumps.

The present RWST Level setpoint function (31 percent),

which alerts the operators to reduce the number of operating

pumps, will be eliminated and a

new Low Level'setpoint function added at a

Lower RWST Level.

The new Low Level setpoint wiLL be the si gna L to stop bot h LHSI.,

of the LHSI valve for the (RHR) pumps and begin the realignment switchover to recirculation.

The new containment spray

pump, safety injection pump 1C operation.

Note that whi repositioned, to transfer to the co'ntainment sump,"

f two are in operation and to trip

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if aLL three HHSI pumps are in Le the LHSI valves are being the LHSI pumps suction from the RWST the HHSI pumps continue to'draw from the RWST in their injection mode.

low level alarm wiLl also alert the operator to trip one The LHSI pumps cannot be restarted taking their suction from the sump until there is sufficient water on the containment floor. to provide adequate NPSH for the pumps.

Therefore, the new RWST Low Level setpoint has been selected such that the

.switchover does not occur untiL refueling water has been pumped into the containment to a depth of two feet of water above the containment floor.

This depth provides about one foot margin on the NPSHa to the LHSI pumps.

After the LHSI pumps have 'been realigned and are operating in their recirculation

mode, the operator may proceed to realign the HHSI pumps.

The Low-Low Level alarm from the RWST is retained to alert the operator to proceed to realign the HHSI

pumps, and in particular to stop any pumps stiLL'aking suction from the RWST.

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The present Low-Low Level aLarm at ten percent RWST Level signaLLed the time to trip aLL operating pu since the containment spray pump has been s

mps.

However, hown to. require slightly more NPSH than would be available at the ten percent Level, the new Low-Low Level aLarm will be raised to fifteen percent to provide a suction pressure margin for the spray pump.

This change was suggested in a previous report by Gilbert/CommonweaLth.

Attachment III presents. additiona l information regarding the estimated times available to complete the required operator actions and Attachment II presents a

summary of the RWST volumes avai lable for use.

I RWST Vo Lume Summa r Attachment II, Figure IIA, presents a

summary of the water volumes available in the RWST considering that the two alarm setpoints. remain at their present values.

The effect of an instrument uncertainty of +3 percent of span a lso.has been shown on the figure around each setpoint.

The tank parameters used to estab lish the volume summary

.,are as fol Lows:

tank diameter total volume avai Lable normaL w'ater volume volume below nozzLe span of instrument volume/-foot voLume/%

span 338,000 300,000 6

165 1000 gal gal gaL inches 4i110 gaL 3,425 gaL 26.45 feet

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Since the new switchover guidelines caLL for the trip of the,.LHSI pumps at the Low a La rm setpoint, if t he present 31 percent vaLue were retained'here wouLd 'be insufficient water on the containment fLoor to provide adequate NPSH for the LHSI pumps.

Note from Figure IIA that there might be as Little as 113,550 gaL of refueling water in the containment, with 30,000 gaLLons held up in the refueling cavity if the I

LHSI pumps w'ere transferred to the sump at the 31 percent Leve l.

Since at Least 154,600 gaLLons must be on the floor of the containmen't to provide sufficient NPSH for the LHSI

pumps, a totaL of 184,600 gallons must be delivered before the LHSI switchover procedure is begun.

Figure IIB describes the RWST volume summary required to be compatible with the new recommended operating guidelines.

Note also that the RWST Low-Low Level setpoint is raised to fifteen percent to provide margin to the spray pump NPSHR

, and an operating margin between the Level at which the HHSI

'nd spray pOmps are" tripped off and the Level where the tank outlet nozzL"e becoates uncovered.

The new value of the Low aLarm setpoint (28 percent) provides a

minimum differentiaL volume of 23,975 gaLLons to support the continued operation of one spray and two HHSI pumps while the LHSI realignment takes place.

The differentiaL volume of 184,950 gallons between the new Low-Low alarm md the new'Technical Specification Limit provides the volume of refueling water required to assure adequate NPSH for the LHSI pumps when they are restarted taking suction from the containment sump.

These new volumes shown on Figure IIB indicate a

Larger Technical Specification volume must be specified which requires a

normaL water Level above the present specified Level.

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> il result will be a slightly smaller operating band for the normaL water Level in the RWST.

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0 erator Time AL'lowances Attachment III describes the operator time aLLowances to perform the various required actions to accompLish the switchover from injection to recirculation during a

Large 4

LOCA when the RWST Leve L i s receding rap i dLy due to a L L safeguards pumps running at their maximum. capacity.

It is assumed in this summary that discrete operator actions are not taken earlier than at one minute intervaLs although realistically the operator can move through the procedure at a

more rapid rate.

It is assumed that multip le pump trips can occur very quickly without pause between and that both trains are acted upon by the operator simultaneously.

ALso, if two simiLar 1

pumps (such as two RHR pumps),

are to be tripped out of

=-service, both switches are moved together with no significant pause between.

In the case of restarting of multipLe pumps however, it is assumed'hat each pump is started individually 4

and verified to be operating before moving to the next pump to be started.

Even though it is expected that a

pump wiLL be in satisfactory operation within a few seconds, the one minute criteria between pump starts is maintained in this eva luat i on.

Specifically in the case of realigning the LHSI valves, (704A/8 and 850A/8), the time aLLowance is lengthened to the a'ctual measured time for the va lves to fuLLy stroke before

'moving to'he next step.

That is, the sump vaLves (850A/8) are not started on their opening stroke untiL" the isolation vaLves from the RWST (704A/8) are completely closed.

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h is to prevent a poossibLe spilL of some RWST into the containment

.sump while the va lives. are being repositioned.

Similarly. the

-; LHSI.pumps-.are:-note.restarted-unt-il.-the-sump"val.ves-have-completed their stroke.

Figure IIIA desscribes the operator time allowances for the LHSI switchove r procedure which begins with the actuation of the RWST Low Le ve l alarm.

It can be seen that using the criteria above, thee realignment of the LHSI consisting of four actions wilL be completed in Less than eight minutes.

The time a L Low~~nces for the HHSI switchover i s by

- Figure IIIB~

N/ote on this fi gure s i x actions'dentified and the one minute criteria is applied

," where it is necess-ary to wait for,isolation vavLes described are except to be fully open before,restarting the pumps.

The realignment of the NSI i.s shown to oc:cur in about seven and one-half minutes.

The evaluation a>ove~

and shown by Figures IIIA and IIIB, describes the expe'cted time allowances for the operator to complete the required actions.

To provide an indication of the time available to the operator for his diagnosis and actions during a

Large LOCA, when the shortest times are avaiLable, an estimate of the maximum flow rates out of the RWST was made.

It was assumed that aLL safeguards pumps were

..in operation and that the containment pressure (backpressure on pumps) remained at zero during the draindown period.

The fLow rates from the LHSI and containment spray pumps were obtained from previous calculations but were increased by five percent for conservatism.

The f Low rates from the safety injection pumps, obtained f rom actua L on-.s ate test

data, were increased three percent to account for f Low instrument uncertainties.

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The pump flow rates used in this evaluation are as foLLows:

TABLE III Pump FLow rate, GPN

'Nominal plus margin Safety injection, two pumps, two cold Legs three

.pumps two cold Legs 934 1080 962 1113 Res i dua L heat remova L

'wo pumps 3250 3413 Containment spray one pump two pumps 1783 3566 1872 3745 Using the flow rate from Table III and the RWST water vo lumes described by Figure IIB it is shown that the minimum time to pump down the RWST from the new minimum TechnicaL Specification Limit of 291,125 gallons to the new low alarm (plus margin) would be 22.4 minutes.

This then is the earliest time that the operator would be required to begin the LHSI pump switchover procedure for a

Large LOCA.

After the LHSI pumps are stopped and only one containment spray pump and two safety injection pumps remain in operation, the flow rate out of the RWST will decrease to about 2834

GPN, while the LHSI pumps are realigned for recirculation.

The estimated eight minutes to complete the realignment at an outfLow rate of 2834 GPN results in a

RWST volume minimum requirement of 22,672 gaLLons between the low and the Low-Low

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setpoints.

After rounding off the setpoints to fifteen percent,and twenty-eight percent this delta volume is 23,97S gaLlons.

The estimated earliest time in a

Large LOCA that the HHSI pumps and containment spray pump would be tripped off based on the above volumes and f Low rates would be 30.9 minutes.

A summary of these estimated time margins are as follows:

Activity Time, minutes 1.

Injection p'hase,'ech Spec Level to Low alarm 22.4 2.

LHSI switchover period 8.5 3.

Injection phase, Tech Spec Level to Low-Low alarm 30.9 Conclusion The Ginna post-LOCA switchover procedure, from the injection mode to the recirculation

mode, can be modified and improved to avoid the termination of alL injection flow by transferring the LHSI and HHSI pumps separately.

The emergency procedure for LOCA mitigation can be modified to transfer the LHSI (RHR) pumps suction from the RWST to the containment sump while the HHSI pumps remain in service to provide emergency core coolant during the transfer.

Similarly, the HHSI pumps suction can be transferred to the recirculation mode while the LHSI pumps remain in ope rat ion

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To provide the required NPSH for the LHSI pumps, after their. suction is. transferred *to,the cont'ainment

sump, the

..RWST. Low -Level.-.aLarm-.which.-signaLs-the...proper...time.to.,begin the switchover procedure must be Lowered to twenty-eight percent.

This new setpoint aLLows the operator a

minimum of '22.4 minutes in a

Large LOCA before the first required action must.take p lace and aLLows. at Least eight minutes to transfer the LHSI pumps suction before the RWST Low-Low Level alarm is actuated.

In addition to decreasing the Low Level aLarm, the nominaL Technical Specification RWST water Level must be raised to 301 400 gallons.or eighty-eight percent (indicated) to i

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assure that sufficient water volume is delivered to the

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containment before the LHSI pumps are,.-restarted taking their P

suction 'from the sump.

This new higher Technical Specification Limit results in a

smaLLer operating margin on the RWST normaL working Level.

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ATTACHNENT I

SUNNARY SWITCHOVER GUIDELINE

..,.1.<<<, As ithe...RWST,.water-- LeveL..decreases, perform-.the---fol'lowing actions:

a.

Open the two component cooLing water isolation va'Lves to provide cooling water to the residua l heat exchangers.

2-;

3.

When. the RWST water level has decreased to the Low Level alarm setpoint, (28 percent) stop both residuaL heat remova l pumps, one containment spray pump, if two are operating, and safety injection pump 1C if aLL three HHSI pumps are operating' Realign the RHR pumps for low head recirculation as foLLows:

a.

Close the two RWST to RHR pump suction isolation va Lves (704A/B).

b.

Open the two sump isolation vaLves to the RHR pumps (850A/B).

c. Sta'rt each RHR pump individualLy.

Note for smaLL breaks, the RHR pumps wiLL recirculate through the RHR heat exchangers with no new flow from the RWST to the RCS.

4 Continue to spray the containment with one spray pump and to inject refueling water into the RCS cold Legs using two safety injection pumps.

5.

6.

When the RWST water leveL decreases to the Low-Low Level setpoint (15 percent) stop the operating spray and safety injection pumps.

Realign the SI for high head.recircuLation as follows:

a.

Close both isolation valves in'the RWST to SI/spray pumps's header (986A/B).

b.

Close both SI pumps to RWST recirculation isolation va ives (897, 898).

c.

Open the RHR to SI pumps crossover vaLves (857A/B/C).

d. Start each SI pump 1A and 1B individuaLLy.

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ATTACHMENT II Normal Water Level 300,000 Gal

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6=183,550 Ga l Minimum Tech Spec.

Volume 230,000 Gal.

=113,550 Ga L.

Instrument Uncertainty i +3%

(10,275 Gal.)

ow Leve l A l arm (31%)

106,175 Ga L.

=51,375 Ga l.

6=17,810 Gal.

Low-Low Level ALarm (10%)

34,250 Gal.

E lev. 237'8" E lev. 236'"2" FIGURE IIA GINNA-RWST gpt

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• 291,125 New Tech Spec Level (8'8%)

'-301',"400"'Ga l 6=184,950 Ga l 106~175 85,625-61 650-41,100-6i165 Y..

x=23 975 Ga l 8=34,935 Instrument Uncertainty

+3% (10,275 Ga l)

Low Leve l A larm (28%)

95,900 Ga l Low Low level Alarm (15%)

51 ~375 Ga l FIGURE IIB GINNA-RWST

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ATTACHMENT III OPEPATOR TIME ALLOWANCES LHSI (RHR)

SWITCHOVER-LARGE BREAK RWST Low ALarm 0

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'IGURE IIXA MINUTES Q

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OPERATOR TIME ALLOWANCES HHSI SWITCHOVER FIGURE IIIB R WS-T Low-Low ALarm MINUTES 0

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ATTACHMENT Iy BOIL-OFF ANALYSIS In conjunction with the development of the revised guideline for 'FCCS swi tc*hover to recirculat ion (FSD/SS-N-2083),

a ca Lculati on was performed to assess the abi Lity of HHSI to compensate for the worst case of vessel coolant boil-off. It was established that the ear liest switchover time would be 22.4 minutes.

Injection water was drawn from the RWST at a conservative maximum temperature of 0

120 F and heated to saturated vapor conditions at atmospheric pressure.

The viable heat sources were assumed to be the fueL and vessel thick metaL.

The decay heat modeL which is assumed for the fuel is described in ANSI/ANS-5.1-1979.

The fueL parameters were 100% core power at time zero, 3-year

burnup, and the fission factions were 92% of U235 and 8% of U238 with a 2-sigma margin.

The vesse l metaL heat contribution is minor accounting for approxi-mately 2% of the totaL heat rate.

Considering the above, it would re'quire approximately 28.6 LB>/SEC of HHSI f Low to compensate for the coolant inventory Lost due to boil-off.

At the LHSI shutoff head of 150 psi, the HHSI can deliver 54.5 LBN/SEC of f Low.

This HHSI f Low value assumes degraded performance (i.e ~,

one train spiLling to containment).

The conclusion is that the HHSI f Low adequately compensates for boi L-off; vesseL coolant inventory would not be depleted during switchover.

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