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Proposed Tech Specs Revising Switchover Pressure Setpoint of motor-driven AFW Pump to Address Vortexing in Condensate Storage Tank
	ML20063G384
Person / Time
Site:	Sequoyah
Issue date:	02/08/1994
From:	; TENNESSEE VALLEY AUTHORITY
To:	;
Shared Package
ML20063G375	List: ML20063G374; ML20063G384;
References
	NUDOCS 9402160046
	Download: ML20063G384 (10)
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ENCLOSURE 1 PROPOSED TECHNICAL SPECIFICATION CHANGE SEQUOYAH NUCLEAR PLANT (SON) UNITS 1 AND 2 DOCKEi NOS. 50-327 AND 50-328 I

(TVS-SON-TS-93-14)

LIST OF AFFECTED PAGES Unit 1 3/4 3-27a LLn_!L2_

3/4 3-27a t

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i 59002160046 940200 PDR- ADOCK'05000327. {-

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m TABLE 3.3-4 (Continued)

E ENGINEEREO SAFETY FEATURE ACTUATION SYSTEM INSTRUMENTATION TRIP SETPOINTS g

TRIP SETPOINT ALLOWABLE VALUES FUNCTIONAL UNIT g 11. RCS Loop AT Equivalent to R145 y Power > 50% RTP Coincident with Steam >15.0% of narrow range >14.4% of narrow l Rt Generator Water Level-- Instrument span range instrument span Low-Low (Adverse) R145 and Containment Pressure (EAM) 50.5 psig 10.6 psig or Steam Generator Water >10.7% of narrow range >10.1% of narrow range l R1 Level--Low-Low (EAM) Instrument span Instrument span

d. S.I. See 1 above (all SI Setpoints) 1 e. Station Blackout 0 volts with a 5.0 second 0 volts with a 5.0 i m time delay 1.0 second time delay

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H.A. H.A.

f. Trip of Hain Feedwater l

Pumps 3. 2 / gg

g. Auxiliary Feedwater Suction > ig (motor driven pump) >1 sig (motor driven pump)

Pressure-Low > 13.9 psig (turbine driven > psig (turbine driven pump)'

g pump) e Auxiliary Feenwater Suction 4 seconds (motor driven pump) 4 seconds 10.4 seconds g

h.

Transfer Time Delays (motor driven pump)

- 5.5 seconds (turbine driven 5.5 seconds 10.55 seconds m pump) (turbine driven pump)

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, TABLE 3.3-4 (Continued) .

ENGINEERED SAFETY FEATURE ACTUATION SYSTEH INSTRUMENTATION TRIP SETPOINTS h FUNCTIONAL UNIT TRIP SETPOINT ALLOWABLE VALUES c- 11. RCS Loop AT Equivalent to

$ Power > 50% RTP Coincident with Steam >15.0% of narrow range >14.4% of riarrow Generator Water Level-- instrument span range instrument span Low-Low (Adverse) and R132 Containment Pressure (EAH) 50.5 psig 10.6 psig or Steam Generator Water >10.7% of narrow range >10.1% of narrow range Level--Low-Low (EAM) Instrument span Instrument span y d. S.I.

See 1 above (all SI Setpoints)

T e. Station Blackout y 0 volts with a 5.0 second 0 volts with a 5.0 i time delay 1.0 second time delay

f. Trip of Main Feedwater H.A.

Pumps N.A.

p qq E g. Auxiliary Feedwater Suction >2 sig (motor driven purap)

[ Pressure-Low > 3.9 psig (turbine driven 2 1 psig (motor driven pump) g pump) 2 psig (pump turbine driven ) m I h. Auxiliary Feedwater Suction 4 seconds (motor driven pump) 4 seconds 10.4 seconds

--) g Transfer Time Delays 3*

(motor driven pump)

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3l' 5.5 seconds (turbine driven pump) 5.5 seconds 10.55 seconds s co ' (turbine driven pump)

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ENCLOSURE 2 PROPOSED TECHNICAL SPECIFICATION CHANGE SEQUOYAH NUCLEAR PLANT (SON) UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 (TVS-SON-TS-93-14)

DESCRh*'ON AND JUSTIFICATION FOR REVISION 01- Ali'.lLIARY FEEDWATER (AFW)

SUCTION LINE PRESSURE SETPOINT ;

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Descriotion of Chance TVA proposes to modify the Sequoyah Nuclear Plant (SON) Units 1 and 2 technical specifications (TSs) to revise the setpoints for the pressure switches used to control switchover of the motor-driven AFW pump suction frt m the normal nonseismic ,

condensate storage tank (CST) supply to the Seismic Category 1 essential raw cooling water (ERCW) supply. The switchover from the CST to the ERCW is described in the SON Final Safety Analysis Report (FSAR), Section 10.4.7.2, " Auxiliary Feedwater System."

The proposed change will increase the trip setpoint for switchover of the motor-driven ,

AFW pump from 2 pounds per square inch gauge (psig) to 3.21 psig and the allowable l value from 1 psig to 2.44 psig. This change affects TS Table 3.3-4, " Engineered Safety Feature Actuation System Instrumentation Trip Setpoints," for both units at SON.

Reason for Chance TVA proposes to revise the setpoints for the pressure switches used to control switchover ,

of the motor-driven AFW pump suction from the normal nonseismic condensate storage water supply to the Seismic Category 1 ERCW source of supply. In the event of a seismically induced failure of the normal water supply to the AFW pumps, the current ,

switchover setpoint ensures a reliable source of water (ERCW)is available to feed the steam generators (S/Gs).

The revision to these setpoints is considered to be an enhancement to the switchover ,

scenario and ensures that air entrainment in the AFW system supply line does not occur ,

upon reaching a low level in the CST. Air entrainment is postulated to occur at extreme

low levels in the CST because of vortex formation. The development of these vortices is a function of the submergence level of the suction nozzle and the fluid velocity at the nozzle. The previous revision to the setpoint calculation did not consider vortexing in the CST and determined the switchover setpoint based on sensing a failure of the nonseismic suction piping.

A revision to the turbine-driven AFW pump setpoint will not be implemented since changing these setpoints would require a change of the pressure switch because of limitations imposed by the current calibrated range. TVA considers the revision of the -

motor-driven AFW pump setpoints to be a cost beneficial enhancement since this may be accomplished through a revision of the instrument setpoint. TVA does not consider the revision of the turbine-driven AFW pump setpoint to be cost beneficial since it would - i require a plant modification to relocate the associated instrumentation.

Justification for Channe in the event of a loss of' main feedwater, the AFW system supplies sufficient feedwater to the S/Gs to remove primary system decay heat. The AFW system is designed to mitigate. j

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the effects of the design basis accidents and anticipated operational transients listed below:

A. Loss of normal feedwater B. Loss of offsite power to station auxiliaries C. Accidental depressurization in the main steam system ;

D. Rupture of a main steam line _l E. Major rupture of a main feedwater pipe i

F. S/G tube rupture ~!

G. Small break loss-of-coolant accident (LOCA) .l J

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i The preferred source of water for the AFW system is from the CST. A backup supply of water is available through the ERCW system. Transfer to the ERCW system is performed automatically on a two-out-of-three low-pressure signal in the CST suction line.

SON identified a condition during the review of an issue ' identified at Watts Bar Nuclear Plant that could potentially allow vortexing to occur at the AFW suction line during low-level conditions in the CST, resulting in air entrainment in the suction line._ in order to i address this condition for the motor-driven AFW pump, SON proposes to revise the low-pressure setpoint for the automatic transfer of the AFW supply from the CSTs to the ERCW system, thus ensuring transfer of the AFW supply before the occurrence of air entraining conditions.

I In each of the events identified above, the proposed TS revision provides additional 'i assurance that the transfer of the AFW water supply will occur prior to reaching the minimum tank level at which vortexing will occur. Taking into consideration that plant emergency procedures require continuous monitoring of the AFW tank level, the revision of the automatic switchover setpoints is considered to be an enhancement.

A revision to the turbine-driven AFW pump setpoint will not be implemented since changing these setpoints would require a change of the pressure switch because of limitations imposed by the current calibrated range. In addition, because of the location of-the switches, the setpoint for the switch would be much higher than that for the motor-driven AFW pump, resulting in a larger accuracy penalty. The increased accuracy penalty would result in the switchover setpoint being relatively close to the normal operating pressure that would increase the probability of an inadvertent switchover. The justification for not revising the turbine-driven AFW pump setpoint is provided below.

The SON design basis requires the operation of the turbine-driven AFW pump in the event of a main feedwater line break (MFWLB), a main steam line break (MSLB), a small break _,

LOCA (SBLOCA), or a station blackout (SBO). In the event of an MFWLB or an MSLB, the !

failure of one S/G could prevent a single motor-driven AFW pump from feeding two S/Gs '

because of the isolation of the failed S/G. The operation of the turbine-driven AFW pump is required throughout these events to ensure the supply of AFW to two S/Gs, as required by the SON FSAR. The turbine-driven AFW pump is required during an SBO because of -

the unavailability of the motor-driven AFW pumps and during an SBLOCA to provide an initial high AFW flowrate to ensure proper heat removal.

In each of these events, the switchover of the turbine-driven AFW pump on low tank level !

is controlled by Operations procedures. This is considered an acceptable operator action since the transfer of suction on the low tank level is a long-term condition, several hours into the event; and sufficient water is maintained in the CST, 190,000 gallons minimum, :

to ensure that sufficient time is available to provide switchover. ;

in the initial stages of an MFWLB, an SBLOCA, or an MSLB, approximately 660 gallons per minute (gpm) is required from the tuGine-driven AFW pump. In addition, the MSLB requires a maximum 2,790-gpm flouv (2,350 gpm to the failed S/G and 440 gpm to two intact S/Gs) during the initial 10 rr nutes of the event, before the S/G isolation. In each of '

these_three events, the initial high-flow requirement is reduced to that required to remove - ,

decay heat and is maintained by S/G level control. Conservatively assuming that 175,000'- i gallons is maintained in the CST (allowance for a calculated vortex height equivalent to 15,000 gallons), sufficient volume remains in the CST for approximately 9.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months of l r

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'3_j operation fol lowing an MSLB and approximately 11.75 hours8.680556e-4 days 0.0208 hours 1.240079e-4 weeks 2.85375e-5 months of operation following an :

SBO.

The MSLB and SBO events described above represent the extremes for providing water to ,

the S/Gs to maintain hot standby conditions. Based upon the time available before vortexing occurs in the CST, TVA considers the revision of the setpoints associated with . !

the switchover of the motor-driven AFW pump to be an enhancement. In addition, TVA does not consider it prudent to modify the setpoints associated with the turbine-driven .

' AFW pump because of the probability of an inadvertent switchover to ERCW resulting I from overranging the pressure switches.

Environmental imoact Evaluation

1 The proposed change does not involve an unreviewed environmental oestion because.

operation of SON Units 1 and 2 in accordance with this change would not:

1. Result in a significant increase in any adverse environmental impact previously j evaluated in the Final Environmental Statement (FES) as modified by NRC's testimony '

to the Atomic Safety and Licensing Board, supplements to the FES, environmental impact appraisals, or decisions of the Atomic Safety and Licensing Board. '

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2. Result in a significant change in effluents or power levels. ;

3. Result in matters not previously reviewed in the licensing basis for SON that may l have a significant environmentalimpact. }

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'r ENCLOSURE 3 PROPOSED TECHNICAL SPECIFICATION CH tNGE SEQUOYAH NUCLEAR PLANT (SON) UNITS 1 AND 2 .

a DOCKET NOS. 50-327 AND 50-328.

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(TVS-SON TS-93-14) -

l DETERMINATION OF NO SIGNIFICANT HAZARDS CONSIDERATION j

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Significant Hazards Evaluation i

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TVA has evaluated the proposed technical specification (TS) change and has determined i that it does not represent a significant hazards consideration based on criteria established in 10 CFR 50.92(c). Operation of Sequoyah Nuclear Plant (SON) in accordance with the proposed amendment will not: ;

1. Involve a significant increase in the probability or consequences of an accident ;

previously evaluated.

The auxiliary feedwater (AFW) system is designed to mitigate the effects of the j design basis accidents and anticipated operational transients listed below:

A. Loss of normal feedwater !

B. Loss of offsite power to station auxiliaries ,

C. Accidental depressurization in the main steam system D. Rupture of a main steam line ,

E. Major rupture of a main feedwater pipe '

F. Steam generator tube rupture ;

G. Small break loss of coolant accident l The AFW system only provides mitigation of the events listed above and cannot i initiate a design-basis accident.. Therefore, the proposed change in the low-pressure setpoint of the motor-driven AFW pump supply line will not result in an increase in the ;

probability of a previously analyzed accident. In addition, the proposed change does !

not affect the overall water supply to the AFW system. Instead, the proposed change results in a transfer from the condensate storage tanks (CST) to the essential raw .

cooling water system at a slightly higher CST water level, thus enhancing the i continuous supply of water. Therefore, this change will not result in an increase in - ,j the consequences of a previously analyzed accident. ;

2. Create the possibility of a new or different kind of accident from any previously analyzed. ;

As discussed previously, the AFW system provides only mitigation functions. In addition, the proposed change does not affect the overall function and operation of the AFW system or its associated water supplies. Instead, this change will provide ;

additional assurance of the proper operation of the AFW system. Therefore, the proposed revision of the low-pressure setpoint of the motor-driven AFW pump supply '

j line will not create the possibility.of a new or different kind of accident from any !'

previously analyzed.

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3. Involve a significant reduction in a margin of safety.

The TS bases for the AFW system require that AFW be available to ensure that the .;

reactor coolant system (RCS) can be cooled down to less than 350 degrees Fahrenheit from normal operating conditions in the event of a total loss of offsite i power. In addition, the TS bases for the CST reouire that a minimum water volume - +

be available to maintain the RCS at hot standby condition for two hours with steam discharge to the atmosphere concurrent with a totalloss of offsite power.

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The proposed TS revision does not affect the overall operation of either the AFW ;

system or the CST. The proposed setpoint revision does slightly reduce the usable I volume of water in the CST. - However, sufficient margin remains to ensure .;

compliance with the bases of the SON TSs, Therefore, the proposed changes to the SON TSs do not involve a reduction in the margin of safety. i t

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ML20063G384

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