ML19259B395
| ML19259B395 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 02/05/1979 |
| From: | Gilleland J TENNESSEE VALLEY AUTHORITY |
| To: | Varga S Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7902090213 | |
| Download: ML19259B395 (10) | |
Text
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TENNESSEE VALLEY AUTHORITY CH ATTANOOGA, TENNESSEE 374o1 500C Chestnut Street Tower 11 Fb 5 1979 Director of Nuclear Reactor Regulation Attention:
Mr. S. A. Varga, Chief Light Water Reactors Branch No. 4 Division of Project Management U.S. Nuclear Regulatory Commission Washington, DC 20555
Dear Mr. Varga:
In the Matter of the Application of
)
Docket No. 50-327 Tennessee Valley Authority
)
In response to a verbal request from the Reactor Systems Branch (RSL) reviewer, Glen Kelly, enclosed is our revised response to question 9 of your letter to N. B. Hughes dated June 28, 1978.
TVA will provide a dedicated operator for unit 1 of the Sequcyah Nuclear Plant (SNP) until first refueling to verify that the Residual Heat Removal System (RHR) suction valves are open and to monitor RHR pump flow whenever the RHR system is in operation with fuel in the reactor.
After first refuelit g of SNP unic 1, a suction flow alarm will be provided to alert operators o the loss of flow to either RHR pump.
This revised response will be incorporated into the SNP Final Safety Analysis Report (FSAR) by Amendment 60.
Very truly yours,
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- f. E. Gilleland Assistant Manager of Power Enclosure
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An Equal Opportunity Employer
4 ENCLOSURE Revised Response to Question 9 of the Letter from S. A. Varga to N. B. Hughes Dated 6/28/78 5.27 Describe the consequences of a failure associated with the isolation valves in the suction line from the hot leg to the RHR pumps during normal shutdown cooling after the head has been unbolted. The failure could be caused by operator error or a passive failure such as the gate separating from the stem.
These failures could cause pump damage due to cavitation and loss of core cooling.
If operator action is required to mitigate the consequences, describe the alarms available to alert him to the situation and the time frame available to perform the required action.
Revised Response:
In the unlikely event of a spurious closure of one of the isolation valves in the RHR suction line from the hot leg during operation of the RHR system, the RHR pumps could be damaged.
The redundant flow indica-tors, provided on both of the RHR injection lines to the RCS cold legs, would provide the operator with indication in the main control room of a loss of RHR flow.
Also, there will be annunciation provided in the main control room which will alarm in the event of a low-flow condition to either RHR pump when running.
A time delay to prevent an alarm during pump start will be incorporated.
(Refer to Figure Q5.27-1.)
This annun-ciation alarm will be provided in time for startup following the first refueling. The indication and alarm of a simultaneous loss of flow in both trains of RHR cooling would lead the operator to directly consider a possible flow blockage in the common RHR suction piping. Also, until the suction flow alarm is installed, TVA will provide a dedicated operator to monitor the RHR flow while the RHR system is in operation.
The operating procedures for a dedicated operator are contained in S0I-74.lA.
This procedure is attached.
Three conditions at the time of loss of RHR pump suction will be consid-ered and the mitigating operator response and time frame available for response will be discussed for each condition.
(1) The reactor is open with the refueling cavity filled.
Approximately 3-3/4 hours are available to the operator to establish an alternate means of core cooling.
This is the time it wcuid take to heat 300,000 gallons of water in the refueling canal from 140 F to 212 F, assuming the maximum 80-hour decay heat load.
In this event, the open mode of reactor cooling would be setuc during the time that the refueling canal water is heating.
This Q5.27-1
mode of cooling is described in section 2.4A.2.2.
To set up this fuel cooling method only requires the installation of two spool pieces and a change in valve alignment. This action would require about two hours. Af ter this arrangement is made, the reactor will be maintained in this cold shutdown condition with decay heat removal via the RHR and spent fuel pool cooling system heat exchangers.
The equipment necessary for this method of core cooling is safety grade.
(2) The reactor is open with the refueling cavity not flooded.
Assuming the minimum time (48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />) until the reactor can be opened (and therefore the maximum decay heat), an initial water temperature of 140 F, and that the reactor coolant system (RCS) has been drained to just below the vessel flange, the water would reach boiling temperature in about 15 minutes if the operator took no action. The water level would be down to the level of the fuel in about an additional 80 minutes.
During this time the injection path valve alignment would be set up to use the safety injection and centrifugal charging pumps to pump water from the refueling water storage tank (RWST) into the reactor vessel and into the refueling canal.
Injection from the RWST could be provided for about five hours (by limiting the injection flow rate to 1000 gpm). During the time of water injection, the operator would set up the open mode of core cooling as discussed in case (1).
After the refueling cavity is filled, the injection from the RWST will be terminated and the open mode cooling circuit activated.
This portion of the procedure would only require a small amount of time since it only involves stopping the injection pumps and closing their respective motor-operated valve from the RWST, starting the spent fuel cooling system pumps, and changing the position of three manual valves.
As in the previous case, the plant can remain for an indefinite time in this cold shutdown condition.
The equipment necessary for this method of ccre cooling is safety grade.
(3) The reactor head is on.
In the event of the loss of RilR suction while the head is still bolted down and tne aCS has been vented, the following analysis applicable. Assuming worst case conditions (maximum 24-hour is decay heat, air in the steam generator tubes, and the RCS drained to just below the vessel flange) and making conservative assump-
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tions about the amount of water available to heat up and boil off, if the operator took no action, boiling would be down to the level of fuel in about 80 minutes (the pressure rise could be limited to about 550 psi by opening the pressurizer power operated relief valves).
Q5.27-2
To restore core cooling, the operator would just attempt to fill and pressurize the reactor coolant system with the centrifugal charging pumps.
If the system can be pressurized to the range of 400-500 psi, the operator would return the plant to heat removal via the steam generators. To do this the operator would have to jog the reactor coolant pumps to sweep the trapped air from the steam generators. He would also have to open the steam dump valves (to atmosphere or the main condenser) and start up the auxiliary feedwater system.
If the head is unbolted but not removed and the system cannot be pressurized (due to flow between the vessel and head and through any open relief paths in the head), the operator would use the procedure outlined in case (2).
In the event of the loss of RHR suction while the head is still bolted down and the RCS has not been vented, the RCS would be allowed to repressurize and go to natural circulation with decay heat removal through the steam generators.
If the RCS was ini-tially at 350 F (the maximum temperature before going to RHR cooling), it would require about 1/2 hour to reach saturation temperature at 400 psia (445 F), assuming the decay heat rate at four hours af ter reactor shutdown (the earliest time to reach RHR cooldown). The operator would then employ either steam dump to the condenser or to the atmosphere with makeup to the steam gen-erators from the auxiliary feedwater system.
The time required is only the few minutes necessary to open the steam dump valves and to start the auxiliary feedwater system.
The equipment and systems actuated can include (depending on whether steam dump is to the atmosphere or the main condenser) the atmos-pheric steam relief valves, the main condenser steam dump valves, the reactor coolant pumps, the auxiliary feedwater system, and other steam plant systems (needed only if steam dump is to the main con-denser). The auxiliary feedwater system is safety grade.
If the nonqualified conde sate supply to the auxiliary feedwater system is exhausted <
.nerwise unavailable, the Category I ERCW supply will be utiliz.o (Reference 10.4.7.2).
The equipment used for steam dump to the condenser and the reactor coolant pumps are not safety grade.
The atmospheric relief valves meet the ASME code for Pumps & Valves, Class II with air supply from the qualified auxiliary control air sy.etem (Reference 9.3.1).
If the relief valves are unavailable, the steam side safety valves will relieve steam to the atmosphere.
In this event, the primary system will reach and be maintained at the normal operating pressure of 2250 psia.
Q5.27-3
.a-n s Page 2 of 5 Rev. 6 IV.
PRECAUTIOQS A.
The boron concentration of the Rl!R system should be equal to or greater than that of the RCS before allowing flow from the RilR system to enter the RCS.
B.
Do not exceed temperature and pressure limits on cooldown rates as
ted in TI-28.
- C.
If RilR system pressure exceeds 700 psig at any time, RilR suction from loop 4 hot leg valves FCV-74-1 and FCV-74-2 will close.
D.
Flow through the RllR system shall be initiated slowly to avoid thermal shock.
E.
Ensure proper RllR pump lubrication.
F.
Component cooling water must be on Ri!R heat exchangers before starting RilR pumps.
G.
4T across the RhR heat exchanger should not exceed 100*F except for start-up and shutdown transients.
11.
Do not isolate component cooling water to an RilR heat exchanger if RCS temperature is > 212' F.
J.
Solid Water Operation 1.
Whenever the RCS is above 160*F, at least one reactor coolant pump must be in operation.
2.
Do not isolate the residual heat removal inlet line from the reactor coolant loop unless the charging pumps are stopped.
This precaution is to assure there is a relief path from the RC loop to the RilR suction line relief valve when the RCS is at and solid water.
low pressure (less than 500 psi) 3.
Whenever the plant is solid water with letdown from RllR, the RilR letdown control valve should be in the full open position and RCS pressure maintained with the low pressure letdown control valve.
During this mode of operation, all three letdown orifices must remain open.
4.
If all RC pumps.. ave been stopped for more than five minutes and the RC temperature is greater than the charging and seat injection water temperature, do not restart a pump until a steam bubble has been formed in the pressurizer.
This precaution will minimize the pressure trans-ient when the first pump is started and cold water previously injected Q5.27-4
S01-74.lA - Units 1 & 2 Page 3 of 5 Rev. 6 IV.
PRECAUTIONS (Cont.)
J.
4.
(Cont.)
by the charging pumps is circulated through the warmer RC components.
The steam bubble will accomodate the resultant expansion as cold water is rapidly warmed.
5.
If all RC pumps are stopped and the reactor coolant is being cooled down by the residual heat exchangers, a non-uniform temperature distri-butian may occur in the RCS.
Do not attempt to restart the RC pump unless a steam bubble exists in the pre s sur ize r.
6.
When the RCS pressure is being maintained by the low pressure le tdown control va lve, FCV-62-81, changes to the flow rate through the RilR loop by throttling of valves or starting and stopping the RilR pumps will result in changes to the RCS pressure.
For example, starting a RilR pump will cause the letdown controller, when in automatic, to sense a high pressure, repositioning the letdown valve and reduce RCS pressure approximate 1,y 30 psig.
Stopping a RllR pump with the primary system solid and on RilR letdown will cause the letdown controller, when in automatic, to sense a lower pressure, repositioning the letdown valve to increase the RCS pressure by approximate ly ICO psi.
K.
Prior to opening RllR suction from loop 4 IIL valves (FCV-76-1 & 2) check FCV's 63-8 and 11 to be f ully closed and remove the pover at the MOV board.
L.
Unit Operator should inform the shif t chemist if there are any necessary deviations from the recommended shutdown operations which could affect system chemistry.
M.
Irtdown to the CVCS should be increased to the maximum le tdown rate prior to cooldown and continued at the maximum flow throughout the shutdown.
- N.
With fuel in the reactor the RilR pumin shall not be run unless there is an operator stationed in t!'e control room with no duties other than to monitor RilR pump flow and verif y FCV's 74-1 and 74-2 remaining open while the pumps are running.
lie is to stop the pumps immediately if a suction va lve is in-advertently closed or flow stops through the system.
This precaution is to prevent dana r,e to the RilR pumps due to loss of suction path and shall be applicable until such time that an acceptabic low flow alarm is installed in the flow path (s).
V.
INSTRUCTIONS A.
Startup of the RllR system for Normal Cooldown Mode The reactor coolant temperature must be less than 350*F and RCS pressure less than 380 psig.
Q5.27-5
S01-74. l A - Units 1 & 2 Pege 4 of 5 Rev. 6 Date Unit V.
INSTRUCTIONS (Cont.)
A.
1.
The RilR system is in the ECC standby condition OR complete valve checklist 74-1 A-1 for standby mode and the RilR system power checklists 74-1A-1, IA-2, IA-3, IA-4.
2.
Place both trains of component cooling water in service for S01-70.1 3.
Open RllR heat exchanger component cooling water outlet valves FCV-10-156 and FCV-70-153.
4.
Close RilR pump suction from RWST FCV 63-1.
5.
Close Rl!R safety injection isolation valves FCV-63-93 and FCV-53-94.
6.
Check FCV-63-8 and FCV-63-11 closed.
7.
Open ACB's for FCV's 63-8 and 63-11.
NOTE,: FCV's 63-8 and 6 3-11 are closed and power pulled to pre-vent inadve r te n t opening when the RilR system is tied to the RCS loop.
Should they inadvertently open during this time, the charging pump and SI pump suction would be overpressurized.
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8.
Open RilR pump suction f rom loop 4 IIL isolatinn valves FCV-74-1 and FCV-74-2.
NOTE:
Valves FCV-74-1 and FCV-74-2 are pressure interlocks and cannot be opened unless RCS pressure is le s s than 425 psig.
FCV-74-1 and FCV-74-2 is also administrative ly controlled at motor control panel.
9.
Close RilR heat exchangers outle t flow control valves FCV-74-16 and FCV-74-28.
10.
An operator is stationed in the control room to monitor RilR flow and suction valve position.
See Precaution N.
11.
Start RllR pumps A-A and B-B and verify miniflow valves FCV 12 and FCV-74-24 open.
J 12.
Af ter five minutes, RllR running time, have water sampled from RilR heat exchanger A and B outlet for boron concentration.
13.
If boron concentration is equal to or greater than the boron concentration of the reactor coolant system, proceed to step 14, if lower than reactor coolant concentration, perform the following:
NOTE :
If boron concentration is lou, the reason should be determined before continuing.
05.27-6
S01-74. l A - Units 1 6 2 Page 5 of 5
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Rev. 6 Date Unit V.
INSTRUCTIONS (Cont.)
A.
13.
,,._a.
Open RilR heat exchanger A and B supply to letdown
.,-Q heat exchanger manual isolation valves74-530 and 74-531.
Check FCV-74-34 closed.
b.
Place CVCS letdown pressure controller PCV-62-81 on hand and desired pressure setting for RCS.
c.
Place CVCS divert valve LCV-62-118 to divert to hold-up tank.
s d.
Immediate ly open RilR pump le tdown to CVCS letdown isolation va lve FCV-62-8 3.
Verify CVCS is maintaining proper VCT level and c.
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~~~
pressure control valve maintaining desired RCS pressure.
f.
Continue letdown from Ri!R system until water sample from RilR heat exchanger out le ts are equal to or greate than RCS boron concentration, Close RilR pump le tdown to CVCS le tdown isola tion valve g.
N FCV-62-83.
,p h.
Place CVCS letdown pressure controller FCV-62-81 on auto and set at desired pressure for RCS.
1 14.
Close RilR heat exchanger bypass flow control valve FCV-74-32.
Jg 15.
Open the following valves.
RilR heat exchanger bypass isolation valves !!CV-74-36, a.
~~ f IIC V-7 4-3 7.
f, b.
SI to RCS loops 1 and 4 flow control valve FCV-63-94.
1 ci SI to RCS loops 2 and 3 flow control valve FCV-63-93.
16.
Slowly throttle open RilR lix bypass flow control valve FCV-74-32 to avoid thermal shock.
i!
17.
When RilR pump flow is 500 gpm, check closed miniflow valves FCV-74-12 and FCV-74-24.
18.
Circulate in this manner until the temperature on the RilR pump discharge as recorded on temperature recorder TR 74-25 and TR 74-14 is within 50*F of the RCS temperature.
19.
Crack open RilR heat exchanger flow out le t control va lve s FCV,
d'*
16 and FCV-74-28 for approximately 10 minutes to warm and ci-iminate thermal shock.
ps 20.
Open Ri!R heat exchanger out le t f low contro l va lve s FCV-74-16 and FCV-74-28 and establish cooldown rate of 100 F per hour.
Coordinat flow through FCV's 74-16, 74-28, and 74-32 to accomplish cooldown of 6100*F/ hour, and 5100*F 4t across heat exchangers.
- Revised comple te page QS.27-7
SOI-74.lA - Units 1&2 Page SA of 5 Re v.
6 Unit VI.
REFERE!;CES 47W810-1 R8 43,'859-4, R3 45N779-9 R8 45N779-10 R7 45N779-Il R7 45N779-i2 R14 45N779-13 RIO 45N663 R6 45N765-13 R5 a
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Q5. 2 7-8
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