ML19346A231
| ML19346A231 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 06/01/1981 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8106050438 | |
| Download: ML19346A231 (6) | |
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Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C.
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Subject:
Virgil C. Summer Nuclear Station Docket No. 50/395 Residual Heat Removal' System SER Licensing condition 1.8.10
Dear Mr. Denton:
Spurious operation of the RHR isolation valves would be a problem only when the reactor coolant system is under pressure.
If both isolation valves which are in series short in the open circuit, then the RHR system could be overpressurized.
In the response to FSAR question 211.49, South Carolina Electric and Gas Company (SCE&G) identified the RHR suction isolation valves.(8701A and 8702A for loop 1, 8701B and 8702B for loop 3) as valves that may be submerged as a result of flooding in the reactor building.
In amendment 10, our response noted that per-formance of isolation functions would be assured by the institution of administrative controls to close the valves and open the circuit breakers at the motor operator reversing starters whenever the reactor was at power.
In performing a more extensive review of the operation of these valves, it was determired that spurious operation (opening these normally closed valves) due to the flooding is not considered credible since the water will short control poo r fuses. This fact will allow the circuit breakers to be closed at all times.
SER licensing condition 1.8.10 may now be resolved since by having the circuit breakers closed, normal operation of these valves can be performed in the control room thus meeting the requirements of Branch Technical Position RSB 5.1.
The response to FSAR question 211.49 will be revised as indicated on the attached pages in our next FSAR amendment.
In our letter dated May 14, 1981, to Mr. Denton on fire protection, in item 5 we noted that resolution of the NRC concerns for spurious operation of these valves would be resolved through the resolution of SER licensing condition 1.8.10.
Based on the above changes, further discussion is warranted.
Since there is a pressure interlock in the solid state protection system in the relay room, a fire in the control room would not cause spurious operation of the RHR isolation valves (8701.A, '3702A/8701B, 8702B). Likewise, the control 810605068 g
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Mr. Harold R. Denton June 1, 1981 Page Two switch in the control room would prevent spurious operation due to a fire in the
,, relay room.,A fire in the control room cable spreading room could cause a short across the control switch and pressure interlock. However, bafore the RHR suction isolation valves (8701A, 8702A/8701B, 8702B) will open, there is an interlock outside the control building with the Refueling Water Storage Tank (RWST) to the
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RHR pump isolation valves (8809A&B).
These valves (8809A&B) must be fully closed before the respective RHR suction isolation valves (8701A, 8702A/8701B, 8702B) can open. Valves 8809A&B are required by Technical Specifications (item 3.5.2d) to be in the open position when the reactor coolant system is pressurized.
Therefore, in order for a spurious operation to overpressurize the RHR system, both the RHR suction isolation valves (8701A, 8702A/8701B, 8702B) must spuriously operate open and the RHR pump isolation valves (8809A&B) must spuriously operate closed. This is a highly n,11kely set of circumstances.
In conclusion, the current design, with the RHR suction isolation valves (8701A, 8702A/8701B, 8702B) circuit breakers closed provides an acceptable design to meet the fire protection flooding and RSB 5-1 concerns.
If you have any questions, please let us know.
Very truly yours, T. C. Nichols, Jr.
RBC:TCN:glb cc:
V. C. Summer G. H. Fischer H. N. Cyrus T. C. Nichola, Jr.
D. A. Nauman W. A. Williams, Jr.
R. B. Clary O. S. Bradham A. R. Koon M. N. Browne B. A. Bursey Dr. J. Ruoff J. L. Skolds J. B. Knotts, Jr.
J. B. Cookinham NPCF File
211.49 Identify valves that will be submerged and cyclunta tha potential consequences of flooding of the valves for both
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short-term and long-term ECCS operation. Verify that the associated valve controt/ actuation systems are also protected from flooding. The. long term should consider the potential pro.blem of.exce.ssive. ex.ter,n,al,concentr.ations of boric acid on s
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co mp one n t s.. Also, following a postulated large break LOCA, what,
is the maximum predicted water level height inside the contain-ment? List all assumptions.
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RESPONSE
The location of valves inside the reactor building has been reviewed to identify safety grade and associated nonsafety grade valves flooded as a result of an accident (see revised Section 6.3.2.2.7 for the. maximum predicted water level inside the reactor building). The review resulted in identification of the valves discussed below which have some portion of the elec trical circuits associated with the valve operatora below the maximum predicted water level. Features that preclude adverse safety consequences or adverse consequences to long or short term emergency core cooling system operation are as follows:
1.
Valve, Tag No. 137 10 This valve, which is associated nonsafety grade equipment, is used for latdown flow control. Fuses provide sufficient protection to prevent adverse consequences to safety grade equipment. The elee-
$h trical circuitry associated with this valve consists of a 4 to 20 ma signal transmitted from a Westinghouse Remote / Manual Setpoint Sta-g tion which is connected to a 45 volt d-c power supply. This 45 volt d-c power is protected by a 1/2 ampere fuse on the load side of the power supply. The circuitry is not " protection grade" and serves only a " control func tion."
Loss of this circuit does not jeopardize plant safety.
211.49-1 AMENDMENT 10 OCTOBER, 1978
4 2.
Valve, Tag.No. 1003 The safety function of this valve is containment isolation.
The valve perf orms the safety function prior to being flooded. Fuses provide sufficient protection to prevent spurious operation after fl.oodin.g si.nce. limit switches,are,not used for seal-in or interlock p~,
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func tion s.
Circuitry for this valve is similar to that described in Item 3, below, for valve 8143.
3.
Valve, Tag No. 8143
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This valve, which is associated nonsafety grade equipment, is used to direct excess letdown flow to either the volume control tank or the reactor coolant drain tank. Fuses provide sufficient protection to prevent adverse consequences to safety grade equipment.
Elec-trical circuits for this valve are illustrated by CAI Drawing B-208-021, Sheet CS79, submitted as part of the Wiring and Schematic Package (see also Section 1.7).
4.
Valves, Tag Nos. 8153 and 8154 r
These valves, which are located in series, are used for redundant l
l isolation of the reac tor coolant system from the excess letdown heat ex changers. These valves are closed during normal plant operation t
l and are open only during startup. Fuses provide sufficient protec-tion to prevent spurious operation af ter flooding since limit switches are not used for seal-in or interlock functions.
Elec-f trical circuits for these valves are illustrated by GAI Drawings
'I B-208-021, Sheet CS87 (valve 8153) and Sheet CS88 (valve 8154) submitted as part of the Wiring and Schematic Package (see also Section 1.7).
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l 211.49-2 AMENDMENT 10 OCTOBER, 1978
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5.
Valve, Tag No. 8701A l'
Safety func tions of this valve are isolation of residual heat removal system f rom the reactor coolant system and containment-isola 9n.
Performance of these isolation functions are assured by
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'. the insti~ tion of administrative controls to close the valve and 4-T4drI 4
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w oran -the circuit breaker--at-the motor -operator-reversing starter tenever-the -reac tor is-'at power.
It should be noted that the electrical circuits associated with valve operation are above the maximum predicted flood level for a double-ended main sceam line I
break (see revised Sec tion 6.3.2.2.7).
6.
Valve, Tag No. 8701B Safety functions of this valve are isolation of residual heat removal system f rom the reac tor coolant system, containment isolation and interl x k of external limit switch to valve 8706B.
Performance of the isolation functions are assured by the institu-tion of administra tive controls to close the valve.and -open-the-
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-circuit breaker at the -motor -opera tor-reversing-starter-whenever-the 10 reac tor is at_ power. The external limit switch, which is inter-locked to valve 8706B, is above the maximum predicted water level.
7.
Valve, Tag No. 8702A l
Safety functions of this valve are isolation of residual heat removal to reac tor coolant system and interlock of external ihnit switch to valve 8706A.
Performance of the isolation func tion is
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assured by the institution of administrative procedures concerning l
l valve 8701A. The external limit switch, which is interlocked to valve 8706A, is moved above the maximum predicted water level.
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8.
Valve, Tag No. 8702B 1
The safety func tion of this valve, isolation of residual heat I
l removal system f rom the reac tor coolant system, is assured by the l
institution of administrative procedures concerning valve 8701B.
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211.49-3 AMENDMENT 10 OCTOBER, 1978
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INSERT A Previously it was planned-to onen the circuit breaker at the motor 3
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control center to prevent spurious operation. This will not be done since it does not meet the requirements of RSB 5-1 requiring operability from tha main.
control board.
Spurious operation.(opening the normally closed-valves) due to flooding is t.ot considered credible since the water will short control.
power to ground and blow the control power fuses.
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