ML17199T990
| ML17199T990 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities, 05000000 |
| Issue date: | 01/21/1988 |
| From: | Silady J COMMONWEALTH EDISON CO. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| References | |
| 4101K, NUDOCS 8802040245 | |
| Download: ML17199T990 (4) | |
Text
Commomailalth Edison One First Nat-Plaza, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 - 0767 Mr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 January 21, 1988
Subject:
Quad Cities Station Units 1 & 2 Dresden Station *units 2 & 3 Effect of Postulated DC Power Failure NRC Docket Nos. 50-254, 50-265, 50-237 & 50-249 Reference (a):
December 22, 1987 letter from J. A. Silady to T. E. Murley (b) :
Dear Mr. Murley:
Decembe~ 22,. 1987 letter from G.-M. Holahan.to L. D. Butterfield.
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The subject issue (effect of battery failure) was addressed by Commonwealth Edison in Reference (a) and by the staff in the related response of :Reference (b).
The staff required that, within 60 days of the letter, the*
following be provided:
a) additional justification for not considering failure of DC power supply simultaneous with LOCA and Loss of Offsite Power, or b) proposed plant modifications and an implementation schedule for assuringacceptable ECCS performance during such a scenario.
In the course of CECO efforts to resolve this issue, our research into the history of previous correspondence related to postulated DC power failure has identified another relevant document.
Verbal notification was provided to M. Grotenhuis by J. Silady on January. 11, 1988 that NRC Question Il.B.11 and the associated CECo Answer (contained in Amendment 11/12 of the Dresden Unit 2/3 original FSAR) address the impact of various single failures in both the AC and DC systems on engineered safety feature loads for one unit and safe shutdown loads for the other unit.
Copies of the appropri~*te Dresden excerpts are attached for your convenience.
No similar question hq!? peen identified in the Quad Cities FSAR.
..,\\
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Mr. T. January 21, 1988 As indicated by the Answer, it was believed at.that time (erroneously) that the available remaining low pressure ECCS subsystems constituted one core spray and two LPCI trains for a 125V battery failure.
It should also be n~ted that a dedicated, rigorous ECCS analysis (i.e. calculation of peak cladding temperature, local and core wide oxidation, etc.) was apparently not required to respond to the Staff question for this scenario.
The conclusion regarding acceptable core cooling was very likely based on comparison to the worst case analyses addressed in FSAR section 6.2.7.2.a, which included a large break case with only one core spray subsystem available.
Please note that all ECCS analyses in the original FSARs for Dresden and Quad Cities were performed using pre-Appendix K models and licensing bases.
Commonwealth Edison would like to arrange a meeting to discuss the status of our evaluation of items a) and b) above as well as any questions related to this excerpt from the original Dresden FSAR Question and Answers.
The schedule and location for such a meeting will be coordinated through the Dresden and Quad Cities Project Managers.
Please contact this office should further information be-required.
cc:
G. Holahan - NRR M. Grotenhuis NRR T. Ross - NRR Very truly yours, f!q,_
Nuclear Licensing Administrator A. Bert Davis - Regional Administrator (RIII)
- NRC Resident Inspector.- Dresden NRC Resident Inspector :_,Quad Cities 4101K/bs
II. B. 11 DRESDEN 2, 3 IL B. 11-1 QUESTION Evaluate the ability of your onsite and offsite electrical power systems to each separately, and independently, supply engineered Safety feature loads for one unit and safe shutdown loads for the other unit assuming a single failure in each power system. The analysis should include:
(a)
Battery failure (250 or 125V de).
(b)
Faulted DC bus (250 or 125V de).
(c)
Faulted transfer devices (ac and de systems}.
(d)
- Any ac or de load fault.
AN SW.ER
- An evaluation of the onsite and offsite electrical power systems assuming a single failure in each system is presented in the answer to question ill. E. An evaluation of the battery systems is presented as follows:
The 250V de power supply is used as a source of power for some of the containment isolation valves. Each de powered isolation valve is backed up by an ac operated isolation valve. Of par-ticular interest is the HPCI steam line isolation valves, the inboard valve being ac, the outboard valve being de supplied from the 250V de battery. Should the 250V de battery fail, the ac oper-ated valve would still isolate the system. Manual switchover to the other 250V de battery is
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possible as can be seen by Figure 8. 2. 6 of the FSAR.
The 125V de power supply is used to supply the automatic switchgear which is required during a loss of coolant accident. Both the Unit 2 and the Unit 3 125V de battery systems are*
shown in Figure 8. 2. 7 of the FSAR. Control power (125V de) at all the 4 kV and 480V switch-gear is monitored. The loss of this control power to any one bus actuates an alarm which is acknowledged by the operator and the alternate supply of power is transferred to the bus. Feeder breakers to all de distribution panel buses have trip alarms to alert the operator of the Joss of power to any de bus. Loss of either battery or any one bus in its entirety will interrupt control power to only one of the two redundant power systems. For example, loss of turbine building main bus 2 or the Unit 2 battery will result in the loss of control power to Switchgear 23, 23-1 and 28 and the normal. supply to diesel generator 2/3. The diesel generator control circuit will transfer to its alternate source. Buses 24, 24-1 and 29 are unaffected. The operator will be alerted and can transfer buses 23, 23-1 and 28 to their alternate sources.
Should the core cooling systems be required before the alternate source is switched in, the core cooling equip-
. ment would be reduced to one core spray and two LPCl's which provides in excess of 100% core cooling.
Loss of the turbine room reserve bus 2 (or the Unit 3 battery turbine room main bus 3) will result in the loss of control power to Switchgear 24, 24-1, and 29, and to diesel generator 2.
As described above, only half of ~he control power system is temporarily lost.
Control power failure to redundant buses and/or diesel generators can be. affected only by thE* e:onc:ur!*er.t lc.s.s 0~ £1*:2 combined turbine building main bus/reactor building distribution panel
DRESDEN 2, 3 II. B. 11-2 and' the turbine building reserve bus. Concurrent failure due to an electrical fault is prevented by keeping the bus tie breakers open during normal operation. The two turbine room buses are located within the same Class 1 structure which houses the control room and auxiliary equipment room. The same fire and' missile protection afforded to control room panels is applied to the turbine room de equipment. The physical separation of the turbine room reserve bus and the reactor building distribution panel will preclude concurrent mechanical damage to both buses.
Alternating current transfer devices will meet single failure criteria as designed. The only de transfer device is for control power to the Unit 2/3 diesel generator and its failure could cause loss of only that diesel.
The emergency power *system is designed so that an overload of any magnitude less than that expected from a direct phase-to-phase fault will not trip breakers or perform any.automatic*
functions. Over-current relays are provided which wilr isolate a fault on bus 23, 23-1, 24 or bus 24-1 when offsite power is available;. Should the fault be on bus 23-1 or bus 24-1, these
- relays will also prevent the diesel generator breakers from closing into the fault after offsite power has been isolat.ed. Similar protection is not provided for those situations when onsite emergency power is being utilized, however, a kW overload alarm is furnished with each diesel generator which will alert the operator to a potentially hazardous situation.
It is concluded that the redundancy achieved by the dual battery systems, both the.250V de a,nd the 125V de, and by the diesel generator arrangement plus the separation employed in all components, transfer devices, etc., assures that no single failure can prevent operation of the engineered safety features. The worst single failure would *result in the loss of one-half of the core cooling equipment, i. e., one core spray pump and two LPCI pumps. One core spray pump and two LPCI pumps would remain to cool the core. In addition it is noted that the switchover capabiiity in each of the battery systems permits the operator to supply battery power to a unit even if that unit's battery has failed. The load capacity of each battery, as shown in Tables 8. 2. 3 and 8. 2. 4, is sufficient to supply power to both units, even to the extent that one unit has sus-tained an accident and the other unit is being shutdown.
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