ML20198A492

Assessment of Manual Loading of Diesel Generators for Loss of Offsite Power,San Onofre,Unit 1

ML20198A492
Person / Time
Site:	San Onofre
Issue date:	03/31/1986
From:	Udy A EG&G IDAHO, INC.
To:	NRC
Shared Package
ML13324A884	List: ML20198A492
References
CON-FIN-D-6023 EGG-NTA-7176, TAC-60807, NUDOCS 8605210116
Download: ML20198A492 (14)

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• Enclosure f EGG-NTA-7176 ASSESSMENT OF THE MANUAL LOADING OF THE DIESEL GENERATORS FOR THE LOSS OF 0FFSITE POWER SAN ONOFRE NUCLEAR GENERATING STATION, UNIT NO. 1

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A.C. UDY f

March 1996 EG&G Idaho, Inc.

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' Idaho Falls, Idaho 83415 l

Prepared for the U.S. Nuclear Regulatory Commission .

Washington, DC 20555 Under DOE Contract No. OE-AC07-761001570 FIN No.06023 lYA .

ABSTRACT This EG&G Idaho, Inc., report assesses the adequacy of the manual loading of the diesel generators for a loss of offsite AC power without a concurrent safety injection signal. This assessment is specific to Unit

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b No. 1 of the San Onofre Nuclear Generating Station, and examines the limit of the time allowable for the diesel generators to be manually loaded, k

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m Docket No. 50-206 TAC No. 60807 1

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, e FOREWORD k

This report is supplied as part of the " Issues Related to the San -

Onofre Event," being conducted for the U. S. Nuclear Regulatory Comission, Office of Nuclear Reactor Regulation, Division of PWR Licensing-A, by EG&G Idaho, Inc, NRC Technical Assistance Division.

Occket No. 50-206 .

TAC No. 60507 iii

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. e CONTENTS 11 ,

ABSTRACT............................................................... .

FOREW0RD...............................................................iii 1

A. INTR 000CTION.........................................................

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2. REVIEW REQUIREMENTS..................................................

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3. EVALUATION...........................................................

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4. CONCLUSIONS................................................./........

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S. REFERENCES...........................................................

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. s ASSESSMENT OF THE MANUAL LOADXNG OF THE DIESEL GENERATORS FOR THE LOSS OF OFFSITE POWER SAN ONOFRE NUCLEAR GENERATING STATION, UNIT NO. I

1. INTRODUCTION On November 21, 1985, Unit No. 1 of the San Onofre Nuclear Generating Station experienced a loss of offsite power event. This event was initiated by the protective relays associated with the unit's auxiliary transformer C that had detected a fault and, as a result, isolated the transformer from the 220 kV switchyard and from the 4160 VAC Class 1E bus 2C. With bus 2C and its associated loads de-energized, the reactor was tripped by the operators as required by procedure. As the redundant Class {

- 1E bus IC was receiving power from unit auxiliary transformer A at the time, bus 1C as well as the remaining in-plant AC loads were de-energized concurrent with the trip of the unit generator.

The diesel generators associated with the Class 1E buses started automatically when their respective buses detected a loss of pcwer; howeverr .without a safety injection signal concurrent with the loss of

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offsite power, they did not automatically load. This is in accordance with the design of the unit's electrical distribution system.

is described in NUREG-1190 (Reference 1). Soutnern The event California Edison Ccmpany, the licensee for the San Onofre Nuclear Generatir.g Station, previded information relative to the manua.1 loading of 1

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e o the unit's diesel generators in Enclosure 3 of their submittal dated March 2, 1986 (Reference 2). This report is based on the information presented in these references. ,

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2. REV!EW REQUlREMENTS The design of the electric distribution system of Unit No. 1 of the Onofre Nuclear Generating Statien was evaluated against the San ,

requirements and recommendations of the following documents.

1. Code of Federal Reoulations, 10CFR 50, Appendix A, General Desion Criteria for Nuclear Power Plants

-Criterion 17, " Electric Power Systems"

-Criterion 20, " Protection System Functions"

2. Standard Review Plan, NUREG-0800

-Chapter 8.2, "Offsite Power Systems"

-Chapter 8.3, "AC Power Systems (Onsite)"

3. Regulatory Guide 1.32, " Criteria for Safety-related Electric Power Systems for Nuclear Power Plants" u

4. IEEE-Std-308, " Criteria for Class 1E Power Supplies for Nu: lear Power Generating Stations" p

5. Clarification of TMI Action Plan Recuirements, NUREG-0737, Item II.E.1.2 ,

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In general, these requirements and recommendations provide for an o electric power system that is free from the effects of single failures that could prevent the performance of any given safety function that miti ga't'e's a design basis accident. Specifically, the auxiliary feedwater system is required by Item II.E.1.2 to be automatically initiated and .

powered by the Class IE buses.

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3. EVALUAT80N l

Design Criterion 17 requires an onsite and an offsite electric General ,

power system, each of sufficient capacity and capability to assure that fuel design limits and that the design limitations of the reactor coolant system pressure boundry are not exceeded and that core cooling, containment integrity and other vital functions are maintained. The criterion recuires only one of the offsite sources to be immediately available. All power sources are to be designed to minimize tne probability of losing any other power source should one power source be lost, be it the unit generator, the offsite power grid or the onsite power ,

sources (diesel generators).

General Design Criterion 20 requires that the protection system initiate automatically the appropriate systems to assure that the fuel design limits are not exceeded as a result of anticipated operational occurrences.

Item II.E.1.2 of NUREG-0737 recuire's the timely initiation of auxiliary feedwater by having power derived from the Class 1E buses, by I being automatically initiated, and by being automatically actuated onto m the Class 1E buses. The auxiliary feedwater system was previously -

approved by the NRC in a Safety Evaluation Report dated November 18, 1982 (Reference 3).

The event discussed herein was precipitated by a phase to phase cacie fault on the secondary side (4160 V) of auxiliary transformer C. This source of oower is the immediate source of offsite power to the Class IE buses. The delayec access source, that was provided four minutes into inc 4

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event, is auxiliary transformers A and B supplied by the main transformer that is backfed from the 220 kV switchyard. The unit generator disconnects automatically from these transformers by the automatic operation (on the unit trip-) of a motor-operated disconnect switch.

The diesel generators automaticallystartwhentheirrespe(tivebuses detect a loss of power. They are automatically loaded only when there is a l

loss of power coincident with a safety injection signal. The diesel l generators started successfully for this event and did not load according to design, as there was no safety injection signal. The fuel design limits and the design limitations of the reactor coolant system pressure boundry were not challenged. However, the low pressure portion of the feedwater system (secondary coolant) was damaged by the loss of feedwater and -

subsequent water hamer, but this was because of the concurrent failure of the feedwater system check valves. The licensee states that even if the diesel generators had automatically picked up the.it loads, this would not have made a significant change in the course of the event'. The feedwater pioing would still have been partially voided before auxiliary feedwater i

flow was established to the steam generators.

Boifi 'the steam driven and the motor driven auxiliary feedwater pumps l

were actuated by the low steam generator level as designed. The steam driven pump started delivery after its warmuo cycle was complete. The motor driven pump (G105) started as offsite power was restored to Class IE bus IC, that supplies power te the 460 V auxiliary feedwater pump motor via 480 V switchgear no. 1. The power routing from the 4160 V bus to the 480 V bus is not affected by the loss of power.

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The controls for the motor driven pump had received an automatic actuation signal as designed. This automatic actuation did not imediately start the auxiliary feedwater pump. The pump was started as power was ,

manually restorad from the offsi.te grid. The licensee has s'hown that the restoration of offsite power is readily accomplished by the manual actions of the operators.

The licensee addressed the following points concerning the manual loading of the diesel generators and the restoration of power to the auxiliary feedwater pump under the event conditions.

1. The diesel generators can, once started, operate unloaded for 30 minutes before power to the diesel auxiliaries must be -

provided. This power can be either from the offsite grid or .

derived from the diesel generator when power to the Class 1E _

4160 V bus is restored. In the November 21, 1985 event, this

- power was provided by the delayed offsite source before the diesel generators were secured.

2. The delayed offsite power source is aligned automatically.

The operator verifies the alignment and closes one circuit breaker in the 220 kV switchyard from the control room to restore system power. This alignment is done by the loss of voltage automatic transfer sequence system. This system takes about one minute to operate after the unit generator has wound down to 40 percent of its nominal output voltage. .

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3. The u' nit has been analyzed to be capable of sustaining a loss

- of AC power in excess of 15 minutes without the loss of the capability to remove decay heat (i.e., the steam generators will not boil off in this time frame).

4. The licensee has previously responded to the station blackout concern, showing that hot standby conditions can be main-tained for more than two hours with no AC power available.

5. The licensee has performed analysis that shows that only the loss of coolant (LOCA) and the main steamline break (MSLB) events recuire immediate actuation of the engineered safety feature (ESF) system components. Automatic loacing of the diesel generators is provided for these events.

6. The licensee has performed analysis that shows that events other than LOCA and MSLB do not recuire the immediate restoration of power.

7. The licensee states that using the diesel generators as the power source for the Class 1E loads when a viable preferrec 6 -

offsite power source is available is not desirable. It would further stress the equipment when offsite power is restored.

The licensee is also evaluating possible improvements to the electrical power systems, including automatic transfer of the 4160 V buses to the presently delayed access second source of offsite -power and installation of another auxiliary transformer to power the Class IE buses independently of transformer IC.

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4 CONCLUSIONS We conclude that the licensee has shown acceptable basis for the ,

manual loading of the diesel generators for a non- LOCA or'MSLB event.

i This is based on the licensee's analysis showing that suffic,ient time exists for the operator to take the manual actions necessary to mitigate the analyzed events in a timely manner.

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5. REFERENCES

1. Loss of Power and Water Hammer Event at San Onofre. Unit 1, on November 21, 1985, NUREG-1190, U.S. Nuclear Regulatory Commission, January 1986.

2. Southern California Edison Company letter, M. O. Medford to A. E.

1 Chaffee, NRC Region V, " Evaluation of November 21, 1985 Loss of Power l

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and Water Hammer Event", March 2, 1986. l

3. NRC lett.or, D. M. Crutchfield to R. Dietch, Southern California Edison -

. Company, " Auxiliary Feedwater System Automatic Initiation and Flow b Indication (TMI Action Plan Item II.E.1.2)," November 18, 1982.

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SIBUOGRAPHIC DATA SHEET EGG-NTA-7176 Mc."/Jy gg g eggttwCf.o%l o ..e ea v gage a . .. ... .

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Assessment of the Manual loading of the Diesel '

Generators for Loss of Offsite Power, San Onofre Nuclear Generating Station, Unit No. 1 ****''"**.;...

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U.S. Nuclear Regulatory Comission Washington, DC 20555 '_

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This EG&G Idaho, Inc. report assesses the adequacy of the manual loading of the diesel generators for a loss of offsite AC power without a concurrent safety injection signal. This assessment is specific to Unit No. 1 of the San Onofre Nuclear Generating Station and examines the .

limit of the time allowable for the diesel generators to be manually

. loaded. .

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