ML19350E221

Station Blackout Rept.

ML19350E221
Person / Time
Site:	Hatch
Issue date:	06/17/1981
From:	GEORGIA POWER CO.
To:
Shared Package
ML19350E213	List: ML19350E212 ML19350E221
References
GL-81-04, GL-81-4, TAC-43915, TAC-43916, NUDOCS 8106170177
Download: ML19350E221 (14)

Text

-.

O EDWIN I. HATCH NUCLEAR PLANT UNITS 1 AND 2

! DOCKET NOS. 50-321 AND 50-326 i

STATION BLACKOUT REPORT IN RESPONSE TO NUCLEAR REGULATORY COMMISSION GENERIC LETTER 81-04 DATED FEBRUARY 25, 1981 I

JUNE 17, 1981

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i TABLE OF CONTENTS

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1. INTRODUCTION 1

2. PRESENT SYSTEM DESCRIPTION

'I A. Offsite Power 1 B. Onsite Power 4

3. RESPONSE TO GENERIC LETTER 81-04 ITEMS 5

4. ADDITIONAL DATA 8

5. FUTURE ACTION ITEMS 8

6. CONCLUSION 9 FIGURES A. GEORGIA POWER GRID SYSTEM 10 B. STATION INC0 KING LINE ARRANGEMENT 11 C. ONSITE EMERGENCY A.C. POWER SINGLE LINE 12 m

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1. ' INTRODUCTION The Nuclear Regulatory Commission (NRC) is currently assessing station blackout events (i.e., loss of all offsite and onsite AC power) on a generic basis. This assessment entitled " Unresolved Safety Issue A-44"is scheduled for completion in 1982. -

In the interim period the NRC at the reconsnendation of the Atomic Safety and Licensing Appeal Board (ASLB) has issued Generic Letter 81-04 dated February 25, 1981 entitled " Emergency 2rocedures and Training for Station Blackout Events". The recommendation from the ASLB results from their decision (ALAB-603) in that the Florida Power and Light Company's St.

Lucie Unit No. 2 Nuclear Plant should consider station blackout as a design basis event.

- This report will answer the concerns of the NRC expressed in Ceneric Letter 81-04 as well as qualitatively show that sufficient stability exists in the Georgia Power Grid System, to make the event of Loss of Offsite Station Power (LOSP) highly unlikely. It will also show that the combination of LOSP and the complete loss of all onsite AC power is an event that,is b ghly improbableduring the operating life of the Edwin I. Hatch Nuclear Units.

The results of this report, in addition to showing that a LOSP and a loss of all emergency AC power is highly improbable will also establish the fact that sufficient training, procedures, and time exist in the design and operation of the Edwin I. Hatch Nuclear Plants to mitigate such an event,

! should it oc<,ur.

Both units of the Edwin I. Hatch Fuclear Plant are of the General Electric Company BWR 4 design with Mark I containments.

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2. PRESENT SYSTEM DESCRIPTION A. 'Offsite Power

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Unlike the Florida Power and Light Crid System, which due to geographical limitations has fewer interconnections to other grid systems

, and reduced locations for alternate connections of a plant to the grid, l

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the Georgia Power Company grid is a network of many interconnections with other grids and multiple locations for tieing its variety of generating plants into the system.

Georgia Power Company is a member of the Southern Company Grid

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System, whose other members are Alabama Fower Company, Gulf Power Company, Mississippi Power Company, and Southern Electric Generating Company. The Southern Company grid system is interconnected with Duke Power Company, Middle South Utilities, South Carolina Electric and Gas Company, TVA and the Florida Peninsula Systems. The interconnection to the peninsular Florida grid is presently separated for' teajor system disturbances. In the near future a new tie, to enable the two systems to remain interconnected, will be made operational.

Although this addition is with the grid system that prompted the ASLB decision, the Georgia Power Company System as shown in Figure A, with

. Its interconnected hydro, fossil-fueled and nuclear. plants will remain a stable secure network.

The Georgia Power system is also designed fo.r connecting its generating units to the grid at the optimum locations. As shown in Figure B, six transmission lines from six different locations and four directions tie the Edwin I. Hatch Nuclear Units to the grid.

l These network connections consist of two 300 kV transmission i lines and four 230 kV transmission lines. A T00/230 kV autotransformer i

connects the 500 kV asitchyard to the 230 kV switchyard'.

I l A ring bus switching scheme is used for the 500 kV switchyard and a breaker and a half scheme is utilized for the 230 kV switchyard.

Three physically independent 230 kV circuits are provided from the switchyard to four startup auxiliary transformers located within the plant security boundary. As shown in Figure B the switchyard boundary -

is less than 100 feet from the plant security boundary.

Electric power required during startup, or shutdown, will be l . drawn from this transmission system through the startup auxiliary transformers. - - . . . -

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1 Although the Loss of Offsite Power (LOSP) is considered highly  ;

unlikely at the Edwin I. Hatch Plant, an analysis of just such an event j was part of the design basis for these units. This analysis is contained in Section 8.3 of the Hatch Unit 2 FSAR and i restated here for continuity of this report.

Steady-state load flow and transient stability studies have been made of the Georgia Power Company grid for 1978 peak and valley load conditions. Haview of 1979 conditions reveals no ' changes which would affect the results of the 1978 studies. The results of these studies demonstrate that:

1. An adequate margin of grid stability is usintained for any,,three-phase faults at Plant Hatch.

The severest stability problems occur during valley load condi-tions as a result of bolted three-phase faults (a highly improbable situ.r. tion) . It is further assumed that the faults are not cleared by backup protective schemes. -

The worst case concerning the 230 kV bus would be a three-phase fault during valley load conditions at the 230 kV terminals of the 500 /230 kV auto transformer. The stability of Plant Hatch and the company grid is maintained for such an improbable occurrence.

The worst case concerning the 500 kV bus would be a three-phase fault during valley load conditions on the 50C kV terminals of the 500 /230 kV auto transformer. In this case, the backup protective

[ scheme also takes the Plant Hatch-Bonair 500 kV circuit out of l service. Again, the stability of Plant Hatch and the grid is maintaincd for such an improbable occurrence.

2. An adequate margin of grid stability is maintained for ann,g, three-phase fault at substations rgete to Plant Hatch.

This fault condition has been considered for all substations remote (one bus away) to Plant Hatch and has been found to be less severs than any fault condition at Plant Hatch (as described in 1. above).

3. For any three-phase fault at Plant Hatch, the tripping of a unit is not required to maintain grid stability.

There are situations where faults involving breaker failure on either the 230 kV bus or the 500 kV bus wculd result in the trip-ping cf a unit by the backup protective scheme. These situations l are less severe than those described in 1. above. In these situations, the tripping of a unit would serve to improve grid stability.

4. The integrity of the grid can be maintained for the loss of any l

generating unit and any transmission element (line or transformer) with any other generating unit being off for maintenanca.

l

This is a generally accepted criterion and poses no significant problems to grid stability.

It should be noted from the foregoing discussion of grid stability that no significant problems are encountered in maintaining the integrity of the grid and that no special methods are employed or necessary to maintain grid reliability.

B. Onsite Power As shown in Figure C the onsite A.C. power supply system consists of the four startup auxiliary transformers fed from the offsite transmission system, five emergency diesel generators, two dedicated and one automatic swing diesel per unit, and four auxiliary transformers fed from the unit's generator system- (not -shown).-On-the- ------

loss of a unit its dedicated auxiliary transformers are disconnected and will not be considered in this report.

Since the operation of the shutdown power syste=s of the two units are identical this report will describe the basic operation of Unit 1 only.

Normal 4160 volt A.C. power to emergency buses lE, IF and 1G is from startup auxiliary transformer ID which is capable of supplying all of the emergency loads required for shutdown. In the event of a failure of transformer ID, or its power supply, undervoltage relays on the emergency buses will detect this condition and an automatic transfer to startup auxiliary transformer 1C will take place. This transformer is also capable of supplying all necessary loads.

! In the unlikely event of a loss of both transformer ID and 1C the emergency buses will be supplied automatically from the Diesel l Generators.

Three separate and distinct Diesel Generatons supply power

o the three emergency 4160 volt buses. Diesel Generator lA supplies l 4160 volt bus lE and its connected loads. Diesel Generator tC 1

supplies 4160 volt bus 1G and its connected loads. Diesel Generator IB, the swing unit, supplies bus IF for Unit 1 or 2F for Unit 2.

During accident conditions, that is a LOSP and a Loss of Coolant 1

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Accident (LOCA), Diesel Generator 1B will be automatically aligned to the accident unit. If a LOSP occurs on one unit and not the other it will automatically align itself to the unit without power. If a total LOSP occurs involving bota units and no accident, it will automatically align itself to a preselected unit. The operator can than best determine which unit should have the use of this system. At no time is Diesel Generator IB supplying power to both units.

The three Diesel Generator Systems are independent such that no single- faflure should prevent them from performing their function.

Further details on starting, loading, testing, and protection of these units can be found in Section 8.3 of the Unit 1 and 2 FSARs.

Orderly shutdowc. under any Sdition can be accomplished with just two of the three Diesel Generator Systems operating. Un der non-acciuent conditions shutdown can he accomplished with either Diesel Generator 1A or 1C for Unit 1 anu _A or 2C for Unit 2.

3. RESPONE TO GENERIC LETTER 81-04 ITEMS A review of procedures and the training program for Edwin I. Hatch operating personnel has resulted in the following replies to the specific items contained in Generic Letter 81-04. The write-up of the item of concern is included for clarity.

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a. "The actions necessary and equipment available to maintain the reactor coolant inventory and heat renoval with only DC power available, including consideration of the unavailability of auxiliary systems such as ventilation and component cooling."

The actions necessary would be identical to the steps delineated in procedure HNP-1-2001 for Unit 1 a d HNP-2-2001 t'or Unit 2. These procedures outline the actions to be taken with the MSIVs closed.

RCIC and/or HPCI would be initiated manually or automatically if the low level setpoint is reached. All valves and auxiliaries of these systems that are required to be operable foe RPV injection are D.C. powered. The RCIC turbine and pump are located in a corner room in the Reactor Building._ The HPCI turbine 5

and pump are located in a separate enclosed room. Cooling for these rooms is provided by qualified units from either Division I or Division II A.C. power. As stated in the reply to item b the RCIC and HPCI area coolers will not be without power for greater than 30 minutes. It is postulated that due to the open stairwell of the RCIC corner room and the volume of,the HPCI compartment t, hat within. this time period no adverse'affects to -he system components will occur.

Georgia Power Company has directed Bechtel Power Corporation to undertake a study to cotdirm this postulation. If the result's prove to be potentially disabling to these component, the NRC will be informed and adequate precautions and/or station modification will be accomplished to alleviate this concern.

b. "The estimate time available to restore A.C. Power and its basis."

Loss of A.C. power to any 4160 Volt Emergency Bus is annunciated by the D.C. backed annunciator system and by indicators in the control room.

Plant procedures HNP-1-1912, HNP-2-1912, HNP 1-1670 and HNP-2-1670 outline the steps to be taken during a LOSP and for starting and operating the Diesel Generator Systems from the Control Room. Procedures HNP-1-3801 and HNP-2-3801 outline the steps to take in starting the Diesel Generators locally.

In the unlikely event of LOSP and no automatic start of a Diesel Generator System, it is conservatively assumed that within t_a (10) minutes an operator can diagnose this occurrence and start any Diesel Generator from the Control Room. If within this ten minute period a diesel cannot be started from the Control Room, an operator will be dispatched to the Diesel Building to start one of the units. This can be accomplished within thirty (30) minutes of the start of the event.

c. "Ihe actions for restoring offsite A.C. power.in the event of a loss of

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the grid."

As discussed in Section 2 of this report the Hatch units are tied into the grid through six separate substations, therefore it is considered highly unlikely that this event will occur. The Georgia Power Company grid with its numerous interconnections is controlled from a central location. Load dispatchers at this location will rest 6Fe' power to M

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the Edwin I. Hatch Nuclear Units on a top priority basis.

They have at their disposal the nece'ssary communications and/or control to restore power to the Hatch units from system interconnections or from the hydro and fossil fueled plaats of the Georgia Power Company system.

d. " The actions for restoring offsite A.C. power when its loss is due to postulated onsite equipment failures."

As noted in the analysis of LOSP (Section 2) no significant problems are en:ountered in maintaining the integrity of the Georgia Power Company grid by events that would occur onsite. In the unlikely event that a failure at the switchyard 'did occur, primary and backup relaying would limit the affect of the failure. In addition, plant operators have control of all switchyard breakers at their disposal in the Control Room.

230 kV and 500 kV switchyard control is performed under the guidance of procedures HNP-1-1646 and HNP-2-1646.

e. "The actions necessary to restore emergency onsite A.C. power. The actions required to restart diesel generators should include consideration of loading sequence and the unavailability of A.C. power."

Existing Edwin I. Hatch Nuclear Plant procedures HNP-1-1670 and RNP 1670 are used by control room operators to start the diesel generators from the Control Room. Procedures HNP-1-1937 and HNP-2-1937 provide guidance in the loading sequence and capabilities of the Emergency Diesels. Procedures HNP-1-3801 and HNP-2-3801 provide the operators with information on starting the diesels locally.

f. " Consideration of the availability of emergency lighting, and any actions required to provide such lighting, in equipment areas where operator or maintenance actions may be necessary."

Emergency lighting is provided throughout the Edwin I. Hatch Nuclear Plant including the Control Room and each Diesel Generator Room. Emergency lighting is also provided in the emergency switchgear rooms, and in the areas required for passage between the Control Room and local operating stations.

g. " Precautions to prevent equipment damage during the return to normal operating conditions following restoration of A.C. power. For example, the limitations and operating sequence requirements which must be followed to restart the reactor coolant pumps following an extended loss of seal injection water should be considered in the recovery procedures." _

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The Edwin I. Hatch Units are of the BWR design. The Reactor Recirculation Pumps are not required for snutdown and are tripped off on turbine trip. In addition, the pump seals do not require injection water to prevent leakage.

The starting and loading sequence procedures for the Diesel-Generators, covered in Item 3, protect them from equipment damage. Other equipment which require service water cooling will receive its supply from the Plant Service Water pumps which are supplied power from their respective Buses.

4. ADDITIONAL DATA Edwin I. Hatch Nuclear Plant Procedure HNP-200 specifies the training and retraining qualification programs required for Licensed Plant Personnel.

This procedure meets the requirements of 10CFR55 and the training program has been approved by the Nuclear Regulatory Commission.

During this program, operators are thoroughly trained in the operation of systems required for safe shutdown including but not limited to HPCI, RCIC, Component Cooling Systems, and the Diesel Generator Systems. Operators

! are also tested on the operation of BWR systems on a BWR simulator. Since this simulator is not site specific the specific simulation exercise of a scation blackout other than HPCI and RCIC operation is not possible.

l Georgia Power Company presently is building a site specific simulator l

to be located within the Edwin I. Hatch plant boundary. This simulator will l be capable of simulating a total station A.C. blackout. The scheduled operational date of this system is early 1983.

P ~5.- EUTURE ACTION ITEMS Georgia Power Company has committed to the implementation of revised caergency procedures in accordance with the schedule specified in Requirement I.C.1 of NUREG-0737. With the implementation of the symptom-l based BWR Emergency Proceduras Guidelines being prepared by the BWR owners groups, of which Georgia Power Company is a member, it is envisioned that a .

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4 symptom-based -specific station blackout procedure will be implemented.

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6. CONCLUSION It is the conclusion of this report that the Georgia Power Company licenses for the Edwin I. Hatch Nuclear Units not be amended to include Station Blackout as a design basis event. This decision is based on the

, following factors as delineated within this report.

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! 3 The\ likelihood of station blackout is not comparable to that of St.

Lucie Unit 2 because of the dissimularities in design, grid connections, and system grids.

9 The Georgia Power Company grid system is a stable secure network with adequate capacity and numerous interconnections to other stable grids.

9 The onsite A.C. power system is a diversified, redundant, and capable i 1 -

system of sufficient capacity which meets the criteria of General Design Criterion 17 and 1EEE 279-]971.

9 The inherent safe design capabilities of the BER nuclear systems lend

• themselves to this type of accident scenario exclusion.

9 Sufficient plant procedures exist to direct the Edwin I. Hatch operators in maintaining the integrity of the Reactor systems and restoring the A.C. power systems.

9 ' Present training programs encompass this situation with training in BWR systems and af te specific equipment operations.

In addition to tha above it is anticipated *. hat the plans of the Georgia Power Company to have ite own site specific simulator and the implementation of symptom based procedurea in compliance with NUREG 0737 will adequately address the highly impr ?bable event of a Station Blackout at the Edwin I. Hatch Nuclear Plant. -

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