Information Notice 1986-70, Potential Failure of All Emergency Diesel Generators

Potential Failure of All Emergency Diesel Generators

ML031250102
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill
Issue date:	08/18/1986
From:	Jordan E NRC/IE
To:
References
IN-86-070, NUDOCS 8608130578
Download: ML031250102 (6)

SSINS No.: 6835 IN 86-70

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, D.C. 20555 August 18, 1986 IE INFORMATION NOTICE NO. 86-70: POTENTIAL FAILURE OF ALL EMERGENCY

DIESEL GENERATORS

Addressees

All nuclear power reactor facilities holding an operating license or a

construction permit.

Purpose

This notice informs recipients of multiple design deficiencies in a vital ac

power system that could potentially result in the loss of all emergency diesel

generators (EDGs). It is expected that recipients will review the information

for applicability to their facilities and consider actions, if appropriate, to

preclude a similar problem occurring at their facilities. However, suggestions

contained in this information notice do not constitute NRC requirements; there- fore, no specific action or written response is required.

Description of Circumstances

On June 10, 1986, in accordance with 10 CFR Part 21, Florida Power & Light

(FP&L) reported the results of a failure modes and effects analysis (FMEA).

This analysis identified multiple design deficiencies in the Turkey Point

Units 3 and 4 vital ac power system that could potentially result in the loss

of both EDGs due to overloading. In addition, one deficiency was identified

that could result in the loss of all ac power to Unit 4. Turkey Point Units 3 and 4 share two EDGs. Simplified diagrams of part of the Turkey Point 3 & 4 electrical distribution system are provided as Figures 1 and 2.

One design deficiency involved a "swing bus." As shown on Figure 1, 480 volt

MCC "D" is normally supplied from EDG "B" but will shift its power supply to

EDG "A" if needed. MCC "D" also feeds a non-safety stub bus through a single

circuit breaker. This breaker is normally opened by the 48 load sequencer to

isolate the non-safety loads from MCC "D" when the 48 4160V bus is loaded on

EDG "B". A single failure in that circuit breaker would leave the non-safety

loads connected to MCC "D". During safety injection for one unit, the addi- tional non-safety loads could overload EDG "B", possibly resulting in a trip

of this EDG. MCC "D" would then transfer its power supply and could overload

EDG "A" as well.

8608130578

IN 86-70

August 18, 1986 In addition to the above design deficiency, five deficiencies in the EDG load

evaluation were found, each of which could contribute to an overloading of both

EDGs. Both EDGs could be overloaded in the event of a safety injection on one

unit and a loss of offsite power to both units. In some cases this could occur

without a single failure. These deficiencies are as follows:

0 The post-TMI Emergency Operating Procedures require an additional charging

pump and high head safety injection pump in the 1-30 minute and 30-60

minute EDG load interval, respectively.

o In the event of a single failure of one EDG, actual testing of component

cooling water and intake cooling water showed that pump loads (KW) were

higher than expected. Under this condition, the cooling water pumps provide

flow to parallel hydraulic trains. Since the flow resistance is lower, the pump flow rate is greater and the pump motor horsepower would increase.

This in turn may increase the load on the EDG to an unacceptable value.

o Recent environmental qualification evaluations per 10 CFR 50.49 assumed

that the emergency containment coolers operate longer than previously

assumed.

0 Load center transformer losses had not been accounted for in prior EDG

load evaluations.

o Some nonsafety loads that are auto-start enabled when the safety injection

signal is reset could result in EDG overloading. These loads would not

always immediately start, but would auto-start when their start setpoints

were reached after the reset.

In addition to the overloading deficiencies above, a design deficiency.was found

that could result in the loss of one EDG, and at the same time could result in

the loss of all ac power to Unit 4 as mentioned earlier. In the event of a

single failure of the 4A battery or the 4A load sequencer subsequent to a loss

of off-site power, the 4A 4160V bus shown in Figure 2 would be prevented from

automatically loading onto the "A" EDG. It would also prevent the transfer of

the 4A MCC swing bus from 4A load center to 4B load center. The "B" EDG has a

self-contained supply of fuel oil that lasts about one hour. After that time, fuel must be gravity supplied by the day tank via a solenoid operated valve.

However, this valve is powered from MCC 4A. Therefore, the above mentioned

single failure would also cause the loss of the "B" EDG and the loss of all ac

power to Unit 4. The Unit 3 3B 4160V bus would also be deenergized, along with

three of the four high head safety injection pumps and the control room

air-conditioning.

Discussion:

The single failure vulnerability of the non-safety stub bus discussed above may

have been evaluated during the licensing review and the loads on the EDGs found

to be low enough so that failure of the stub bus breaker would not overload the

diesel. Subsequent to initial operation, however, additional loads have been

IN 86-70

August 18, 1986 added on the diesels. Prior to November, 1985, there was the potential for

loading the EDGs to 3544 kw in the 1-30 minute period and 3451 in the 30-60

minute period following a LOCA in one unit with a loss of offsite power in both

units. These load levels exceed the highest FSAR value (1/2 hour exceptional

rating) of 3050 Kw by a substantial margin. With the EDGs overloaded, the

potential exists that safety-related loads would not start or would not operate

at design ratings. Under these conditions, the EDG engines could stall and

damage to the generator and/or engine could occur. There are no test data

available to demonstrate that the EDGs could accept the above load levels.

As an interim solution to the above design deficiencies, FP&L disabled the

automatic transfer between EDGs and established a dedicated operator to take

corrective action (i.e., manipulate appropriate breakers) as necessary. The

licensee has now modified EDG loads, loading sequences and plant procedures.

This example illustrates the importance of reviewing EDG load limits under all

possible operating configurations for a range of design basis accident condi- tions. FP&L, through an FMEA, system testing, and evaluation of EDG load limits, found design deficiencies that may have prevented one or both EDG's from

performing their required function.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate regional office or this office.

Jordan, Director

Divisi of Emergency Preparedness

and Engineering Response

Office of Inspection and Enforcement

Technical Contacts: Henry Bailey, IE

(301) 492-9006 Joseph Giitter, IE

(301) 492-9001 Attachments:

1. Figures 1 and 2, Turkey Point - Units 3 & 4*

2. List of Recently Issued IE Information Notices

Attachment 1 IN 86-70

August 18, 1986 FIGURE 1 TURKEY POINT - UNITS 3 E 4 EDG "B"

I)

LOAD CENTERS

h

480V 4C 3D 480V

N.C.

N.C.

480V MCC D NON-SAFETY

SAFETY

UNIT 3 UNIT 4

'Simplified Diagram of Portion of Electrical Distribution System.

Attachment 1 IN 86-70

FIGURE 2 August 18, 1986 TURKEY POINT - UNITS 3 & 4*

If

EDG "'A" /-\ 4160V 3A 3B 4160V EDG 'B"

4160V 4A 4B 4160V

4A 3S

I)

I Cl38 4B

Si Si Si Si

LOAD CENTERS

480V 4A 4D 480V

N.O.

N.O.

480V NON-SAFETY

SAFETY

"B1 EDG

AUXILIARIES

'Simplified Diagram of Portion of Electrical Distribution System.

Attachment 2 IN 86-70

August 18, 1986 LIST OF RECENTLY ISSUED

IE INFORMATION NOTICES

Information Date of

Notice No. Subject Issue Issued to

86-69 Scram Solenoid Pilot Valve 8/18/86 All BWR facilities

(SSPV) Rebuild Kit Problems holding an OL or CP

86-68 Stuck Control Rod 8/15/86 All BWR facilities

holding an OL or CP

86-67 Portable Moisture/Density 8/15/86 All NRC licensees

Gauges: Recent Incidents -And authorized to possess, Common Violations Of Require- use, transport, and

ments For Use, Transportation, store sealed sources

And Storage

86-66 Potential For Failure Of 8/15/86 All power reactor

Replacement AC Coils Supplied facilities holding

By The Westinghouse Electric an OL or CP

Corporation For Use In Class

lE Motor Starters And

Contractors

86-65 Malfunctions Of ITT Barton 8/14/86 All power reactor

Model 580 Series Switches facilities holding

During Requalification Testing an OL or CP

86-64 Deficiencies In Upgrade 8/14/86 All power reactor

Programs For Plant Emergency facilities holding

Operating Procedures an OL or CP

86-63 Loss Of Safety Injection 8/6/86 All PWR facilities

Capability holding an OL or CP

86-62 Potential Problems In West- 7/31/86 All power reactor

inghouse Molded Case Circuit facilities holding

Breakers Equipped With A an OL or CP

Shunt Trip

86-61 Failure Of Auxiliary Feed- 7/28/86 All power reactor

water Manual Isolated Valve facilities holding

a CP

OL = OperatinG License

CP = Construction Permit