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, 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 L 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

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 480V 4C 3D 480V* h 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 August 18, 1986 FIGURE 2 TURKEY POINT -UNITS If 3 & 4*EDG "'A"/-\ 4160V 3A 3B 4160V EDG 'B" 4160V 4A 4B 4160V I)I 3S Si Cl 38 Si 4A Si 4B 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 86-68 86-67 86-66 86-65 Scram Solenoid Pilot Valve 8/18/86 (SSPV) Rebuild Kit Problems Stuck Control Rod 8/15/86 Portable Moisture/Density

8/15/86 Gauges: Recent Incidents -And Common Violations

Of Require-ments For Use, Transportation, And Storage Potential

For Failure Of 8/15/86 Replacement

AC Coils Supplied By The Westinghouse

Electric Corporation

For Use In Class lE Motor Starters And Contractors

Malfunctions

Of ITT Barton 8/14/86 Model 580 Series Switches During Requalification

Testing Deficiencies

In Upgrade 8/14/86 Programs For Plant Emergency Operating

Procedures

Loss Of Safety Injection

8/6/86 Capability

Potential

Problems In West- 7/31/86 inghouse Molded Case Circuit Breakers Equipped With A Shunt Trip Failure Of Auxiliary

Feed- 7/28/86 water Manual Isolated Valve All BWR facilities

holding an OL or CP All BWR holding All NRC licensees authorized

to possess, use, transport, and store sealed sources All power reactor facilities

holding an OL or CP All power reactor facilities

holding an OL or CP All power reactor facilities

holding an OL or CP All PWR facilities

holding an OL or CP All power reactor facilities

holding an OL or CP All power reactor facilities

holding a CP facilities

an OL or CP 86-64 86-63 86-62 86-61 OL = OperatinG

License CP = Construction

Permit