Information Notice 1985-91, Load Sequencers for Emergency Diesel Generators

Load Sequencers for Emergency Diesel Generators

ML031180138
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, 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, Crane
Issue date:	11/27/1985
From:	Jordan E NRC/IE
To:
References
IN-85-091, NUDOCS 8511250335
Download: ML031180138 (3)

SSINS No.:

6835 IN 85-91

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, D.C.

20555

November 27, 1985

IE INFORMATION NOTICE NO. 85-91:

Addressees

All nuclear power reactor facilities holding an operating license (OL) or a

construction permit (CP).

Purpose

This information notice is provided to advise licensees and applicants of

potential design deficiencies that could bypass load sequencers, thereby.

causing loss of redundant emergency diesel generators (EDGs).

Recipients are

expected to review the information for applicability to their facilities and

consider actions, if appropriate, to preclude similar problems occurring at

their facilities.

However, suggestions contained in this information notice

do not constitute NRC requirements; therefore, no specific action or written

response is required.

Description of Circumstances

On August 22, 1985, the licensee for the Duane Arnold nuclear plant discovered

that an accident signal and the loss of the standby transformer (a source of

offsite electric power) would cause engineered safety feature (ESF) loads to

be applied as a single block load onto the EDGs (the sources of onsite electric

power), which would likely cause loss of both EDGs.

Pending replacement of the unit auxiliary transformer (lost in a transformer

fire in October 1984), the licensee was operating the plant with the non- safety-related loads on the station startup transformer and the safety-related

loads on the station standby transformer.

The plant design objective was to

sequence the ESF loads onto the EDGs if offsite power to the ESF buses should

be lost and an accident signal was present.

The licensee's training staff

realized that the logic and sensors used to determine the availability of off- site power were such that the offsite power feeder breakers to the ESF buses

could be tripped, but offsite power would be indicated as being still available.

Under these conditions the design would cause the ESF diesel generator load

sequencers to be bypassed.

To justify continued safe operation, the licensee has temporarily placed

certain sequencer test switches in the test position, which forces the sequen- cers to function even though offsite power is sensed as being available.

8511250335

IN 85-91 November 27, 1985 For the longer term, the licensee is developing a permanent design change

which is to be reviewed by the NRC.

Discussion:

The design of the electric power system at the Duane Arnold nuclear plant

includes features to sequence ESF loads onto the EDGs, but not to sequence

loads onto offsite power.

In a sense, these design objectives are in conflict;

that is, one is for sequencing and the other is for not sequencing.

When

design objectives are potentially conflicting, careful analysis is necessary

to ensure that failures of various types do not result in implementation of

the improper objective.

In this case, the logic was designed so that if any

source of offsite power is "available" (such as at either the standby trans- former or the startup transformer) the ESF load sequencers would be bypassed.

Thus, iTthe standby transformer were lost, causing a loss of power to the

safety-related loads, the logic would still indicate offsite power as available.

This design was provided by Bechtel Corporation.

The result was the potential for an interaction between the offsite electric

power system and the onsite electric power system that could have caused the

loss of redundant sources of onsite power.

Such an interaction is incompatible

with'the requirements of 10 CFR 50, Appendix A, General Design Criterion No. 17,

"Electric Power Systems." The Duane Arnold original-design was such that the

availability of-offsite electric Dower was-determined indirectly;that is, by

an upstream measurement rather than directly at the ESF buses.

This deficiency

existed in the original plant design and was not discovered when the design was

reviewed again by the licensee after the loss of tne unit auxiliary transformer

in October 1984.

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

If you have questions about this matter, please contact the Regional Adminis- trator of the appropriate NRC regional office or this office.

rDirector

Divisio

f Emergency Preparedness

and E gineering Response

Office of Inspection and Enforcement

Technical Contacts:

J. T. Beard, NRR

(301) 492-7465

Eric Weiss, IE

(301) 492-9005 Attachment: List of Recently Issued IE Information Notices

Attachment 1

IN 85-91

November 27, 1985

LIST OF RECENTLY ISSUED

IE INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issue

Issued to

85-58 Sup. 1

85-90

85-89

85-88

85-87

85-86

85-85

85-84

85-83

Failue Of A General Electric

Type AK-2-25 Reactor Trip

Breaker

Use Of'Sealing Compounds In

An Operating System

11/19/85

11/19/85 Potential Loss Of Solid-State 11/19/85

Instrumentation Following

Failure Of Control Room

Cooling

Licensee Control Of

11/18/85

Contracted Services Providing

Training

Hazards Of Inerting

11/18/85 Atmospheres

Lightning Strikes At Nuclear 11/5/85

Power Generating Stations

Systems Interaction Event

10/31/85

Resulting In Reactor System

Safety Relief Valve Opening

Following A Fire-Protection

Deluge System Malfunction

Inadequate Inservice Testing 10/30/85

Of Main Steam Isolation Valves

All power reactor

facilities designed

by B&W and CE holding

an OL or CP

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 power reactor

facilities holding

an OL or CP; and

fuel facilities

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 power reactor

facilities holding

an OL or CP

Potential Failures Of General 10/30/85 Electric PK-2 Test Blocks

OL = Operating License

CP = Construction Permit