Information Notice 1997-21, Availability of Alternate AC Power Source Designed for Station Blackout Event

Availability of Alternate AC Power Source Designed for Station Blackout Event
	ML031050325
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, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	04/18/1997
From:	Martin T; Office of Nuclear Reactor Regulation
To:	;
References
	IN-97-021, NUDOCS 9704180103
	Download: ML031050325 (8)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 April 18, 1997 NRC INFORMATION NOTICE 97-21: AVAILABILITY OF ALTERNATE AC POWER

SOURCE DESIGNED FOR STATION BLACKOUT

EVENT

Addressees

All holders of operating licenses for nuclear power reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert

addressees to potential unavailability of an alternate ac (AAC) power source during a station

blackout (SBO) event. It is expected that recipients will review this information for

applicability to their facilities and consider actions, as appropriate, to avoid similar problems.

However, suggestions contained in this information notice are not NRC requirements;

therefore, no specific action or written response is required.

Description of Circumstances

On March 11-29, and May 13-22, 1996, a special inspection team from the NRC assessed

the engineering and licensing activities at Millstone Nuclear Power Station. During a review

of the Millstone Unit 3 SBO systems, the team identified a concern about the design of the

AAC power source, the SBO diesel generator (DG), and its dedicated battery. The AAC

power source may not be available if an SBO occurs as a result of a loss of onsite power, i.e., the EDGs, following 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months of loss of offsite (preferred) power (LOOP). The AAC power

source at Millstone Unit 3 is controlled and monitored by a computer. The AAC power

system includes two batteries, one 48-volt battery for the computer and one 125-volt battery

for DG field flashing, oil pump, and breaker control power. The battery chargers for these

batteries are fed from offsite power when the AAC power is not operating. If offsite power is

lost for a significant period, these batteries will be depleted as a result of the connected loads

(the computer for the 48-volt battery and the EDG oil pump for the 125-volt battery). If AAC

power is needed more than 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months after the loss of offsite power, the batteries will be so

depleted that the SBO DG cannot be started and therefore, will not be available if EDGs are

lost.

On March 7, 1997, during a refueling outage at Pilgrim Unit 1 a main transformer failure

resulted in both safety buses losing power. One safety bus was energized from the

shutdown transformer and the other from EDG "B." Approximately 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months into the event, operators attempted to start the SBO DG, but failed. The SBO-DG failed to start because the

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IN 97-21 April 18, 1997 DG support systems, particularly the lubricating oil system, was powered by a nonsafety- related power supply and had been out for an extended period during the loss of offsite

power. This extended loss of auxiliary power caused the oil temperature to drop and that

resulted in oil pressure below the minimum pressure required for DG operation.

Discussion

The Millstone licensee reviewed the design and operation of the MC power source at

Millstone Unit 3 and determined that the MC power source required modification to assure

availability of the SBO DG for no less than 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months (the probable time needed to restore

offsite power) following a postulated LOOP event.

The Pilgrim licensee discovered that the SBO DC was susceptible to a failure to start as a

result of low oil temperature if power was lost to the lubricating oil keep-warm system for an

extended period. The licensee is considering enhanced monitoring of SBO DG auxiliaries, procedural changes, or modifications to SBO DG start logic.

The SBO DG capability to start on demand depends on the availability of the necessary

support systems to fulfill their required function. The SBO DG support systems may require

varying combinations of dc or ac power for varying periods to maintain operational readiness.

Prompt operator actions to conserve battery capacity, support system power supply

modifications, use of special procedures, or start logic modifications may be necessary to

preserve the operational readiness of the SBO DG under challenging environmental

conditions. The staff is evaluating these events and the consequential need for additional

generic communications.

This information notice requires no specific action or written response. If you have any

questions about the .nformation in this notice, please contact one of the technical contacts

listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.

Thomas T. Martin, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: A. Pal, NRR David Skeen

(301) 415-2760 (301) 415-1174 E-mail: anpenrc.gov E-mail: dlsenrc.gov

Thomas Koshy

(301) 415-1176 E-mail: txkenrc.gov

Attachment: List of Recently Issued NRC Information Notices

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Attachment 1 IN 97-21 April 18, 1997 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

97-20 Identification of 04/18'97 All holders of OLs

Certain Uranium for nuclear power

Hexafluoride Cylinders

that do not comply

with ANSI N14.1 Fabrication

Standards

97-19 Safaty Injection 04/1 8,'/7 All holders of OLs

System Weld Flaw at or CPs for nuclear

Sequoyah Nuclear power reactors

Power Plant, Unit 2

94-14, Failure to Implement 04/14/97 All holders of OLs

Supp. 1 Requirements for or CPs for nuclear

Biennial Medical power and non-power

Examinations and reactors and all

Notification to the licensed reactor

NRC of Changes in operators and senior

Licensed Operator reactor operators

Medical Conditions

97-18 Problems Identified 04/14/97 All holders of OLs, During Maintenance CPs, and decommissioning- Rule Baseline Inspections stage licenses for

nuclear power reactors

97-17 Cracking of Vertical 04/04/97 All holders of OLs

Welds in the Core or CPs for boiling- Shroud and Degraded water reactors

Repair

OL = Operating License

CP = Construction Permit

IN 97-21 April 18,1997 DG support systems, particularly the lubricating oil system, was powered by a nonsafety- related power supply and had been out for an extended period during the loss of offsite