ML20247H447

Special Rept:On 890621,fire Occurred in Containment at Polar Crane Auxiliary Hoist Speed Control Resistor Bank Cabinet Located in Cat Walk.Caused by Melting of Plastic Parts of Temporary Area Fan.Fire Brigade Activated

ML20247H447
Person / Time
Site:	Millstone
Issue date:	07/21/1989
From:	Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
MP-13326, NUDOCS 8907310024
Download: ML20247H447 (3)

Text

_ ___ _. _ - - _ _ _ _

. . ;.n c

.p UEEE

~

General Off6ces

• Seiden Street, Berlin, Connecticut tog CowachCd 90# mppowen c0Wm wiew sue.wams saemc cwas P.O. BOX 270 won * 'ea o*e cwa HARTFORD, CONNECTICUT D6141-0270 no.w.st eum emce c""  ;

g onwas, uca imecw= .

(203) 665-5000 i l

i July 21, 1989 i MP-13326 Docket No. 50-4.23 4 i Re: 100FR50.72 (a) (1) (i) )

c4 l j U. S. Nuclear Regulatory Commission Attn: Doct. ment Control Desk Washingt on, D. C. 20555  ;

Gentlemen: 1 1

Millstone Nuclear Power Station, Unit Number 3 i Pelar Crane - Speed Control Cabinet Fire, In Containment This Special Report is being submitted to provide further information i regarding the fire which occurred in containment at the Polar Crane Auxiliary Hoist Speed Control Resistor Bank Cabinet. On June 21, 1989 at 0225, while in Mode 5 (Cold Shutdown), at 0% power, 83 degrees Fahrenheit, atmospheric i pressure, a fire occurred in Containment at the Polar Crane Anniliary Heist l Resistor Bank Cabinet located in the Catwalk area for the Polar Cram . The l Polar Crane was being used for the lifting and removal of the Refueling Pit Seal Ring performed as part of the Reactor Head Restoration Sequence. The fire was caused by the melting of plastic parts of a temporary area fan which was placed above the resistor bank for cooling. At the time of the fire, the f an was not operating. The heat generated by the resistors during crane operatien melted the plastic grill and fan blades. Molten plastic which dropped into the cabinet was the ignition source for the fire. An immediate notification per 10CFR50.72 (a) (1) (i) was made to document that an Unusual Event, r.e. a fire greater than 10 minutes in duration, had occurred. There are no 30 Day Report requirements per 100FR50.73 for this event. l On June 19, 1989, the upper protective cover for the speed control cabinet was removed and a temporary fen was placed over it as an exhauster, to aide in j

!. cooling. The neat had been generated by numerous start-stop-slow speed crane operations needed for Reactor Head placement. This arrangement worked fer i several days, but the fan was turned off at the completion of the sequence and I was not turned back on for the seal ring lift evolution. Shift personnel within the containment noticed the fire and immediately reported it to the Control Room. The Fire Brigace was activated to extinguish the fire. The fire was confined to the resistor bank Speed Control Cabinet with no damage to any adjacent equipment or panels. Only the upper resistor assembly associated with the Electric Brake was damaged and required replacement. The fire was extinguished with a dry chemical extinguisher E.nd followed up with carbon dicnice extinguisher to ensure that the fire was totally out. The location of the Speed Control Cabinet is on the catwalk of the polar crane in the i Containment overhead and accessed only via ladders. This ac:ounted for the 10 '

6907310024 890721 PDR S

ADOCK 05000423 PDC

[# s l t

m .- . . %

minute duration for getting personnel and fire fighting apparatus on location to extinguish the fire, and reporting back to the Control Room.

The crane was then electrically tagged out. The refueling pit Jaal ring lifting operation was secured and .the seal ring was suspended by the Auxiliary Hook (-Hoist) and the Main Hook at approximately 5 feet below the Reactor Top Hat, which corresponds to approximately 35 feet above the cavity floor. The hooks and loads were in a stable configuration pending resolution of the Auxiliary hook protlem.

Upon full investigation, the only damaged component which required replacement was the upper resistor bank. Adjacent cabinets were fully inspected and no damage was found. All crane repairs and retests were completed at approximately 2345 on June 21, 1989.

The fire was caused by the placement of combustible material - the temporary fan, too close to a significant heat source - the resistor bank, and was not properly controlled or monitored for intended operation. The root cause of this event was the failure to adequately address the polar crane overheating-problems which occurs during extended slow speed operation. The following are areas which contributed to the fire:

1. .The design of the speed control resistor bank cabinet did not provide enough air flow for ventilation.

2. Due to the delicate lifting and handling of reactor components and equipment over the reactor, operation of the polar crane in slow speed is required. This slow speed operation causes full resistor bank loading and subsequent heat buildup.

3. Success of previous temporary cooling arrangements for the resistor bank cabinet to allow extended operations, precluded permanent resolution in the past.

4. The temporary installation should have been controlled under the Unit's established Bypass Jumper program for temporary or altered systems.

The corrective actions associated with this event have been broken down as follows:

1. Immediate corrective action was to repair the Polar Crane Auxiliary Hook. The crane vendor was bought in to assist the unit staff in performing a full evaluation of the damage to the equipment. All repairs and retest were completed at approximately 2345, on June 21, 1989.

2. Walkdowns were performed in all areas of the plant to ensure that combustibles were properly isolated from ignition sources in accordance with good housekeeping practices and to inspect other cranes with speed control resistor banks for similar temporary cooling configurations. Only minor housekeeping problems were identified, which have been addressed by the respons'ble departments. None of the other cranes inspected had any temporal,. cooling equipment installed.

l l

4

~

, 3

3. Unit Chemistry analyzed the Dry Chemical agent for potential adverse effects on the reactor plant. Only small amounts of chlorides and fluorides were found in the agent, approximately 1% per weight of agent, which has an insignificant impact on the plant.

4. A memo was written to all department heads from the Unit Superintendent discussing the event and emphasizing the requirement to initiate a Bypass Jumper to document temporary cooling modifications when installed on plant systems and equipment.

5. An Engineering Evaluation of the overheating problem is ongoing. A design and operational review will be performed by Unit Engineering with long term resolution required prior to the next refueling outage.

The licensee contact for this Special Report is Gary T. Bd 4, who may be contacted at (203) 444-5515.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY For: Stephen E. Scace Station Superintendent Millstone Nuclear Power Station By:

Jbb ohn P. Stet.

Unit 1 Superintendent Millstone Nuclear Power Station SES/GBT:dlr cc: W. T. Russell, Region I Administrator D. H. Jaffe, NRC Project Manager, Millstone Unit No. 3 W. J. Raymond, Senior Resident Inspector, Millstone Units No.1, 2 and 3 I

l 1