ML19269C264

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Submits Reportable Occurrence on 790115:confinement Fan 1 Failed to Start.When Transferred to Auxiliary Generator, Smoke Was Observed from Fan 1 Load Transfer Cabinet.Caused by Fuses Opening;Smoke Caused by Trip Coil Overheating
ML19269C264
Person / Time
Site: North Carolina State University
Issue date: 01/24/1979
From: Bohannon J
North Carolina State University, RALEIGH, NC
To:
Office of Nuclear Reactor Regulation
References
ADM-1-1-16-1, NUDOCS 7901310023
Download: ML19269C264 (2)


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NORTH CAROLINA STATE UNIVERSITY AT RALEIGH SCIIOOL OF ENGINEERING DEPARTMENT OF NUCLEAR ENCINEERING NuctEAR REAQVR PRERAM Box 5636 Zie 27650 ADM l-1-16-1 Directorate of Regulatory Operations Office of Regulation U.S. Nuclear Regulatory Commission Washington, DC 20545 Docket No. 50-297 Gentlemen:

In compliance with PULSTAR Technical Specification 6.5.c. and 6.7.2.c.

we hereby submit the following report:

During the PULSTAR reactor pre-operational check-out on 15 January 1979 Confinement Fan No. 1 failed to start as required. Confinement Fan No. 2 then started as a normal part of the Confinement Mode sequence. (Fan No. 1 failed to start because the three 15 amp. disconnect fuses in the Motor Control Center had opened.) The Auxiliary Generator was started, Fan No. 2 was stopped and Fan No. 1 was transferred to auxiliary generator power. Shortly after Fan No. 1 was transferred, smoke was observed coming from the Fan No. 1 Load Transfer Control cabinet located adjacent to Fan No. 1. 3 auxiliary generator was immediately secured and the source of smoke antified as coming from a small trip coil inside the load transfer control cabinet.

Subsequent maintenance indicated that the trip coil, designed for momentary duty only, had remained energized, overheated and failed. Energizing current for the trip coil is controlled by a microswitch that had developed mechanical binding in the switch contact actuator, thereby preventing normal release of the trip coil current.

A factory representative replaced the faulty microswitch and the trip coil.

The new trip coil failed immediately after installation due to a moulding defect in the coil bobbin. After careful inspection, another trip coil was installed and proper fan operation was achieved.

The only identifiable factor common to both the blown disconnect fuses and the binding microswitch actuator was evidence that water had entered the load transfer cabinet and caused corrosion of the microswitch actuator.

Under this condition the disconnect fuses would be expected to open because proper load transfer had not been accomplished.

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Page 2 . . . 24 January 1979 To prevent recurrence, inspection of the load transfer control cabinets for both confinement fans will be added to the routine reactor surveillance schedule, the cabinet will be shielded from leakage water and the water leak (seepage from overhead loading platform slab) will be secured.

There were no violations of technical specifications, the system operated as designed in .ase of fan failure and remedial action has been completed.

J Bohannon, Jr.

Nuclear Operations Administre sor JRBjr:ake cc: Mr. Tom McHenry USNRC, Region II Dr. T. S. Elleman RPC