ML19256B402
| ML19256B402 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 05/02/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Crane P PACIFIC GAS & ELECTRIC CO. |
| References | |
| NUDOCS 7906130132 | |
| Download: ML19256B402 (1) | |
Text
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4, UNI T E D STATES
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NUCLEAn nEGULATonY COMMISSION
,k Zl REGION v SUITE 202. W ALhUT CRE E K PL A 7 A
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W ALN UT C REEK, C AL IFOR NI A 9M96 May 2, 1979 t
u.4 Docket flo. 50-133
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Pacific Gas and Electric Company 77 Beale Str:et San Francisco, California 94106 Attention:
Mr. Philip A. Crane, Jr.
Assistant General Caunsel Gen tlemen:
The enclosed IE Circular fio. 79-07 is forwarded to you for information.
fio written response is required. Should you have any questions related to your understandin9 of this matter, please contact this office.
Sincerely, lh d{,
m R. H. En9elken Director
Enclosure:
IE Circular fio. 79-07 cc w/ enclosure:
p W. Raymond, PG&E E. Weeks, PG&E (Humboldt Bay) a b
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UtlITED STATES NUCLEAR REGULATORY COMMISSI0ft 0FFICE OF IllSPECTIO!! AND EllFORCEMEtiT WASHIflGT0fl, D.C.
20555 May 2, 1979 IE Circular fio. 79-07 UtlEXPECTED SPEED IfiCREASE OF REACTOR RECIRCULATION MG SET RESULTED Ifl REACTOR POWER IfiCREASE Description of Circumstances:
On November 24, 1978, an unexpected rapid speed increase was experienced on the 'B' Reactor Recirculation MG set (RRMG) at the Cooper fluclear Station.
Prior to the event, the RRMG set had been inadvertently tripped during the performance of routine maintenance.
Upon restart, the MG set would not respond to a speed increase signal.
Licensee personnel com-renced trouble shooting this problem in accordance with the instructions in the manufacturer's technical manual.
One step of these instructions suggested removing the fuse from the Bailey scoop tube actuator circuit (a blown fuse would de-energize the actuator and not permit the scoop tube to move).
When the terminal panel cover was removed, licensee personnel noted two fuses instead of one as shown on the vendor drawings.
When licensee personnel removed the second fuse to verify fuse integrity, a rapid speed increase of the MG set occurred.
This increase was terminated by replacement of the fuse or tripping of the MG set by the control room operator (both actions took place almost sinultaneously).
The input signal to the scoop tube actuator is received from the speed controller via a function generator.
This signal is a scoop tube posi-tion demand signal. As the actuator drives the scoop tube in or out of the fluid coupler, a position followup signal is generated to null the input signal and stop scoop tube notion at the required position.
The vendor's drawings of the scoop tube actuator circuit showed only one fuse in the circuit. The licensee contacted the vendor regarding the second fuse and was informed that this fuse had been added as a change in the initial circuit design to provide protection for certain elec-tronic components in this circuit.
This additional fuse is located in the position followup circuit.
Removal or loss of the fuse would result in a loss of the nulling signal and would cause the scoop tube to drive to the naximum speed position.
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