ML19327B734

LER 89-027-00:on 891011,automatic Reactor Trip Occurred W/Reactor in Stable Operation at 58% Rated Thermal Power. Caused by Dropped Rod Due to Diode Failure.Diode for Rod K-2 replaced.W/891103 Ltr

ML19327B734
Person / Time
Site:	Vogtle
Issue date:	11/03/1989
From:	Hairston W, Odom R GEORGIA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ELV-01029, ELV-1029, LER-89-027, LER-89-27, NUDOCS 8911090270
Download: ML19327B734 (4)

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Georgia Power Cantany

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.e 333 Prodmont Avorn;e

. Atlanta. Gcorg>a 30308  ;

. klephone 404 526-3195 I Mehrh A&ltoss 40 Inarness Cerm Parkway .i Post O' fee Don 1?95 .

Dirmingham, Alabama 35701

. %phme 205 808 5581 -

the saattvin cyttrc sprem .

I W. G. h(iirston, til 5 '7,'ff'j,'g[*"'

d November 3, 1989 CLV-01029 0088 Docket No. 50-425 f

U. S. Nuclear Regulatory Commistion '

ATTh: Document Control Desk Washington, D.'C. 20555  :

Gentlemen: ,

V0GTLE ELECTRIC GENERATING PLANT 3 o LICENSEE EVENT REP 0F.T REACTOR TRIP ON HIGH FLUX RATE OUE TO R0D DROP in accordance with 10 CFR 50.73, Georgia Power Company hereby submits the enclosed report related to an event which occurred on Oc+.ober 11, 1980 Sincerely, l,).) hrwW W. G. Hairston. III .

WGH,III/NE/gm. ,

Enclosure:

LER 50-425/1989-027 l

1 xc: Georaia Power Compan.Y

.Mr. C. K. McCov Mr. G. Bockhold, Jr.

Mr. P. D. Rushton Mr. R. M. Odom i

U. S. Nuclear Reaulatory Commission L. Mr. 3. D. Ebreter, Regional Administrater.

Mr. J. B. Hopkins, Licensing Project Manager, NRR h Mr. J F. Rogge,' Senior Resident Inspector, Vogtle 1

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On 10-11-89, at 2333 CDT, an automatic reactor trip occurred with the reactor in stable operation at 58% of rated thermal power. All automatic safety features functioned as required and the reactor was stabilized in Mode 3 without incident.

No annunciator oc other warning of a problem preceded the reactor trip.

Following a review of computer printouts of data essociated with the trip, the first out annunciator was identified as a high flux rate trip ennunciator.

Operability testing of the control rods then indicated that a problem existed with rod K-2 in control bank B. Investigation of the control rod circuitry identified a failed diode which had apparently resulted in a loss of current to the rtationary gripper coil. This allowed the rod to drop into the core and initiate a negative flux rate trip.

Corrective action included replacing the diode for rod K-2.

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l A. REQUIREMENT FOR REPORT This report is required per 10 CFR 50.73 (a)(2)(iv) since the event resulted in an automatic actuation of the Reactor Prctection System (RPS).

UNIT STATUS AT TIME OF EVENT B.

At the time of the event, Unit 2 was in Mode 1 (Power Operation) at 58% of rated thermal power. The unit was being returned to full power following .

completion of a 4 day snubber inspection and maintenance outage.

C. DESCRIPTION OF EVENT' On 10-11-89, at 2333 CDT, an automatic reactor trip occurred with the reactor in stable operation at 58% of rated thermal power. No annunciator or other warning of a problem was received prior to the reactor trip. When the trip occurred, a " Turbine Trip /P9 Reactor Trip" and a "NIS High Flux Rate Power Range Reactor Trip" annunciator were received simultaneously in 3 the control room. A Feeowater Isolation (FWI) occc~ad as expected following the reactor trip and Auxiliary Feedwater (AtW) actuation occurred ,

on steam generator low-low level as expected. At 2352 CDT, the reactor was stabilized in Mode 3 (Hot Standby) and unit operating Procedure 12006-C l " Unit Cooldown'to Cold Shutdown" was entered.

l D. CAUSE OF EVENT Review of the data associated with the reactor trip indicated that tha first i out annunciator had been a High Flux Rate Trip annunciator. The negative flux rate trip bistables were found tripped at the nuclear instrumentation system (N.'S) cabinets. This indicated that a dropped red was the likely L cause of the reactor trip. To investigate this possibility, testing was performed per Procedure 14410-2, " Control Rod Operability Test," to determine the operability of the control rod banks. This testing revealed that rod K-2 in control bank "B" would not withdraw. Investigation of the control circuitry for rod K-2 found that a diode in the centrol rod drive power supply had failed. The Failure of the diode had apparently resulted in a loss of current to the stationary gripper coil for rod K-2 allowing this rod to fall into the reactor. Discussions were held with Westinghouse and it was confirmed th;it a drop of rod K-2, due to its location in the core, would give a reactor trip on negative flux rate (2 out of 4 coincidence required). The failure of the diode is the root cause for the reactor trip.

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0 l0 0 l3 OF 0 l3 1m ca -..,,-.. m ... w wrer , w .,nn l-c' ' E. ANALYSIS OF EVENT Following the reactor trip, all control rods were observed to fully insert '

into the. core. All automatic erigineered safety features functioned as

! required following the reactor trip and the reactor was stabilized in Mode 3 without incident. Based on these considerations, there was no adverse

, affect on plant safety or on tha health and safety of the public.

F. CORRECTIVE ACTIONS Diode CR4 for control rod K-2 was replaced and rod K-2 was verified to be operable.

G. ADDITIONAL INFORMATION ,

I. Failed Components Identification Diode - Westinghouse Electric Part No. IN1206AR

2. Previous Sir,iilar Events i

None

'; 3. Energy Industry Identification System Codes 1,

l Control Rod Drive System (PWR) - AA -

Plant Protection System - JC l

l. Incore/Excore Monitoring System - IG i

- NRC POR W 3464 *d.S. C I'O s 1 93 420 5N1 DW hi w - - - - - , . - ,._ . . . - - - .