ML20084H889

AO BFAO-7420W:on 740325,rod Sequence Control Sys Malfunctioned.Caused by Failed Integrated Circuit.Failed Sequence Logic Board Replaced & Rod Sequence Control Sys Logic Tested Satisfactorily

ML20084H889
Person / Time
Site:	Browns Ferry
Issue date:	04/04/1974
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
AO-BFAO-7420W, NUDOCS 8305060095
Download: ML20084H889 (3)

Text

( "

TENNESSEE VALLh/ AUTHO AITY r-~~YT 7 r CHA4 s ANCOGs, TENNESSEE '

s 3740'l J '.

, . . . - ,,, 7

' b,1:)'y ~ ~1 April 6, 1974 c. . \I ST&YEkeE PARTNi~ AGHtP A- (As ~A 6-'

- Appy .374 > .. ,

'w r~ w\ ,A M

s C ! VM[ju

- u,

%"' 'd. MM Mr. John F. C' Lear /, Director $4k a ?

Directorate of Licensing  % \ ,. ~

Office of Regulation C I -

U.S. Atomic Energy Cornission Washington, DC 20545

Dear Mr. O' Leary:

TEI;IESSEE VALLEY AUTHORITY - BROMIS FEFRY ITUCLEAR FIAIiT UNIT 1 -

DOC 13T 170. 50-259 - FACILITY OPERATIIU LICEIISE DPR ABIIORIE OCCURIEICE REPORT BFAO-7420U The enclosed report is to provide details concerning a malfunction of the rod sequence control systen (RSCS) e.nd subsequent control rod movenent with the reactor belov 30-percent power and the RSCS inoperable. This event occurred on Brouns Ferr/ Huclear Plant unit 1 on l' arch 25, 1974, and is subnitted in accordance with Appendix A to Regulatory Guide 1.16, Revision 1, October 1973 Very truly yours, TEIIITESSEE VALLEY AUTHORITY G L.

f f V f [Y' E. F. Thonas Director of Power Production Enclosure CC (Enclosure):

Fr. Nornan C. Moseley, Director Region II Regulatory Operations Office, USAEC 230 Peachtree Street,I?J., Suite 818 Atlanta, Georgia 30303 t>

0 f

b fC B305060095 740404 PDR ADOCK 05000239 bCf)h d s S FDR COPY SENT REGION

~' ~ ~

O O ,

ABN01UML OCCURRZlCE REPORT Report lio.: BFAO-7420W Report Date: April 4, 1974 Occurrence Date: March 25, 1974 Facility: Browns Ferry nuclear Plant unit 1 Identification of Occurrence ,

Malfunction of the rod sequence control cystem (RSCS) cnd subsequent control rod movement with the reactor below 30-percent power and the RSCS inoperable.

Conditions Prior to Occurrence The reactor was operating at approximately 15-percent power during a routine ctartup following a scram. o Description of Occurrence Durin$ the startup, it was discovered that, with all group "A" and group "B" sequence rods fully withdrawn, the group "C" rods could be selected although the reactor was below 30-percent power. This was reported as a failure of the rod sequence control system which permitted group "C" rods to be selected below 30-percent reactor power. To prevent movement of the group "C" rods while the problem was being corrected, a. controlling relay was pulled to ensure that the RSCS group "C" select inhibit was in the enforcing condition; and no group "C" rods were tuoved until the R5C3 was 2cest.ored to nornal operativa. During this tit.3, however, several group "B" rods were notched in for power shaping. It was later

,. recognized by the Plent Operations Review Conmittee during preparation of the 10-day report that the RSCS was not inhibiting the selection of all rods. The RSCS relay which had been manually activated was inhibiting selection of only groups "C," "A1," and "A2."

Analysis of Occurrence The malfunction was isolated to the sequence logic board of the RSCS. A failed integrated circuit resulted in a premature group "C" rod withdrawal permissive.

See Abnormal Occurrence Report BFAO-7415W for additional details regarding analysis of this type of occurrence.

Corrective Action The failed sequence logic board was replaced with a spare and the RSCS logic tested satisfactorily. The cause of the logic board failure was determined to be an input NAITD gate in integrated circ.uit U9 Instructions will be changed to specifically require that no rods be moved except for scram while the RSCS is inoperable and to specifically require RSCS testing in all sequences follovire any correction or repair.

f

. . ~__

. ~ . . , ,

o

~

O i

Failure Datn .

l 3/12/74--Pressureswitchesimproperlysetwithfeedwaterheatersoutofservice. >

3/25/74--IntegratedcircuitU9ofthesequencelogicboard,G3 drawing 828E164, failed. .

1 i

~

i I

t i

1 J

l h

I 1

i 4

k N

6 e

i .

4 a

l 6 t

+

e i .

?

L 1

I I .

. .y