ML20085L725

RO 50-267/75/3:on 750203,drop in Loop 2 Instrument Bus Voltage Caused Loop 1 Helium Circulator to Trip.Cause Not Stated

ML20085L725
Person / Time
Site:	Fort Saint Vrain
Issue date:	03/04/1975
From:	Brey H PUBLIC SERVICE CO. OF COLORADO
To:	Howard E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20085L723	List: ML20085L725
References
RO-50-267-75-3, NUDOCS 8311020383
Download: ML20085L725 (4)

Text

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O C) public service company oe ochmea P. O. Box 361, Platteville, Colorado 80651 March 4, 1975 q ,-( M % i

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~ ~ / / s, J; r-Mr. E. Morris Howard, Director I p n U jf';' " C

"'d Nucicar Regulatory Commission ,

s Region IV ',

Office of Inspection & Enforcement '

611 Ryan Plaza Drive .,,-

' ..;;. -;,2; '-, \ '

Suite 1000 -

Arlington, Texas 76012

Dear Mr. Iloward:

REF: Facility Operating License No. DPR-34 Docket No. 50-267 Enclosed please find a copy of Unusual Event Report No. 50-267/75/3, submitted per the requirements of the Technical Specifications.

Very truly yours, My ($9 Y

11. Larry Brey Superintendent-Operations Fort St. Vrair. Nucicar Cencrating Station llLB:11 cc: Mr. Angelo Ciambusso 0

8311020383 770630 28 PDR ADOCK 05000 S

COPY SDR M _

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REIMT DATE : rebrunry 22,,,__1975 ,

UNUSUAL EVENT

• 0CCUlutE?:CE DATE February 3, 1975_ -

1 .

FORT ST. VRAIN NUCLEAR CENFPATING' STATION (,es

, ,[/4 g PUBLIC SERVICE COMPANY OF COLORADO f ,-

P. O. BOX 361 /-  % -[!d'/ M'I*g

. PLATTEVILLE, COLORADO 80651 ff Ed IS *,, ,' # )'T -

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.g ej REPORT 1;0. 50-267/75/3 < l. '3

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Preliminary '/ " * * 's

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IDENTIFICATION OF OCCURRENCE:

OnFebruary3,1975,bidr in the Loop 2 instrunent bus volta:;c caused a Loop 1 llelium Circulator to trip This is identified as' an Unusual Event per Technical .

Specification definition AC 7.6.C.3.

CONDITIONS PRIOR -

TO OCCURRENCE: Steady State Power Routine Shutdown

, Hot Shutdown Routine Load Change Cole :.diardv.a -

Other (specity)

Refueling Shutdown __

Routine Startup The major plant parameters at the time of the event were as follows:

Power PTR, MWth

. ELECT, MWe Secondary Coolant Pressure psig Temperature 140*h'MainSteam 500'F Rcheat-Flow f /hr. -

• Primary Coolant Pressure jsig Temperaturc 'F Core Inlet' l 'F Core Outlet

' _ Flow * #/hr.

i *A, B, D, Helium Circulators self turbining between 300-500 rpm C llelium Circulator,at 2000 rpm -

1 c .

250s t _ :c*

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j Page 2 DESCRIPTION OF OCCUPJ:ENCE:

At 1445 hours0.0167 days <br />0.401 hours <br />0.00239 weeks <br />5.498225e-4 months <br /> en February 3,1975, a construction electrician accidently grounded the Loop 62 instrument bus. Helium Circulators B, C and D Tripped of f primarily due to a buf fer/mid-buffer upset.

A fault on the Loop Inst rument Bus should not have af fected a Loop 1 liclium Circulator ("B" Helius Circulator) .

APPARENT CAUSE OF OCCUERECE: Design Unusual Service Cond.

Including Environ.

Manufacture Component railure Installation /

Const. X Othcr (Specify)

Operator The cause of this occurrence in Procedure presentiv unknown.

ANALYSIS OF OCCUnnFNCE:

The upset in the buffer system caused by the instrument bus voltage dip some how reflected from Loop 2 into Loop 1.

This incident along with a Helium Circulator upset uhich occurred on January 15, 1975, wher. firing of a Loop 2 bearing water accumulator to meet a Technical Specification Surveillance Test requirerent caused an upset in the buffer systea which could be seen on the Loop 1 Helium Circulators was presented to the Plant Operations Review Committee. The Committec-revitued both incidents and determined them to be " Safety Significant",

The NTSC was appraised of the situatlon and has recommended that the system vendor be notified cf the problems and that the risc-to-power testing program be delayed until the problems are satisf actorily resolved.

CORRECTIVE .

ACTION:

The Corrective Action has not, as yet, been determined. This will be transmitted with the " Final" Unusual Event correspondence for Unusual Event No. 50-267/75/1.

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FAILUn_E DATA /SIMILAR REPORTED OCCUllRENCES:

None PROGPR fATIC IMPACT:

Unknown CODE IMPACT:

None RECO.TIENDED : APPROVED:

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~_urri. J H. L. Brey, puperintendent, Operations rederic C. Swart , Superintendent, Production

. Fort St. Vrain Nuclear Station [ Fort.St. Vrain Nuclear Station l - f.. #

DATE: DATE: N / <N ff / / O 9

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