ML20085L751

LER 75/003B:on 760112,plant Instrument Bus 2 Tripped, Tripping One Circulator in Each Loop on Buffer Upset & Other Loop 2 Circulator on Loss of Bearing Water.Caused by Loss of Power.Buffer Sys Valve Failure Mode Changed

ML20085L751
Person / Time
Site:	Fort Saint Vrain
Issue date:	05/13/1976
From:	Hillyard H PUBLIC SERVICE CO. OF COLORADO
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20085L744	List: ML20085L742 ML20085L746 ML20085L751 ML20085L761 ML20085L767 ML20085L772
References
LER-75-003B, LER-75-3B, NUDOCS 8311020440
Download: ML20085L751 (6)

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LICENSEE EVENT REPO CONTROL BLOCK:l l l l l l l (PLEASE PRINT ALL REQUIRED INFORMATION) ,

1 6 N E LCENSE NUMBER E T PE 01 Id lo lFl51V I ll 10101-10101016161-10101 1411lll2lOl lOl31 7 89 14 15 25 26 30 31 32 CATEGORY TY SO DOCK;T NUMBER EVENT DATE REPORT DATE O 1 CONT I h l(hl 7 8 57 58

]59 lL I 60 I OI SI 61-1 DI 216171 61 68 I d / I /12.17l(el 10161/I317161 69 74 75 80 EVENT OESCRIPTION EE I The plant instrument bus #2 tripped. This tripped one circulator in each loop on l 7 89 80 SE l buffer upset and the other Loop 2 circulator on loss of bearing water. Reported l 7 89 80

@ l as Supplement B to UE 75/03. I 7 89 80 SE I I 7 8 80

@9 7 89 l

pnus (UE 75/03B) 80 l

DE ODE CCV:ONENT CODE VIOLATION 95 is161 lEj lairIzlzizizi l z_.l l zl c/19 I 91 [yj 7 89 10 11 12 17 _43 44 47 48 CAUSE DESCR;PTION g [ Loss of power isolated buffer system. No cause identified for 10 c tr: Intor trip. l 7 89 80 g[ l Buffer system valve failure mode changed. l 7 89 80 1 1 I -

S Us  % POWER OTHER STATUS SCOVERY DISCOVERY DESCRIPTCN Iolof ol lulA EE] LeJ I Laj l u/g l 7 8 9 10 12 13 44 45 46 80 ACTMTV COATENT RELEASED OF RELEASE AMOUNT OF ACTMTY LOCATON OF RELEASE BE 7 8 LzJ 9

LzJltJ/A 10 11 I

44 45 I N/A' I

80 PERSONNEL EXPOSURES NUMBER TYPE DESCR OTCN 1

7 89 IOloln l 11

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12 I N/A

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80 PERSONNEL INJURIES NOV8ER CN EE 1010101 iDESCRIP/ti N I 7 89 11 12 80 OFFSITE CONSEQUENCES DE I N/A l-7 89 80 LOSS OR OAMAGE TO FACtWTY TYPE DESCRIPTON EE IB 7 89 IN/A 10

l 8311020440 760513 80-

! PUBUCITY DR ADOCK 05000267 no I tr/A PDR l

7 89 80 '

ADDITIONAL FACTORS nm I e/A .I 7 89 . 80 13 l ,

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REPORT DATE:

o May 13. 1976 O -

UNUSUAL EVENT 75/03B ,

SUPPLEMENT OCCURRENCE DATE: January 21, 1976

, Page 1 of 5 FORT ST. VRAIN NUCLEAR CENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO w P. O. BOX 361 PLATTEVILLE, COLORADO 80651 REPORT NO. 50-267/75/03B SUPPLENENT IDENTIFICATION OF j OCCURRENCE:

On January 21, 1976, instrument bus #3 tripped and caused both Loop 2 circu-lators_and one Loop 1 circulator to trip. This report is,a supplement to Unusual Event Report No. 50-267/75/03, dated February 22, 1975.

00NDITIONS PRIOR TO OCCURRENCE: Steady State Power Routine Shutdown Hot Shutdown Routine Load Change X Cold Shutdown Other (specify)

Refueling Shutdown Routine Startup .

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

Power RTR 0 MWth

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ELECT 0 MWe t

Secondary Coolant Pressure < 1.600 psig

" Temperature 217 'F .

. Flow 400,000 f/hr.

Primary Coolant Pressure 274 psig 4

1 Temperature 113 'F. Core Inlet l

113 *F Core Outlet

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Flow 1.3 x 106 f/hr.

lA circulator was shutdown,1B circulator was self-curbining,1C circula-tor was self-turbining..and ID circulator was at 2,500 RPM. 1 1

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UNUSUAL EVENT 75/03B

. . . SUPPLEMENT Page 2 of 5 DESCRIPTION OF w OCCURRENCE:

While oper5 ting 1D circulator at 2,500 RPM, and 1B and 1C circulators at self-turbining, instrument bus #3 breaker tripped and circulator 1B, Loop 1, and circulator IC, Loop 2, tripped due to buffer-mid-buffer. Circulator ID tripped due to a loss of bearing water signal.

APPARENT CAUSE OF OCCURRENCE: X Design Unusual Service Cond. ,

Including Environment Manufacture Component Failure-Installation /Const. Other (specify)

Operator Procedure l The apparent cause of IB and 1C circulator tripping was design of the buffer helium system. The cause of 1D circulator tripping due to loss of bearing water, is unknown.

ANALYSIS OF OCCURRENCE: ,

The loss of instr' ument bus f3 isolates the helium dryer flow from the buffer helium supply system to the circulators. All helium dryer valves are " energize to open" and fail closed on loss of electrical power from instrument bus #3.

In addition, the helium dryer bypass valve, HV-2152 (see PI-21-3, attached),

which fails open on loss of air, requires electrical power to open and is supplied by instrument bus f3. It therefore remained closed on loss of power

to instrument bus #3.

Each circulator buffer helium supply is partially supplied _ by the helium flow from the dryer. The loss of power in this incident stopped approximately half

, of the buffer helium supply ~ flow and ' tripped 1B and 1C circulators due to _ ab-normal buffer-mid-buffer differential pressure.

Circulator ID tripped due to " loss of bearing water". No logical reason for this trip could be identified.

CORRECTIVE ACTION:

! The helium dryer bypass valve has been changed to f ail open on either loss of i

air or loss of electrical power.

A test will be performed which will duplicate the loss of' instrument bus 3 to identify the reason for circulator ID trip. . The test will also verify _ that: .

changing the helium dryer bypass valve. failure mode will prevent the buffer-mid-buffer tripc of the helium circulator.~

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' UNUSUAL EVENT 75/03B

SUPPLEMENT Page 3 of 5 FAILURE DATA /SIMILAR REPORTED OCCURRENCES:

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UNUSUAL EVENT 75/03B el SUPPLEMENT i I

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Submitted by:

[p M-H.W.Hillyage,Jr. /'

Technical Services Supervisor Reviewed by: hl * *\

H.LarryBreg \

Superintendent, Operations

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l Approved by: . A .N oJa y Fre/ericE. Swart Superintendent, Nuclear Production e

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