/ ~''

O UCENSEE EVENT REPCT. CONTRet StOCx:1 1 I I I I I catsasa paint au asouinso iNFoamaTiaN)

1 6,

NAME LCENSE NUMBER PE TV

O1 16101 FMI vl / l l C1 Cl-I d Cl Cl CICl-lOlOl 14|/l/121Cl 101517 89 14 15 25 26 30 31 32

CATEGORY TV $ RC DOCKET NUMOER EVENT DATE REPORT DATE

@ CONT | FI Ol y it I 16|S c|-l(;|f_id-|M 16|312|Sl7|SI | | | | | | |7 8 57 58 59 60 61 68 69 74 75 80

EVENT DESCRIPTION

35 l Ce h r u m Fwkon b e i-;,,o witb r 4 s c r.., e e. n n t u d ,1 17 89 d '

J 80

h I hr $+' f ~ VM i b ~ h e S V~ rtnt?k 1U$1i0h +finh?d ftGO * f f HOD & f e' e |7 89 80

nn4N htGOg.jmgg,1 pgg 't r$ f t \f1&fC s02_n he b S I) r O f M bC . lS$ ItMMek hnOYn hv &f e7 89 * ' ' '\ J 80'

Bs |res k t+ect h vo eJr?refn~Lert. I7 89 80@l (m ~76 /o6 A I7 89 80m

C CE COMPONENT CCCE MANuFacTumR viOLAt1ON

83 IcIBl lei IV Iv lx IV I xl Yi LEl 12 ir if If I [fjj7 89 10 11 12 17 43 44 47 48'

CAUSE DESCRIPTION

SE | 0.USd c.ut$ res port Ce of DrtCSM ct), W /t Wd/ CD/t)f"0 //c/~S I7 89 8005 10 C'***FUrt-|e$ d)/k b7/t t k C/1) b ettf*//'a f LY7 |d /~ $ 1/ $ f ? M b d <~ l7 89 / / 80

'

li@ | Ae v, ,-e wwc/ a>1) fesA el I

% PCwtR CTHER STATUS DESCOVE DISCOVERY CESCRipTON

8 LGJ l ol ol ci i I Laj |v4 17 8 9 10 12 13 44 45 48 80

ACTIVITY CCMTENT

REL[E[j [f.1 1 M [~ CUNT CF ACTMTVl I /VA I

ED CF RELEASE LOCATON OF RELEASE87 8 9 10 11 44 45 80

PERSONNEL EXFOSURESNUM8ER TYPE

CESCNTCN 4IH Idl olo i IEl I # 17 89 11 12 13 80

PERSONNEL INJURIES

3 1010101 1 N hN.

NUMBER DESC M'

I7 89 11 12 80

OFFSITE CONSEQUENCES

asI//4 ~j7 89 go

LOSS OR DAMAGE TO FACILITYTYPE DESCRIPTON

8L?Jlu4 I7 89 10 8311020344 760621

PDR ADOCK 05000267 80PUSUCITY s PDR

DE I /V M i7 89 80

| ADDITIONAL FACTORS

MIN 4 17 89 80

32 I n I-

W 30 M 7 7 7- 2*L.C2,NAME:- y

'

PH ,ON- , - .. ......,

. . - . .

,

*

O O'

;.

'Ci- ,-j.

_! pubne service company ce cdladal P. O. Box 361, Platteville. Colorado 80651*

e. .. J

2 3

SECE 7

I'g?yggh June 21, 1976,y,1, '7g

- Fort St. Vrain-_

Unit No.1* --.

# D' P-76140Of b

G 8Mr. E. Morris Howard, DirectorNuclear Regulatory CommissionRegion IVOffice of Inspection and EnforcementSuite 1000Arlington, Texas 76012

REF: Facility Operating LicenseNo. DPR-34

4Docket No. 50-267._ ,

Dear Mr. Howard.

Enclosed please find a copy of Unusual Event Report No. 50-267/75/05A,Final, submitted per the requirements of the Technical Specifications.

Also, please find enclosed one copy of the Licensee Event Report forUnusual Event Report No. 50-267/75/05A.

& L ad[Very truly yours,

Frederic E. SwartSuperintendent, Nuclear ProductionFort St. Vrain NuclearGenerating Station *

FES/alk

cc: Mr. Roger S. Boyd

gg ggEIORd384

_ __ __. _.

e . * pV

' REPORT DATE: June 21, 1976 UNUSUAL EVENT 75/05A'

Page 1 of 4

OCCURRENCE DATE: March 23,1975

FORT ST. VRAIN NUCLEAR CENERATING STATIONPUBLIC SERVICE COMPANY OF COLORADO

P. O. BOX 361 -

PLATTEVILLE, COLORADO 80651

REPORT No. 50-267/75/05A

Final

IDENTIFICATION OFOCCURRENCE:

A situation occurred while testing the helium circulator backup bearing watersystem which resulted in "A" and "B" circulators automatically tripping offand the buffer indication on "C" and "D" circulators to drop resulting inoperator action to set the brake and seal.

This is identified as an Unusual Event, per Technical Specification definitionAC 7.6c, paragraph 3.

7CONDITIONS PRIORTO OCCURRENCE: Steady State Power Routine Shutdown

Hot Shutdown Routine Load Change

Other (speckfy)X Cold Shutdown

Refueling Shutdown

Routine Startup

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

i Power RTR 0 MWth

ELECT 0 MWe

Secondary Coolant Pressurb N/A psig

Temperature N/A 'F

Flow N/A f/hr.

Primary Coolant Pressure 85 psig

Temperature N200 *F Core Inlet

%200 *F Core Outlet

Flow Helium circulator self- f/hr.- .''' '' *

turbining

;s-- - .

_-

- .

i : O OUNUSUAL EVENT 75/05A-

^

Page 2 of 4

'

DESCRIPTION OFOCCURRENCE:

~

The emergency feedwater header had been isolated via V-21453 in order torepair the pressure control for valve' PV-21105. Upon completion of thisrepair, pressurization of the emergency feedwater header was initiated byslowly opening the isolation valve V-21453. The following events thenoccurred:

- _ . - -

1. Helium circulators lA and IB tripped on negative buf fer-mid-buffer differential pressure.

2. HV-2366-1 and HV-2366-2 changed from supplying makeup buffer gasto the helium circulators via the purified helium header, to thehelium storage system. At a PCRV pressure of 85 psig heliumdensity is barely suf ficient to place the purified helium com-pressors in service. Loss of a major helium user such as circu-lator lA and IB buffer caused the purified helium compressor totrip and the automatic controls to switch to the high pressurehelium storage system.

y 3. The bearing water surge tank pressure in both loops increased to140 psi, causing the buffer return flows to drop to 0 on theremaining circulators. Circulator 1C buffer dif ferential pressure~

decreased to 10" negative but did not trip. Circulator ID bufferdifferential pressure dropped but did not go negative. Theoperator set the brake and seal on both of these circulators be-

cause the return flow was so low. The Rix recovery compressorswere then set up to vent to atmosphere in order to get the bearingwater surge tank pressure down. When surge tank pressure equalledreactor vessel pressure, 1C and ID helium circulators wererestarted.

.

. APPARENT CAUSE,' 0F OCCURRENCE: X Design Unusual Service Cond.- Including Environment

Manufacture ~ - Component Failure '. - -

Installation /Censt. Other (specify),

~ ~

Operator ~ " *

.. . - - - Procedure.,

- . - -

!:

The increased. pressure in the surge tanks due to the water inflow displaced,

j- helium from these tanks thereby increasing the buffer helium recirculstion-

suction pressure. This reduced the buffer return flow from the helium circu-|~ 1ators causing them to trip on buffer-mid-buffer.

,

; *, - -

.-

e

Y e

>- .

9

*

m { '

g g/_

,

U CUNUSUAI. EVENT 75/05APage 3 of 4

ANALYSIS OF'~~~ ~ ~ '

OCCURRENCE: ~ "~~ ~' ~

It appears that PC-21105 failed to control as did PCV-2191 and PCV-2192. Withthese valves not operating while V-21453 was being opened, there was no con-trol of the backup bearing water flow. The large amount of flow into thebearing water surge tanks caused a displacement of the helium from the surgetanks (due to a level increase). This helium flowed backward through the

~ eq' alization line 'to the sucEion' of the buffer helium recirculators, whichucaused reverse flow of the buffer return from the helium circulators. Thereverse flow of buffer return caused a buffer-mid-buffer dif ferential suffici-ently nega:ive to initiate the automatic circulator trips.

The level increase would not have occurred under normal circumstances becausewith the normal bearing water pumps tripped and bearing water supplied from thebackup bearing water system, a feedforward signal from the control system wouldhave opened the surge tank drain valves. Under these conditions, the possibilityof high rate of change in the surge tank level and the reversal of return flowfrom the circulators, is eliminated.

CORRECTIVE -

ACTION:

A test of the backup bearing water system was completed. This test, RT-356, was.performed to verify that backup bearing water will function correctly and re-laced transients are repeatable. This test was performed at (1) pressuressimulating the most adverse requirements for backup bearing water, and (2) atthe pressure which also causes the most adverse helium buffer-mid-buffer inter-actions.

'~~ ~

The test of (1) was performed five (5) times, by simultaneously transferring allfour circulators to backup bearing water. The results of the test results showthat on the most severe' transient there was a margin of 25 psid between the

~

transient and the circulator trip point.margin.

"

All other test results show a larger

The test of (2) was performed and the results show that the cost sev'ere differ-__.

ential pressure transient on the buffer-mid-buffer decreased but remained

, positive. The trip point is -9" water dif ferential pressure. The results of2 test RT-356 verify the operability of the backup bearing water system and con-,

'

_ _ ,_ _cludes_this report.

| No further corrective action is planned or required.\ ... -- . .... . . _ _ . - .. ._ a - .. - . ,,. -- ,

j FAILURE DATA /'

SIMILAR REPORTED OCCURRENCES: - - - - - - -

Unusual Occurrence No. 50-267/75/02 reports a failure of PV-21105-1 in the backupbearing water system which occurred on April 10, 1975.

-

w-_

9

- _____ _- _

f- __

e .

UNUSUAL EVENT 75/05A*

Page 4 of 4.

PROGRAMMATIC UfPACT:

None. . - ... . . . . . .. .. .

CODE D! PACT:

-

None.

.. . .

Submitted by: N c t u (L % U I. M ...

H. W.' Hillyard , Jr. *.

.

Technical Services Supervisor -.

Reviewed by: ) M ...

K.LarryBQy .

..S. u.pe. rint.ende. n.t ..Oper tions. z. ... ..

.

.- . .. __. .....,

t

.,.. , , . _ . . . ... .

.. ._..

Approved by: as m,, .M a a,_

..FrpericE.. Swart. . . ..

'

. .m. . .... . _ . . . .. . . . - .._ .

. . ...S.upe r.. int _e.ndent . Nuc. l..e. ar. .P.r.o.d.u. c ti.o. n. . . ... _.. , .. . . _ . . ..

.. . .. . .......

. . . . .. . ... . .

. . . . . .. . , . . ... _.. ...;.... . . . . . . . . _ . . ..s. . . . . . . . . . ....

. . . .. . .

.., _. . . . .... ..: . . . . . . . . . . . .. . . . , . . . .. . . .. . . . . .. . _.. .. . .. ..

..

. . , , . . . . . .. ..... m .. .

. .. ... .. . . . .. .... .. .. . . . , - .. ..

.......

-

. . . ,.. . .. . .. .s. ,__. . . . . .. . . . ... . . . - . ... . ..

. . . .. . , . .. ..... .. .

... : :.: : .. . : . . * .: .. .. . .. .=:-.... -. . . . . . . .

.

.. . .. ._ . u.......... . . . . . ..- t. .-- . . . .. . _..... ..... ... . . . .a.. _ .... .,....w. . ....

_ . . , . , . , , .. . . . . . . . . _ . . _ . . .. .._ .. .- ... . . .. . . _ . ... .. .. . _ . .. . ... . . ...

.. . . ..

_.. . _ .

* . . .... .. ,..,,y._ . . . . , , . . , ,*

. ... . . , ..h,. .. 3 .. . .. .. .. g..f.....,. . . . . . .

. . . . . .. , . . . . . _ ,

,. .. ...- ..

. . . ..

.

* ,. ... .. . . . . . . . . . . . . , , . . .,a. ..

... . - . . - . . . . . . . . g...... .

.-

.

. .-

.

.....,. ... . .- . u.... .. .... ._..._.. . m. _ . _ . .s. . . . . . . .... .. -

. m. . .. .

. *

,-. * .* . ..1....., ._.

.. . . . , . ,.ypp .. .n,. ._. . , , .

.

.,9. ,..a .,. ' . . * ,... ,g. ..

. <' ". . . . .' eg . . ._ ._. * .Y

.

. . . . . . . . . . . . . . . . _ . . . ._ , ,.- . . . .

... :

w

e 8s

.___._. _ _ _ _ _ _ _ _ _ _ _ _ _ _ .