ML20090E183

AO 50-220/74-4:on 740402,during Refueling Outage Test,Low Condenser Vacuum Sensors Actuated Low Resulting in Reactor Scram.Caused by Switch Setpoint Drift.Sensor Switch Recalibr

ML20090E183
Person / Time
Site:	Nine Mile Point
Issue date:	04/11/1974
From:	Burt P, Perkins T NIAGARA MOHAWK POWER CORP.
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
References
3313, AO-50-220-74-4, NUDOCS 8303140084
Download: ML20090E183 (2)

Text

_

i O O NIAGARA MOHAWK POWER CORPORATION NIAGARA MOHAWK Nine Mile Point Nuclear Station Post Office Box 32 Lycoming, New York g, p April 11, 1974 f,s

'i

'

• h I Mr. Donald J. Skovholt J ii[  %

Assistant Director for Reactor Operations Division of Reactor Licensing (2

6- APR151974 - 9 -

United States Atomic Energy Commission Washington, D. C.

"[-WyG q 20545

% a - .n na sua Re: Provisional Operating License: DPR-17 #

% fp Docket No.: 50-220 Abnormal Occurrence 50-220-74-4

Dear Mr. Skovholt:

On April 2, 1974 during the Spring 1974 refueling outage the low condenser vacuum sensors were tested as required by Technical Specification 3.6.2 Nine Mile Point Nuc1 car Station Unit #1. Persuant to Technical Specifications 1.13b and 6.6.b.1 the four (4) sensors NAMCO SNAP LOCK

1. D1200GU406 PT1 and D1200GSR0423 PT1 were reported to RO:I as drifting beyond allowable limits on April 2. 1974.

The low condenser vacuum sensors provide a reactor scram of 23 + .5" of 1 IIg. The primary reason for this trip is protection of the Turbine-Generator unit and does not have a nuclear related safety function.

With the drift in sensor switch settings a reactor scram would have occurred slightly later in time in the event of decreasing condenser vacuum.

The following is a tabulation of the test results:

Number 6/11/73 4/;:/74

1. 11 22.55 21.80

1. 12 22.70 22.00

1. 21 22.62 ~ 21.90

1. 22 22.57 21.80 The immediate corrective action was to recalibrate the sensors switched to required actuation point. This is the first failure of this type on these sensors.

As these sensors are required only for Turbine Generator unit protection and that protective function would have occurred only slight.ly later in time, no hazard was presented to the general public. ,

Very truly yours, .[  !

8303140084 740411 *

. y g "78&

- - f [zly } %

D PDR ADOCK 05000220 >

S PDR , _

P. Allister Burt ~ 33.13 General Superintendent .

Nuclear ~ Generaj; ion - -

gr REGION!

e TJD:cm t. . .

FRON: THOMAS J. PERKINS - NINE NILE P01h7 h9 CLEAR STATION #1 O O ABNORMAL OCCURRENCE S0-220-74-4

PERSUAh7 TO THE TEODJICAL SPICIFICATIONS I.13b and 3.6.2, WE ARE REPORTING AS AN ABNORMAL OCCURRENCE 11F DRIFT IN THE LOW CONDENSER VACUUM SENSORS.

WE IhW CONDENSER VACUUM SENSORS NORMALLY PROVIDE A REACTOR SCRAM AT 23 + .S" 0F HG. THE PRIMARY REASON FOR 7ME TRIP IS PROTECTION OF T11E TURBINE GENERATOR UNI.T AND DOES NOT HAVE A NUCLEAR RELATED SAFETY FUNCTION.

THE FOUR SENSORS ACTUATED thX MlICH h0ULD CAUTE THE REACTVR SCRAM TO I' -

OCCUR SLIQtTLY LATER IN TIME IN THE EVEh7 0F DECREASING CONDENSER VACIMt. THE ICLIDWING IS A TABULATION OF THE TEST RESULTS; I y l'

NUMBER 6/11/73 4/2/74 REQUIRED l

• Il 22.55 21.8 23 + .S 22.0 W

$12 22.7 "

21.9 821 22.6:

822 22.S' 21.8 1HE CORRECTIVE ACTION WAS TO RESET 1ME SENSORS, NANCO SNAP-LOCK FD1200GU406f71.+ #DI200GSRU423PTI TO THE REQUIRED 11tIP POINT. ,.

AS THE SENSORS PROVIDE TURBINE-CENERATOR PROTECTION ONLY AND kVL9

~

HAVE CAUSEC TIMT PROTECTIVE FUNCTION ONLY SLIGHTLY LATER IN TIME h9 .

IRIARD WAS PRESEhTED TO THE STATION OR 1HE GENERAL PUBLIC.

T. J. PERKiNS STATION SUPERINTENDENT

,?

l [

\ 5

.