ML20084Q985

Ro:On 691120,one Rod Failed to Scram within Tech Spec Limit of 5.32 Seconds.Other Control Rods Took Excessive Time to Scram.No Cause Stated.Different Size Mesh Inner Rod Drive Strainers Installed

ML20084Q985
Person / Time
Site:	Nine Mile Point, 05000000
Issue date:	12/06/1969
From:	Burt P NIAGARA MOHAWK POWER CORP.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084Q984	List: ML20084Q985
References
99043, NUDOCS 8306140747
Download: ML20084Q985 (2)

Text

f. _ _. a ,_ . . u

._.._m..

r o' m: m me m - - ____

e s

~ '

~ A.

wmL(Ne h,==&O ,

,y >

) _

NIAGARA MOHAWK PowEn CORPORATION NIAGARA A jNOHAWK Ninc >!ile Point Nuclear Station

, t> P. O. Box 32

., Lycoming, New York 13093 7%

December 6, 1969 g-(JM / /p .

,o.y

.,,,,7,g 7, i; v f ,A~ ./

. g s, /',% ..zy

p

?

.a s a

2 v ,

United States Atomic Energy Commission b, ,,g j q Division of Reactor Licensing ,

% gj Washington, D. C. 20545 s .' s v

)s'. ,\ \

/ / .F Attention: Dr. Peter A. 51 orris, Director '

' v. ,, / i o ,[ W Gentlemen: .

Un Thursday, November 20, 1969, the Nine .'lile Point reactor was scrammed from 25 percent power. Thirty control rods, which were hooked up to a brush recorder, averaged 4.17 seconds for 90 percent inserticm. The original 90 percent insertion time for ALL rods was 3.00 seconds.

During the approximate six-week time interval between the original and November 20t_h, scrams, eight drivec were continuously monitored for spurious as well as planned scrams. 'their times for 90 percent insertion increased approximately 40 percent during the monitoring period. During the November 20t_h scram, one rod was outside the Technical Specification limit of 5.3 seconds; Rod No. 24-23 scrammed in 5.32 seconds.

Cruo

@Q- Inasmuch as excessive rod insertion time was experienced at Oyster Creek due to y

,o n partially plugged 400 mesh inner rod drive strainers and the rate at which our tim-0 ing was increasing gave cause to suspect our next scram might be above the Technical 3 Specification limit of 5 seconds average, it was decided to change out the strainers.

et bo oo A screen having clear rectangular openings of 10 by 100 mils was installed in place

• d of the original 400 United States standard mesh. In this manner, the drive is o n. protected while decreasing screen pluggage probability by an order of magnitude clo

" of approximately 400 times. The work was completed, including dri"e timing, on t December 6, 1969. At this time all rods have been scram tested unoer cold pressur '

ined conditions with an average 90 percent :tnsertion time of 2.7 seconds. hnen the reactor reaches operating pressure and temperature and with approximately 5 percent bypass steam to the condenser, all rods will be. individually scram tested.

k M//d/df g We shall continue to honor commitments previously made of reporting rods whose i 90 percent insertion time do not fall withia the range of 1.9 to 3.6 seconds, SL also, if the average of 129 rods is not wit 4in the range of 2.4 to 3.1 seconds.

I M The same eight driv'es as before will continac to be constantly monitored and scram ,

g g checked once every two weeks should a scram not occur in that period. In addition, they will be similarly tested before planned scrams from 50 percent power. Feed-

~

cM water quality will be controlled at all times and especially monitored when impuri--

ties might be added, such as when cutting.cin.feedwater strings, new pumps, piping systems, and so on.

DEC 101969 { , g COPY SENT REGICN n -

~

1

• - -- n p; q G

l 1

United States Atomic Energy Coraission '

Page 2 December 6, 1969 J

The following chemistry surveillance is performed and will continue to be in order to evaluate,the crud introduced into the reactor water:

1. A 242h our integrated crud sample is taken on the feedwater entering the reactor and analyzed daily. This sample tap is located so that it sampic.s the feedwater just before the reactor regardless of feed-water path used.

2. A continuously recording turbidimeter is installed on the reactor feedwater to give assistance in evaluating trends.

3. A daily grab sampic for crud is taken on the reactor water.

4. hhen either conductivity or the turbidimeter indicate that a con-densate demineralizer should be changed, the operating deminerali cr outputs will be evaluated for both conductivity and crud to deter-mine which bed or beds should be switched.

5. Every effort will be made to keep fqedwater crud IcVels low by frequent changing of demineralizers and by reduction of flow through the demineralizers where necessary.

6. h' hen new parts of the feedwater cycle are being cut into service, every effort will be made to recirculate as much condensate back to the condenser, thereby polishing it through the demineralizers at a higher rate.

It is expected that the Nine Mile Point reactor will be brought critical and the turbo-generator set placed on the line on December 8, 1969. During the following week, additional feedwater heaters will be brought into service.and power raised to the 50 percent level.

Very truly yours, P. Allister Burt Station Superintendent mjs cc: Mr. M.11. Pratt Mr. F. J. Schneider Mr. J. N. Ewart, Chairman, SR f A Board Mr. M. lilldreth, A.E.C. Compliance

\

r* y y

, j! l h

6 a ,

-