ML20084P563

Responds to AEC Request to Rept Electrical Output Oscillations on Generator When Approaching 510-MW Gross Outut.Possible Bases for Problem Listed

ML20084P563
Person / Time
Site:	Nine Mile Point, Oyster Creek
Issue date:	12/15/1970
From:	Burt P NIAGARA MOHAWK POWER CORP.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084P527	List: ML20084P563
References
04690, 4690, 701206, NUDOCS 8306100315
Download: ML20084P563 (5)

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. i NI AGARA MOHAWK POWER CORPORATION HlAGARA MOHAWK Nine Mile Point Nuclear Station P. O. Box 32 Lycoming, New York 13093 December 5, 1970 GQN J. u. ..

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Dr. Peter A. Morris, Director  :"

Division of Reactor Licensing [

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United States Atomic Energy Commission

Washington, D. C. 20545

Dear Dr. Morris:

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Re: Docket Number 50-220 Provisional Operating License DPR-17 We have been requested by the Compliance Section to report electrical output oscillations on the Nine Mile Point generator when approaching 510 MW(c) gioss output. Tests are in progress to ' identify the origin of the problem which could be one or a combination of the following:

1. Liquid being drained from moisture separators and reheaters is saturated. The extraction heaters to which it is ultimately directed is approximately 60 feet above the drain tank. Therefore, as the liquid rises and the static head becomes less, the latent heat boils off and two-phase slug flow exists. Control of a mixture is not possibic with present design, and. heater shell levels cannot be maintained constant. Extraction steam being intimately in contact with the shell side of the heater can be affected. l Nozzles have been installed in the drain lines and cooler water injected to provide sub-cooling. On test, two-phase flow appears ',,,

to have been eliminated. The heater level vasci11ations have become sinusoidal and therefore, with control modifications, be damped out. Lead-Lag modules will ';e added to the control system y

early in 1971. Design studies are being carried forward relative to piping modifications between moisture separators and drain tapks to insurc ' "scif-venting".

2. Lo!id swinging starts when the turbine admission valve cam shaft reaches a position indicating 83% valve opening. At this position electrical output cycles about 20 M.W. with a 3 second period, t Steam flow varies in similar fashion causing reactor water 1cvel to, vary by 6 inches. '

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2. Ilowever, during the upset, the arbine inlet pressure is cohtrolled to.1 psi. These control valves do not have a perfect linear characteristic through their range and there is a " knee" in the curve at about this valve position. Cams contours have been changed but may still require adjustment. Checks are being made during. load changes relating control relay, cam shaft, and valve moveuents to steam flow. At their completion, an evaluation will be made by the manufacturer.

3. In order to mdntain be most stable reactor operation, the pressure has tcen controlled to within 0.5 psi at steady state ope ra*. ion . Ewa with the oscillations previously described, it varies only 1.9 psi'. This is excellent regulation, but to achieve ,

it a high degree of sensitivity must be built-in to the control.

Close regulation can produce " hunting", particularly if a mis-match of sensitivity between the system being controlled and the control occurs.

Sone problems have been encountered with the initial pressure regulators, particularly during the start-up test period. Since that time, their performance has been quite good. Please refer to a report from T. J. Dente te.J. A. Burt, " Performance of Initial Pressure Regulators", iclosed herein.

Motivation for the power' osci11ations could originate from change in sensitivity of control valve response at 83% opening, as the swings start at this point when operating with the second stage of reheat out of service.

Ilowever, with the second stage of reheat in service, the oscillations are produced irrespective of valve position.

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Therefore, either or a combination could start the cycling. Testing has indicaced the corrective measures necessary,to neutralize the liquid 4

removal problem. Testing is continuing to define if and to what extent adjustment of control valve characteristics is necessary. The possibility of reducing the initial pressure regulator sensitivity is being looked into.

i An early resolution of the problem is expected.

I Yery truly yours, i

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. P. Allister Burt.

1 Superintendent - Nine Mile Point I

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raoM T. J. Dente c 1 o. M, To Mr. P. A. Burt 5,d, Q,sussect Performance of Initial Pressure

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.( 5 The problem with the Mechanical Pressure Regulator (MPR) and the Electrical Pressure Regulator (EPR) can be placed into two categories: 1. Those occurring during start-up testing program and 2. Those occurring since start-up.

4 During the start-up testing program various problems were encountered with both the MPR and the EPR. Primarily, most of these corrections were ones that would be expected in the usage of a new piece of equipment. Modifications were made to the MPR and EPR as follows:

1 MPR - A needle valve was added to the sensing line to adjust- sensitivity and improve the stability of .

the system. A bleed line was added to sensing line. The one micron filter was changed to a ten micron filter.

EPR - Capacitor 104C was changed from 1NF to SNF improving the stability.

i The pilot valve, bushing and dash pot.on the MPR were damaged by dirt particles and had to be replaced.

I Following the start-up program, the plant was shutdown

from March 4,1970 until July 12, 1970. From this date to the present, modifications were made to the MPR and EPR as follows: ,

MPR - The piping to the sensor line bellows was lengthened

! and changed to stainless steel from carbon steel.

This eliminated the problem of corrosion products

!' blocking the filters. Lengthening the line prevents condensate surges and provides_ control dumping.

EPR - Capacitor 104C was increased to 6NF from 5NF improving stability. Zener diodes were changed to cut the response voltage from 9 volts to 5 volts to stop saturation of the amplifier'and stabilize the EPR-MPR take-over.

During this period of time, the EPR held pressure within 1/2 psi. After initial start-up and with experience, we have been able to match sensitivities between the EPR and MPR so that a smooth transfer can now be made from one.to the other.

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Date . . Power Level Problem Correction l'/5/69 0 '

flot Standby With the MPR in operation and by-pass valve open switched to El'R bypass valve closed causing high pressure scram 10/18/69 7% MPR in control with Closed down on sensing 6 psi swing line slightly - MPR stable 11/10/69 15% MPR in control with Installed bleed off line.

+ 2 psi oscillations on MPR. Found rotating all bypass valves bushing on MPR stuck with opened depressurizing particles reactor causing scram 11/13/69 Ilot Standby While lowering the MPR, Added needle valve to MPR 4 bypass valves opened sensing line and replaced causing low Rx water plugged dash pot, pilot-level'peram valve and bushing 12/7/69 Ilot Standby ,

+ 2 psi oscillations Vented sensing line-

, I second period with EPR in control 12/18/69 50% During start-up tests Filters for M006 valve EPR demonstrations, the pluggeJ. Replaced and EPR takeover of the EPR stable from the MPR a drop of 7 psi occurred (979 psig l to 972 psig),

2/2/70 98%. During start-up tests on Found that-adjustment Pressure Regulators needed on ' sensing line switched from EPR to MPR . needle valve.' Made adjust-and after 10 and MPR stable a6psipeak,jsec.st'artedment to peak oscillation l

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2/8/70 98's MPR in contr'ol and Adjusted MPR needle valve started 8 psi peak to and MPR stable peak oscillations ,,

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• 7/8/70 5%' MPR causing slight Adjusted needle on 7/10/70.<

cycling in bypass changed sensing valve line i valves. GE people from carbon steel-to stain-

[- adjusting EPR and NPR less steel on MPR and for bette'r stability change capacitor 104C to 6 NF on EPR j 2 t

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, Dat e *- Power Level' Problem ~ Correction i

7/20/70 20% Changed from EPR ta. Adjustment to MPR '

MPR and 200 psi peak to peak in pressure  :

occurred - high flux M scram level dropped

$ 2.1/2' below normal e

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4X106 then to 6X106 f.

10/19/70 5% MPR in control and Adjusted sensor line pressure oscillating needle valve 8 psi peak to peak it' j ..

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