ML17037C107

Request to Report Electrical Output Oscillation When Approaching 510 Mw(E) Gross Output

ML17037C107
Person / Time
Site:	Nine Mile Point
Issue date:	12/05/1970
From:	Burt P Niagara Mohawk Power Corp
To:	Morris P US Atomic Energy Commission (AEC)
References
Download: ML17037C107 (10)

Text

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NIAGARA MOHAWK POWER CORPORATION

~ci9I'4, NIAGARA I MOHAWK Nine Mile Point Nuclear Station P. 0. Box 32 Lycoming, New York 13093 December 5, 1970 c,KL > '(g~

DDCmED Dr. Peter A. Morris, Director USAEG Division of Reactor Licensing United States Atomic Energy Commission DEt;y >970 0 .g Washington, D. C. 20545 IIgU+TORV

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Dear Dr. Morris:

DOCI~EI I'~~ ~8 Re: Docket Number 50-220 el/ ( Cl~

Provisional Operating License DPR-17 lfe have been requested by the Compliance Section to report electrical output oscillations on the Nine Mile Point generator when approaching 510 Mll(e) gross output. Tests are in progress to identify the origin of the problem which could be one ox 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 possible 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.

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 vascillations have become sinusoidal and therefore, with control modifications, be damped out. Lead-Lag modules will be added to the control system early in 1971. Design studies are being carried forward relative to piping modifications between moisture separators and drain tanks to insure "self-venting".

2. Load swinging starts when the turbine admission valve cam shaft reaches a position indicating 83'o valve opening. At this position electrical output cycles about 20 M.N. with a 3 second period.

Steam flow varies in similar fashion causing reactor water level to vary by 6 inches.

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2. However,- during the upset, the turbine inlet pressure is controlled 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 rel'ay, cam shaft, and valve movements to steam flow. At their completi.'on, an evaluation will be made by the manufacturer.

3. In order to maintain the most stable reactor, operation, the pressure has been controlled to within 0.5 psi at steady state operation. Even with the oscillations previously described, -it varie's onl'y 1.0 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.

Some problems have been encount'ered with the initial pressure regulators, particularly during the start-up test" period.

time, their performance.has been quite'ood. Please refer Since'hat to a report from T. J. Dente to P; A. Burt', "Performance of Initial Pressure Regulators", enclosed herein.

Motivation for the power oscillations could originate from change in sensitivity of control valve response at 83'o opening, as the swings start at this poin't when operating with the second stage of reheat out of service.

However, with the'econd stage of reheat in service, the oscillations are produced irrespective of valve position.

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

removal problem. Testing is continuing to define if adjustment of control valve characteristics is necessary.

and to what extent The possibility of reducing'he initial pressure regulator sensi'tivity is being, looked into.

An early resolution, of the problem is expected.

Very truly yours, P. Allister Burt Superintendent '- Nine Mile Point Enclosure

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INTERNAL "ORRESHNDENCE FORM R2 2 R I JI NIAGARA ', 'MOHAWK Regulatory 'File Cy ~

ois~Rio~ Nine Mile.POint December 3, 1970 FRoM T. J . Dente vo Mr. P. A. Burt, svs~scv Performance ',of Initial Pressure, Regulators

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--5-7 The problem with the Mechanical Pressure Regulator (MPR) and the Electrical Pressure Regulator.(EPR), can be-placed into two categoric's: 1. Those occurring during start-up testing program.and.2. Those'ccurring .since start-up.

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'he'sage of a new piece of equipment. Modifications, were made to the MPR and EPR as follows:

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 t'o SNF" improving the stability.

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

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.'engthening the line prevents condensate surges. and provides control dumping.

EPR - Capacitor 104C was increase'd to 6NF from SNF improving stability. Zener diodes" were changed to, cut-the response voltage. from 9 volts to S 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 10/5/69 Hot Standby I'lith the MPR in operation and by-pass valve open switched to EPR bypass valve closed causing high pressure scram 10/18/69 7+o MPR in control with Closed down on sensing 6 psi swing line slightly - MPR stable 11/10/69 15 ~o 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 Hot Standby i<hile 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 scram val've and bushing 12/7/69 Hot Standby + 2 psi oscillations Vented sensing line 1 second period with.

EPR in control 12/18/69 50< During start-up tests Filters For M006 valve EPR demonstrations, the plugged. Replaced and EPR takeover of the EPR stab le from the MPR a drop of 7 psi occurred (979 psig to 972 psig) 2/2/70 98o~ 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 sec. started ment and MPR stable a 6 psi peak to peak oscillation 2/8/70 98~o MPR in control and Adjusted MPR needle valve started 8 psi peak to and MPR stable peak oscillations 7/8/70 5 o< MPR causing slight Adjusted needle on 7/10/70 cycling in bypass changed sensing valve line valves. GE people From carbon steel to stain-adjusting EPR and MPR less steel on MPR and for bette'r stability change capacitor 104C to 6 NF on EPR

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• Date Power Level Correction

'Problem'hanged 7/20/70 20~o from EPR to Adjustment to MPR MPR and 200 psi peak to peak in pressure occurred - high flux scram level dropped 2 1/2'elow normal Flf flow dropped to 4X10 then to 6X10~

10/19/70 g O~ MPR in control and Adjusted sensor line pressure oscillating needle valve 8 psi peak to peak

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