ML20024H301
| ML20024H301 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/22/1991 |
| From: | Clement C NORTHEAST NUCLEAR ENERGY CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| MP-91-430, NUDOCS 9105310163 | |
| Download: ML20024H301 (2) | |
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(0031665-5000 Docket No: 50-423 Re: 10CFR50.36 May 22, 1991 MP-91-430 U. S. Nuclear Reculatory Commission Document Contro'l Desk' Washincton, DC 20555 Gentlemen:
Millstone Nuclear Power Station, Unit No. 3 hialfunctioning Loose Parts Monitor Channel This Special Report is beine submitted pursuant to Millstone Unit 3 Technical Specification 3.3.3.S.n, Loose Parts Detection System. Plant Technical Specification 3.3.3.8.a requires that a Special Report be submitted to the NRC 10 days following one or more channels of the Loose Parts Detection System being declared inoperable for more than 30 days, while in Mode 1 (Power Operation) or 2 (Startup).
On April 12,1991, at 0855 hours0.0099 days <br />0.238 hours <br />0.00141 weeks <br />3.253275e-4 months <br /> with the plant in Mode 3 (Hot Standby), LPM Channel 3 went into Alarm. Channel 3 monitors Loose Parts activity in the Reactor Head. LPM Channel 3 was taken out of service at that time due to repetitive spurious alarms.
Channel 3 was turned of' to clear the main control board alarm and the data acquisition disk was removed from the system computer. This procedure enables the operators to re-boot the LPM computer with a new disk which allows subsequent valid loose parts impacts to be detected and recorded.
l On April 13,1991, at 1743 hours0.0202 days <br />0.484 hours <br />0.00288 weeks <br />6.632115e-4 months <br /> when the plant entered Mode 2 (Startup) at OG power, i
2250 psia, and 557 degrees Fahrenheit, LPM Channel 3 was declared inoperable. The other eleven (11) LPM channels were operating normally.
Loose parts impacts in the Reactor Coolant System (RCS) are detected by accelerometers attached to major RCS components. An impact generates an electrical j
signal from one or more accelerometers, which triggers the LPM to record information L
from all twelve channels on a computer disk. and actuates an alarm on the main control i
board.
I All detector cables and connectors were examinee Arinc the recent refueline outace for l
ruptures of the external cable sleeves, which wow! resuit in a loss of signal transmission capabilities. The sienal transmission data 'as empared with the current signal data which indicated that neither signal nnr chle sleeve degradation had occurred.
The results of the examination of '; e previous channel failure also determined that the accelerometer was functionine propc dy The accelerometer had been tested along with similar accelerometers on a vibration test. mare. The resulting performance data was compared with the current performance data and the results fell within the normal operating parameters, and Channel 3 was declared operable to support plant startunat the completion of the refueling outage.
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Further investication of the failure was initiated upon receipt of a subsequent Channel 3 failure on April 12,1991 du ing power ascension from the third refueling outape. This review invectipated the output data from the channel and determined that the spurious alarms were generated due to excessive noise on the channel. This noise source was isolated to a malfunctioning pre-amplifier umt. The amplifier unit was injecting its output signal back into its input channel thereby amplifying the signal, causing the resulting outpui signal to exceed the channers high setpoint parameter subsequently generating an alarm signal.
The conclusior. of this investigation determined that the taot cause of the Channel 3 failure was the malfunctioning pre-amplifier unit and that Loose Parts impacts were not actually occurring.
Redundant LPM channels monitoring the Reactor Head were operating satisfactorily and did not indicate that any impacts were occurrine l
l The pre-amplifier unit was replaced and the channel was declared operational on May 14,1991, at 1517 hours0.0176 days <br />0.421 hours <br />0.00251 weeks <br />5.772185e-4 months <br />. As of this date, the channel is functioning properly and i
has not displayed any furthei problems.
The Loose Parts Monitoring trouble shooting procedure is currently under review. The present procedure requires that the LPM output data on the computer disk be forwarded to an off-site location for analysis. This is very time consuming and has a significant impact upon the Instrumentation & Control Department's work prioritization to address l
and repair failures. The revised procedure will increase the response time for impact analysis and any subsequent channel repairs.
The Licensee contact for this Special Report is Burtel N. Forrest, who may be contacted at (203) 444-5442 Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY FOR: Stephen E. Scace Director. Millstone Station E
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BY:
H. Clement Millstone Unit 3 Director SES/BNF:cle ec:
T. J Martin Region i Administrator W. J. Raymond. Senior Resident inspector. Millstone Units Nos.1, 2. and 3 D. H. Jaffe, NRC Project Manager, Millstone Unit Nos. 1 and 3 i
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