ML20236L562
| ML20236L562 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/05/1987 |
| From: | Nobles L TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 87-04, 87-4, NUDOCS 8708100293 | |
| Download: ML20236L562 (3) | |
Text
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l heq aE ya ee Post Office Box 2000 Soddy-Daisy, Tennessee 37379 August 5, 1987 I
U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 Gentlemen:
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TENNESSEE VALLEY AUTHORITY - SEQUOYAH NUCLEAR PLANT UNIT 1 - DOCKET NO.
50-327 - FACILITY OPERATING LICENSE DPR SPECIAL REPORT 87-04 REVISION 1 The enclosed revised special report provides additional details concerning l
the meteorological instrumentation being inoperable greater than seven days l
due to component failures. This event was reported in accordance with Technical Specification Limiting Condition for Operation 3.3.3.4, action statement (a), on May 21, 1987.
Very truly yours, TENNESSEE VALLEY AUTHORITY W
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L. M. Nobler Plant Manager Enclosure cc (Enclosure):
J. Nelson Grace, Regional Administrator U. S. Nuclear Regulatory Cortmission Suite 2900 101 Marietta Street, NW Atlanta, Georgia 30323 Records Center Institute of Nuclear Power Operations Suite 1500 1100 Circle 75 Parkway Atlanta, Georgia 30339 NRC Inspector, Sequoyah Nuclear Plant 8708100293 870005 DR ADDCK 05000327 n}
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PDR 7'
r'i 1983-TVA 5OTH ANNIVERS.ARY An Equal Opportunity Ernployer
SPECIAL REPORT 87-04 REVISION 1 SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 DESCRIPTION OF EVENT On May 2, 1987, at 1750 EST with units 1 and 2 in mode 5 (0 percent power, 337 psig, 120 degrees F and 0 percent power, 260 psig 129 degrees F, respectively), the meteorological instrumentation was declared inJperable and Limiting Condition for Operation (LCO) 3.3.3.4 was entered. The problem was discovered by operator observation of the meteorological instrumentation giving intermittent false readings.
The meteorological tower was contacted, and it was determined to be a problem with plant equipment and not with meteorological tower equipment. The meteorological tower is located approximately 1/2 mile southwest of the plar.t.
The data generated by the meteorological tower equipment is transmitted to the Sequoyah Nuclear Plant auxiliary instrument room by telephone wires which carry radio frequency signals. These signals are transmitted through a demultiplexes to the plant computer and the recorders in the main control room in order to generate the appropriate parameters. After component replacements and circuit changes by the vendor personnel,'the instrumentation was declared operable at 1736 EST on June 24, 1987. LCO 3.3.3.4, action statement (a), requires a special report to be written if the meteorological instrumentation is out longer than seven days. Due to the cause of this event not being determined at the time of the special r,eport submittal, a commitment was made to submit this revised report.
CAUSE OF EVENT Initial troubleshooting by Instrument Maintenance personnel found several gate and timing circuits defective in the demultiplexes, and these were replaced. These defects were attributed to normal life expectancy failures. This did not completely solve the problem, and the vendor (Fischer and Porter) was contacted for further investigation. The vendor investigation determined the problem was in the meteorological tower demultiplexes.
It was found that occasional spurious signals were triggered at the trailing edge of the data resulting from noisy resetting of the data mark or space bit out of the radio frequency link equipment.
ANALYSIS OF EVENT This event was reported under the requirements of action statement (a) of LCO 3.3.3.4.
The meteorological tower equipment measures wind direction, wind speed, and air temperature. These parameters are used to determine plume conditions in the event of an unexpected airborne radioactive release to the environment. With both units in mode 5, it is highly unlikely that such an accident could occur since there is not sufficient energy in this mode to create a harsh environment.
Also, the meteorological data could be obtained from meteorological tower since its computer was operable during this event.
Had the plant been in a different operating condition, the significance of this event would be unchanged since the meteorological information would still have been available from the meteorological tower computer.
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CORRECTIVE ACTIONS The defective gate and timing circuits were rtplaced in the demultiplexes when discovered. The problem with the spurious signals was resolved by installing a circuit which will make the leading edge of the data into a pulse of 20 microseconds. This allows for a reset at the beginning of each data set and will prevent too many signals from entering the clock.
ADDITIONAL INFORMATION There has been one previous special report written on the meteorological instrumentation being out of service more than seven days - Special Report 87-03.
This event was due to recorders not functioning caused by a bad cable in the telephone line which transmits the meteorological data from the meteorological tower to the plant.
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