ML20138A020
| ML20138A020 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 11/13/1985 |
| From: | Lempges T NIAGARA MOHAWK POWER CORP. |
| To: | Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| NMP-15017, NUDOCS 8512110513 | |
| Download: ML20138A020 (2) | |
Text
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V NMP-15017 ENIAGARA MOHAWK POWER CORPORATION NIAGARA
, MOHAWK 300 ERIE BOULEVARD. WEST
$YRACUSE. N. Y.13 202 November 13, 1985 Dr. Thomas E. Murley
. Regional Administrator zUnited States-Nuc1 car Regulatory Commission Region-I.
'631 Park' Avenue King of Prussia, PA.19406
. RE: Docket 50-220 SPECIAL REPORT Gentlemen:
_In -accordance with Table 3.6.11-1 and Action Statement 3 of Table 3.6.11-2 of the Nine Mile Point Unit I Technical Specifications, we hereby submit the following Special Report concerning an ' inoperable containment high range gamma radiation monitor:
At 0730 on October 31, 1985, the Channel #11 Containment liigh Range Radiation Monitor tripped upscale and was momentarily inoperable while it was out'of service for troubleshooting (in' order to determing whether the unit was functional).
It was found that the sensing and indication portions
. of the unit were in fact operating properly. The monitor is one of two i -
General Atomic liigh Range Gamma Radiation Monitoring System units that monitor containment radiation levels.
It'has been determined that the trip #1 setpoint of the monitor was conservatively. set below that recommended by the calibration procedure. This u.it has both low and high trip setpoints. According to the calibration procedure (N1-ISP-201.7) the low-level trip-for this monitor should be set to' trip at three times the normal operating background radiation level.
This is done not only to reduce spurious trips, but to allow'enough deadband for a consistent reset point. The normal operating background level for the channe1~#11 monitor is 5-6 Rem /hr. Ilowever, the low 1cvel trip was set at 10 Rem /hr.
It is believed that a spurious electrical spike induced by welding activities
- caused the initial upscale spike. Since the backgound level was elevated, the reset deadband was not obtainable and the monitor could not be immediately reset. Once the signal fell below the reset point, the monitor reset properly.
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l JThe monitor.was' returned to service on October 31, 1985. To avoid-K recurrence, the trip'setpoint of the channel #11 Containment fligh Range l-Radiation Monitor was adjusted to 15 Rem /hr. per Nine Mile Point Unit I procedure N1-ISP-201.7-on November 2,~1985.
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Very truly yours,
~ _
Thomas E. Lempges Vice President l-Nuclear Generation
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