ML19344D257

Final Deficiency Rept:Readout Instruments for 12 Radiation Monitors Spiked Upscale in Unison for 2-h.Caused by Interference Produced by Welding Machines.Signal Cable for Monitor O-RE-90-101A Being Rerouted in Conduit

ML19344D257
Person / Time
Site:	Sequoyah
Issue date:	03/04/1980
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML19344D254	List: ML19344D253 ML19344D257
References
NCR-20P, NUDOCS 8003110599
Download: ML19344D257 (1)

Text

- -

} ENCLOSURE SEQUOYAH NUCLEAR PLANT Uh4T~ 1 AND 2 .

RADIATION HONITORS SPURIOt SIGNALS  !

NCR 20P 10 CFR 50.55(e)

FINAL REPORT Description of Condition The readout instruments in the main control room for 12 radiation monitors were spiked upscale in unison for two hours on December 12, 1979, and for one hour on December 13, 1979. The spikes generally peaked at one million counts per minute. The 12 monitors identification numbers

, and their applications are listed below:

0-RE-90-132A Service Building Vent (Particulate)

U-R E- 90-13 2 B

• Service Building Vent (Caseous) 0-RE-90-101A Aux. Building Vent (Particulate) 1-RE-90-170 Boric Acid Evap. Condensers 1-RE-90-120* Steam Generator Blowdown Liquid Hon.

1-RE-90-121* Steam Generator Blowdown Liquid 11on.

0-R E- 90-118

• Waste Gas Disposal System Cas Effluent Hon.

0-R E 123 Component Cooling Water Heat Exchanger Liq. lion.

l-RC-90-123 Component Cooling Water heat Exchanger Liq. flon.

2-RE-90-123 Component Cooling Water IIcat Exchanger Liq. Mon. -

1-RE-90-100B* Shield Building Vent (Gaseous) 1-RE-90-104 Reactor Coolant Letdown Liquid Monitor

• Has radiological effluent monitoring technical specification The upscale readings were determined to be caused by the operation of a heliarc welding machine in the Auxiliary Building, two floors below the elevation of the cable spreading room which is under the main control room. The monitor signal cables apparently picked up radio frequency interference produced by the welding machines. The cables are run in '

cable trays.

Safety Implications Similar spurious indications during normal plam operation could mask actual above-normal radioactivity releases through any of the plant vents which

, are monitored by several of_the monitors, if operation were permitted to result in higher than allowable releases as set by the, plant technical '

specifications.

Corrective Action The 12 radiation monitors discussed here are not considered to be safety

• related in the Sequoyah Plant design, and the associated cabling is not Class IE. It is, therefore, not necessary that the cabling be run ih conduit. Also, the operation of heliarc welding machines causing the ,,

readout instrument spikes cannot be assumed to be a normal plant operational occurrence. The signal cable for monitor 0-RE-90-101A is being rerouted in conduit, and administrative procedures will be used to preclude the use of radiofrequency interference sources known to adversely affect the subject radiation monitoring equipment during plant operation. These changes will be implemented before unit i reaches one percent power.

800811o 597