ENS Event | |
|---|---|
07:00 Oct 11, 2012 | |
| Title | Part 21 - Potential Grounding Pathway Between Heat Sink and Chassis of Control Modules |
| Event Description | The following information was obtained from the vendor via facsimile:
This report notifies the Nuclear Regulatory Commission of a defect in CMM830 and TMD830 [modules] that could result in an unintended ground loop that could lead to a low impedance connection between the module output circuitry and chassis. There is a mechanical interference between the sheet metal housing and the heat sink for transistor Q1 on the master board assembly. The heat sink of transistor Q1 is connected to the drain of Q1, which is the output of the current loop circuit. Should the heat sink of transistor Q1 short to chassis because of the interference, then an unintended ground loop could lead to a low impedance connection between the module output circuitry and chassis. The effect of grounding Q1 to chassis will vary with the application. If Q1 is grounded to the chassis, but no ground connection exists in the output loop, the incidental ground may produce no observable effect on the performance of the module. In that case, any subsequent independent event which introduces a ground in the output loop will cause a loop fault, potentially affecting the module output current. Alternatively, if Q1 and chassis are initially isolated, the defect may not manifest unless vibration causes mechanical wearing of the oxide coating of the heat sink. It is possible that a seismic event could cause sufficient wearing to initiate a loop fault, again potentially affecting the module output current. The affected facilities are HB Robinson and Turkey Point. |
| Where | |
|---|---|
| Scientech Idaho Falls, Idaho (NRC Region 4) | |
| Organization: | Scientech |
| Reporting | |
| 10 CFR 21.21(d)(3)(i), Failure to Comply or Defect | |
| Time - Person (Reporting Time:+680.47 h28.353 days <br />4.05 weeks <br />0.932 months <br />) | |
| Opened: | Vince Chermak 16:28 Nov 8, 2012 |
| NRC Officer: | Howie Crouch |
| Last Updated: | Nov 8, 2012 |
| 48494 - NRC Website
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Scientech with 10 CFR 21.21(d)(3)(i), Failure to Comply or Defect | |
WEEKMONTHYEARENS 500962014-05-07T06:00:0007 May 2014 06:00:00
[Table view]10 CFR 21.21(d)(3)(i), Failure to Comply or Defect Part 21 - Potential Defect in Nus-710Du Trip Unit to Produce a Valid Trip Output Signal ENS 484942012-10-11T07:00:00011 October 2012 07:00:00 10 CFR 21.21(d)(3)(i), Failure to Comply or Defect Part 21 - Potential Grounding Pathway Between Heat Sink and Chassis of Control Modules 2014-05-07T06:00:00 | |