ML20148E013
| ML20148E013 | |
| Person / Time | |
|---|---|
| Site: | University of Iowa |
| Issue date: | 09/27/1978 |
| From: | Hendrickson R IOWA STATE UNIV., AMES, IA |
| To: | |
| Shared Package | |
| ML20148E010 | List: |
| References | |
| NUDOCS 7811060074 | |
| Download: ML20148E013 (3) | |
Text
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Department of Chemical Engineering and Nuclear Engineering 261 Sweeney llall lOWA STATE
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- UNIVERSITY w-e m2msi September _ 27, 1973 Docket:
50-116 Mr. Angelo Giambusso Deputy Director for Reactor Projects Directorate of Licensing Office of Regulation U. S. Atomic Energy Commission Washington, D.
C.
20545
Dear Mr. Giambusso:
This report summarizes documentation on' file at the UTR-10 facility which has been reviewed and approved by the Radiation Safety Committee of Iowa State University.
Subiect:
Malfunction of the UTR-10 Shim-safety Rod Description of the Event At the conclusion of a Laboratory experiment on September 14, 1973, the shim-safety rod of the Iowa State University UTR-10 reactor' failed to insert when a manual scram was executed.
The safety rods and moderator-coolant dump functioned normally.
The reactor was more than 30 percent subcritical after the scram.
The reactor was secured in the fully shutdown condition.
Depart-mental administration and the Radiation Safety Committee Chairman were notified.
A verbal report was made to the Regulatory operations office, Glen Ellyn, Illinois on September 15, 1973.
Investigation and Corrective Action Inspection of the rod drive unit showed that the position potentiometer mounting nut was loose allowing the potentiometer gear to mismatch with the rod drive gear.
The mismatch prevented normal spring-force insertion.
Two modifications were initiated.
The potentiometer mounting hardware was changed to permit use of a lock washer.
See. Figures la and Ib.
A fiducial mark was added to the nut and mounting bracket 9
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Mr. Angelo Giambusso Page 2 September 27, 1973 l
to indicate during visual inspection if nut rotation has occurred.
Second, the inspection interval has been reduced to six months.
Safety Evaluation and Review l
The changes outlined do not involve a change in the technical specifications nor do they constitute an unroviewed safety question.
The changes are effective and reduce the possibility of recurrence of the malfunction.
The functions of the shim-safety control rod drive unit have not been changed.
More frequent inspections can i
be performed without degradation in the functions of the drive unit.
I Telephone conversations with Mr. John Fishbaugher, Region III, Regulatory Operations, provided guidance for and approval of actions of the licensee, during the period September 17 - 25, 1973.
Sincerely yours, dkat</
kt Richard A. Hendrickson UTR-10 Reactor Supervisor Approved:
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A. F. Voigt[ Chairman I
RAH /jh Radiation Safety Committee l
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