ML20011D773
| ML20011D773 | |
| Person / Time | |
|---|---|
| Site: | University of California - Irvine |
| Issue date: | 12/18/1989 |
| From: | Geoffrey Miller CALIFORNIA, UNIV. OF, IRVINE, CA |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 8912280396 | |
| Download: ML20011D773 (2) | |
Text
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0 UNIVERSITY OF CALIFORNIA, IRVINE
.- stRKELEY e Davis e IRVINE o LOS ANCELFS e RIVERSIDE e SAN DIEGO e SAN FRANCISCO I j SANTA BARBARA e SANTA CRUZ DEPARTMENT OF CHEMISTRY IRVINE. CALIFORNIA 92717 NUCLEAR REACTOR FACILITY SUPERVISOR: DR. o.E. MILLER TEL: (714) 856-6649 oP. 714-8564,')82 U.S. Nuclear Regulatory Commission, December 18th,1989 Document Control Desk, Div ision of ReactorLicensing, l Washington, D.C.20555 Docket: 59S26 Licensee renort of Abnormal Occurrence Ref: Technical Specifications 1.13.c. and 6.7.c.3.
Gentlemen:
i This is a written follow-up to a telephone report made 12/12/89 to the NRC Region V office in the person of Michael Cillis, by the undersigned.
Routine start-up checks at our facility call for each control rod to be raised and lowered to test SCRAM capability. The Senior Operator making these checks noted that the Fast Transient Contml Rod (FTR) still indicated an UP status after a SCRAM initiation. The Reactor Supervisor was called and investigated the problem. It was found that the rod was indeed stuck towards the upper end of its travel. It could be mechanically induced to drop, j but on re-firing, again stuck. Planned reactor operations that day were cancelled and a telephone report made.
Subsequently, the complete rod assembly was removed for inspection. The deceleration adjustment provided for this system has a water pressure damper unit a few feet above the core. This unit consists of a small plastic piston, riding on a 1/4th inch steel rod, pulled upwarxis into an aluminum cylinder. The displaced water is forced out through a series of adjustable holes. This plastic piston had deteriorated, showing several chip,s and cracks, allowing the set screw holding it in place to rotate through 90 degrees, foremg the plastic apart somewhat. This created an expanded diameter and was thus binding in the cylinder.
The piston-cylinder contact is made only during the last few inches of travel, so that the rod onlyjammed close to the upper limit of travel.
A new plastic piston, of polyethylene, is being manufactured to original specifications.
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This will be installed as soon as completed, the unit tested, and returned to service.
Safety Concerns: In spi:e of the fact that this must be reported as an abnormal occurrence by the terms of our technical specifications, there is really nD. safety concern whatsoever as -
a result of malfunction of this rod. While it is used, for convenience, as a " safety rod", i'.
was not included in the core design for safety, but entirely for experimental use reasona (to aid in creating larger pulses). The rod worth is approximately $0.65,less than 107. of the total rod worth at this facility. Since we maintain large shutdown margins (in exct,ss of ~
$5.00)well in excess oflegal limits, whether or not this rod is operational, or even present, is not significant.
8912280396 P 891218 S.DR - ADOCK 05000326 PDC !
NRC FTR Abnormal Occurrence R:: port Page 1 12/18/89
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Fortunately our history of recent operation had been quite light, so that the md was only some 20-50 mr/hr at the surface (maximum) on removal from core. The section holding the piston is sufficiently above the core, that no detectable radiation above background is as,sociated with the section that has to be rebuilt. Thus exposure to facilhy personnel will be mimmal. L Historv In 1983, a problem was reported with the FTR that was attributed to dirt in the air supply system. This is not relevant to this issue (though a full inspection has been made of that portion of the system), because the piston / cylinder is water related and no air is -
involved at this part of the FTR system. During routine annual inspection, ahnost exactly one year earlier, it had been noted in the logbook that the piston (described as " teflon" by the writer, but in fact made of polyethylene) showed slight evidence of small superficial ' ,
chipping, but no cracks were seen. This was not perceived to affect performance at that [
time, ud, in fact the unit has gone through several hundred operational cycles (mostly for routine start-up testing!) since that inspection until it failed. However, the color of the plastic and its hardness have obviously undergone a slow change since new, presumably as a result of simple aging, this presumably aided by some exposure to radiation (mostly gamma radiation at this locanon a few feet above core). Since the device was manufactured in 1968-69, an age of 20 years could easily have that effect on plyethylene.L Hindsight would suggest that we should have planned to reylace it earlier in the year, or at last year's annual maintenance: however the effort involvec - other than the repomng requuements -
would have been the same, since removal and replacement would have been needed. No
" interim" repair would have been helpful.
Sincerely, C( ,DNb ,
George E. Miller Reactor Supervisor u
cc: Reactor Operations Committee members General Atomic,Inc.,
attention Donna Cowser, P.O. Box 85608, San Diego, CA 92138-5608 US NRC Region V,1450 Maria Lane, Suite 210, Walnut Creek, CA 94596 l
1 NRC FTR Abnormal Occurrence Report Page 2 12/18/89