ML20244A853
| ML20244A853 | |
| Person / Time | |
|---|---|
| Site: | General Atomics |
| Issue date: | 04/06/1989 |
| From: | Asmussen K GENERAL ATOMICS (FORMERLY GA TECHNOLOGIES, INC./GENER |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 67-1368, NUDOCS 8904180228 | |
| Download: ML20244A853 (3) | |
Text
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CENERAL JETOh@lCS April 6, 1989 67-1368 Document Control Desk 3
U.S. Nuclear Regulatory Camission Washington, D.C. 20555 1
Subject:
Docket No. 50-163: Reactor Facility License No. R-67; Reportable Otx:urrence Gentlemen:
i At approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> on Friday, March 31, 1989, General Atmics (GA) notified the NRC office of Region V by telephone of a reportable occurrence concerning GA's TRIGA Mark F Reactor (License R-67).
At that tine, details of the occurrence were presented to Messrs. Ross Scarano, Greg Yuhas and Imelio Garcia.
This written report is being subnitted within 10 days as required by the applicable license, as amnded (Section C.4).
The reportable occurrence is described in detail below.
h?*new of Events The Mark F reactor is currently in a round-the-clock operating mode to perfom in-pile irradiations on direct conversion (thermionic) devices. On Wednesday, March 29, 1989, a scheduled shutdown of the GA TRIGA Mark F reactor was cmpleted in order to perform some manipula-tions with the thermionic devices, as well as perform certain reactor maintenance activities.
One of the planned maintenance activities was the replacement of the control rod drive on control rod #5 (the Mark F configuration was modified prior to 1985 for use in the thermionics irradiation program by removal of the transient rod and insertion of a standard control rod and rod drive to allow the use of five standard control rods for steady-state power operations).
All five control rods are fuel follower control rods (FFER).
The required maintenance activity was scheduled because of observed problems in driving this rod out of the core with the installed rod drive.
At approximately 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> on Thursday, March 30, the on-duty operations staff (one senior operator and one operator) completed the task of replacing the control rod drive (serial #304005) on rod #5 l
with a refurbished control rod drive (serial #W60339-1).
All proper control rod maintenance procedures were followed for this activity, including the verification of the required shutdown margin. Following successful verification of r6d drop times to ensure compliance with the applicable technical specifications, the senior operator proceeded to withdraw rods to attain a power level of 1000 watts in order to perform the required control rod worth calibration using a reactivity camputer. Towards the end of the calibration (control rod nearly full 4 p-I 8904180228 890406 PDR ADOCK 05000163 S
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10955 JOHN JAY HOPKINS DRIVE, SAN DIEGO, CA 92121-1194 PO, DOX 85608. SAN DIEGO, CA 92138-5608 (619) 455-3000
. 1 UP), the operators noticed an unusual behavior in the shape of the rod 1
worth curve.
The curve was found to have an anamaly at the top end, indicating negative reactivity insertions as the rod continued to be withdrawn.
Suspecting that the rod was eming out too high, the l
operators stopped the calibration and manually scrantned the reactor, I
but could not get rod #5 to drop, nor could the rod be driven in using the ROD DOW switch on the console. Note that the other four rods had been inserted into the core as a result of the reactor being scrammed, thereby assuring that the required shutdown margin was adequately met.
l The senior operator was able to manually insert the control rod from l
the reactor bridge by slightly twisting the aluminum rod that connects l
the drive assembly (located on the bridge) to the control rod in the Core.
The physicist-in-charge and the de prcmptly notified of the situation. puty physicist-in-charge were
'Ib investigate, the on-duty staff removed the rod drive, again following proper control rod maintenance procedures.
It was discovered that a two-inch aluminum spacer used to limit the upward travel of the FFCR by actuating the ROD UP limit switch was missing frm its position on the drive shaft.
This aluminum spacer is used to limit the travel of the control rod to the required 13 inches on the Mark F reactor; normally, the travel of the control rod is 15 inches.
To correct the situation, the staff removed the spacer fram the defective control rod drive and installed it on the refurbished rod drive.
They then reinstalled the rod drive on the reactor, perfonned l
the required checks and proceeded with the normal calibration activities.
The operations staff was instructed to also check the other four rods to ensure the presence of spacers on all rods; all spacers were in place.
In addition, the travel of each rod was physically verified to be 13 inches.
Analysis During the conversion of the Mark F reactor to a FLIP fueled core in 1973, it was found necessary to limit the travel of the FFCRs to 13 inches in order to eliminate the type of anomaly in the control rod calibration curve that was observed by the operator on March 30.
The conversion of the standard 15-inch travel rods to 13 inches was carried out by attaching 2-inch long aluminum spacers to the drive shafts, thus causing the ROD UP limit switch to actuate after a 13-inch withdrawal from the core.
The use of 13-inch travel rods has been in effect since 1973 when all Mark F control rod drives were equipped with such spacers to provide the reduced travel.
A new standard 15-inch control rod drive assembly was purchased during 1987 (serial #304005) and installed as a replacement drive on rod #5 during a scheduled reactor shutdown during June 1988.
At that time, the aluminum spacer from a spare drive (serial #W60339-1) was removed and installed on the replacement drive to modify it for a 13-inch travel.
The defective drive was sent out for refurbishment and
i 1 '
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i returned for storage to the reactor facility upon completion of the necessary repairs. When it was recently again necessary to change out the drive assmbly on rod #5, i.e., on March 30, 1989, the spare drive-without the spacer was used. The operators assumed that spacers were present on all drives and did not specifically verify the presence of a spacer on the spare drive being installed.
With a 13-inch travel, the rod assembly is designed so that the bottm end of the FFCR is at least 3/4-inch below the top of the 1.25-inch thick bott m core grid plate when the rod is in the full UP position.
However, on March 30, 1989, when the rod (with the missing 2-inch long spacer) travelled beyond the 13-inch length, the bottom fitting of the FECR was able to clear the top of the bottm grid plate and, when reinserted, came to rest away from the centerline of the locating hole in the plate.
A slight movment of the connecting rod by the senior operator then allowed the rod to be reinserted through the bottm grid plate location.
CmwLive Actions Two actions were initiated immediately:
1.
All spare rod Mark P drive ass mblies are being checked to ensure the presence of the aluminum spacers.
If necessary, new spacers will be fabricated and installed on all drives.
2.
Since standard Mark F drive assemblies are modified to provide the required 13-inch travel, a change in the maintenance procedure will be implemented whereby the operator changing out the rod drive assembly on the Mark F will be required to verify the presence of these spacers before installation.
Correction action item 1 has been conpleted. Corrective action item 2 is in progress.
Item 2 will be c m pleted prior to any future changing out of control rod drive assemblies on the Mark F reactor.
We trust you will find the above description of the reportable occurrence and corrective action satisfactory.
If you have any questions concerning this occurrence, you may contact me at (619) 455-2823 or Dr. Ottnaid Razvi at (619) 455-2441.
Very truly yours, C
Keith E. Asmussen, Manager Licensing, safety and Nuclear Cmpliance KEA/JR/mk cc: Mr. John B. Martin, Administrator, NRC Region V
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