ML20236Y594
| ML20236Y594 | |
| Person / Time | |
|---|---|
| Site: | University of Missouri-Columbia |
| Issue date: | 08/06/1998 |
| From: | Mckibben J, Schoone A MISSOURI, UNIV. OF, COLUMBIA, MO |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9808120330 | |
| Download: ML20236Y594 (5) | |
Text
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'% I Research Reactor Center Research Park Columbia. Missouri 65211 j II Telephone (573) 882-4211 FAX [573)882=3443 UNIVERSITY OF MISSOURI-COLUMBIA August 6,1998 4
Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555
REFERENCE:
Docket No. 50-186 University of Missouri Research Reactor License R-103
SUBJECT:
Report as required by Technical Specification 6.1.h.(2) concerning the operation of the reactor with a subpart of an experiment not rigidly held in place, in the center test hole (Technical Specification 3.6.e) Introduction On July 6,1998, while loading the flux trap sample holder for the next week of operation, an operator noted that one sample (can #53), listed as 3 inches long on the loading sheet, was only 2 inches long. Review of this error revealed that during the previous week of operation, one of three tubes of the flux trap sample holder had 1 inch of unoccupied volume. This could potentially allow the samples in that tube to move upward 1 inch, although no credible mechanism can be identified which would cause this to happen. The flow direction through the flux trap and sample holder is downward, so hydraulic forces and gravity hold the samples down in the tube. Technical Specification 3.6.e requires " Experiments in the center test hole shall be removed or installed only with the reactor shut down and shall be rigidly held in place during reactor operation." With the Technical Specification 1.5 definition of a experiment, this tube of samples not loaded to the correct height constitutes an experiment not rigidly held in place. /
/
Description The center test hole at the University of Missouri Research Reactor (MURR)is a high flux region G Z. used for the irradiation of 1.125 inch diameter sample cans which vary in length from 2 to 5 inches. The flux trap is made of three 1.5 inch nominal diameter tubes with three vertical welded spacer bars in each tube to center the sample cans. The tubes are welded together in a triangular array with a vertical sample profile of 30 inches. l 4 MURR Technical Specification 3.6.e. requires that experiments in the center test hole shall be removed or inserted only with the .eactor shut down and that such experiments shall be rigidly held in place during reactor operations. The bases states: Although the reactivity of worth of experiments in the center test hole is restricted to less than the reactivity insertion which would cause fuel element failure, this specification eliminates a potential mechanism for uncontrolled addition of reactivity. PDR Qgy --- l 8 ADOCK 05000186 PM -
o o l Letter to Document Cont'rol Desk August 6,1998
- Page 2 ;
These requirements are met by loading individual samples to be irradiated into the aluminum flux trap described above and depicted in attached Figure 1. A three pronged hold down device is
, pinned in place preventing movement of the samples in the flux trap (Figure 2). The flux trap is ,
loaded vertically into the center test hole with two steel spring clips latching onto the inner l pressure vessel to hold the entire apparatus rigid. To remove the holder from the reactor, a remote tool engages the holder, expanding the latching clips. During the week of operation, from June 29,1998 to July 6,1998, the flux trap holder was secured in place properly with the devices described above. The deviation from normal operation was that one tube (Tube A) had 29 inches of samples instead of the expected 30 inches of samples. This was detected by operators who were loading the flux trap.for the next week of operation starting July 6 (flux trap loading sheet 9744). The error was corrected before the subsequent startup. Review of the loading (flux trap loadin'g sheet 9743) from the previous week revealed the same error in the sample height for sample #53. The sample was listed as 3 inches long when it was only 2 inches long. This meant that samples in Tube A potentially could move up 1 inch during reactor operation, although no credible mechanism is known that could generate such movement. The operators also reloaded the samples that had just been taken out of flux trap tube A and verified I it had approximately 29 inches of samples. The flux trap loading program was used to determine the maximum change in reactivity if the one - inch water gap occurred at any of the possible positions between samples in tube A. This maximum reactivity change was calculated to be less than 0.00019 Ak/k.- Analysis The reactor operated from 1828 on June 29,1998 to 0400 on July 6,1998 (a period of 153.5 hours) with one tube of the flux trap sample holder loaded with 29 inches of samples rather than the expected 30 inches of samples. This was due to an entry error by a technician in the Irradiations Group who enters sample information into the computer program which calculates reactivity of the flux trap . ;
' loading. This error went unnoticed by operators who loaded the samples into the flux trap sample holder on June 29, but was detected by operators loading the flux trap on July 6. ]
Reactor operators perform a visual inspection of tube height after each tube is loaded, but did not detect the one inch deviation during the June 29 flux trap loading. This inspection is a visual through eight feet of water. The error could have been detected and corrected at this point. ie These errors constitute an observed inadequacy in the implementation of administrative and a ! procedural control, although the inadequacy could not have caused the existence or development of l an unsafe condition in connection with the operation of the reactor. A scheduled sample loading with height errors greater than 1 inch would have been detected by operators after or during ' ! loading. If the upper samples had moved up in Tube A to create a water gap between two samples of 1 inch, the maximum effect would have been less than 0.00019 Ak/k of reactivity change. No credible mechanism can be identified that would cause this' water gap because both gravity and the i
Letter to Docaent Control Desk August 6,1998 Page 3
- downward flow of the pool cooling system through the center test hole hold the samples down against the bottom of the flux trap sample holder tube.
No unreviewed safety questions existed during this period of operation. The reactivity of all samples in the flux trap is restricted by Technical Specification 3.1.h to less than 0.0060 Ak/k, and the maximum worth would have been 0.0040 Ak/k. CorrectiveActions The seriousness of the personnel errors that occurred have been reviewed with the persons involved with the loading sheet error and the sample tube height verification. This error is also being reviewed with the remainder of the operating staff and group that schedules irradiation to reiterate its significance and ways to prevent recurrence. The procedures in the Irradiations Group have been revised to add an additional verification of sample height for samples scheduled into the flux trap. This will be donc prior to delivering the samples to reactor operations for loading. The Reactor Operations Standard Operating Procedure (SOP) for handling the flux trap has also been reviewed. The height check done by the reactor operators to validate the proper flux trap tube loading height will be more explicitly described with specific requirements in the SOP. Sincerely, ENDORSEMENT: Reviewed and Approved ()4 0 >yr A d c90L. d [ Anthony Schoone J. Charles McKibben Acting Reactor Manager Associate Director xc: Mr. Alexander Adams, Jr., USNRC Mr. Tom Burdick, NRC Region III Dr. Brady Deaton g@[
' Dr. Edward Deutsch Reactor Advisory Committee
-{.= ggh Reactor Safety Subcommittee CHRISTTNE M.FJ1RANTE Notary Public-Notary Seal Attachments: Figure 1 STA'IB OFMISSOURI Figure 2 Boone County My Comminalon Expires: April 14,1999 j
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