ML20203J868
| ML20203J868 | |
| Person / Time | |
|---|---|
| Site: | University of Missouri-Columbia |
| Issue date: | 02/27/1998 |
| From: | Mckibben J MISSOURI, UNIV. OF, COLUMBIA, MO |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9803040325 | |
| Download: ML20203J868 (2) | |
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Columbia, Missouri 65211 Telephone (573) 882-4211 UNIVERSITY OF MISSOURI-COLUMBIA FAX [573) 882=3443 February 27,1998 US Nuclear Regulatory Commission ATTN: Document Control Desk Wasb%tton, DC 20555 RUFTh SCE:
Docket No.59-186 The Curators of the Umversity of Missouri License No. R 103
SUBJECT:
Follow-up Information to the January 8,1998 letter concerning unanticipated reactivity insertion.
Dear Sir:
The University of Missouri Research Reactor (MURR) sent a letter dated January 8,1998 to the NRC concerning an unanticipated reactivity insertion. Under follow up actions MURR stated that the control blades and their drive mechanisms would be pulled and inspected during the I
maintenance periods in January and February. MURR has already removed and inspected two of the four control blades and drive mechanisms and found no problems in she blades or drives.
l The second mechanism inspected had rod drop times which had increased to longer than were normal but were within technical specification limits, this had been discussed with the NRC inspector during his January inspection. This mechanism was replaced and subsequent rod drop times have been normal. If bubbling from a control blade caused the event, it would most likely have beta control blade A because ofit's location. It was inspected first and there we; e no abnormalities noted with the blade. As discussed with Mr. Alexander Adams, USNRC, on February 20,1998, MURR has decided to inspect the last two n.echanisms at their normal replacement intervals. Control blade B will be replaced in April or May and control blade D in October or November. This will help us reduce tha radiation exposures to personnel, an ALARA l
consideration, and the likelihooi that the reactivity insertion was caused by the control blades is very remote.
The NRC inspector noted also the sticking of the chart recorder pen for the power range channel 5 in his January inspection report, in November 1998, the decision had been made to replace channel 5 and 6 chart recorder. The new recorder will resolve the problem with the channel 5 and
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6 recorder pens sticking. The new recorder is in hand and is being bench tested. When the safoty
/y review is completed it will be installed.
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',TUS Nuclear Regulatory Commission February 27,1998 Page 2 The reactor physicist har performed additional computer modeling using MONP to test the feasibility of the hypothesis that a large gas bubble being releaaed from a wedge caused the unanticipated reactivity transient and corresponding nuclear instrumentation indication The modeling involved comparing a base case to cases with voids in the water in either the control rod gap or water gaps in the graphite redector region. The control rod gap void modelindicates that a positive reactivity insertion would result from a void in this region. Voids in either region showed an improved coupling between the channel 4 and 6 detector region and the reactor core,i.e., more thermal neutrons around the detector for the same reactor power level. These results support our earlier hypothesis, but the chaages are small with signi6 cant statistical uncertainty.
Eftective February 2,1998, Mr. Walter Meyer was promoted to Assistant Director for Reactor income Operations and Mr. Anthuy Schoone assumed the position of Acting Reactor Manager, Mr. Schoone has been the Reactm Operations Engineer since April 1989 and in the absence of Mr.
Meyer would serve as Acting Reactor Manager, Sincerely,
/
.w J. Charles McKibben Associate Director xc:
Mr. Alexander Adams, Jr., USNRC Mr. Tom Burdick, NRC Region III Dr. Edward Deutsch Rea: tor Advisory Committee Reactor Safety Subcommittee
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