ML20028E944
| ML20028E944 | |
| Person / Time | |
|---|---|
| Site: | University of Michigan |
| Issue date: | 01/18/1983 |
| From: | Kerr W MICHIGAN, UNIV. OF, ANN ARBOR, MI |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| NUDOCS 8301280287 | |
| Download: ML20028E944 (2) | |
Text
P E.
THE UNIVERSITY CF MICHICAN PHOENIX MEMORIAL LABORATORY FORD NUCLEAR REACTOR ANN ARBOR, MICHIGAN 48109 (313) 764-6220 January 18, 1983 U.
S.
Nuclear Regulatory Commission Region III Attention:
Mr. James G. Keppler 799 Roosevelt Road Glen Ellyn, Illinois 60137 Gentlemen:
After further reflection concerning the classification of the event (single rod scram) reported to you by telephone on January 7 and confirmed by telegram on January 7, 1983, we have concluded that it was not a " reportable occurrence" as defined by our Technical Speci-fications. Ilowever we have concluded, after analysis of the event, that we can make some improvements in our control and indicating systems and we propose to do so.
The reactor was shutdown by a high power scram at 2.4 MW.
The scram was the result of a failure in the reactor automatic control system during a rod adjustment procedure.
Following is a description of the event and some changes which we plan to make.
HIGli POWER SCRAM SEQUENCE OF EVENTS 0120:
The lead operator observed the control rod at 23+ inches.
The control rod upper limit is 24 inches. He bumped the shim rods outward so the control rod would be driven inward by the automatic control system. The purpose of this action was to determine the xenon buildup rate for a subsequent control rod shim; to twelve inches if xenon were near equil-ibrium, lower if equilibrium xenon were still being approached.
A shim to twelve inches would have avoided having to adjust linear level, "A" and "B" ion chambers.
Following the bump, the lead operator observed a steady trace on linear level and indication of in-out cycling on the control rod.
0135:
Both the lead operator and the operator heard the control rod relay open as the control rod dropped out of automatic.
The audible thud of a rod dropping into the core was simultaneously heard. The lead operator observed "A" rod magnet contact light extinguished. The lead operator inserted the control rod and the remaining shim rods. No audible alarm was initiated.
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The lead operator observed a power indication _of 2.4 MW.on "A"
safety channel and 100% on.tlue linear level recorder.
When the ' operator placed recorders 'c. fast, linear level indication jumped down to approximately 20%.
The Supervisor of Reactor Operations was informed. Routine checks and inspections showed all conditions and' systems-to be normal.
0147:
The reactor was restarted and' returned to full. power.
CONCLUSIONS It appears that the automatic control feedback system failed elec-I trically, either in the slide wire or in the amplifier card. 'The control rod may have started to insert, but stopped before sufficient-
~
l negative reactivity was added to compensate for the shim rod bump.
A small net positive reactivity caused power'to increase over fifteen i
Because of the long period, channel "A" slow scram tripped first, dropped "A" rod, and caused power to-decrease before any other slow scram, multi-rod fast scram, or audible alarm contact closure was initiated.'
1 ACTION i
1.
Linear level' recorder'will be thoroughly checked and tested in order to reduce the probability of another failure.
2.
A shim stamp will be prepared which will include "A" and "B" l
power levels after the shim.
3.
A linear level monitor / alarm will be installed, if feasible,.
to sound an alarm at a setting between 2 and 2.4 MW. ~ The
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i monitor will come directlyifrom the linear level system detector, not the recorder.. The linear level system is a control system. The modification will not affect.the safety system. This will serve to warn of power increase and do it independently of the recorder. circuit.
Sincerely, William Kerr Director Michigan Memorial-Phoenix Project WK/z XC: FNR Safety Review Committee I
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