ML20006B658
| ML20006B658 | |
| Person / Time | |
|---|---|
| Site: | Dow Chemical Company |
| Issue date: | 01/19/1990 |
| From: | Kocher C DOW CHEMICAL CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9002050196 | |
| Download: ML20006B658 (2) | |
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DOW CHEMICAL U.S.A.
January 19, 1990
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MIDLAND. MICHIGAN 0067 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 DOW TRIGA RESEARCH REACTOR - DOCKET 50-264 REPORT &BLE OCCURRENCE At about 12:54 pm on 16 January 1990 the wide-range LOG CHANGEL failed while the reactor was being taken to power with the core supercritical by about 0.0022 8k/k the period was about 13 seconds; as the reactor power passed the 10-watt level the LOG CHANNEL indication leveled off at about 12 watts, the PERIOD indicator went to zero, and the independent wide-range LINEAR CHANNEL indicated that : the power level continued to rise. The third independent single-range PEROSNT POWER linear chant.el is not sensitive enough to operate at such a low power level. The manual scram was immediately activated and the.
reactor was safely secured.
The wide-range LOG CHANNEL operates on pulse-counting circuitry at low power levels and on an evaluation of the RMS part of the: neutron signal (Campbell technique)- at higher power levels; the crossover point is at about 12 watts. This f ailure indicates a loss of the RMS circuits.
Similar failures occurred December 3, 1984, January *1, 1985, November 12, 1985,- and December 20, 1989. The actual' cause of these. failuros.
was identified af ter the November 1905 events a poor connection in a rotary switch in the wide-range log channel (calibrate swhch).
This switch is' a seven-position multi-wafer rotary switch which is open to the atmosphere; six positions are used for injocting calibration signals into the LOG CHANNEL during the daily chockout procedure, while the seventh position is used during normal operation of the reactor. 'Following both the November 1985 and the December-a 1989 failures it.was observed that the framework holding the wafers in
' place had become loose, allowing some mis-alignment'of the components.
The mechanis.n was tightened after t.he 1985 incident and the-system eperated properly for just over' four years.
The mechanism was also:
tightened after the 1989 incident, but the system f ailed within one month.
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Acting on the premise that the cause of the present failure was a poor contact, the operator used compressed air to blow out any material in l
the switch. The system was tested and worked properly. The reactor I
was returned to service the sane day.
j The following day, January 17, the switch was examined by an j
electronics technician, who cleaned the contacts with an appropriate commercial fluid. There was no evidence of mechanical failure.
1 Discussions with General Atondos have identified the particular wafer in'the switch which is responsible for these failures. noplacanent parts are available.
The Reactor Operations Committee has reviewed these incidents and has concluded that the reactor may be operated safely in its present condition, but in order to reduce the probability of further problene with the same parts the switch should'be repaired or replaced soon.
General Atomics personnel are prepared to replace part or all of the switch during an on-site visit which is expected to take. place during the first quarter of 1990.
A request for capital authorization to replace the entire control 4;[
console was initiated early in January 1990, with the aim of installing a new control system during 1990.
Such an installation will eliminate any further problems with this particular circuit.
t C. W. Kocher I
Reactor Supervisor Analytical Laboratories
,f 1602 Building 1
(517)636-0304 dmp
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cc: Regional Administrator, U.S. Nuclear Regulatory Commission, Region III, 799 Roosevelt Road, Glen Ellyn, IL 60137 Mark Ring, Section Chief, U.S. Nuclear Regulatory Commission l
Region III, 799 Roosevelt Road, Glen Ellyn, IL 60137
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