Part 21 Report - 1995-189
ACCESSION #: 9512280071
TELEDYNE BROWN ENGINEERING
DATE; July 14, 1995
TO: Brian Green
FROM: Kim Johns
REFERENCE: Niagara Mohawk Power Corp. Letters dated March 10 and
March 18, 1995
SUBJECT: Engineering Evaluation of above referenced problems
On March 10 and March 18, 1995 we received two letters from Niagara
Mohawk stating that they had encountered four (4) operational problems
when testing the two (2) Model 225 CMA-X Containment Monitoring Systems
installed at the Nine Mile Point Unit 1 Nuclear Station. The following
is the Engineering evaluation of the relay problem which could result in
a 10CFR21 report filing.
Analysis of the Suspected Defect
The reported failure is that the relay (TBE/AI P/N R919) contacts either
fuse together or disintegrate in a short period of time. One of the
defective parts from Niagara Mohawk shows burning and disintegration of
one of the contacts.
A relay from the same lot as the NMPC components, has been taken from
TBE/AI stock and cycled for at least 18,000 cycles at 4 seconds per
cycle. This relay had a H121, 1,500 watt heater connected to the
contacts in the same configuration as the NMPC enclosure heater circuit.
After 18,000 cycles there was no sign of any significant deterioration.
These relay contacts are rated for 15 amps at 120 VAC for up to 100,000
cycles. A 1,500 watt heater uses about 12.5 amps at 120 VAC. Since the
relay contacts are appropriately rated under normal cycling conditions,
TBE/AI engineering staff concluded that the failure must be due to
possible abnormal cycling.
It was reported by NMPC engineering staff that the relays would sometimes
"buzz" or "chatter" when the enclosure doors were left open for testing
and the ambient temperature was close to the thermoswitch set
temperature. Any "buzz" or "chatter" of these relays for any significant
period of time would cause premature failure due to exceeding the minimum
cycle time at the rated current.
TBE/AI engineering staff performed a test to determine if the
thermoswitch (TBE/AI P/N T590) could be made to "chatter" when the
temperature was close to the setpoint. The results of the test
demonstrated that their was significant "chatter" only when the
temperature was right at the setpoint and if vibrated mechanically.
Without mechanical vibration the "chatter" was minimized.
The manufacture of the thermoswitch provided information that verified
our test reading. The manufacture provided a solution consisting of a
capacitor in parallel with the thermoswitch contacts for all applications
involving vibration in order to minimize contact "chatter". The
(illegible) of the recommended capacitor was 0.01 [symbol omitted]F
(TBE/AI P/N C340). The above test was repeated several times with and
without the capacitor. In each test the "chatter" was entirely
eliminated with the capacitor.
Corrective Action Plan
Based on history, this is the only reported incident of failure of the
R919 relay due to "chatter". This appears to only happen if the
enclosure doors are open while the analyzer is running and the ambient
temperature is approximately near 65 degrees F.
TBE/AI engineering will modify the current design to include a 0.01
[symbol omitted]F capacitor (TBE/AI P/N C340) to the thermoswitch.
John C. Moore
TELEDYNE BROWN ENGINEERING
16880 CHESTNUT STREET, P.O. BOX (illegible
CITY OF INDUSTRY, CALIFORNIA (illegible)
TELEPHONE (213)-illegible 7181 & (818) (illegible)
TWX: (910) (illegible)
FAX: (818) (illegible)
We at Teledyne Brown Engineering/Analytical Instruments are writing to
inform you of a defect we have become aware of in an assembly of the
Model 225 Hydrogen Containment Monitor. This assembly is part number
We received a report from Niagara Mohawk Power Corporation which
described a problem related to power relay, TBE/AI part number R919,
which is a component of assembly D24107. We have concluded this problem
is caused by "chatter" of thermoswitch, TBE/AI part number T590, when the
operating temperature is maintained at the thermoswitch setpoint and
At this point we have notified the NRC region V office of the issue and
have submitted the attached analysis and corrective action plan.
We are in the process of procuring the necessary items, establishing the
critical characteristics, and performing the qualification tests
necessary to complete the corrective action plan stated in the attached
memorandum dated July 14, 1995.
We expect the qualification testing to be complete by December 1, 1995.
Following qualifications, we will be sending you the subassembly, part
number A64871 capacitor assembly, and the necessary documentation. The
capacitor will ensure hysteresis in the Thermoswitch needed to correct
If you have any questions or need further clarification, please contact
Brian E. Greene at (818) 961-9821 Ext. 248. Brian is our QA Manager.
CC: USNRC Region V General Electric Co.
Duquesne Light & Power Co. Commonwealth Edison Co.
Carolina Power & Light Co. Bernische Kraftwerks AG
Florida Power Corp. Westinghouse Nuclear Espanola
Korea Electric Co. Louisiana Power & Light
Duke Power Co. Taiwan-Power Co.
Vermont Yankee Nuclear Perfect Technologies LTD
Hydroelectrica Espanola, S.A. ACAL Aurietna LTD
Niagara Mohawk Power Corp.
SENSORS o ANALYSERS o SYSTEMS
TOTAL QUALITY COMMITMENT
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