ML20084Q839
| ML20084Q839 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 08/28/1973 |
| From: | Stephenson B COMMONWEALTH EDISON CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8306140286 | |
| Download: ML20084Q839 (2) | |
Text
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11 M Post Othcc Box 216
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Cordova, I!!inois 61242 s.
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Telephonc 309/654-2241
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j August 28, 1973 J. P. O' Leary, Directer t
,v sW Directorate of Licensing
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-1 U.S. Atomic Energy Core 11ssion
'l.bW Washington, D.C.
20545
Reference:
Quad-Cities Nuclear Power Station Unit 2 Docket No. 50-265, License DPR-30 Appendix A, Section 6.6.B.2
Dear Mr. O' Leary:
The purpose of this letter is to report an unusual event concerning the reactor protection system wiring of Unit 2 at Quad-Cities Nuclear Power Station. A wiring error was discovered on July 29,' 1973 in the noutron monitoring trip and mode switch interlock portion of the circuitry. This error was discussed with Mr. J. Fishbaugher of the Directorate of Regulatory Operations - Region III.
PROBLIG1 AND INVESTIGATION While perfoming routine instrument surveillance tests prior to a Unit 2 reactor startup a wiring error was found which effectively bypassed the scram function of Imd 18 whenever APM14 was on-scale or bypasced regardless of the mode switch position. Trouble shooting subsequently detemined that a two conductor cable (no. 28353) had its leads reversed at teminal board 1B in the 902-37 panel. Bc6ause of the physical configuration of the associated wiring this resulted in the mode switch contact (intended to bypass the IRM trip in the Run mode only) being removed from the circuit.
EVALUATION AND CORRECTIVE ACTION The Intermediate Range Monitoring (IRM) System provides protection against excessive power levels and short reactor periods in the startup and intermediate power ranges. The arrangement of the neutron monitoring trip circuit is such,,
that although the mode switch contact was bypassed, the IM4 would have perfomed its trip function properly throughout the startup and intemediate ranges due to the APM4's being downscale at these power lovels. Only in the overlap region at greater than 5% power or if channel 4 of the APK4 system had been bypassed would the IRM trip function.have been defeated under normal startup er shutdown conditions. This represents a very short period of time since the reactor is placed in the Run mode when the APR1 downscale trips clear during a startup.
In addition, if the reactor were maintained in the Startup mode in this overlap region the primary neutron monitoring protective trip would be the 15% APN4 scram which was not affected by this wiring error. In view of these conditions und the fact than only one of the eight IRM channels was affected, the safety implications of this event are minor.
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The wiring error on the mode switch contact existed from the time of initial startup and as cuch the exact cause of the error cannot be determined.
The IRM high flux trip is functionally tested prior to startups. In this condition the AFE!'s are downscale and the error could not be detected since the Im! produced the required RPS trip. On July 29th, however, APE! 4 was bypassed during the checks and a trip was not received. Upon locating the error, corrective action was taken to wire the circuit in accordance with design drawings. The modo switch interlock was functionally tested on all other IMI channels on both units with their associated APM! channels bypassed.
No other errors were found.
The Unit 2 preoperational test of the Reactor Protection System was reviewed in an attempt to ascertain why this error had not been detected at that time. The interlock check was included as a part of the test and was signed off as being co=pleted. It is apparent though that the procedure was deficient in this area. As the last step in a 21 step procedure to test the neutron monitoring system trips, IE!'s 15, 16, 17 & 18 were to be given upscale trips individually with APE!'s 4, 5 & 6 onocale for three different mode switch positions (Shutdown, Refuel and Startup). The proper operation of the bypass switch was also to be checked in this step. This lack of detail and breakdown to a step-by-step procedure is considered to be the reason that "this error was not detected.
The Commonwealth Edison Company Quality Assurance anual has designated the System Mechanical and Structural Engineer as the individual responsible for coordinating the preparation of all startup and preoperation tests. He has been advised of the deficiency in the test procedure and will insure that ths preoperational tests for future nuclear stations include sufficient detail.
Very Truly Yours, CO EONWEALTH EDISON COMPANY QUAD-CITIES NUCIFTAR POWER STATION f^
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B.h..Stephenson Station Superintendent V
cc: Regional Director Directorate of Regulatory Operations - Region III BBS/rhb BBS-73-169
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