ML20004B030

Ro:On 810420,meter Control Relay Unit Scram Did Not Actuate in Response to Low Pressure Signal.Caused by Reduced Capacitance Value Preventing Capacitor from Charging Sufficiently.New Meter Relay Control Unit Installed

ML20004B030
Person / Time
Site:	University of Missouri-Columbia
Issue date:	05/18/1981
From:	Brugger R, Mckibben J MISSOURI, UNIV. OF, COLUMBIA, MO
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 8105270133
Download: ML20004B030 (3)

Text

{{#Wiki_filter:Research Reactor Facility UNIVERSITY OF MISSOURI coiun,eia. M ssoun es211 May 18, 1981 Telephone (314) 882-4211

y. \2 %

A 9 - Qj Director of Licensing -

                                                                                       ;         D               L  :

U. S. Nuclear Regulatory Commission U;, [2) Washington, D. C. 20555 U, ,-{[ /pj

s. a

Reference:

Docket 50-186 University of Missouri M I';'dM,7 License R-103

Subject:

Report as required by MURR Technical Specification 6.1.h(2). Description On April 20, 1981 while performing a routine semi-annual compliance check on the reactor low pressure scram unit 943, it was found the meter ' relay control unit scram did not actuate in response to a low pressure signal. Operation of the reactor with this meter relay trip inoperable deviates from MURR Technical Specification 3.3.1 in that one of the four reactor low pressure scrams was not operable. Analysis The reactor was in the shutdown mode, with all control rods fully inserted. A test signal was being fed into the 943 meter relay trip unit as part of the compliance check procedure. The meter indication was in calibration but the meter relay contacts failed to open. A new meter relay control unit was installed. To investigate the malfunction, the old meter relay control unit was disassembled and the value of a capacitor located in the meter relay con-trol circuit measured. The original value of the capacitor was 330 pf

           @ 6V. The measured value of the capacitor had decreased to about 47 uf.

Because of the reduced capacitance value, the capacitor did not charge sufficiently for the meter relay control circuit to function properly. OM Y / O E ' ' COLUMBIA KANSAS CITY ROLLA ST. LOUIS

          -4

, an eaual opportunity institution

              !8105270/J3                                  J

  ~

Director of Licensing May 18. 1981 Page 1 The 943 reactor low pressure transmitter is original equipment in-stalled to provide an indication only for 5 MW operation. During the 10 MW upgrade in 1974, additional scram protection was added with the addition of a G.E. display-meter relay control unit. There have been no other operational compliance problems with the 943 channel since its installation. This channel is one of seven instrumentation channels that contain meter relay control units at MURR. Two other deviations from technical specifications due to a failure of a meter relay control unit have occurred. On July 3,1978, mechanical binding in the relay caused the failure (L.E.R. dated August 2,1978), and September 22, 1980, a defective capacitor caused the failure (L.E.R. dated October 20, 1980). Reviewing the L.E.R. of October 20, 1980, the corrective action specified "The control circuit capacitor for the other six meter relay control units will be tested when their respective semi-annual compliance check procedures are scheduled to be completed". This commitment did not get added to the compliance checks or tne Electronics Shop Preventive Maintenance Schedule. This was the first compliance test of 943 since that corrective act'.on was generated. However, the compliance check of meter relay unit 917 was completed December 29, 1980, and this corrective action was not performed at that time. The December ccmpliance check of 917 verified the scrams operating within technical specification limits. After the 943 failure, the capacitance values of seven spare trip units ~ were measured and found to be within design tolerance. The seven were installed on 943, 917 (Dual trip unit), 944 A/B and 980 A/B. The seven trip units removed were bench tested with the capdeitor value in each unit measuring satisfactory. The capacitance salue measured for each trip unit was recorded on the side of the relay unit. The reactor safety system was still capable of performing its safety function if a low reactor pressure condition had occurred, due to the other three reactor low pressure scrams being operable. Corrective Action The meter relay control unit was replaced with a new unit and the 943 compliance check was performed. On April 27, 1981, all installed meter relay units [943, 917 (Dual trip units), 944 A/B, 980 A/B] were replaced with bench tested spares, and compliance checks were performed. All scrams actuated within technical specification limits. All seven meter relay units removed were disassembled and their capacitor values measured to be within design tolerances. We are adding to each compliance check procedure a step to " Verify elec-tronic P.M. 's completed". In addition we are addir.g to our Electronics Shop

o-Director of Licensing May 18, 1981 Page 3 Preventive Maintenance Schedule to replace til seven relay units with bench tested spares within one year and measure the capacitance values of those presently in service. If no abnormalities occur, we will re-institute the five year verification check as specified in the L.E.R. of October 20, 1980. Additionally, a review was made of all past L.E.R.'s to see if any commitments to the N.R.C. were not being met. The only one found was not checking the capacitance on meter relay unit 917 on December 29, 1980. Sincerely Av J. C. McTibben Reactor Manager Endorsement: / Reviewed and Approved / ' I A Robert M. Brugger [ k Director JCMK:vs cc: U.S. Nuclear Regulatory Commission c/o Document Management Branch James Keppler, Director Regulatory Operations - Region III Reactor Advisory Committee i Reactor Safety Committee 1

                                               -   - - - - - -      .,,   , , -   - - -,}}