ML20116D985

14 Day Rept:On 960710,non-conservative Setting for Safety Channel 2 High Voltage Sensing Circuit Occurred.Caused by Failures in Safety Channel 2 High Sensing Circuit.Performed Successful Check of Sensing Circuit Loss of Voltage Setting

ML20116D985
Person / Time
Site:	05000083
Issue date:	07/24/1996
From:	Vernetson W FLORIDA, UNIV. OF, GAINESVILLE, FL
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20116D986	List: ML20116D985 ML20116D992
References
NUDOCS 9608050035
Download: ML20116D985 (3)

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. UNIVERSITY OF De FLORIDA Nuclear Iteactor Facility 202 Nuc1 car Sciences Center Department of Nuclear Engineering Sciences P x 118300 Tel: 0 52) 392 1429 Fax: 052)392-3380 E-mail: vernet @ server.nuceng.ua.edu July 24,1996 Regional Administrator, Region II 14 Day Report:

U.S. Nuclear Regulatory Commission PotentialTech Spec Violation-101 Marietta Street, N.W., Suite 2900 Non-Conservative Setting Atlanta, GA 30323 on Safety Channel 2 High Voltage Sensine Circuit

Dear Sir:

Re: University of Florida Training Reactor ,

Facility License: R-56, Docket No. 50-83 Pursuant to the reporting requirements of paragraph 6.6.2 (3)(a) and (g) of the UFTR Technical Specifications, a description of a potential violation of the technical specifications was reported I;y telephone on July 11,1996 with a following fax (telecopy) on July 12,1996 (Attachment I) and tiie so-called 14 day written report is submitted with this letter including occurrence scenario, NRC notification, evaluation of consequences, corrective action and current status.

The potentially promptly reportable occurrence involved failures in the Safety Channel 2 high voltage sensing circuit which resulted in a non-conservative setting for the Safety Channel 2 High Voltage Sensing Circuit as determined on July 11, 1996. This is the same circuit which had previously been the subject of maintenance efforts due to spurious trips per a 14-day report to NRC dated April 25,1996.

Scenario / Corrective Action On July 10, 1996, the Quarterly Scram Checks (Q-1 Surveillance) were being performed as scheduled after last having been successfully performed on March 27,1996. Upon performance of step 6b (Neutron Chamber High Voltage Reduction for Safety Channel 2), Safety Channel 2 failed to effect a water drop and blade drop full trip as required when a test pushbutton was depressed simulating a 10% loss of high voltage. Because of earlier problems, this test had last been checked operable on April 15,1996 in response to the circuit failures discussed in the April 25 report. The Reactor Manager was informed and Maintenance Log Page (MLP) #96-23 was opened. The high voltage to the detector was verified to be normal at 841.6 VDC; however, upon inspection of the resistor string which reduced the high voltage to a 4 VDC sensing circuit, a resistor was found to be intermittent. Subsequently, on July 11, 1996, the resistor was  ;

removed from the string and verified to be functional. The solder joint to the 9608050035 960724 I

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Regional Administrator, NRC Region II Page 2 July 24,1996 mounting post was a cold solder joint, limiting the contact of the resistor, dowever, when the resistor was correctly reinstalled, the trip circuit was still inoperative in that pushing the test pushbutton did not effect a loss of high voltage trip on Safety Channel 2.

Under 10 CFR 50.59 Evaluation #96-07, the Safety Channel 2 high voltage power supply (HVPS) was temporarily replaced with an identical supply, to be used as a variab!c voltage power source. The voltage was then reduced until the trip occurred at 727 VDC (a 13.6%

voltage drop); this value was noted to be outside the Tech Spec limit of 10% loss of high voltage to yield a trip per UFTR Technical Specifications Section 2.2(5) and Table 3.1 on Limiting Safety System Settings. At this point, the sensing circuit system was adjusted to trip at 8.6%

and tested satisfactorily three times.

On July 12,1996, the circuit was again tested, but would not effect a trip unless the sensitivity of the comparator circuit was raised to 789 VDC (~ 6.3%, a more conservative setting). The circuit was left at that setpoint and again tested satisfactorily three times.

The Executive Committee of the Reactor Safety Review Subcommittee (RSRS) reviewed this event on July 12,1996 and agreed that this event should be promptly reported to NRC as a potential tech spec violation based upon the discovery of the 13.6% voltage drop required on July 11,1996 to effect a trip versus the 10% drop cited in the UFTR Technical Specifications Section 2.2(5) and Table 3.1. The Executive Committee also noted that the event had been reported on July 11,1996 with a one-day letter to be sent on July 12, 1996. In agreement with UFTR Management recommendations, the RSRS Executive Committee also required I implementation of an increased surveillance frequency on the limiting safety system setting for voltage loss on the detector in Safety Channel 2. It was decided that the operability of the trip on loss of Safety 2 high voltage would be tested as part of the daily checkout for two weeks and weekly thereafter for the rest of the quarter before reinstituting the quarterly frequency of checks. In addition, to check and assure circuit stability, UFTR Management checked that the .

6.3% setting on the loss of voltage circuit had remained unchanged on July 15 and again on l July 22 with all checks satisfactory to date.

The Executive Comrnittee agreed there was negligible impact on reactor safety or the health and l safety of the public. The Executive Committee also approved restart subject to successful post-repair checks. As a result, the UFTR resumed normal operations on July 15,1996 with all checks of the sensing circuit negative to date.

NRC Notification After the sensing circuit for the loss of high voltage trip on Safety Channel 2 was measured to require a 13.6% voltage drop, the evaluation was made to treat this non-conservative settig as a reportable occurrence. Therefore, NRC Region II was informed of this event per a telephona conversation with Mr. Ed McAlpine on July 11, 1996 relative to the potential violation of technical specifications. Subsequently on July 12, 1996 the event was further discussed wi'.h Mr. Craig Bassett of NRC Region II. The event was also discussed briefly with NRC Project

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. s l Regional Administrator, NRC Region II l Page 3 l July 24,1996 Manager Ted Michaels on July 12, 1996 as part of an unrelated conversation. It has been emphasized that the high voltage to Safety 2 has remained normal throughout this event. It has only been the high voltage sensing circuit which became non-conservative with the Safety i Channel 2 overpower trip not affected.

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Current Status /Consecuences l

As indicated above, the reactor was approved for restart on July 15, 1996. The two checks of the sensing circuit loss of voltage setting at 6.3% and the daily checks of the test pushbutton  !

have all been successful with no further problems noted.

As indicated, the RSRS Executive Committee met on July 12, 1996 to review this event and I approved restart subject to successful post-repair checks and other periodic checks. The Executive Committee essentially agreed with actions taken and with the initial staff evaluation '

that the occurrence did represent a potential violation of the UFTR Technical Specifications and should be treated as promptly reportable which was accomplished. Reactor. Management and l the RSRS agree that this occurrence is not considered to have involved any significant reduction j in reactor safety margins and it is not considered to have involved any significant effect, '

potential or real, on the health and safety of the public. This occurrence is now considered I closed though the checks of the effectiveness of the 10% loss of high voltage trip will continue as committed to the RSRS Executive Committee.

1 If further information is needed, please advise. l 1

Sincerely, Y  % l l

William G. Vernetson l Director of Nuclear Facilities l WGV/dms Attachment Copies: U.S. NRC Document Control Desk .

Ted S. Michaels, NRC Project Manager Reactor Safety Review Subcommittee D. Simpkins, Reactor Manager l

Sworn and subscribed this & day of July,1996.

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