ML20151B368

Reportable Occurrence:On 880314,safety Channel 1 Circuit Failed to Provide Proper Power Indication for Several Seconds on Two Occasions.Caused by Capacitor Failure. Capacitor Replaced W/Substitute of Different Mfg

ML20151B368
Person / Time
Site:	05000083
Issue date:	03/28/1988
From:	Vernetson W FLORIDA, UNIV. OF, GAINESVILLE, FL
To:	Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 8804080192
Download: ML20151B368 (7)

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NUCLEAR ENGINEERIND SCIENCES DEPARTMENT Nuclear Reactor Facility ,

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,o-Phon. (904) 3921429.Tel.a E4330 Nuclear Regulatory Commission Suite 2900 101 Marietta Street, N.W.

Atlanta , Georgia 30323 Attention: J. Nelson Grace Regional Administra tor, Region II Re: University of Florida Training Reactor Facility License: R-56, Docket No. 50-83 Gentlemen:

Pursuant to the reporting requirements of paragraph 6.6.2(3)(c) of the UFTR Technical Specifications, a description of a potential abnormal occurrence as defined in the UFTR Technical Specifications, Chapter 1 is described in this interim 14-day report to include NRC notification, occurrence scenario and current solution status. The potential promptly reportable occurrence involved the failure of Safety Channel #1 circuit to provide proper power indication for several seconds on two occasions, the second during a test run.

NRC Notification The Executive Committee of the Reactor Safety Review Subcommittee reviewed this occurrence on March 15, 1988 and concluded that it is a potential abnor-mal occurrence as defined in UPTR Technical Specifications, Chapter 1. The RSRS then instructed NRC notification as per Section 6.6.2 of the UFTR Tech Specs. This notification was carried out by both telephone to Mr. Paul Fred-erickson and a following telecopy on March 15, 1988 (see Attachment I). Subse-quent to replacement of the failed feedback noise controlling capacitor in the Safety Channel #1 with successful checkout, the same occurrence (~4 second loss of indication on Safety Channel #1) recurred. This event was again re-ported via telephone conversation with Mr. Stephen Vias and a following tele-ccpy on March 16, 1988 (see Attachment II). In addition to the discussion to update Mr. Frederickson on 18 March 1988, this interim report represents the 14 day followup report for this event as required in UFTR Tech Specs, Para-graph 6.6.2 ( 3 ) ( c ) .

Initial Event Scenario At 1437 on March 14, 1988, with a Reactor Operations Laboratory class (ENU-5176L) in progress at 50% power, Safety Channel 1 failed to the bottom meter stop. P.M. Whaley, opera tor a t the controls, noted the indication on Safety channel 2, the log pen recorder, and the wide range indicator were normal and directed a reactor shutdown. Before the shutdown could be started, Safety Channel 1 returned to normal indication. The subjective evaluation was that the return was not instantaneous, but the meter returned to nornnl indication rela tively slowly (i.e., not as if switched on, but rather as if recovering from an electrical transient). The shutdown was completed with all instruments responding normally at 1438.

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'M Nuclear Regulatory Commission March 28, 1988 Page Two Corrective Action The immediate indications were that an intermittent fault had developed in the circuitry for Safety Channel 1 (part of the wide range drawer) but not in any other section of the wide range drawer. With the reactor secured, Maintenance Log Page #88-9 was initiated to investigate the problem. The wide range drawer was de-energized and the linear channel circuit board removed for visual in-spection. All components and connections were verified in good condition. Dis-cussion of the fai'ure mode indicated a possible failure of a capacitor, pos-sibly an intermittent short circuit which was followed by a recharging of the ca pa ci tor. A capacitor in the feedback loop (in parallel to the primary feed-back/ current limiting resistor) was identified as the most likely component failure. The capacitor was removed and failed a bench test; the capacitor had open-circuited. The probable cause was now evaluated to be a short circuited capacitor that F ned open from high current, resulting in first maximum feed-back from the short then normal feedback from the feedback resistor as sup-ported by the initial downscale indication followed by return to normal noted by SRO Whaley. The componant was replaced with a substitute of dif ferent manu-facturer under 10 CFR 50.59 Evaluation #88-4 with identical specifications in-tended to restore the circuit to normal opera tion.

Eva lua tion Except during the transient, the functions of indication and trip were not in-hibited or changed (except for situations where high circuit noise might cause erratic meter indications); tha t is , there was only a temporary loss of indi-cation and trip function in Safety Channel #1. Since this capacitor is a noise suppression device in a DC circuit, the impact of this failure on system op-eration is minimized because this is a DC amplifier where the feedback coeffi-cient is set by a precision resistor.

This Safety Channel #1 circuit failure is potentially a promptly reportable occurrence per UFTR Technical Specifications, Section 6.6.2 delineating re-quirements for Special Reports where Paragraph ( 3)(c) states certain safety system failures are prorptly reportable. Specifically, a special report is needed for a "reactor safety system malfunction that renders the reactor safety system incapable of performing its intended safety function, unless the malfunction or condition is discovered during maintenance tests or periods of reactor shutdowns" or involves components or systems in addition to these re-quired by Tech Specs (see Attachment III for quotes of applicable Tech Spec Sections).

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9 Nuclear Regulatory Commission March 28, 1988 Page Three Similarly one definition of Abnormal Occurrences for the UFTR in Tech specs Section 1.0 is "a malfunction of a safety system component or other component or system malfunction that could, or threatens to, render the (safety) system incapable of performing its intended safety function." Since Reactor Safety- '

System is also defined in Tech Specs Section 1.0 to be "a con.bination of mea-suring channels and associated circuitry that forms the automatic protective action to be initiated, or provides information which requires the initiation of manual protective action," this initial event was thought not to be strict-ly required to be promptly reported; tha t is , since the failed feedback capa-citur only serves to reduce noise in the circuit, it is not really needed for I

the safety function of Safety channel #1 which was recovered within a few seconds of the failure.  ;

Basically, this event was considered to have no direct impact on safety and not to impact the health and safety of the public. However, reporting was .

recommended since there was at least a partial failure of the safety system.

Nevertheless, safety implications are negligible since Safety Channel #2 was always operable and Safety Channel #1 was only lost for a few seconds af ter +

which it would have been subject only to more noise. Af ter replacement of the ,

failed capacitor, meeting the two requirements of a successful daily checkout  ;

and a 15 minute or longer power run was considered suf ficient to assure prcper  ;

operation and approval for return to normal operation. l Updated Event Scenario j i

Following a successful daily checkout, a 15 minute run at 100 kw was set as j the final crite ion prior to return to norwal operations. Five minutes into  !

this run, the failure indication en Safety Channel 1 recurred; initial checks indicated the capacitor was not failed this time so work has. continued with a new prompt report filed with NRC on 16 March 1988 per communication with the RSRS Executive Committee. ~

j Corrective Action / Evaluation The reactor has been put on administrative shutdown per Attachment I'! ar.d the RSRS met on March 22, 1988 with this event as one item on its agenda. All 4 agree the situation is being addressed properly although the exact cause of the event has not yet been identified. Via a seri,es of troubleshooting main-tenance activities, the problem has been isolated to the fission chamber, preamp or connections shown in Attachment V which is Figure 1-8 of the UFTR Safety Analysis Report. There is a strong possibility that cleaning connectors on these components may have corrected the problem per conversation with one vendor.

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Nuclear Regulatory Commission March 28, 1988 Page Four At this point a procedure is b?ing prepared for RSR3 review and approval to allow declaring the UFTR operable pending successful completion of all normal checks and proposing to permit restart as a test to verify proper operation of Safety Channel #1 by monitoring voltage levels in the linear channel section of the preamplifier with respect to ground, the current drawn by detector op-eration f rom high voltage supply and the high voltage power supply output vol ta ge. Voltage measurements are the measurement of choice to prevent moni-toring from af fecting the operation of the system; the voltage measurements will be made by devices with large input impedances and will not draw signifi-cant current from the monitored points. In general, current measurements must be made in such a way as to minimize the potential for altering the signal pa rameters ; to minimize the potential for such effects, the input to the high voltage filter in the preamplifier has been selected as the current monitoring point.

Based on the results of this test restart, the problem is expected to be de-monstrated to be corrected or to be isolated to one of the components indi-cated in the Safety Channel #1 circuitry. Further information will be supplied and Region II will be notified prior to commencing the restart test.

Sincerely, j $- V William G. Vernetson Director of Nuclear Facilities WGV/ps At tachments cc: P.M. Whaley Reactor Safety Review Subcommittee

NUCLEAR ENGINEERIN9 SCIENCES DEPARTMENT Nuclear Reactor Facility University of Florida I l wav me.on,om.cio, .

NUCL1AR REACTOS SULDWG can fsas suit ATTACilMENT I

? hone (904 M2 MM .telsa 66330 March 15,1988 Safety Channel #1 Circuit Failure Nuclear Regulatory Commission Suito 2900 101 Marietta Street, N.W.

Atlanta , GA 30323 Attention: J. Nelson Grace Regicnal Administrator, Region II Re: University of Florida Training Reactor Facili'.y License: R-56, Docket No. 50-83 As per telephone conversa cion on 15 March 1988 with Mr. Paul Frederickson, relativa to failure of Safety Channel #1 Circuit for the UFTR, the Reactor Safety Review Subcommittee (RSRS) Exe-cutive committee has reviewed this event and concluded this oc-currence is potentially reportable occurrence per UFTR Technical Specifica tions , Section 6.6.2 delinea ting requirements for spe-cial reports. Paragraph ( 3)(c) indicates certain safety system failures are promptly reportable. The RSRS Executive Committee has instructed NRC notification as por Section 6.6.2 of the UFTR Tech Specs though the event may not be required to be proraptly reportable depending on interpreta tion of the Tech Specs. Since the failed component was only a feedback noise controlling capa-citor, its replacement has restored Safety Channel #1 to normal with RSRS permission granted to restart dependent only on a suc-cessful daily checkout.

William G. Vernetson Director of Nuclear Facilities 15 t; arch 1988 WGV/ps cc: P.M. Whaley RSRS

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NUCLEAR ENGINEERIN3 SCIENCES DEPARTMENT Nuclear Reactor Facility University of Florldc

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$ h7 rnone poo m.we .t.m uno ATTACilMENT II March 16, 1988 Safety Channel #1 Circuit Failure - 2 Nuclear Regulatory Commission Cuite 2900 101 Marietta Street, N.W.

Atlanta, GA 30323 Attantion: J. Nelson Grace Regional Administrator, Region II .

Re: University of Florida Training Reactor Facility License: R-56, Docket No. 50-83 As per telephone conversation on 16 March 1988 with Mr. Stephen Vias, relative to failure of Safety Channel #1 Circuit for the UFTR, the nvent described in our letter of 15 March 1988 recurred during a power run conducted an a final requirement set prior to returning to normal operations. Although a failed feedback noise controlling capacitor had been replaced, its replacement has not restored Safety Channel #1 to nonnal so that further checks and repairs are required.

l The RSRS Executive Committer s ' ,ructed NRC notification as per Section 6.6.2 of the UFTR , w;. dpecs though the event may still not be required to be promptly reportable depending on in-terpretation of the Tech Specs. I Further information will be provided prior to approving return to normal operations.

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William G. Vernetson Director of Nuclear Facilities 16 March 1988 I WGV/ps cc: P.M. Whaley RSRS

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A'1"rACllMENT III UFTH TECil SPEC QUOTES 1.0 DEFINITIONS

• Abnormal Occurrences : An abnormal occurrence is any one of the following:

(3) A malfunction of a safety system component or other compoennt or l system malfunction that could, or threatens to, render the system incapable of performing its intended safety function.

Reactor Safety System: The reactor safety system is that combination of mea-  ;

suring channels and associated circuitry that forms the automatic protective '

action to be initiated, or provides informa tion which requires the initiation of manual protective action.

6.6.2 Special Reports There shall be a report not la ter than the following working day by telephone and confirmed in writing by telegraph or similar conveyance to the Commission, to be followed by a written report that describe; the circums tances of the event within 14 days of any of the following:

(3) Any of the following:

(c) A reactor safety system component malfunction that renders the reactor safety system incapable of performing its intended safety function, unless the malfunction or condition is dis-covered during maintenance tests or periods of reactor shut-downs (Note: Where components or systems are provided in addi-tien to those required by the Technical Specifications, the failure of the extra components or systems is not considered reportable provided that the minimum number of components or systems specified or required perform their intended reactor sa f ety function).

i NUOLEAR ENGINEERING SCIENCES DEPARTMENT Nuclear Reactor Facility  ;

University of Florida ,

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March 18, 1988 i

MEMORANDUM TO: ReSctor Staff  ;

FROM: W.G. Vernetson, irector of Nuclear Facilities

SUBJECT:

Administrative Shutdown of the UF~11 Because of the Safety channel #1 Circuit t'ailure problem, the UFTR is placed on Administrative Shut.down until further netice.

This administrative shutdowr. precludes all reactor operations for which the reactor woald be declared operable until further notice for wiiich RSRS approval will be required. Perfortning weekly and

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daily checkouts as far c.s possf_bie as well as norme.1 maintenanco activities ara allowed.

The only other activities allowed during this admiaistrative shutdown are routine administra ti'rr, work (updating training re-cords, n te. ) , tours of the facilicies (no opera cions) as well as housekeeping and maintenance activities. Ha br maintenance is also possible provided approved by proper levels.

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