ML20044C980

LER 91-010-01:on 910719 & 0805,CR a Ventilation Emergency Makeup Fan auto-started on Spurious Trip of CR Air Intake Process Radiation Monitor.Caused by Normal Variations in Background Radiation.Supply Board replaced.W/930507 Ltr

ML20044C980
Person / Time
Site:	LaSalle
Issue date:	05/07/1993
From:	Sparacino J, Spedl G COMMONWEALTH EDISON CO.
To:	Office of Nuclear Reactor Regulation
References
LER-91-010-01, LER-91-10-1, NUDOCS 9305140255
Download: ML20044C980 (5)

Text

'

l Commonw:alth Ediron LaSa!!e County Nuclear Station

• @ 2601 N.21st.Rd.

Marseilles, illinois 61341 Telephone 815/357-6761 May 07, 1993 Director of Nuclear Reactor Regulation ,

U.S. Nuclear Regulatory Commission Mail Station Pl-137 Hashington, D.C. 20555

Dear Sir:

Licensee Event Report #91-010-01, Docket #050-373 is being submitted to your office in accordance with 10CFR50.73(a)(2)(iv).

f x s G. F. edl Station Manager LaSalle County Station GFS/JDS/gry Enclosure xc: Nuclear Licensing Administrator i NRC Resident Inspector NRC Region III Administrator INP0 - Records Center IDNS Resident Inspector 140032 49

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l 9305140255 930507 {

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l LICENSEE EVENT REPORT (LER)

Focility Name-(1) Docket Number (2) Pace (3) l LaSalle County Station Unit 1 015(r1010131713 1 l ofl 0 l 4 Title (4) pourious Auto Start Of Control Room Ventilation Emeroenev Makevo Train Due To Hioh Radiation Soike Event Date (5) LER Number (6) Reoort Date (7) Other Facilities Involved (B)

Month Day Year Year / Sequential //j/ Revision Month Day Year Facility Names Docket Number (s)

,/,/j/

// Number ff

/// Number of 51 01 01 01 I l

~ ~

01 7 11 9 91 1 9l 1 011 10 0l1 0I8 11 9 91 1 01510101Of f I OPERATING MODE (9)  ;

1 20.402(b) _ 20.405(c) _K_ 50.73(a)(2)(iv) _ 73.71(b) l POWER _ 20.405(a)(1)(i) _ 50.36(c)(1) _ 50.73(a)(2)(v) _ 73.71(c)

LEVEL 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vii) Other (Specify l0 l0 (10) 1

_ 20.405(a)(1)(iii) _ 50.73(a)(2)(i) _ 50.73(a)(2)(viii)(A) in Abstract

/ /,/,/f/, /,/,/, /,/,//,/,/ / /,/ /,/, / /, /,/,/,/,/ _ 20.405(a)(1)(iv) _ 50.73(a)(2)(ii) _ 50.73(a)(2)(viii)(B) below and in

///ffffffjffffffff/f///' / ' ///,/////' '//' 'ff///

ff jff _ _ 20.405(a)(1)(v) _ 50.73(a)(2)(iii) _ 50.73(a)(2)(x) Text)

LICENSEE CONTACT FOR THIS LER (12)

Name TELEPHONE NUMBER AREA CODE Joseph Scaracine. Technical Staff Enoineer. Extension 2779 8 l 1 15 3l 51 71 -l 61 71 61 1 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE / CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE f

TURER TO NPRDS / TURER TO NPRDS B P!R _ l I l I l l Y / l l 1 l l l I .

I  ! I l l  ! l ! / l l l l I I l SUPPLEMENTAL REPORT EXPECTED (14) Expected Month l Day l Year Submission

!Yes (If ves. complete EXPECTED SUBMISSION DATE) "

X l NO l !l !l ABSTRACT (Limit to 1400 spaces, i.e, approximately fif teen single-space typewritten lines) (16) l l

On July 19, 1991 at approximately 0520 hours0.00602 days <br />0.144 hours <br />8.597884e-4 weeks <br />1.9786e-4 months <br /> with Unit 1 in Operational Condition 1 (Run) at 100 percent power, the "A" Control Room Ventilation Emergency Make-Up (VC) (VI) Fan OvC03CA auto started on a spurious trip of the control room air intake Process Radiation (PR) [IL) Monitor 1018-K751B.

l On August 5,1991 at approximately 0742 hours0.00859 days <br />0.206 hours <br />0.00123 weeks <br />2.82331e-4 months <br /> with Unit 1 in Operational Condition 1 (Run) at 98 percent j power, the "A" Control Room Ventilation Emergency Make-Up (VC) [VI) Fan OVC03CA auto started on a spurious I

trip of the Control Room air intake Process Radiation (PR) [IL) Monitor 1DlB-K7518.

1 The apparent cause of the first event was random spikes f rom the power supply board of the Radiation Monitor '

1D18-K7518. The observations of the power supply signal indicated that random spikes were taking place and that this could be a cause of the high radiation spikes.

The apparent cause of the second event was determined to be from normal variations in background radiation readings.

The safety consequences of both of these events were minimal because the system worked as designed according to the high radiation indication. Also the fact that only one out of the four detectors registered high radiation readings, indicated that the initiation was not due to radiation.

To correct the problem of the first event the power supply board was replaced and the rad monitor electronic signals were observed again. The action of replacing the power supply board appears not to have worked because the event reoccurred on August 5, 1991. The work had been completed three days prior to this most recent occurrence. The corrective action for the High Radiation Spike is to modify the Radiation Monitor Ci rcui t. The modified circuit gives the nonitor a smoother wave form and a more stable response.

1 I . i I

. LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Fom Rey 2.0 l FACILYTY NAME-(1) DOCKET NUMBER (2) LER NUMBER (6) Pace (3)

Year /// Sequential //

/jj Revision fjj f

/// Number /// Number j taSalle County Station Unit 1 01510l010131713 911 -

0I110 -

O l1 01 2 0F 01 4 TEXV Energy Industry Identification System (EIIS) codes are identified in the text as [XX)

PLANT AND SYSTEM IDENTIFICATION General Electric - Boiling Water Reactor Energy Industry Identification System (EIIS) codes are identified in the text as IXX).

A. CONDITION PRIOR TO EVENT l

Unit (s): 1 Event Date: 07/19/91 Event Time: 0520 Hours Reactor Mode (s): 1 Mode (s) Name: Run Power Level (s): 1}M B. DESCRIPTION OF EVENT l

On July 19, 1991 at approximately 0520 hours0.00602 days <br />0.144 hours <br />8.597884e-4 weeks <br />1.9786e-4 months <br /> with Unit 1 in Operational Condition 1 (Run) at 100 percent l

power, the "A" Control Room Ventilation Emergency Make-Up (VC) [VI) Fan OVC03CA auto started on a spurious trip of the Control Room air intake Process Radiation (PR) [IL) Monitor 1D18-K751B. The radiation monitor readings were .3 mrem / hour before the spike and .4 mrem / hour af ter the spike had occurred. The trio setpoint is 3 mrem / hour and only one detector out of four is needed to cause this actuation. Control Room HVAC System (VC) [VI) and Auxiliary Electric Equipment Room ventilation (VE) l [VI) remained in standby during this event.

On August 5,1991 at approximately 0742 hours0.00859 days <br />0.206 hours <br />0.00123 weeks <br />2.82331e-4 months <br /> with Unit 1 in Operational Condition 1 (Run) at 98 percent power, the "A" Control Room Ventilation Emergency Make-Up (VC) [VI) Fan OVC03CA auto started on a spurious trip of the Control Room air intake Process Radiation (PR) [IL) Monitor 1018-K7518. The high radiation signal imediately returned to normal and was manually reset. The Emergency Safety Feature (ESF) signal was reset and the VC Emergency Make-Up Fan was placed in Pull-To-Lock pending further inves ti gation. A seven day timeclock was entered due to the VC Emergency Make-Up Fan being in the Pull-To-Lock position. The other three Radiation Monitors indicated normally throughout the event.

C. APPARENT CAUSE OF EVENT The apparent cause of the first event was randa spikes from the power supply board of the Radiation Monitor 1D18-K751B. This was discovered by, first installing a Temporary System Change (TSC-1-1194-91) to defeat the trip signal from this Radiation Monitor, and second to observe the electronic signals of the radiation monitor for a period of time. The observations of the power supply signal indicated that random spikes were taking place and that this could be a cause of the high radiation spikes. No other unusual observations were made from the radiation monitor electronic signals. There was also no other evolutions that were taking place at the time of this incident.

The apparent cause of the second event was due to a spurious high radiation spike from the 1D18-K751B radiation monitor. The high radiation spike was due to nomal variations in background radiation.

i i

. LfCENSEE EVENT REPORV (LER) TEXT CONVINUAVION Form Rev 2.0 FACILITY KAME (1) DOCKET NUMBER (2) LER NUMBER (6) Pace (3)

Year /

fj/j/ Sequential / Revision

/// Number //j/

g/

/ Number LaSalle County Station Unit 1 01510l010131713 9l1 - 011 10 -

O l1 Of 3 Or 01 4 '

TEXT Energy Industry Identification System (EIIS) codes are Mentified in the text as (XX) 1 C. APPARENT CAUSE OF EVENT (CONTINUED) 1 In all of the previous events listed below, the exact cause of the event is unknown. A possible cause l that is cormon to a few of the Licensee Event Reports is a spurious electronic noise within the  !

radiation monitor, but in most of the cases the only corrective actions performed were to troubleshoot i the problem and then recalibrate the instrument. Af ter one of the previous events (373/86-021) took l Pl ace, the Radiation Monitor was replaced and recalibrated. This showed to have had no effect since the event repeated itself four days af ter the work was complete. None of the previous events seem to only happen on one of the detectors. In fact all four of the Radiation Monitors have caused an initiation at some time. From the previous event reports, it appears that the initiations are random in time and on which radiation monitor it occurs.

Nuclear Plant Reliability Data Systems (NPRDS) was reviewed and there is not an industry problem with ,

this Process Radiation Monitor or the General Atomics Company.

l D. SAFETY ANALYSIS OF EVENT ,

I The safety consequences of both of these events were minimal because the system worked as designed l according to the high radiation indication. Also the fact that only one out of the four detectors registered high radiation readings, indicated that the initiation was not due to radiation.

t E. CORRECTIVE ACTIONS To correct the problem of the first event the power supply board was replaced and the radiation monitor electronic signals were observed again. The power supply signal showed no signs of erratic behavior and the Temporary System Change was removed and the detector was considered operable. The action of replacing the power supply board appears not to have worked because the event reoccurred on August 5, 1991. The work had been completed three days prior to this most recent occurrence. The work request was reopened and troubleshooting will resume. The supplement to the LER will be tracked by Action Item Record 373-180-91-08201.

To correct this second problem, a Root Cause Investigative Team was formed. To assist with the solution to this problem, a Senior Design Engineer from the manufacturer was on site during the week of October 5, 1992. At that time a proposal was made to modify the electronics of the radiation monitors and detectors. This modification took place between March 10 and March 17, 1993, on all eight of the Control Room Ventilation Radiation Monitor Assemblies, (both A and B trains). The change to the radiation monitors consisted of replacing four of the existing capacitors with new capacitors of a different capacitance. There were several improvements resulting from the capacitance change. The most important was the change in which the monitor reads the signals f rom the radiation detector. The response time of the monitor was increased thus allowing the circuit to monitor a smoother waveform.

This should prevent the spurious spikes from occurring because the monitor will not allow the quick instantaneous spike to occur. Another capacitance change was done to the circuit which prevents an initiation signal from being sent to the monitor while it is in the check source mode. The dead time is the time delay that prevents an initiation signal from being sent out af ter the monitor is taken out of the check source mode.

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Form Rev 2.0 FACILITY KAME (1) DDCKET NUMBER (2) LER NUMBER (6) Pace (3)

Year /// Sequential //j / Revision fj/j/

/ Number j///

f Number l

LaSalle County Station Unit 1 0 1 5 I O I O I O I 31 71 3 9l1 -

0l110 -

0 I1 01 4 0F 01 4 TEXT Energy Industry Identification System (EIIS) codes are identified in the text as [XX)

E. CORRECTIVE ACTIDNS CONTINUED 6 The dead time had been increased because of the previous change. Because the reponse time for the monitor has been increased, it reans that it will also take longer for the levels to decrease af ter the monitor has been taken out of the check source mode. The last change that was made to the monitor was to increase the malfunction trip delay time. This is the time in which the monitor must see some sort of background radiation level. If no background radiation can be detected within that time frame, then the monitor will extinguish its (green) operate light to warn the user that maybe something is wrong.

Actual changes to the radiation detectors themselves have not taken place as of yet but will be accomplished as soon as tha weather permits. This is due to the f act that the detectors are located on top of the Auxiliary Building Roof inside of sealed boxes. The detectors are very susceptible to moisture. These changes will include a new Geiger Mueller (G-M) Tube and bracket, and two resistors will be replaced because of the new G-M tube.

The perfonmance of the radiation monitors has already shown improvements.

Also, a Modification (M01-0-88-003) is planned which will change the logic of the actuation to initiate

on high radiation signals of two out of four Process Radiation Monitors instead of just one out of four.

F. PREVIDUS EVENTS LER Number Title 373/91-008-00 Spurious Auto Start Of Control Room Ventilation Emergency Makeup Train 373/86-016-00 Auto Start Of Control Room ventilation EMJ Train Due To Spurious Spike Of The Intake Rad Monitor 373/87-034-00 Auto Start Of "A" VC EMU On Spurious Rad Spike 373/86-025-00 Spurious Trip Of Control Room Ventilation Hi Radiation Monitor 373/86-021-00 Control Room Ventilation Actuation Due To Spurious Rad Monitor Trip 1

G. COMPONENT FAILURE DATA There was no component f ailures.

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