ML20044E416

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LER 92-009-01:on 920923,spurious Auto Start of CR Ventilation Emergency make-up Train Occurred Due to High Radiation Spike.Radiation Monitor Circuit modified.W/930528 Ltr
ML20044E416
Person / Time
Site: LaSalle Constellation icon.png
Issue date: 05/28/1993
From: Sparacino J, Spedl G
COMMONWEALTH EDISON CO.
To:
Office of Nuclear Reactor Regulation
References
LER-92-009-02, LER-92-9-2, NUDOCS 9305240327
Download: ML20044E416 (5)
v • d • e


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,Commonw=lth Edi:on LaSalle County Nuclear Station 2601 N. 21st. Rd.

fAarseilles. Illinois 61341 Telephone 215/357-6761 May 28, 1993 Director of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Station Pl-137 Hashington, D.C. 20555

Dear Sir:

Licensee Event Report #92-009-01, Docket #050-373 is being submitted to your office in accordance with 100FR50.73(a)(2)(iv).

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gopA Gary F. Spedl Station Manager LaSalle County Station GFS/JS/grv l Enclosure xc: Nuclear Licensing Administrator NRC Resident Inspector NRC Region III Administrator INPO - Records Center IDNS Resident Inspector 240058 y 9305240327 930528 3 DR ADDCK 0500 1

N LICENSEE EtfENT 01EPORT (LER) [

Facility 13ame (1) Docket Number (2) Pace (3)

LaSolle County Station Unit 1 015101010131713 1lofl0l4 Title (4) f

}pyrious Auto Start Of Control Enom Ventilation Emeroency Make-Do Train Due To Hioh Radiation Soike f Event Date (5) LER Number (6) Report Date (7) Other Facilities Involved (B) l Month Day Year Year // Sequential / Revision Month Day Year Facility Names Docket Number (s) f j/pj/

// Number j/ //j/j/Number '

01 51 0! 01 Ol' i 1

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01 9 21 3 91 2 91 2 0IOI9 011 0I5 21 8 91 3 01 51 01 01 01 I I OPERATING  !

I.[ heck one or more of the followino) (11)  ?

1 20.402(b) _ 20.405(c) X 50.73(a)(2)(iv) _ 73.71(b) i 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) .m 50.73(a)(2)(vii) Other (Specify (

l0 !O (10) 1 _._ 20.405(a)(1)(iii) _ 50.73(a)(2)(i) _ . , 50.73(a)(2)(viii)(A) in Abstract

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

/ / / / / /

/}/?}/,//}/j?/j//j////j/j/}/}// _ 20.405(a)(1)(v) _ _ 50.73(a)(2)(iii) _ 50.73(a)(2)(x) Text) f f J

LICENSEE CONTACT FOR THIS LER (12)

Hame TELEPHONE NUMBER AREA CODE .

Joseph SDaracino. Technical Staff Enoineer. Extension 2779 811 15 315171-l617161 COMPLETE ONE LINE FOR EACH COMPO NT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE / CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE j

TURER TO NPRDS / TURER TO NPRDS +

B 1iL l ! l I i 1 N /

p l l l I I l l  ;

I l ! I I l l / l l ! I l l I  ;

SUPPLEMENTAL REPORT EXPECTED (14) Expected Month l Dav i Year Submission

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lyes (If ves. comolete EXPECTED SUBMISSION DATE) X l NO Date (15)  ; l,l, I ABSTRACT (Limit to 1400 spaces, i.e approximately fif teen single-space typewritten lines) (16)

On September 23,1992 Unit 1 and Unit 2 were both in Operational Condition 1 (Run) at 100 percent power. At ,

approximately 1719 hours0.0199 days <br />0.478 hours <br />0.00284 weeks <br />6.540795e-4 months <br /> the 'B' Control Room Ventilation Train (VC) [VI) received a spurious trip signal  ;

from the 'B' Process Radiation (PR) (IL) Detector (2018-K751B). This high radiation spike auto started the '

Emergency Make-Up (EMU) Train as expected. The initial investigation indicated that the high radiation }

signal was f alse. l t

i The apparent cause of the auto start of the Emergency Make--Up Train event was a high radiation spike from the

'D' Control Room Ventilation Radiation Detector. The apparent cause of the high radiation spike was  ;

determined to be from normal variations in background radiation readings.

I The safety consequences of this event were minimal due to the fact that the Control Room Ventilation System ,

and Emergency Make-Up Train f unctioned as designed.
  • To correct this problem the 'B' detector was adjusted by the Instrument Maintenance Department so that it f

will operate at a lower level on the scale. This will give the instrument more room for fluctuations and a  ;

larger window bef ore the trip setpoint is reached. The trip setpoint was not adjusted and the trip will j still occur if a real hi radiation signal is seen by the detector. The Radiation Monitor Circuit was . ,

modified to correct the spurious spikine, publem.

This event is reportable to the Nuclear Regulatory Commission as a Licensee Event Report in accordance with 10CFR50.73(a)(2)(iv) due to an automatic actuation of an Engineered Safety Feature (ESF).

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!? LICENSEE Et!ENT REPORT (LER1 TEYV CONTINUATf0N Fem Ree 2.0

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FACILITY .NAME (1) DOCKET NUMBER (2) LER N'JMPER (6) Pace (3)  !

Year Sequential Revision g/// Number g/// Numble  !

LaSalle County Station Unit 1 0 i S I O l 0 l 0 I 31713 9l2 -

0IOI9 - 0 11 01 2 0F 01 4 l TEXV Energy Industry Identification System (EIIS) codes are identified in the text as [XX) l l ^[

PLANT AND SYSTEM IDENTIFICATION  !

General Electric - Boiling Water Reactor ,

Energy Industry Identification System (EIIS) codes are identified in the text as [XX). .

A. CONDITION PRIOR TO EVENT Unit (s): _.1/2 Event Date: 9/23/92 Event Time: 1719 Hours Reactor Mode (s): 1/1 Mode (s) Name: Run/Run Power Level (s): 1001/100%  ;

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3. DESCRIPTION OF EVENT  !

On September 23,1992 Unit 1 and Unit 2 were both in Operational Condition 1 (Run) at 100 percent ,

power. At approximately 1719 hours0.0199 days <br />0.478 hours <br />0.00284 weeks <br />6.540795e-4 months <br /> the 'B' Control Room Ventilation Train (VC) [VI) received a spurious trip signal f rom the 'B' Process Radiation (PR) [IL) Detector (2018-K751B). This high radiation spike ,

auto started the Emergency Make-Up (EMU) Train as espected. The initial investigation indicated that - l the high radiation signal was false due to the fact that the other three detectors indicated normal radiation readings, and because the radiation readings from the 'B' detector dropped down to the normal level af ter the spike. The EMU was then shut down and placed in pull-to-lock position. The 'B' Control Room Ventilation Train was declared Moperable and Technical Specification 3.7.2 was entered. i i

C. APPARENT CAUSE OF EVENT The apparent cause of the auto start of the Emergency Make Up Train event was due to a high radiation spike f rom the 'B' Control Room Ventilation Radiation Detector. The apparent cause of it.e high ,

radiation spike was determined to be from normal variations in background radiation readings.

l Radiation detector indications normally fluctuate within a certain span. The detector will see a small  !

amount of radiation, quickly rise to that level, then slowly drop to the original _ level. This slow drop I takes approximately two seconds. This constant fluctuation requires a

  • Indow for the radiation monitor ,

to operate. If this window is too narrow for the normal variations eventually there will be a normal l radiation spike just large enough to go over the trip setpoint.

Approximately one week prior to this event, Unit 2 came back on line af ter a short forced shutdown. ,

During this shutdown the 'B' detector had gone downstale, meaning there was insufficient background  ;

radiation levels to keep detector on scale. Because of the proximity of the Control Room Ventilation j Radiation Detectors to the Main Turbine Building Roof, it is believed that the reflected radiation from the main turbine contributed to the background radiation levels. In the past when . radiation detector e f

went downscale, the Instrument Maintenance Department was called and adjusted the instrument so that it .;

would be back on scale. This was done in this event also, but a Temporary System Change was installed  ;

to' defeat the EMJ initiation from this detector as allowed by the Technical Specification. This was {

done because it was believed that it was possible once Unit 2 main turbine came back on line after the forced shutdown the reflected radiation levels caused by the main turbine would increase above the trip setpoint.

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- LICENSEE EVENT REPORT (LER) TEXT CONT 7NUAT70N Form Rev 2.0 '

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FACILITY.NAME (1) DOCKET NUMBER (2) LER NLMBER (6) Pace (3)

, Year M Sequential & Revision  ;

fff Number f Num!er

  • LaSalle County Station Unit 1 01510l010131713 9I2 - 01019 - 0 I1 01 3 0F 01 4 VEXT Energy Industry Identification System (EIIS) codes are identified in the text as [XX]

i C. APPARENT CAUSE OF EVENT CONTINUED i l

Once the main turbine was back on line, the indicated radiation levels from the 'B' detector did get higher but the trip setpoint was not reached. Af ter approximately' a week without the trip setpoint being reached, the Temporary System Change was removed. Two days later, this event occurred. The '

detector has since been readjusted by the Instrument Maintenance Department. A Limited Procedure. l LLP-92-159, was written to prove that these radiation detectors are still operable when they go e downscale due to a lack of background which can be directly related to the main turbine reflected

  • radiation.

I D. SAFETY ANALYSIS OF EVENT The safety consequences of this event were minimal due to the fact that the Control Room Ventilation  !

System and Emergency Make Up Train functioned as designed.

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E. CORRECTIVE ACTIONS  !

The 'B' Control Room Ventilation fan was placed in pull-to-lock (PTL), the Train was declared inoperable, and Technical Specification 3.7.2 was entered. To correct this problem the 'B' detector was adjusted by the Instrument Maintenance Department so that it will operate at a lower level on the scale. This will give the instrument more room for fluctuations and a larger window before the trip setpoint is reached. The trip setpoint was not adjusted and the trip will still occur if a real l radiation signal is seen by the detector. Additionally, LLP-92-159 is now in place which allows a [

source check to prove detector operability when background radiation is too low to maintain the operate '

light on. The detector will still be able to see high radiation levels if they were to arise and the l trip function will operate as designed.

Over the past five months, all four of the detectors on both (Jnits have been overhauled. The Geiger-Mueller Tubes have all been replaced and the wire connectors have been upgraded to fit in the I shield housing better and to be less susceptible to corrosion.

A Senior Design Engineer f rom the manufacturer was on site during the week of October 5,1992 and at L 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 each of the radiation monitors  !

consisted of replacing four of the existing capacitors with new capacitofs of a different capacitance.

There were many changes resulting f rom the capacitance change. The most important of which was the change in the way 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 r prevent the spurious spikes f rom occurring because the monitor will not allow the quick instantaneous (

spike to occur. Ancther capacitance change was done to the circuit which prevents an initiation signal ,

f rom being sent out from 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 after the monitor is taken out of the check '

mode. This dead time has been increased because of the previous change. Because the response time for f

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LICENSEE EVENT REPORT (LER) VETT COWINUAVION Fern Rev 2.0  !

I FECILITY.NAME(1) DOCKET NUMBER (2) LER NUMPER (6) Pace (3)

Year ///

ffj Sequential /// Revision  ;

/// Number j///ff Number LaSalle County Station Unit 1 0 i S I O I O I O I 31 71 3 9l2 - 010l9 -

O l1 01 4 0F 01 4 [

TEXT Energy Industry Identification System (EIIS) codes are identified in the text as [KX) f E CORRECTIVE ACTIONS (CONTINUED) ,

the monitor has been increased, it means that it will also take longer ,for the levels to decrease af ter the ,

monitor has been taken out of the check 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 i 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. f i

The changes to the radiation detectors have not taken place as of yet, but will be accomplished as soon as f the weather permits. This is due to the fact 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 G-M tube and bracket, and two new resistors will replace two cid resistors because of the new G-M tube.

The perf ormance of the radiation monitors has already shown improvements. I i

F. PREVIOUS EVENTS j LER Number Title 374-92-007 Spurious Auto Start Of Control Room Ventilation Emergency Make-Up Train Due To High Radiation Spike  ;

i 373-92-007 Spurious Auto Start Of Control Room Ventilation Emergency Make-Up Train Due To High Radiation Spike  ;

LER Number Title 373-91-010 Spurious Auto Start Of Control Room Ventilation Emergency Make-Up Train Due To  ;

High Radiation Spike '

t 373-91-008 Spurious Auto Start Of Control Room Ventilation Emergency Make-Up Train 373-88-016 Auto Start Of "A" VC EMU On Spurious Spike Of The Intake Rad Monitor 373-87-034 Auto Start Of "A" VC EMJ On Spurious Rad Spike }

373-E6-025 Spurious Trip Of Control Room Ventilation High Ra ation Monitor 373-86-021 Control Room Ventilation Actuation Due To Spurious Rad Monitor Trip i

G. COMPONENT FAILURE DATA /

f There was no component f ailure. '

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