ML20044D516

LER 92-007-01:on 920613,high Radiation Spike Received from CR Ventilation Process Radiation Monitor,Initiating Emergency Makeup Train B.Caused by Normal Variations in Radiation Readings.Spike modified.W/930515 Ltr

ML20044D516
Person / Time
Site:	LaSalle
Issue date:	05/15/1993
From:	Sparacino J, Spedl G COMMONWEALTH EDISON CO.
To:	Office of Nuclear Reactor Regulation
References
LER-92-007-01, LER-92-7-1, NUDOCS 9305190242
Download: ML20044D516 (5)

Text

_.

2 o CommInwealth Edison LaSalle County Nuclear Station 2601 N. 21st. Rd.

IAarseilles, Illinois 61341 Telephone 815/357-6761 ,

May 15, 1993 Director of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Station PI-137 l Nshington, D.C. 20555

Dear Sir:

Licensee Event Report #92-007-01, Docket #050-374 is being submitted to l your office in acc:>rdance with 10CFR50.73(a)(2)(iv).  ;

l I G. F.

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edl p l i Station Manager LaSalle County Station GJD/JDS/1ja Enclosure xc Nuclear Licensing Administrator NRC Resident Inspector NRC Region III Administrator INPD - Records Center IDNS Resident Inspector 180040 1

9305190242 930515 gDR ADOCM 05000374 l PDR V '

- l LICENSEE EVENT REPORT s .ER)

Facility hame (1) Docket Number (2) Page (3) taSalle'Ceunty Station Unit 2 015101010131714 1 l of! 0 l 4 Title (4)

Sourious aute Start ef Control Room Ventilation Emercency Make-vo Traia Ne to Hic 5 Radiation Soike

, Event Date (5) '

LER Number (6) I Reoort Date ( 9 Other racilities Involved (B)

Month Day Year Year /

,//pj/

Sequential j//

/j//

f Revision Month Day Year Facility Names Docket Number (s)

// Numter / Number 1

01 51 01 01 01 I I 01 6 11 3 9! 2 912 01017 01 1 015 11 5 9; 3 0151010101 l I l THIS REPORT IS SUBMITTED PURSUANT TO THE REMREMENTS Or icjR OPM%

(Check one or more cf the f ollowinci (11) 1 20.402(b) _ 20.405(c) _L 50.73(a)(2)(iv) _ 73.71(b)

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)(4) ___ 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

///////////////// //////// 20.4C5(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 Joseoh Scaracino. Tec6nical Staff Encineer Est. 2421 8I1 15 315171-l613161 COMPLETE ONE LINE FOR EACW COMPO NT FAltVRE DESCr(D IN THIS REPORT (13, CAUSE SYSTEM COMPCAENT MNUFAC- Ri v)RTABLE / CAUSE SYSTEM COMPONENT MANUFAC- ' REPORTABLE j

TURER TO NPF05 / TURER TO NPRDS B P IR I I I I I I No / 1 l l 1 l l l l x v!C l l 1 1 I I No '/ l l l l ! 1 l l l

, SUPPLEMENTAL REPORT EXPECTED (14) Expected Month I Day I Year Submission lyes (If ves. complete EXPECTED SU6MISMON DATE) X l NO l l1 ll ABSTRACT (Limit to 1400 spaces, i.e, approximately fif teen single-space typewritten lines) (16)

On June 13, 1992 at approximately 1617 hours0.0187 days <br />0.449 hours <br />0.00267 weeks <br />6.152685e-4 months <br /> Unit 2 was in Operatioral Condition 1 (RUN) at 100 perce-t power. At that time a High Radiation Spike was recein .d from the Cc-trol Room Ventilation (VC) (VI) Process Radiation Monitor (RP) (IL] 2D18-K751C. This High Radiation Spike initiated the "B" Emergency Make-up Train

( EMU) . As the Detector was being reset, the Nuclear Station Operater (NS0) noticed that the EMU Train had shut down. The NSO informed the Shif t Control Room Engineer (SCRE) tnat the EMU Train had shut down without being reset. Af ter consulting the electrical schematic drawings, the SCRE deterzined that the EMU Train should have continued running until it was reset, due to the seal-in circuit.

The apparent cause of the High Radiation Spike was determined to be f rom normal variations in background radiation readings. The apparent cause of the shutdown of the EMJ Train withcut being reset was do to the f ailure of the seal-in logic. The reset of the logic occorred becat.se the reset push button OHS-VC184 had failed, causing an open circuit within the seal-in circuitry. ,

Vhe safety consequence of this event was minimal due to the fact that the Emergency Make-t.p Train did start i as designed.

The corrective action for the High Radiation Spike was to modify the Radiation Monitor Circuit. The modified circuit gives the monitor a smoother waveform and a more stable resp:-se. The corrective action for the open circuit was to replace the reset push button OHS-VC184 for the VC Dt.J Train.

This event is reportable pursuant to 10CFR50.73(a)(2)(iv) due to an a.tomatic actuation of an Engineered Safety Feature.

l l

LICENSEE EVENT REP 0a7 (LER) VEXT CONTINUATION rerm See 2.0 FACILITY NAME (1) DOCKET NUMBER (2) LER NUw!ER (6) Pace (3)

Year Sequential Revision

{/((

// N>mber f/,l/

[ Number 015101010l31714 0IOI7 Ol1 O! 2 0F taSalle County S t a ti on VENT 912 - -

Energy Industry Identification System (EIIS) codes are identified in the text as [XXl 01 4 f

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

A. CONDITION PRIOR TO EVENT >

Unit (s): 2 Event Date: 06/13/92 Event Tine: 1617 Hours Reactor Mode (s): 1 Mode (s) Name: Run Power Level (s): lQQ1 B. DESCRIPTION OF EVENT Dn June 13, 1992 at approximately 1617 hours0.0187 days <br />0.449 hours <br />0.00267 weeks <br />6.152685e-4 months <br /> Unit 2 was in Operational Condition 1 (RUN) at 100 percent power. At that time a High Radiation Spike was received from the Control Room Ventilation (VC) [VI)

Process Radiation Monitor (PR) [IL} 2D18-K751C. This High Radiation Spike initiated the "B" Emergency Make-up Train (EMU). At the time of the event the "B" VC Train was in the Operation Mode and the "A" .

Train was in the Standby Mode. Upon investigation, it was verified that the High Radiation Signal was false and the detector could be reset. As the detector was being reset, the Nuclear Station Operator (NS0) noticed that the EMU Train had shut down. The NSO informed the Shif t Control Room Engineer (SCRE) that the EMU Train had shut down without being reset. After consulting the electrical schematic drawings, the SCRE determined tbst the EMU Train should have continued running until it was reset, due to the seal-in circuit. The Electrical Maintenar.ce Department was notified to troubleshoot the problem.

C. APPARENT CAUSE OF EVENT The cause of the auto start of the Emergency Make-up Train was due to a spurious High Radiation Spike from the 2018-K751C. The High Radiation Spike was due to normal variations 3.n background radiation.

The apparent cause of the shut down of the EMU Train without being reset was do to the failure of the t seal-in logic. The reset of the logic occurred because the reset push button OHS-VC184 had failed, causing an open circuit within the seal-in circuitry. This open circuit prevented the seal-in relay from staying energized af ter the High Radiation Signal was reset.

t

• LICENSEE EVENT CEPORT (LER) TEXT CONT:v;ATION rorm Ree 2.0 FACILITY NAME (1) DOCKET NUMSER (2) LER W.NSER (6) Pace (3)

Year /// Sequential /// ' Revision

' fff fff

/// Number /// ' Number LaSalle County Station 015101010131714 9I2 -

Ol017 - Of1 01 3 Or 01 4 TEXT Energy Industry Identification System (EIIS) codes are identified in the text as [XX)

D. SAFETY AAALYSIS OF EVENT The safety consequence of this evert was minimal due to the f act that the Emergency Make-up Train did start as designed. The fact that the Train did not seal-in can be answered because if it was a true ,

High Radiation Signal then all four of the VC Radiation Moniters would have seen the High Radiation i Signal and the moniters would not have been able to be reset. The High Radiation Signals would have performed in the same manor as a seal-in circuit. Also the "A* EMU Train was in Standby if it was needed.

E. CORRECTIVE ACTIONS To correct this problem, a Root Cause Investigative Team was ferred. 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, and 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 al' eight of the Control Room Ventilation Radiation Moniter Assemblics (both A and B trains). The chaage to each of the radiation monitors consisted of replacing four of the existing capacitors with new capacitors of a j different capacitance. There were many changes resulting f rom the capacitance change. The most important of which was the change in the may in which the moniter reads the signals from the radiation  !

detecter. The response time of the monitor was increased thus allowing the circuit to monitor a l smoother waveform. This should prevent the spurious spikes f rom occurring because the monitor will not all ow the quick instantaneous spike to occur. Another capacitance change was done to the circuit which prevents an initiation signal from 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 af ter 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 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 radiation level. If no background radiation can be detected within that time f rame, then the monitor will extinguish its (green) operate light to warn the user that maybe something is wrong.  ;

1 The changes to the radiation detectors have not taken placs as of yet, but will be accomplished as soon  !

as the weather permits. This is due to the detectors being located on top of the Auxiliary Building l Rocf inside sealed bcxes. The detectors are very susceptible to moisture. These changes will include a l new Geiger-Moeller (G-M) Tube and bracket. Two resistors will be replaced because cf the new G-M Tube.

The performance of the radiation monitors has already shown improvements.

The corrective action for the open circuit was to replace the reset push button OHS-VC184 for the VC EKJ Train. Troubleshooting of the reset pushbutton lead to the cor.clusion that dirty contacts caused the probl em. No similar problems have been experienced. Once the reset push button was replaced, the Electrical Maintenance Department checked for circuit continuity which was satisfactory. Then the Technical Staff perfonmed LTS-400-17 " Control Room HVAC Isolation Damper Surveillance Smoke And  !

Radiation Detection", to ensure proper operation of the EMU Train. This surveillance was also completed l sati s f actorily. l l

l l

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LICENS E EVENT BEPORT ITER) TEXT CONTINUATION Form Re< 2.0 FACILITY NAME (1) DOCKET NUMBER (2) LER NUMSER (6) pace (3)

Year /// Sequenti al //,j/ Revision fff f

/// Numb er /// Number LaSalle County Station 015101010131714 9I2 -

01017 - 011 01 4 0F 01 4 h a

TEXT Energy Industry Identification System (EIIS) codes are identified in the text as [XX) i F. PPEVIOUS EVENTS LER Numter Title 373/91-010-00 Spurious Auto Start Of Control Room ventilation Emergency Make-up Train Due to High Radiation Spike 373/91-008-00 Spurious Auto Start Of Control Room Ventilation Emergency Make-up Train 373/88-016-00 Auto Start of "A" VC EMU On Spurious Spike of The Intake Rad Monitor 373/87-034-00 Auto Start of "A" VC EMU On Spurious Rad Spike 373/86-C25-00 Spurious Trip of Control Room Ventilation High Radiation Monitor 373/S6-021-00 Control Room Ventilation Actuation Due To Spurious Rad Monitor Trip ,

1 G. COMPONENT FAILURE DATA There are no known component failures for the High Radiation Spike problem. A NPRDS search was done f or the PRM and nothing was found.

There was a component f ailure for the open circuit problem for the VC EMU Train. The f ailed component was the OHS-VC184 reset push button. A NPRDS search was done for the push button and nothing was found.

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