ML17347A487

LER 86-040-01:on 861218,potential Discovered for Loss of Three Air Conditioner Compressors & Air Handlers of Control Room Ventilation Sys.Caused by Excessive Clearance Between Cover Plate & Relay.Part 21 related.W/861218 Ltr

ML17347A487
Person / Time
Site:	Turkey Point
Issue date:	05/19/1987
From:	Hart R, Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
REF-PT21-87-130-000 L-87-218, LER-86-040, LER-86-40, PT21-87-130, PT21-87-130-000, NUDOCS 8705280270
Download: ML17347A487 (9)

Text

REGULATORY I RMATION DISTRIBUTION SYS (R IDS)

,ACCESSION NBR: 8705280270 DOC. DATE: 87/05/19 NOTARIZED: NO DOCKET 0

,<<'FACIL: 50-250 Tuv keg Point Plant. Uni+ 3> Florida Powev'nd Ligh+ C 05000250 AUTH. NAME AUTHOR AFF ILI AT I Oil HART> R. D. Flov'ida Powev' Light Co.

WOODY. C. 0. Flov ida Powev Zc Light Co.

RECIP. NAME RECIPIENT AFFILIATION

SUBJECT:

LER 8b-040-01: on Sb1218> deficiency discovered v e potential for loss of thv ee air conditioner compressors 4 air handlers of contv ol room ventilation sos. Caused bg excessive clearance between covev pla+e 5 relay. W/8b1218 ltr.

DISTRIBUTION CODE; IE22D COPIES RECEIVED; LTR ! ENCL TITLE: 50. 73 Licensee Event Repov t .(LFR) > Incident Rpt>

g SIZE:

etc.

NOTES:

RECIPIENT COPIES RECIPIENT COP IES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 1 PD2-2 PD 1 McDONALD> D 1 INTERNAL: ACRS MICHELSON 1 *CRB MOELLER 2 2 AEOD/DOA AEOD/DBP/ROAB 2 2 AEOD/DSP/TPAB 1 DEDRO 1 1 NRR/DEBT/ADE 1 NRR/DEST/ADS 1 0 NRR/DEBT/CEB 1 NRR/DEBT/ELB 1 1 NRR/DEBT/ 1CSB NRR/DEBT/MEQ 1 1 NRR/DEST/MTB 1 NRR/DEST/PSB 1 1 NRR/DEST/RSB NRR/DEBT/SGB NRR/DLPG/HFB 1 NRR/DLPG/GAB 1 NRR/DOEA/EAB l'!RR/DREP/RAB 1 1 NRR/DREP/RPB >RR ~M*S~ILRB 1 1 NRR/PMAS/PTBB 1 1 RES DEPY QI '1 RGN2 FI LE 01 1 EXTERNAL: EGS(G QROH> M 5 H ST LOBBY WARD 1 LPDR 1 -

NRC PDR 1 1 NSIC HARRIS> J l'I!SIC MAYS> G 1 1 TOTAL NUMBER OF COPIES REQUIRED: LTTR 42 ENCL 40

19431'ICENSEE NRC form 3EEA EVENT REPORT ILER) TEXT CONTINUATION U.E. NUCLEAR REOULA'TQR Y COMMISSION APPROYEO OME NO 31EO~IDE EXPIRES: 8/31/IEI fACILITYNAME 111 DOCKET NUMEE R 121 LER NUMEER IE) PACE l31 YEAR Xp:, EEOUENT/AL NUMEEA jK. AEV 3/ON

"'.3 NVMEEA Turkey Point Unit 3 o s o o o 2 5 0 8 6 0 4 0 0 1 02OFO TEXT /N moro orrooo ir /olrrro/L rroo o/r///// h'RC /yrrrrr 3/FEE 3/ I IT/

EVENT:

On December 18, 1986, at 1745, with both Units 3 and 4 at 100% power, it was determined that a deficiency existed concerning the potential for loss of three air conditioner compressors and three air handlers of the Control Room Ventilation System (CRVS). At Turkey Point, the design basis for the heating and air conditioning portion of the CRVS is to maintain an environment which does not exceed 120 degrees F and 95% relative humidity. In order to satisfy this design basis, one of three air conditioning compressors and one of three air handling units would be required to be operating.

The temperature control circuit is normally powered from Motor Control Center (MCC) 3A. MCC 3A is temporarily deenergized after a loss of offsite power, during sequencer operation. Upon loss of power from MCC 3A, the transfer switch in panel DP-312A functions to transfer the power source from MCC 3A to MCC D.

Based on the above, the evaluation concluded that during CRVS operation, should a loss of power from MCC 3A occur, and the transfer switch fails to transfer between the two positions (MCC 3A and MCC D), no control circuit power will be available, and all CRVS air conditioning compressors and air handlers will be disabled. Should this occur, the maintenance of a control room environment which does not exceed the design basis cannot be assured. This may result in the failure of safety related components which are located in the control room, due to potentially high temperatures and relative humidity. This in turn may substantially inhibit 'he ability to safely 'shutdown and/or maintain the units in a safe shutdown mode. On December 18, 1986, it was determined that this condition constituted a substantial safety hazard and was reportable under 10 CFR 21 engineering evaluation identified two'ther single active failures. These

'he are the failure of the thermostat, or failure of the temperature controller.

Failure of either of these components would result in the loss of control power to all three air conditioning compressors, with the air handlers continuing to operate. However, as the air handlers will continue to operate, the average control room air temperature would not exceed that required for equipment protection, and therefore no substantial safety hazard exists.

On April 19, 1987 while Unit 3 was in refueling shutdown (mode 6) with the

'ore off loaded into the Unit 3 spent fuel pit and Unit 4 in mode 6 another failure mode of the transfer switch DP-312A was discovered. At 1900 on April 19, 1987 the operators received an annunciator for a D.C. ground on the 3A 4160 volt bus at the same time they noticed a loss of light indication for the 3A motor control center (MCC). In addition DP-312A failed to transfer to its alternate power supply upon loss of power to the 3A MCC. An investigation discovered that the telemand swap circuitry for the 3A MCC had actuated but since the alternate power supply breaker for the 3A MCC had been taken out of service, the 3A MCC could not transfer to its alternate power supply so the MCC remained deenergized.

NRC FO/IM 3EEA N3/31

NRC form 3SSA U.S. NUCLEAR REQULATCRY COMMISSION I9431 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVED OMS NO. 3150MIOS EXPIRES: S/31/Ie FACILITY NAME ll) DOCKET NUMSER lll LER NUMBER LEI ~ AQE l31 VEAR '.% .'; SEQUEISTIAL Rre REVISIO/s Lsr.v rsUM TR err NUM TA Turkey Point Unit 3 0 s o 0 o 250 8I6 OIqO 0 030FO 5 TExT illmoro s/Mso I ~ rer/vtrerL vse er/I//e'orM/ Hllc For/sr 3/l//A'/117)

Investigation of the DP-312A failure to swap discovered that upon removal of the cover panel for the transfer switch, the switch transfered by itself as designed. Further investigation of this failure discovered that the clearance between the cover plate and a relay in the transfer switch was such that the-cover plate could prevent the transfer switch from performing its intended function. The weekly surveillance test is performed with the cover plate removed so this test would not be able to detect this failure mode.

CAUSE OF EVENT:

An engineering evaluation of the CRVS, following the loss of control room air conditioning due to the transfer switch sticking during a safeguards test on July 26, 1986, revealed the concerns for the potential loss of the CRVS during an accident.

Additional investigations revealed that the clearance between the cover plate and a relay in the transfer switch was such that the switch could be prevented from performing its intended function.

ANALYSIS OF EVENT:

The interim measures taken include weekly surveillance of the transfer switch, and the installation of quick-connect jumpers which'verride the thermostat and temperature controller. An engineering evaluation, in accordance with 10 CFR 50.59, has determined that these temporary changes eliminate the consequences of the above single failures.

A calculation has been performed which indicates that, based on the performance of a weekly operability surveillance, the unavailability of the transfer switch is reduced to 9 x 10-5. This is considered acceptable in that it is comparable to the unavailability of both on-site emergency power sources.

It is unlikely that the control room operators would be required to use the quick-connect jumpers during an accident or transient condition, since continuous operation of the CRVS assures operability of the thermostat and the temperature controller. Nevertheless, in the unlikely event that a failure in the thermostat or the temperature controller should render all compressors inoperable, the connection of the described jumper could be accomplished quickly.

An analysis has been performed which concludes that with loss of the air conditioner compressors but with the air handlers continuing to operate, the average air temperature in the control room would not exceed that required for equipment protection. Therefore, no specific time limit is required for the control room operators to restart the air conditioning compressors.

The potential failure of the transfer switch constitutes a substantial safety hazard as defined by 10 CFR 21; however, since no actual loss of the CRVS during plant operation occurred this condition did not affect the health and safety of the public.

NRC FORM 3SSA 1943/

V 4 NVCLEAR REQVLATCRY CPM'Mls'ION NPC FOIIII 544A (949 I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVEO PMS NO, 515CM105 EXPIR'ES SIElI44 POCKET NVMSER (TI LER NVMSER (4I ~ ACE l5l FACILITY NAME Ill

.,r. 54PVENTIAL . rr>> IIEYISION IIV>> ER r. HVM55A Turkey Point Unit 3 TEXT llfII>>re a>>ce lI >>Powwow II55 ~ HRC FpmI JSEASI l ill 0 s 0 0 0 250 86 0 40 01 04 QFO 5 At the time that the additional failure mechanism was found both units were in mode 6 and Unit 3 had its core off loaded into the Unit 3 spent fuel pit. No CORE ALTERATIONS or positive reactivity additions were in progress during this event so the control room ven'tilation isolation system was not required to be operable. In addition, prior to this event, the fuel element shuffle in the Unit 3 spent fuel pit had been stopped and did not recommence until after the event. Therefore, the health and safety of the public were not affected.

CORRECTIVE ACTIONS:

1) Until permanent design changes are implemented, the panel DP-312A transfer switch unavailability due to a single failure will be reduced to an acceptable level by the implementation of a Plant iIaintenance Instruction to verify the operability of the transfer switch on a weekly basis. This surveillance has been entered in O-OSP-200.1,"Schedule of Plant Checks and Surveillances", to assure timely performance of this surveillance.

2) Quick-connect jumpers have been installed around the control circuitry (located in control room panel C-45) for the air conditioner compressor units.

These jumpers are not connected during normal plant operation. Once connected, these jumpers will override operation of the thermostat and the temperature controller, thus eliminating any impact on the air conditioning compressors from the failure of either of these devices. No specific time limit is required for the restart of the air conditioning compressors with continued air handler operation.

3) Training Brief 186 was issued, describing the concern, the above modifications, and the weekly surveillance. Upon identification, the concern and corrective measures were discussed with the shift operators.

4) 'ermanent plant modifications to correct this condition are being pursued on an expeditious basis.

5) The method of mounting the cover plate was enhanced to increase the clearance between the transfer switch and the cover plate.

6) The weekly surveillance of the transfer switch has been modified to allow for testing the transfer switch with the cover plate installed on an interim basis by installing a temporary toggle switch that is removed upon completion of the test.

7) A request for technical assistance has been written to investigate the feasibility of installing the toggle switch on a permanent basis until the long term modifications are complete .

NRC FPR>> 5444 PSST l

NRC Form SSSA U.S. NUCLEAR REGULATCRY COMMISSION ISSS I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROYEO OMS NO. 3150-0104 ExPIRES: S/3 1 I Ie FACILITY NAME III DOCKET NUMSER 13)

LER NUMSER ISI ~ ADE IS) yEAR ~ SEQUENTIAL .. O. REVISION NVM TR 'vI NVM FR Turkey Point Unit 3 TEXT llfmoro NMco ir Poqor'rNL uoo ~ IYIIC form 3%A'Fl lit) o s o o o 8 6 0 4 0 0 1 0 5 OF 0 5 ADDITIONAL DETAILS:

The individual informing the Commission is: C. 0. Woody, Group Vice President, Nuclear Energy, P.O. Box 029100, Miami, Florida 33012.

The transfer switch manufacturer is: Asco Electrical Products Co., Inc.

Model No.: 9041.

The original designer of the CRVS is the Bechtel Corporation.

The other nuclear plants in Florida Power and Light s system have been made aware of the potential problem. An entry will be made in the INPO Network to make other nuclear facilities aware of the potential problem.

NRC FORM SSSA ISIS I

', O. 14000, JUNO BEACH. FL 33408 FLORIDA POWER 5 LIGHT COMPANY MAY >J I98l'-87-2I8 IO CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: Turkey Point Unit 3 Docket No. 50-250 Reportable Event: 86-40 Rev. I Date of Event: April l9, l987 Single Failures in CRVS May Result in Loss of Control Room Ventilation S stem The attached Licensee Event Report is being submitted pursuant to the requirements of IO CFR 50.73 to provide notification of the subject event.

Very truly yours, Group Vi President Nuclear Energy COW/SDF/gp Attachment cc: Dr. J. Nelson Grace, Regional Administrator, Region II, USNRC Senior Resident Inspection, USNRC, Turkey Point Plant PEOPLE... SERVING PEOPLE SDF I /0 I 7/ I

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