ML17219A653

LER 87-005-00:on 870527,while Operating in Mode 1,control Element Assemblies 5 & 7 Simultaneously Dropped to Bottom of of Core.Possibly Caused by Random Intermittent Failure of Control Element Drive Mechanism component.W/870626 Ltr

ML17219A653
Person / Time
Site:	Saint Lucie
Issue date:	06/26/1987
From:	Green W, Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
L-87-270, LER-87-005-03, LER-87-5-3, NUDOCS 8706300813
Download: ML17219A653 (5)

Text

R LATORY INFORMATION DISTRI ION SYSTEM (RIDS3 ACCESSIQN NBR: 8706300813 DOC. DATE: 87/Ob/26 NOTARIZED: NO DOCKET F*CIL: 50-38'7 St. Lucie Plant> Unit 2> Florida Power & Light Co.

AUTH. NAME AUTHOR AFFILIATION GREEN> W. C. Florida Power & Light Co.

WOODY> C.'. Florida Power & Light Co. 05000385'UBJECT:

RECIP. NAME RECIPIENT AFFILIATION LER 87-005-00: on 870505> while operating in Mode '1 Unit 2 simultaneously dropped control element assemblies 5 & 6 to bottom of core. Investigation being conducted bg plant &

vendor support personnel. W/870626 itr.

DISTRIBUTION CODE: IEEED COPIES RECEIVED: LTR J ENCL fS.IIE:

TITLE: 50. 73 Licensee Event Report (LER) Incident Rpt>

~ etc.

NOTES:

REC IP IENT CQP IES REC IP lENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 PD2-2 PD 1 TQURIGNY> E 1 1 INTERNAL: ACRS MICHELSON 1 1 ACRS MOELLER AEOD/DOA 1 1 -AEOD/DSP/ROAB 2 2 AEOD/DSP/TPAB 1 DEDRO 1 NRR/DEST/*DE 1 0 NRR/DEST/ADS 0 NRR/DEST/CEB 1 1 NRR/DEST/ELB 1 NRR/DEST/ICSB 1 1 NRR/DEST/MEB 1 1 NRR/DEST/MTB 1 1 NRR/DEBT/PSB 1 NRR/DEBT/RSB 1 1 NRR/DEST/SQB 1 NRR/DLPG/HFB 1 1 NRR/DLPG/GAB 1 1 NRR/DOEA/E*B 1 1 NRR/DREP/R*B 1 NRR/DREP/RPB 2 2 NRR/ AS/ ILRB 1 1 NRR/PMAS/PTSB 1 1 EQ FIL 02 1 RES DEPY QI 1,. 1 N E 01 1 EXTERNAL: EG&G GRQH> M 5 5 H ST LOBBY WARD LPDR 1 NRC PDR NSIC HARRIS> J 1 1 NSIC MAYS> G TQT*L NUMBER OF CQP IES REQUIRED: LTTR 42 ENCL 40

NRC Form 366A U.S. NUCLEAR REOULATORY COMMISSION

)943)

LICENSEE EVENT REPORT ILER) TEXT CONTINUATION APPROVED OMB NO. 3)50&)05 EXPIRES: 8/31/88 FACILITY NAME u) OOCKET NUMBER )2) LER NUMBER )8) PACE )3)

YEAR SEOVENTIAL REVISION NVMSEII eel NVMSER St. Lucie Unit I) 2 005 0 0 0 2 OF p 6 p p p TEXT /I/moro FPoco lr /or/Ir/rOd, IIFO afdir/ono/l/RC Farm 35/IA3/ I )7)

DESCRIPTION OP EVENT At 0420 hours0.00486 days <br />0.117 hours <br />6.944444e-4 weeks <br />1.5981e-4 months <br />, on May 27, 1987, St. Lucie Unit I)2 was operating in Mode 1 at 100 percent power when for no apparent reason two Control Element Assemblies (CEA) (EIIS:AA) 15 and I)7 dropped simultaneously to the bottom of the core.

The utility licensed operators after acknowledging 'and verifying CEA control room alarms, immediately took steps to promptly shutdown the unit without attempting to recover the CEAs. Technical Specification 3.1.3.1.C requires with more than one full length CEA inoperable or misaligned from any other CEA in its group by more than 15 inches, be in Hot Standby within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. After safely taking the unit to Mode 3 at 0523 hours0.00605 days <br />0.145 hours <br />8.647487e-4 weeks <br />1.990015e-4 months <br /> (Hot Standby), the operability of both CEAs was verified. An analysis of the core power distribution was performed using the incore instrumentation system, which verified the acceptability to return to full power operation and the unit was taken critical at 1804 hours0.0209 days <br />0.501 hours <br />0.00298 weeks <br />6.86422e-4 months <br /> and was returned to 100 percent power at 0525 hours0.00608 days <br />0.146 hours <br />8.680556e-4 weeks <br />1.997625e-4 months <br /> on May 28, 1987.

CAUSE OP THE EVENT The root cause of the event seems to be a random intermittent failure of a Control Element Drive Mechanism Control System (CEDMCS) component.

CEAs I)5 and I)7 were dropped prior to this event on April 28, 1987, but were recovered before a Technical Specification required shutdown was necessary.

At that time plant personnel ran a series of checks on the CEAs control system, assuring proper voltages, currents, coil/gripper operation, and system settings.

No specific problem could be identified at that time and the plant was returned to operation.

Subsequent to the most recent event vendor personnel were brought in to assist plant personnel in the investigation.. Again no specific failure mechanism was found and the plant was returned to power. The random intermittent nature of the failures dictates that the investigation be best accomplished by monitoring the system's operation while it is in an operational configuration. The two CEAs have been placed on a maintenance hold bus while their normal power supply is being continuously monitored to determine its intermittent failure mode.

Plant personnel along with vendor support personnel will continue to investigate and monitor CEDMCS components and parameters until the root cause of the failures is found and corrected.

NRC FORM 355A I9431

NRC Form 366A U.S. NUCLEAR REOULATORY COMMISSION (943)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVEO OMB NO. 3160M)04 EXPIRES: 8/31/68 FACILITY NAME (ll DOCKET NUMBER (3) LER NUMBER (6) PACE (3)

YEAR @~,:

SEOVENTIAL REVISION NVMSER ARS NVMSER St. Lucie Unit I)2 o s o o o 0 5 000 3 OF 0 3 TEXT /// morr t/Mor /t tr//rrwrd, Irtr odd/dorM//YRC %%drm 366r('t/ (17)

ANALYSIS OF THE EVENT The event is reportable under 10 CFR 50.73 (a)(2)(i) as any event or condition that results in the completion of any nuclear plant shutdown required by the plant's Technical Specifications. This event when compared against the analysis in section 15.4.2.3.8.1, "CEA Drop Event", of the St. Lucie Unit e2 Final Updated Safety Analysis Report (FUSAR) is determined to be of little significance.

The actual plant response was more conservative than the FUSAR analysis because the FUSAR assumes that the CEA detection system is inoperable, that turbine load remains the same, and that all charging pumps (EIISSCB) and pressurizer proportional heaters are inoperable.

A subsequent Florida Power and Light analysis of this event was performed that verified that the dropped CEAs had no significant effect on core parameters and that the recovery act'ions were technically adequate. In fact, the analysis showed that a simultaneous drop of CEAs II5 and i7 is less severe than the worst case single CEA drop. Thus, the health and safety of the public were not affected by this event.

CORRECTIVE ACTIONS

l. The plant was .taken to Mode 3 Hot Standby and the CEAs were withdrawn to assure operability.

2. A specific analysis has been performed for these two dropped rods, which verifies that the recovery actions taken during this event were technically adequate. Also, the analysis verified that if these two rods drop together in the future that recovery of the rods can be performed before completion of shutdown.

3. The CEAs have been placed on the maintenance hold bus as a precautionary measure while their normal power supply output is being monitored. Plant personnel along with vendor personnel are continuing to investigate and monitor CEA components and parameters.

ADDITIONAL INFORMATION FAILED COMPONENT INFORMATION:

No specific component failures have been identified during this event and the investigation is continuing.

PREVIOUS SIMILAR EVENTS:

See LER 389-85-06 for a previous similar event involving two simultaneously dropped CEAs.

NRC FORM 366A (983)

. O. BOX 14000, JUNO BEACH, FL 33408.0420 198 t L-87-270 IO CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gent lemen:

Re: St. Lucie Unit 2 Docket No. 50-389 Reportable Event: 87-05 Date of Event: May 27, l 987 Technical Specification Required Reactor Shutdown Because of Two Dro ed Control Element Assemblies for Unidentified Reason The attached Licensee Event Report is being submitted pursuant to the requirements of IO CFR 50.73.a. to provide notification on the subject event.

Very truly yours,

. O. dy

+Group ice President Nuclear Energy COW/GRM/gp Attachment cc: Dr. J. Nelson Grace, Regional Administrator, Region ll, USNRC Senior Resident inspector, USNRC, St. Lucie Plant GR M5/055/ I an FPL Group company