ML17354A612

LER 97-007-00:on 970730,automatic Reactor Trip Occurred. Caused by Closure of B Main Steam Isolation Valve.Failed W Relay & Equivalent Relays Were replaced.W/970829 Ltr

ML17354A612
Person / Time
Site:	Turkey Point
Issue date:	08/29/1997
From:	Hovey R, Lafleur D FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-97-219, LER-97-007-01, LER-97-7-1, NUDOCS 9709030284
Download: ML17354A612 (12)

Text

~ CATEGORY REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9709030284 DOC.DATE: 97/08/29 NOTARIZED: NO DOCKET g FACIL:50-250 Turkey Point Plant, Unit 3, Florida Power and Light C 05000250 AUTH. NAME AUTHOR AFFILIATION LAFLEUR,D.R. Florida Power a Light Co.

HOVEY,R.J. Florida Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 97-007-00:on 970730,automatic reactor trip occurred.

Caused by closure of B main steam isolation valve. Failed W relay a equivalent relays were replaced.W/970829 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

NOTES:

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NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE. TO HAVE YOUR NAME OR ORGANIZATION REMOVED FROM DISTRIBUTION LISTS OR REDUCE THE NUMBER OF COPIES RECEIVED BY YOU OR YOUR ORGANIZATION, CONTACT THE DOCUMENT CONTROL DESK (DCD) ON EXTENSION 415-2083 FUIL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 24 ENCL 24

AUG 29 1997 L-97-219 10 CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re: Turkey Point Unit 3 Docket No. 50-250 Reportable Event: 97-007 Date of Event: July 30, 1997 Automatic Reac or Tri due to losure of the B Main S am Isolation Valve The attached Licensee Event Report is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.

Sincerely, Ni R. J. Hovey Vice President Turkey Point Plant DRL Attachment cc: Regional Administrator, USNRC Region II Senior Resident Inspector, USNRC, Turkey Point Plant Illllllll.lllllllllllllllll lllllllllllll!

970'ir030284 970829 PDR ADOCK 05000250 8 PDR an FPL Group company

LICENSEE EVENT REPORT (LER)

FACILITY NAME (1) DOCKET NUMBER (2) PAGE (3)

TURKEY POINT UNIT 3 05000250 OF TITLE (4) Automatic Reactor Trip due to Closure of the B Main Steam Isolation Valve EVENT DATE (5) LER NUMBER(6) RPT DATE (7) OTHER FACILITIES INV. (8)

MON DAY YR YR SEQ 4 Rl MON DAY YR FACILITY NAMES DOCKET I (S) 07 30 97 97 007 00 08 29 97 OPERATING MODE (9)

PONER LEVEL 100 (1O)

LICENSEE CONTACT FOR THIS LER (12)

TELEPHONE NUMBER D. R. Lafleur, Licensing Engineer 305-246-7150 CCMPLETE ONE LINE FOR EACH COMPONENT fAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM CCMPONENT MANUFACTURER NPRDS2 CAUSE SYSTEM COMPONENT MANUFACTURER NPRDS2 SB RLY W120 N B BA TAC D245 N EXPECTED MONTH YEAR SUPPLEMENTAL REPORT EXPECTED (14) HO SUBMISSIOH DATE (15)

(lf yes, complete EXPECTED SUBMISSION CATE)

ABSTRACT (16)

On July 30, 1997, Florida Power & Light (FPL) Company's Turkey Point Unit 3 was operating in Mode 1 at 100% power.'t 1506 hours0.0174 days <br />0.418 hours <br />0.00249 weeks <br />5.73033e-4 months <br />, the 3B Main Steam Isolation Valve (MSIV) failed closed.

The resultant level decrease in the 3B Steam Generator (SG) caused the reactor to trip automatically on low-low level in the 3B SG. All control rods fully inserted.

A 3B steam line Main Steam Safety Valve (MSSV) opened then reseated as expected during the initial transient, as pressure in the 3B SG exceeded the MSSV setpoint pressure of 1085 psig.

The A Auxiliary Feedwater (AFW) Pump tripped on overspeed during the event. Plant response was otherwise as expected.

The cause of the MSIV closure was attributed to a failed BFD22S relay. The six relays on the 3A, 3B, and 3C MSIV's were replaced.

The most probable cause of the A AFW pump overspeed trip was a spurious electronic overspeed signal caused by the A AFW pump tachometer module.,The A AFW pump tachometer module was replaced with a different vendor model, operability was verified, and the pump was returned to service.

FACILITY NAME DOCKET NUMBER LER NUMBER PAGE NO.

TURKEY POINT UNIT 3 05000250 97-007-00 2OF6 I. DESCRIPTION OF THE EVENT On July 30, 1997, Florida Power a Light (FPL) Company' Turkey Point Unit 3 was operating in Mode 1 at 100% power. At 1506 hours0.0174 days <br />0.418 hours <br />0.00249 weeks <br />5.73033e-4 months <br />, the 3B Main Steam Isolation Valve (MSIV) [SB:isv] failed closed. The 3B Steam Generator (SG) [SB:sg] level decreased as a result of the MSIV closure. Upon indications of MSIV closure, the reactor operator attempted to trip the reactor manually. However, the reactor tripped automatically on low-low level in the 3B SG approximately ll seconds after MSIV closure and less than a second before the manual trip was actuated. All control rods fully inserted.

A Main Steam Safety Valve (MSSV)[SB:rv] on the 3B steam line opened as pressure in the 3B SG exceeded the 1085 psig safety valve setpoint. As pressure in the steam line decreased to below the setpoint, the MSSV reseated as expected.

The reactor operators started the 3B Charging Pump [CB:p] to maintain pressurizer [AB:pzr] level, and closed the MSIV's on the 3A and 3C SG's to stop the reactor coolant system average temperature from decreasing. Upon plant stabilization, the Emergency Operating Procedures (EOP's) were exited and General Operating Procedure, 3-GOP-103, was entered to place the plant in Hot Standby.

At 1509 hours0.0175 days <br />0.419 hours <br />0.0025 weeks <br />5.741745e-4 months <br />, the A Auxiliary Feedwater (AFW) Pump [BA:p]

(normally aligned to Train 1) tripped on mechanical overspeed.

The 3A and 3B Steam Generator Feedwater pumps and the B and C AFW pumps (normally aligned to Train 2) continued to supply feed to the SGs. Plant response was otherwise as expected.

After stabilization of the plant, the A AFW Pump (and therefore Train 1) was declared out of service, placing the plant in Technical Specification LCO 3.7.1.2, Action Statement 1. The AFW system was realigned with the C pump on Train 1 and the B pump on Train 2, to provide for dual Train operation, exiting Action Statement 1 and entering Technical Specification LCO 3.7.1.2, Action Statement 3. This Action Statement requires that the AFW pump be restored to an Operable status within 30 days. This pump was returned to Operable status after replacement of the tachometer that supplies its electronic overspeed trip signal, exiting the LCO.

The NRC operations center was notified at 1621 on July 30,. 1997, in accordance with 10 CFR 50.72 (b) (2) (ii), Reactor Protection System Actuation and Engineered Safety Feature Actuation.

An Event Response Team was formed to investigate the causes for the failure of the 3B MSIV and the overspeed trip of the A AFW Pump.

FACZLZTY NAME i

LXCENSEE FM NT REPORT DOCKET NUMBER t

(LER) TMVP CONTXNUATXON LER NUMBER PAGE NO.

TURKEY POINT UNIT 3 05000250 97-007-00 3OF6 II. CAUSE OF THE EVENT MSIV Closure The cause of the MSIV closure was determined to be the failure of a Westinghouse BFD22S relay coil (tag number 3-AX/2605A)[SB:rly],

which is part of the 3B MSIV actuator circuitry. FPL believes that the relay was installed in November of 1983. This relay is normally energized. When this relay is energized, it solenoid valve which delivers air to the MSIV actuator. When the actuates a relay deenergizes, the solenoid allows air to vent from the MSIV actuator, allowing the MSIV to close. Each MSIV has two relays, one for each actuation train, which perform this function. The failed relay coil was open and its casing was cracked, showing signs of thermal aging.

A AFW Pump Mechanical Overspeed Trip Turkey Point plant design includes a common AFW system composed of three steam driven pumps, each designed to operate at 5900 rpm. Each pump turbine is protected by both an electronic and a mechanical overspeed trip. The electronic overspeed trip, set at 6200 RPM, uses a speed sensor to provide a trip signal to close the pump turbine steam inlet valve. The mechanical overspeed trip, set to actuate at 6500 RPM, uses a pin-type trip weight attached to the pump turbine rotor. When sufficiently displaced by centrifugal force, the trip weight will actuate a spring loaded lever to trip closed the pump turbine steam inlet valve.

When an AFW actuation signal is present, the electronic overspeed trip will automatically reset after actuation. During this event, approximately 1 minute after AFW initiation, the A AFW pump turbine cycled in this manner (from trip to reset) for approximately 70 seconds. Based on AFW flow recorder traces and operator reports, the A AFW pump tripped on electronic overspeed, then reset, several times. Pump speed increased due to this cycling process, eventually tripping on a mechanical overspeed trip.

The most probable cause for the electronic overspeed trip of the A AFW pump was a spurious electronic overspeed signal caused by the A AFW pump tachometer module (Dresser-Rand part ¹890009A03)

[BA:tac]. This style module was installed in August of 1995, replacing the original Airpax module (Airpax part QFSS1416; Dresser-Rand part ¹890061A20).

A review of the circuitry was performed to compare the original Airpax module (Airpax ¹FSS1416; Dresser-Rand ¹890061A20) to the Dresser-Rand part ¹890009A03. The original Airpax module .

schematics identified an L-C filter network, which would effectively filter electric noise from its 125 Vdc vital power

FACILITY NAME i

LXCENSEE INTENT REPORT (LER)

DOCKET NUMBER TE3VP t

CONTINUATION LER NUMBER PAGE NO.

TURKEY POINT UNIT 3 05000250 97-007-00 4 OF 6 supply. No schematics were available for the Dresser-Rand module

¹890009A03. However, visual inspection of the module revealed differences in the filtering capabilities of the module circuitry.

Review of the plant's AFW pump history indicates that the A AFW pump tripped on January 7, 1997, due to a spurious electronic trip with the new style Dresser-Rand tachometer module installed.

No spurious electronic overspeed trips have been recorded for either the B or C AFW pumps, which have the original style tachometer module (Airpax ¹FSS1416; Dresser-Rand ¹890061A20) .

The A AFW pump tachometer module was replaced with an Airpax 300 Series tachometer module which is the recommended replacement for the now obsolete original module (Airpax ¹FSS1416; Dresser-Rand

¹890061A20). FPL Engineering review of the Airpax Series 300 and the original Airpax (Airpax ¹FSS1416; Dresser-Rand ¹890061A20) modules has determined that the operational characteristics are identical.

Industry research identified that in 1993, Vogtle Nuclear Station experienced problems with spurious tripping of an AFW pump due to electric noise introduced from 125 Vdc vital control circuits, with the same Dresser-Rand part number module. A 10 CFR Part 21 notification was made for this module (LER 50-425/93-007-00). FPL has found no record of having received this notification.

.III. ANALYSIS OF THE EVENT A reactor trip due to a low-low level in a steam generator is a previously analyzed event. Upon closure of the 3B MSIV, the sudden loss of steam flow from the 3B SG caused an increase in pressure in that SG. The pressure increase resulted in a decrease of water level in the 3B steam generator to the low-low level reactor trip setpoint of 10% narrow range level.

The Updated Final Safety Analysis Report (UFSAR) assumes a loss of normal feedwater to all steam generators due to the loss of the steam generator feed pumps or valve malfunction. The analysis shows that following a loss of normal feedwater, the AFW system is capable of removing the reactor's stored and residual heat assuming that only one pump is available. Since the normal feedwater flow as well as two of the three AFW pumps were

,available. for removing stored and residual heat, the event did not compromise the health and safety of the public.

FACZLZTY NAME i DOCKET NUMBER t

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION LER NUMBER PAGE NO.

TURKEY POZNT UNZT 3 05000250 97-007-00 SOF6 IV. CORRECTIVE ACTIONS The failed Westinghouse BFD22S relay 3-AX/2605A, as well as equivalent relays on each actuation train of all three MSIV's (3-AX/2605B, 3-AX/2604A,3-AX/2604B, 3-AX/2606A, and 3-AX/2606B) were replaced with Westinghouse BFD65 relays. These relays are of an improved dual-coil design which uses a lower wattage (producing a lower operating coil temperature) to hold the relay'when energized.

2. Equivalent function relays on Unit 4 MSIV's will be replaced during the next unit outage of sufficient duration.

3. Use of normally energized Westinghouse BFD relays will be reviewed to determine require replacement.

if other normally energized relays 4 ~ A review of the plant Preventative Maintenance (PM) program will be performed to verify whether the MSIV relays are included in the program and inspected on a sufficiently frequent basis.

5. The A AFW pump tachometer module was replaced with an Airpax 300 Series tachometer module which is the recommended replacement for the now obsolete Airpax HFSS1416 model.

Operability of the A AFW pump was verified by successful performance of the required surveillances.

6. FPL is performing surveillance testing on the A AFW pump at an increased frequency. Initial surveillance testing will be

. performed weekly for a month, then biweekly for two months.

Then, following successful completion of the increased surveillances, the pump testing frequency will be returned to the normal frequency of once per month.

7. FPL will perform additional testing to determine noise susceptibility of the Dresser-Rand 'part 5890009A03 tachometer module.

8. An investigation was performed to determine if a 10 CFR Part 21 report would be required for the defective Dresser-Rand part 8890009A03 tachometer module. Industry research identified that in 1993, Vogtle Nuclear Station issued a 10 CFR Part 21 notification for the same part (LER 50-425/93-007-00).

LICENSEE E'MLITT REPORT (LER) TE3VZ CONTINUATION FACILITY NAME DOCKET NUMBER LER NUMBER PAGE NO ~

TURKEY POINT UNIT 3 05000250 97-007-00 6OF6 V. ADDITIONAL INFORMATION Licensee Event Report 251/89-020, dated 1/18/90, reported a reactor trip due to an inadvertent closure of an MSIV. That closure was due to corrosion of a terminal block supplying 125 Vdc vital power to the MSIV actuator solenoids.

EIIS Codes are shown in the format [EIIS SYSTEM: IEEE component function identifier, second component identifier (if appropriate)] .

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