ML17339A569
| ML17339A569 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 05/31/1974 |
| From: | Schmidt A FLORIDA POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML17207A819 | List:
|
| References | |
| NUDOCS 8002150485 | |
| Download: ML17339A569 (8) | |
Text
P.O. BOX 3100 MIAMI,FLORIDA 33101 Reference 5
FLORIOA POWER Ei LIGHT COIiiIPANY May 31, 1974 Mr. Norman C. Moseley, Director Region II Directorate of Regulatory Operations U. S. Atomic Energy Commission 230 Peachtree
- Street, N. N., Suite 818
- Atlanta, Georgia 303'03
Dear Mr. Moseley:
TURKEY POINT PLANT DOCKET NOQ. 50-250 AND 50-251 UNIT TRIPS - APRIL 25 1974
. At the request of Mr'. Austin Hardin of your staff, we are re-porting the tripping of Units 3 and 4 at the Turkey Point Plant.
SUl MARY About 3:49 p.m.,
on April 25, 1974, Unit Nos.
3 and 4 generators tripped when both generator circuit breaker protection system relays were energized during functional testing of Unit No.
4 Startup Transformer protection system relays.
Trip of Unit Nos.
3 and 4 turbine-generators caused an auto-matic trip of both Unit Nos.
3 and 4 reactors.
The reactor protection systems and.engineered safeguards system equipment performed satisfactorily after the reactors tripped.
There was no equipment
- damage, abnormal occurrence or unusual event as a result of the unit trips.
Unit No.
3 was returned to service at 5:45 p.m.,
on April 25, 1974.
Unit No.
4 was returned to service at 5:40 a.m.;
on April 26, 1974.
UNIT CONDITIONS BEFORE TRIPS Unit No.
4 Startup Transformer was electrically isolated for functional testing of protection system'relays and periodic maintenance on associated equipment.
All of the specified 80 OS150% f5 HELPING 8UI LO FLO R I 0 A
Mr. Norman C. Moseley Page 2
May 31, 1974 clearance requests,'otifications, authorizations and approvals necessary to begin work on No.
4 Startup Transformer were met.
All of the conditions specified in the Technical Specifications for this work were also met.
Unit No.
4 had been operating at 723 Mle (984 R.P.)
stead> -state power level for several hours before the trip.
Unit No.
3 had been operating at 720 Nfe (97< R.P.) steady-state power level for several hours.
DESCRIPTION OF OCCURRENCE No.
4 Startup Transformer protective relays were tested and de-monstrated satisfactory operation.
- However, when the Startup Transformer lockout relay was "reset", current flowed through an unanticipated path ("sneak circuit")
and energized Unit No.
4 generator breaker protection system relays.
This opened both of the generator breakers on Unit Nos.
3 and 4.
Both No.
3 and 4
reactors automatically tripped when the turbine-generators tripped.
The minimum system frequency recorded during the transient was 58.6 Hz., Underfrequency load shedding relays operated to reduce the interconnected system load by automatically opening feeder breakers.
Frequency was restored to 60 Hz within six seconds.
Interconnected system power flows were returned to normal within twenty minutes.
Ne estimate 99~ of FPL's customers were back in service within twenty minutes, though some isolated outages lasted up to an hour.
Some short term power interruptions also occurred to customers on other Florida systems as a result of the incident.
The instantaneous loss of 1443 MNe, when both Unit Nos.
3 and 4
tripped, is the largest single loss of generation experienced in FPL's system.
In comparison to previous system disturbances, customer load was restored faster than any previous occurrence.
Refer to Table I for load shedding data.
DESIGNATION OF APPARENT CAUSE OF TRIPS Review, analysis, and evaluation of Unit Nos.
3 and 4 annunciators, records and Turkey Point Plant switchyard oscillographs concluded that both Unit Nos.
3 and 4 generators breakers.operated as a
result of the actuation of the generator back-up protection relays during functional testing of Unit No.
4 Startup Transformer relays.
Mr. Norman C. Moseley Page 3
May 31, 1974 ANALYSIS OF OCCURRENCE UNIT NO'.
3 When No.
3 reactor tripped, the reactor protection system and engineered.
safeguard.
system equipment operated properly to place the unit in a safe condition.
There was no equipment
- damage, abnormal occurrence or unusual event as a result of this trip.
After the cause of the trip was determined and conditions ev-aluated as satisfactory, the reactor was returned to service.
No.
3 unit, conditions after the unit trip were more conservative than similar incidents analyzed and presented in Section 14 of Turkey Point Unit Nos.
3 and 4 FSAR.
Therefore, Unit No. 3,trip did not present any danger to the health and safety of the public.
UNIT NO.
4 Nhen No.
4 reactor tripped, all reactor protection system and engineered safeguards system equipment operated properly to place the unit in a safe condition even though No.
4 Startup Transformer was electrically isolated and normal auxiliary power supply was unavailable.
Emergency power supply was supplied by automatic start of both A and B Emergency Diesel-generators.
The emergency Diesel-generators continued to operate until No.
4 Startup Transformer was returned to service.
About five minutes after No.
4 reactor tripped, the 1085 psig safety valve on No.
4A Steam Generator main steam line header lifted and did not reseat.
Immediate operator actions included additional boration of the reactor coolant system to ensure that adequate reactor shutdown margin was maintained.
Feedwater flow to No.
4A Steam Generator was controlled to maintain adequate water level while efforts were made to close the safety valve.
When the manual lifting device was removed from the safety valve, the safety valve reseated.
(Refer to Figure 1 for details)
Review of Unit No.
4 recorder charts, indicators and annunciators show that No.
4A loop cold leg temperature was reduced to a minimum of 517 F (compared to normal hot shutdown temperature of 547 F) and maintained this temperature for about. thirty minutes.
No.
4A loop cold leg temperature returned to 547 F within an additional thirty minutes.
This rate of temperature change is well within allowable cooldown rates.
Nos.
4B and 4C loop cold leg temperatures increased 10 to 15 F to about 565 F after the unit trip, then returned to 547 F within about thirty minutes.
Mr. Norman C. Moseley Page 4
May 31,
- 1974, There was no equipment damag'e, abnormal occurence, or unusual event as a result of this trip.
After the cause of the unit trip >>as determined, No.
4 Startup Transformer returned to
- service, and auxiliary power supply restored; the reactor was returned to service.
Comparison of No.
4 reactor conditions after the trip with similar incidents analyzed and presented in Section 14 of Turkey Point Unit Nos.
3 and 4 Final Safety Analysis Report concludes that actual conditions were equal to or more conservative than the conditions assumptions in the Safety Analysis.
Therefore, the Unit No.
4 trip did not pr'esent any danger to the health and safety of the public.
CORRECTIVE ACTION Florida Power 5 Light Company Relay Engineers have recommended that both Unit Nos.
3 and 4 Startup Transformer protective system be modified by installing additional isolation switches and a
diode to provide for complete isolation of the primary and the back-up protection system relays during relay tests.
This recom-mended change is being reviewed to obtain approval and authorization necessary to make this change.
If you have further questions about this occurrence, please do not hesitate to call me.
Very truly yours, D; Schmidt Director of Power Resources VTC/kmw cc:
Mr. John F. O'eary Jack R.
Newman, Esquire
FLORIDA POWER ( LIGHT COMPANY TURKEY POINT UNIT NOS.
3 6
4 UNIT TRIPS - APRIL 25 1974 TABLE I The underfrequency relay trips shed the interconnected system load as follows:
UTILITY Florida Power 5 Light Company Florida Power Corporation Tampa Electric Company ll Jacksonville Electric Authority Orlando Utilities Commission City of Lakeland LOAD - N'f 850 330 130 100 34 18 TOTAL 1 462
FIGURE 1
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RICO 4-C~SC ADORER aOA RIRQ T SOSWJeS coax
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RECX I
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The failure of the safety valve to reseat after opening was found to be caused by the loss of a cotter key in the safety valve topworks.
This cotter key locks the manual lift collar in proper position on the safety valve spindle.
Nhen the cotter key vibrated out, the manual lift.collar vibrated down and made contact with the manual lifting device.
Nhen the safety valve operated, the manual liftcollar rotated further do:.
the.spindle.
This physically prevented the safety valve from reseating as the steam pressure decreased.
The safety valve was reseated by removing the manual lifting arm..
The safety valve was repaired by returned the manual. lift collar to its original position, installing a new cotter key, and replacing the.mapual lifting arm...The safety valve is now operable.