05000250/LER-2006-004, Regarding Emergency Diesel Generator Automatic Actuation Due to Loss of Power to a Vital Bus
| ML061360222 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 05/08/2006 |
| From: | Jones T Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2006-119 LER 06-004-00 | |
| Download: ML061360222 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(ix)(B) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(1) 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(iv)(B), System Actuation |
| 2502006004R00 - NRC Website | |
text
10 FPL 10 CFR § 50.73 L-2006-119 May 8, 2006 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re:
Turkey Point Unit 3 Docket No. 50-250 Reportable Event: 2006-004-00 Date of Event: March 8, 2006 Emergency Diesel Generator Automatic Actuation due to Loss of Power to a Vital Bus The attached Licensee Event Report 50-250/2006-004-00 is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(iv)(A) to provide notification of the subject event.
If there are any questions, please call Mr. Walter Parker at (305) 246-6632.
Very truly yours, Terry 0. Joes Vice President Turkey Point Nuclear Plant Attachment cc:
Regional Administrator, USNRC, Region II Senior Resident Inspector, USNRC, Turkey Point Nuclear Plant an FPL Group company
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06/30/2007 (6-2004)
Estimated burden per response to comply with this mandatory collection request:
50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br />. Reported lessons learned are incorporated Into the licensing process and fed back to industry. Send comments regarding burden estimate to the Records and FOLA/Prlvacy Service Branch (T-5 F52), U.S. Nuclear Regulatory Commission, LICENSEE EVENT REPORT (LER)
Washington, DC 20&550001, or by ntenet e-mail to infocollects~nre.mgo, and to the Desk Oficer, Office of Information and Regulatory Affairs, NEOB4 0202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to Impose an Information collection does not display a currently valid OMB control (See reverse for required number of number, the NRC may not conduct or sponsor, and a person is not required to digits/Characters for each block) respond to, the information collection.
- 1. FA UILITY NAME 2 DOCKET NUMBER
- 3. PAGE Turkey Point Unit 3 05000250 1 OF 5
- 4. TITLE Emergency Diesel Generator Automatic Actuation due to Loss of Power to a Vital Bus
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
I FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL R MONTH DAY YEAR 05000 NUMBER NO.
FACILITY NAME DOCKET NUMBER 3
8 2006 2006 - 004 -
00 5
8 2006 05000
- 9. OPERATING MODE
- 11. THIS REPORTIS SUBMrITED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check allthat apply) 0 20.2201(b) a 20.2203(a)(3)(li) 0 50.73(a)(2)(i)(C) 0 50.73(a)(2)(vii) 5 0 20.22013(d) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(viii)(B) 0 20.2203(a)(1) 0 20.2203(a)(4) 0 50.73(a)(2)p§)(i) 0 50.73(a)(2)(ix)(B) 0 20.2203(a)(2)(1) 0 50.36(c)(1)(I)(A) 0 50.73(a)(2)(i11) 0 50.73(a)(2)(ix)(A)
- 10. PO ERL L
0 20.2203(a)(2)(ii) 0 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(v)(A) 0l 50.73(a)(2)(x) l 0
20.2203(a)(2)(iii) 0 50.36(c)(2) 0 50.73(a)(2)(v)(A) 0 73.71 (a)(4) 00 20.2203(a)(2)(iv) 03 50.46(a)(3)(i0) 0 50.73(a)(2)(v)(B)
El 73.71(a)(5) 0 0
20.2203(a)(2)(v) 0 50.73(a)(2)(1)(A) 0 50.73(a)(2)(v)(C) 0 OTHER 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B) 0 50.73(a)(2)(v)(D)
Specify in Abstract below I_____
or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER NAME iTELEPHONE NUMBER (WIciude Aea Code)
Paul F. Czaya - Licensing Engineer 305-246-7150
- 13. COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPIX FACTURER TO EPIX
.SS E
I_
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR SUBMISSION 0 YES (If yes, complete 15. EXPECTED SUBMISSION DATE) 0 NO DATE ABSTRACT (Limit to 1400spaces, lIe., approximately 15single-spaced typewlitten lines)
On March 8, 2006 at approximately 1553, a loss of the Unit 3 3A 4 kV electrical distribution bus occurred during restoration of the 3C load center (LC) following outage maintenance. The 3A load sequencer performed bus load stripping and a loss of offsite power occurred due to a degraded voltage condition that was sensed on the 3C LC. This was caused by a misaligned auxiliary switch contact on the newly Ifurbished 3C 480V LC feeder breaker. The 3A emergency diesel generator automatically started End restored power to the 3A bus. Core cooling was reestablished at approximately 1600 utilizing the 3B I esidual heat removal (RHR) pump on the 3B 4 kV bus which was unaffected by the loss of the 3A 4 kV bus. The cause was a vendor human error during breaker refurbishment in the configuration of the auxiliary switch contacts on the 3C 480V LC breaker which went undetected by the vendor test and inspection program and Turkey Point pre-installation checks. Corrective action includes: The auxiliary switch contacts were re-configured and the breaker was returned to service, and the breaker refurbishment standard will revise the final test and inspection procedure to record as left auxiliary switch contact configuration and compare it to the as found configuration. These checks will be independently verified. Core cooling was restored in approximately seven minutes with a reactor coolant system temperature increase of approximately 25 degrees F. using the most conservative available temperature indication. The increase in risk due to loss of core cooling is judged to be very small given the availability of the redundant RHR pump and power source and the short period for restoration of cooling. As a result, the health and safety of the public were not affected by this event.
lJlC FORM 356(6-2004)
PRINTED ON RECYCLED PAPER NRC FORM 366 (6-2004)
PRINTED ON RECYCLED PAPERU.S. NUCLEAR REGULATORY COMMISSION
(-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACIT NC E
FACILITY NAME (1)
NUMBER 2 LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL REVISION Turkey Point Unit 3 05000250 SI NUMBERU NUMBER Page 2 of 5 20o6 00 TEXT I more space is required, use additional copies of NRC Form 366A) (17)
DESCRIPTION OF THE EVENT At the time of the event, Unit 3 was in Mode 5 with reactor (EIES: AC] coolant system temperature at approximately 108 degrees F with the 3A residual heat removal (RHR) pump [ERIS: BP, P] supplying core cooling. The power supply to Unit 3 was from a back feed alignment via the Unit 3 main transformer [EIIS:
EL, XFMR] and auxiliary transformer [EIIS: EA, XFMR]. Unit 4 was in Mode 1 at 100% power.
On March 8, 2006 at approximately 1553, a loss of the Unit 3 3A 4 kV electrical distribution bus [EIIS: EB, BU] occurred during restoration of the 3C load center (LC) following outage maintenance. The 3A load sequencer performed bus load stripping and a loss of offsite power (LOOP) occurred due to a degraded voltage condition that was sensed on the 3C LC. This was caused by a misaligned auxiliary switch contact
([lS: CNTR] on the 3C 480V LC feeder breaker [EUS: EB, BKR]. The 3A emergency diesel generator (EDO) UES: EK, DG] automatically started and restored power to the 3A bus. LOOP loads were sequenced and core cooling was reestablished utilizing the 3B RHR pump on the 3B 4 kV bus which was unaffected by the loss of the 3A 4 kV bus. Core cooling via the 3B RHR pump was restored at approximately 1600 on March 8, 2006. The event was self evident as various alarms alerted operators.
Operators were in the process of draining the reactor coolant system (RCS) to approximately 1.5 feet below the reactor vessel flange in preparation for refueling activities. The RCS was at approximately 60% drain down level at the time of the loss of the 3A 4 kV bus. When power to the 3A 4 kV bus was lost, RCS draining was stopped and level was stabilized via the chemical and volume control system (charging and letdown). Condition Report (CR) 2006-7036 was initiated to evaluate the event.
This event was determined to be reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A). The event was reported in accordance with 10 CFR 50.72(b)(3)(iv)(A) via event notification 42399.
BACKGROUND puring the refueling outage, when the Unit 3 startup transformer was removed from service, power to Unit 31was via a back feed from the 240 kV switchyard through the Unit 3 main and auxiliary transformers.
Each Turkey Point unit has two associated EDGs. Technical Specification (TS) Limiting Condition for Operation (LCO) 3.8.1.1.b requires a unit's two ED~s and one of the opposite unit's EDGs to be operable to provide standby electrical power for required equipment in support of plant operation in Modes 1-4. The safety related function of the EDGs is to automatically start and provide power to required safety related loads during a loss of offsite power in order to achieve and maintain safe shutdown of the reactor. TS LCO 3.8.1.2.b.1 requires one EDG associated with a unit to be operable to provide standby electrical power for required equipment in support of safe shutdown in Modes 5 and 6.
The RHR system is designed to remove residual and sensible heat from the core and reduce the temperature of the RCS during the second phase of plant cool down. During the first phase of cool down, the temperature of the RCS is reduced by transferring heat to the steam and power conversion system.U.S. NUCLEAR REGULATORY COMMISSION (7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACLTY NAME (1)
INUMBER LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL REVISION Turkey Point Unit 3 05000250 2006 004 00 Page 3 of 5 NUMBER NUMBE Page 3 of.
TEXT (If mor space Is required, use addtional copies of NRC Forn 38A) (17)
Two RHR pumps and two heat exchangers perform the decay heat removal functions for the reactor. After RCS temperature and pressure have been reduced to 350 degrees F and 450 psig respectively, decay heat removal is initiated by aligning one RHR pump to take suction from the reactor outlet line and discharge through the heat exchangers and into the reactor inlet line. If only one heat exchanger is available, reduction of reactor coolant temperature is accomplished but at a lower rate.
CAUSE OF THE EVENT
T he cause of the event was a vendor human error in the configuration of the auxiliary switch contacts on the 480V LC feeder breaker which went undetected by the vendor test and inspection program and Turkey oint pre-installation checks. Actions from previous events invoked by the vendor were not successful in p reventing this event. The barrier put in place was a verification of the as left auxiliary contact configuration against the customer schematic. The technician performing the work and two independent people performing the verification missed the condition. The vendor reported that the schematic was not part of the verification package for this breaker. However, the as found configuration was included and could have been used for final verification. Although this condition was not a vendor wiring error, the measure put in place should have detected and corrected this condition.
ANALYSIS OF THE EVENT
On March 7, 2006, the 3C 480V LC was removed from service for routine preventive maintenance and breaker exchanges. Included in this scope was the replacement of the 3C 480V LC feeder breaker with a newly refurbished breaker. On March 8,2006, during the restoration of the 3C 480V LC a 3A load sequencer actuation occurred. The 3A sequencer actuation resulted in a loss of power to the 3A 4 kV and 3A 480V LC, and a 3A EDG automatic start. The EDG reenergized the 3A 4 kV bus and 3A 480V LC.
The sequence of events follows:
- The 3A sequencer was in service and enabled.
- The 3C 480V LC was de-energized.
- The 3C 480V LC feeder breaker was racked in and open.
Troubleshooting determined the cause to be a misalignment of the auxiliary switch contact block in the newly refurbished 3C 480V LC feeder breaker. The misalignment caused the auxiliary switch contacts to operate in reverse of their design state. The contacts required to be normally open were closed and vice versa. This condition, in conjunction with the 3C 480V LC being de-energized and the 3C 480V LC feeder breaker being closed, satisfied the sequencer actuation logic.
The vendor's final test and inspection procedure does not require the as left auxiliary contact configuration to be documented and compared with the as found configuration. The procedure only requiresU.S. NUCLEAR REGULATORY COMMISSION (7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
Turkey Point Unit 3 TEXT (If more space is required, use additional copies of NRC Form 366A) I documentation of pass or fail. This does not provide a robust barrier to prevent breakers with incorrect configurations or wiring errors of the auxiliary switch contacts from being returned to the customer.
The pre-installation checks and tests at Turkey Point of refurbished 480V ABB LC breakers do not check or verify the proper operation of all auxiliary switch contacts.
Reportability
A review of the reporting requirements of 10 CFR 50.72 and 10 CFR 50.73 and NRC guidance provided in "Event Reporting Guidelines," 10 CFR 50.72 and 10 CFR 50.73 (NUREG-1022, Rev. 2) was performed for the subject condition. As a result of this review, the condition is reportable as described below.
10 CFR 50.73(a)(2)(iv)(A) requires a licensee event report (LER) to be submitted as follows:
"(A) Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section, except when:
(1) The actuation resulted from and was part of a pre-planned sequence during testing or reactor operation; or (2) The actuation was invalid and; (i) Occurred while the system was properly removed from service; or (ii) Occurred after the safety function had been already completed.
(B) The systems to which the requirements of paragraph (a)(2)(iv)(A) of this section apply are:
(8) Emergency ac electrical power systems, including: emergency diesel generators (EDGs); hydroelectric facilities used in lieu of EDGs at the Oconee Station; and BWR dedicated Division 3 EDGs."
EDGs are included in 10 CFR 50.73(a)(2)(iv)(B) as a system whose actuation is potentially reportable.
Since the actuation of the 3A EDG in response to the loss of power to the 3A 4 kV bus did not result from bWing part of a pre-planned sequence during testing or reactor operation and was a valid actuation, the actuation did not meet the exceptions in 10 CFR 50.73(a)(2)(iv)(A). Therefore, the actuation of the 3A EDG is reportable.
ANALYSIS OF SAFETY SIGNIFICANCE Based on the analysis described below, it is concluded that the health and safety of the public were not affected by this event.
Core cooling was interrupted for approximately seven minutes when the 3A RHR pump lost power due to the loss of the 3A 4 kV bus. Operations personnel entered the appropriate procedures to recover core cooling and restore power. Using the most conservative available indication, RCS temperature increased approximately 25 degrees F while core cooling was being restored by starting the 3B RHR pump. NoU.S. NUCLEAR REGULATORY COMMISSION (7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILTY NME
()
DOKET FACILITY NAUME (1)
NUMBER 2 LER NUMBER (6)
PAGE (3)
YERSEQUENTIAL REVISION Turkey Point Unit 3 05000250 NUMBER NUMBER Page 5 of 5 YE0R RE4
.I TEXT (if more space Is required, use additional copies of NRC Form 366A) (17) inadvertent mode change occurred as sufficient margin was available to the 200 degree F limit for cold shutdown. The 3A EDG automatically started and supplied power to the 3A bus loads until power was restored via an offsite power back feed through the main and auxiliary transformers. The 3A RHR pump was operable and could have been loaded onto the 3A 4 kV bus after the 3A EDG started. The increase in risk due to loss of core cooling is judged to be very small given the availability of the redundant RHR pump and power source and the short period for restoration of cooling.
CORRECTIVE ACTIONS
I The auxiliary switch contact was re-configured and the breaker was returned to service.
- 2. The remaining refurbished breakers being installed during refueling outage U3C22 were reviewed. The review encompassed breakers that have functions performed by auxiliary contacts that would not be i verified by normal breaker cycling. For these breakers, auxiliary contact verification was added to the applicable work orders. No additional discrepancies were found.
- 3. The functions provided by the auxiliary switches in all safety related 4 kV and LC breakers will be reviewed to determine if additional verifications are required.
- 4. Breaker refurbishment standards shall be revised to require the vendor to record as found and as left auxiliary switch configuration and compare the two to ensure proper configuration. This is required for 4 kV, GE, ABB and Siemens breakers and 480V ABB, and Westinghouse (DS, DB) breaker.
- 5. Receipt inspection at Turkey Point will review the overhaul report provided by the vendor for each refurbished breaker and ensure the as left configuration of the auxiliary switches matches the as found configuration or as specified in the purchase order. This will be required for 4 kV, GE and ABB breakers and 480V ABB, and Westinghouse (DS, DB) breakers.
6 Checks of the auxiliary contacts at the secondary disconnects will be added to the applicable plant procedures for refurbished breakers.
ADDITIONAL INFORMATION
ELIS Codes are shown in the format [EUlS: IMEE system identifier (EEIS), component function identifier (INC),
second component function identifier (if appropriate)].
FAILED COMPONENTS IDENTIFIED:
None
SIMILAR EVENTS
None