05000390/LER-2012-005, Regarding Automatic Start of Emergency Diesel Generators Due to Failed Transfer of Power to 6.9kV Shutdown Board
| ML12349A317 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 12/15/2012 |
| From: | Grissette D Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| LER 12-005-00 | |
| Download: ML12349A317 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(ix)(A) |
| 3902012005R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 December 15, 2012 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Subject:
10 cFR 50.73 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No.50-390 Licensee Event Report 39012012-005, Automatic Start of Emergency Diesel Generators due to Failed Transfer of Power to 6.9kV Shutdown Board Encfosed find Licensee Event Report (LER) 39012012-005 that is being submitted pursuant to 10 CFR 50.73(a)(2)(ivXA). This LER describes the details concerning an automatic start of the four Watts Bar Nuclear WBN) Emergency Diesel Generators as a result of a failed transfer of power supply to a 6.9kV Shutdown Board.
In accordance with 10 CFR 50.4, copies of this LER are being forwarded to the Nuclear Regulatory Commission Regional Office, Region ll and the Senior Resident Inspector. Should you have questions regarding this submittal, please contact Donna Guinn, WBN Site Licensing Manager, at(423) 365-1589.
Tennessee Valley Authority makes no regulatory commitments in this letter.
Respectfully,
\\*{f,M*,
D. E. Grissette Site Vice President Watts Bar Nuclear Plant Enclosure cc: see Page 2
U.S. Nuclear Regulatory Commission Licensee Event Report 39012012-005 Page2 December 15,2012 Enclosure cc (Enclosure):
NRC RegionalAdministrator - Region ll NRC Senior Resident Inspector - Wafts Bar Nuclear Plant Unit 1
U.S. Nuclear Regulatory Commission Licensee Event Report 3901201 2-005 Page 3 December 15, 2012 DKG: TPM Enclosure bcc (Enclosure):
NRC Project Manager - Watts Bar Nuclear Plant G. Arent T. J. Carter G.M. Cook S.M. Douglas B. M. Duckett K. D. Dutton D. H. Gronek D. K. Guinn D. E. Grissette D. E. Jernigan J. A. Perrel W. J. Pierce W. L. Prevatt J. W. Shea P. D. Swafford E. J. Vigluicci NSRB Support (T. J. Bradshaw)
EDMS, WT CA.K I NPO: LEREvents@inpo.org
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (10-2010)
LTGENSEE EVENT REPORT (LER)
(See reverse for required number of digits/characters for each block)
APPROVED BY OMB: NO.3150-0104 EXPIRES: 1O13112O13
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME Watts Bar Nuclear Plant, Unit 1
- 2. DOCKET NUMBER 05000390
- 3. PAGE 10Fs
- 4. TITLE Automatic Start of Emergency Diesel Generators due to Failed Transfer of Power to 6.9kV Shutdown Board
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REV NO.
MONTH DAY YEAR FACIL]TY NAME N/A DOCKET NUMBER N/A 10 16 2012 2012 -005-0 12 15 2012 FACILITY NAME N/A DOCKET NUMBER N/A
- 9. OPERATING MODE 5
tr 50.73(ax2xD(c) tr s0.73(aX2XiiXA) n s0.73(aX2XiiXB) n s0.73(ax2xiii) tr 50.73(a)(2)(iv)(A) tr s0.73(aX2XvXA) n 50.73(aX2XvXB) tr 50.73(aX2XvXc) tr 50.73(aX2XvXD)
- 11. THIS REPoRT lS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR$: (Check all that apply) tr 2o.z2o1(b) tr 2o.2zo1(d) n 2a.z2o3(aX1) tr 2o.22o3(a)(2)(i) n 2o.2zo3(a)(2)(iD tr 2o.2zo3(aX2Xiii) tr zo.22o3(a)(2)(iv) tr zo.2zo3(a)(2)(v) tr 2o.2zo3(aX2Xvi) n 2o.z2o3(aX3Xi) tr 2o.2zo3(a)(3)(ii) tr 2o.22o3(aX4) tr 50.30(cX1 XIXA) tr 50.36(cxl XiiXA) tr so.3o(c)(2) n 50.46(ax3)(i1 n 50.73(aX2XiXA) fl 50.73(aX2XiXB) tr 50.73(aX2Xvii)
El 50.73(aX2XviiiXA) tr 50.73(a)(2)(viii)(B) tr 50.73(a)(2)(ix)(A) tl 50.73(aX2Xx) tr r3.r1(aX4) tr r3.r1(aXs) tr orHER Speciff in Abstract below or in NRC Form 3664
- 10. POWER LEVEL 000
- 12. LICENSEE CONTAGT FOR THIS LER FACILITY NAME Tommy Morgan, Watts Bar Site Licensing Engineer TELEPHONE NUMBER (lnclude Area Code) 423-365-1401CAUSE SYSTEM COMPONENT MANU-FACTURER REPORTABLE TO EPIX
CAUSE
SYSTEM COMPONENT MANU.
FACTURER REPORTABLE TO EPIX
- 14. SUPPLEMENTAL REPORT EXPECTED El VES (tf yes, complete 15. EXPECTED SUBM/SSION DATE)
EI No
- 15. EXPECTED SUBMISSION DATE TUONTI-I I DAY YEAR BSTRACT (Linit to 1z100 spaces, i.e., approximately 15 single-spaced typewiften lines)
On October 16,2A12, at 2330 EDT, Watts Bar Nuclear Plant (WBN-1) licensed operators attempted a manual fast transfer of the 1B-B 6.9kV Shutdown Board (SDBD) from the normal feeder breaker to the alternate feeder breaker. The transfer was not successful, resulting in the automatic start of the four Emergency Diesel Generators (EDGs). After the 1&B 6.9kV SDBD de-energized and the loads were shed, the alternate feeder breaker closed and re-energized the 1B-B 6.9kV SDBD. The loads supplied by the 1B-B 6.9kV SDBD were subsequently reconnected, and required tests were successfully completed to ensure operability of the 1B-B 6.9KV SDBD.
At the time of the event, WBN-1 was in MODE 5 following a refueling outage. Operations personnel promptly entered the appropriate response procedure and re-established power to required loads. Required safety systems functioned as designed. This condition did not adversely affect the safe operation of the plant or the health and safety of the public.
The cause of this event was that plant operators did not ensure the alternate feeder breaker hand-switch was held firmly in the "closed" position while initiating the fast board transfer.
This report is being submitted in accordance with 10 CFR 50.73(aX2Xiv)(A), a condition that resulted in automatic actuation of the EDGs.
NRC FORM 366 (10-2010)
Alltimes are approximate and Eastern Daylight Savings Time (EDT) unless noted otherwise.
I.
PLANT CONDITIONS
Watts Bar Nuclear Plant (WBN) Unit 1 was in MODE 5, 0% Rated Thermal Power (RTP) following the 11th refueling outage (1R11). At the time of the event, WBN-1 was reliant on train A safety equipment.
II.
DESCRIPTION OF EVENT
Background:
The WBN-1 plant alternating current (AC) Electrical Power Distribution System sources consist of the offsite power sources (prefened power sources, normal and alternate(s)), and the onsite standby power sources (train A and B emergency diesel generatorc (EDGs)). The design of the AC electrical power system provides independence and redundancy to ensure an available source of power to the Engineered Safety Feature (ESF) systems.
The onsite Class 1E AC Distribution System supplies electrical power to four power trains, shared between the two units, with each train powered by an independent Class 1E 6.9 kV Shutdown Board (SDBD). Power trains 1A and 2A comprise load group A, and power trains 1B and 28 comprise load Group B. Two EDGs associated with one load group can provide all safety related functions to mitigate a loss-of-coolant accident (LOCA) in one unit and safely shutdown the opposite unit. The A and B train ESF systems each provide for the minimum safety functions necessary to shut down the plant and maintain it in a safe shutdown condition.
An EDG starts automatically on a safety injection (Sl) signal or on a 6.9 kV SDBD degraded voltage or loss-of-voltage signal. Afterthe EDG has started, it will automatically tie to its respective 6.9 kV SDBD after offsite power is tripped as a consequence of 6.9 kV SDBD loss-of-voltage or degraded voltage, independent of or coincident with an Sl signal. Following the trip of offsite power, a loss of-voltage signal strips (sheds) nonpermanent loads from the 6.9 kV SDBD. When the EDG is tied to the 6.9 kV shutdown board, loads are then sequentially connected to its respective 6.9 kV SDBD by the automatic sequencer. The sequencing logic controls the permissive and starting signals to motor breakers to prevent overloading the EDG by automatic load application.
A.
Event:
On October 16,2012, at 2330, WBN-1 control room operators, in the conduct of scheduled maintenance activities, attempted a manual fast transfer of the 1B-B 6.9kV SDBD from the normal feeder breaker (preferred offsite power source) to the alternate feeder breaker (altemate preferred offsite powersource). The transferwas unsuccessful and resulted in a momentary loss of power to the 6.9kV SDBD. The momentary loss of power caused the supplied loads to be shed and initiated a designed loss-of-voltage signal that resulted in the automatic start of the four EDGs [EllS Code EK].
Approximately 6 seconds after the 1B-B 6.gkv SDBD de-energized, the alternate feeder breaker closed-in and re-energized the 1B-B 6.9kV SDBD. The EDGs did not connect to the 1B-B SDBD because the momentary disruption of power did not allow sufficient time for the EDGs to reach nominal voltage and frequency and tie to the 1B-B SDBD.
NRC FORM 3664 (10-2010)
ll.
DESCRIPTION OF EVENT (continued):
Control room operators promptly entered the appropriate response procedure and re-established power to required loads and completed required testing to ensure operability of the 1B-B 6.9kV SDBD. The required safety systems functioned as designed.
B.
Inoperable Structures, Components, or Systems that Contributed to the Event None C.
Dates and Times of Major Occurrences Date October 16,2012 October 16,2012 October 16,2412 October 16,2012 October 16,2012 October 16,2012 October 17,2012 October 17,2012 October 17,2012 October 17,2012 October 17,2012 October 17.2012 Time (EDT) 23:30:00 23:30:01 23:30:03 23:30:06 23:42:00 23:57:49 00:24:19 00:33:34 00:41 :03 00:51:37 03:00:00 05:46:00 Event Control room operators attempt to transfer the 1B-B 6.9kV SDBD to the alternate feeder breaker. Momentary loss of power to the 1B-B 6.9kV SDBD occurs EDGs started on loss of power to the 1B-B 6.9kV SDBD Loads supplied by 1B-B 6.9kV SDBD are shed Alternate feeder breaker re-energizes 1B-B 6.9kV SDBD Control room operators enter the response procedure Control room operators restart Train B spent fuel pool cooling per procedure Control room operators secure EDG 1A-A Control room operators secure EDG 2A-A Control room operators secure EDG 1B-B Control room operators secure EDG 2B-B Control room operators re-Gonnect loads to the 1B-B 6.9 kV SDBD.
Control room operators notify NRC (Event Number: 48414)
Functions Affected D.
Other Systems or Secondary None E.
F.
Method of Discovery
This event occurred during the performance scheduled maintenance activities on the 1B-B 6.9kV SDBD. During the maintenance activity, control room operators observed that the transfer of the 1B-B 6.9kv SDBD from the normal breaker to the altemate breaker was unsuccessful and that the momentary loss of power caused supported loads to be shed and the four EDGs to start.
Operator Actions
Control room operators entered the appropriate procedure in response to the momentary loss of power to the 1B-B 6.9kV SDBD. The loads that were shed from the 1B-B 6.9kV SDBD during the failed transfer were restored and the four EDGs were secured.
ll.
DESCRIPTION OF EVENT (continued):
G.
Safety System Responses Following the loss-of-voltage to the 1B-B SDBD, nonpermanent loads were shed and the four EDGs started. The EDGs did not connect to the 1B-B 6.9 kV SDBD because the alternate supply connected before the EDGs reached nominal voltage and frequency.
III.
CAUSE OF EVENT
The cause of this event was that control room operators did not ensure the alternate feeder breaker hand-switch was held firmly in the 'closed' position while initiating the fast board transfer.
IV.
ANALYSIS OF THE EVENT
During this event, WBN-1 was in MODE 5 following a refueling outage and the 1B-B 6.9kV SDBD was not being relied upon for safety systems. Power supplied to the 1B-B 6.9kV SDBD was restored through the alternate feeder breaker six seconds after the failed transfer. The functionality of the 1B-B 6.9kV SDBD was restored afier the loads were reconnected. Required testing to ensure operability of the 1B-B 6.9kV SDBD was successfully completed. A post event review did not identify any adverse conditions relating to the offsite power sources, the onsite standby power sources or the related control circuits.
WBN's investigation revealed the event was the result of an isolated human performance enor. The board transfer process requires the control room operator to place and hold the hand-switch for the alternate feeder breaker firmly in the "closed" position, then to place the hand-switch for the normal feeder breaker in the 'trip" position. The control room operator responsible for performing the transfer did not firmly hold the alternate feeder breaker hqnd-switch in the "closed" position during the tripping of the normal feeder breaker, resulting in the momentary loss of power to the 1B-B 6.9kV SDBD. Control room operatos have re-performed the transfer without subsequent human performance issues. The investigation did not conclude that time pressure or situational pressure contributed to this event.
V.
ASSESSMENT OF SAFEW CONSEQUENCES During this event, WBN-1 was in MODE 5 following a refueling outage and the 1B-B 6.9kV SDBD was not being relied upon to support needed safety systems. Power supplied to the 1B-B 6.9kV SDBD was restored through the altemate feeder breaker six seconds after the failed transfer. The functionality of the 1B-B 6.9kV SDBD was restored after the loads were reconnected. Required testing to ensure operability of the 1B-B SDBD was successfully completed and a post event review did not identify any adverse conditions relating to the offsite power sources, the onsite standby power sources or the related control circuits.
There are three additional 6.9kV SDBDs at WBN. These three 6.9kV SDBDs passed surveillance requirement testing to demonstrate capability to automatically and manually transfer power from normal to altemate supply prior to the October 16,2012 event and were capable of performing their safety function. This event did not adversely affect the safe operation of the plant or the health and safety of the public.
VI.
CORRECTIVE ACTIONS
A.
lmmediate Gorrective Actions The 1B-B 6.9kV SDBD was restored using the appropriate response procedure.
B.
Corrective Actions to Prevent Recunence The WBN procedure that describes generic equipment operating guidelines will be revised to provide special instructions on manipulation of switches for board transfers to ensure that switches are firmly held in place.
VII. ADDITIONAL INFORMATION
A.
Failed Components None B.
Previous LERs on Similar Events LER 390/2009-002 reported an event on July 17,2009 where the four diesel generators actuated due to a loss of power to the 2B-B 6.9kV SDBD. The cause of the event was a misaligned breaker actuation arm which prevented the proper positioning of the fast transfer microsivitch.
The previous event did not involve the same underlying concern or reason as this event, such as the same root cause, failure, or sequence of events.
C.
Additionallnformation None D.
Safety System Functional Failure None E.
Loss of Normal Heat Removal Consideration None
VIII. COMMITMENTS
None