05000390/LER-2002-004, Partial Loss of Offsite Power
| ML023190082 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 11/12/2002 |
| From: | Lagergren W Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 02-004-00 | |
| Download: ML023190082 (9) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3902002004R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spnng City, Tennessee 37381-2000 William R. Lagergren, Jr Site Vice President, Watts Bar Nuclear Plant NOV 1 2 20D2 U.S. Nuclear Regulatory Commission 10 CFR 50.73 ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:
TENNESSEE VALLEY AUTHORITY - WATTS BAR NUCLEAR PLANT (WBN)
UNIT 1 - DOCKET NO. 50-390 - FACILITY OPERATING LICENSE NPF LICENSEE EVENT REPORT (LER) 50-390/2002-004 This submittal provides Licensee Event Report 2002-002. This LER addresses an event where one of the two offsite power feeds was lost for a brief period. The interruption of the offsite supply resulted in the actuation of engineered safety feature equipment and due to this, the event is being reported under 10 CFR 50.73(a)(2)(iv)(A)
There are no regulatory commitments in this submittal. Should there be questions regarding this event, please call P. L. Pace at (423) 365-1824.
Sincerely, W. R. Lagergren Enclosure cc (Enclosure):
P.Mnted w.w recyde paper
U.S. Nuclear Regulatory Commission Page 2 INOV 12 '202 cc (Enclosure):
NRC Resident Inspector Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, Tennessee 37381 Mr. L. Mark Padovan, Senior Project Manager U.S. Nuclear Regulatory Commission MS 08G9 One White Flint North 11555 Rockville Pike Rockville, Maryland 20852-2738 U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303
Abstract
l11111v While operating at 100% power on September 21, 2002, Watts Bar Unit 1 experienced a momentary loss of the 161 kV offsite power feed to Common Station Service Transformer (CSST) D. WBN's two offsite power supplies are fed from a remote switchyard located at the Watts Bar hydroelectric plant. The affected offsite power source through CSST D is the primary power source for 6900V Shutdown Boards 1 B-B and 2B-B. The partial loss of offsite power was caused by the inadvertent manual operation of a breaker at the hydroelectric plant switchyard. The opening of the breaker occurred at 11:00:20 (EDT) and the breaker was reset to provide offsite power at 11:00:34 (EDT). Due to this event, and the loss of the primary feed to the shutdown boards, a valid engineered safety function (ESF) actuation occurred which started all four of the standby diesel generators (DGs), along with, as designed, the 1 B-B Motor Driven Auxiliary Feedwater (AFW) Pump and the Turbine Driven AFW Pump. The DGs provided power to the affected Shutdown Boards and other required blackout loads during the event.
NRC FORMt 366 (7-2001)U.S. NUCLEAR REGULATORY COMMISSION(4-95)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET i LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL REVISION Watts Bar Nuclear Plant (WBN) Unit 1 105000390 NUMBER 2 OF 7 l
2002--
004 00 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
PLANT CONDITION(S)
At the time of event, Watts Bar Unit 1 was in Mode 1 at 100 percent reactor power.
II.
DESCRIPTION OF EVENT
A.
Event:
While operating at 100% power on September 21, 2002, Watts Bar Unit 1 experienced a momentary loss of the 161kV offsite power feed to Common Station Service Transformer (CSST) D (Energy Industry Identification System (EIIS) Code XFMR). WBN's two offsite power supplies are fed from a remote switchyard located at the Watts Bar hydroelectric plant approximately 1.5 miles from WBN on the same reservation. The affected offsite power source through CSST D is the primary power sources for 6900V Shutdown Boards 11B-B and 2B-B. The partial loss of offsite power was caused by the inadvertent manual operation of a breaker(Breaker 934) at the hydroelectric plant switchyard by a hydro plant operator. The opening of the breaker occurred at 11:00:20 (EDT) and the breaker was reset to provide offsite power at 11:00:34 (EDT).
Due to this event, and the loss of the primary feed to the shutdown boards, a valid engineered safety function (ESF) actuation occurred which started all four of the standby diesel generators (DGs) (EIIS Code EK/DG), along with, as designed, the 11B-B Motor Driven Auxiliary Feedwater (AFW) Pump (EIIS Code BA/P) and the Turbine Driven AFW Pump (EIIS Code BA/TRB).
The DGs provided power to the affected Shutdown Boards and other required blackout loads during the event.
The event was documented in the TVA corrective action program as problem evaluation report (PER) 02-013430-000.
B.
Inoperable Structures, Components, or Systems that Contributed to the Event:
There were no Inoperable Structures, Components, or Systems that Contributed to the Event.U.S. NUCLEAR REGULATORY COMMISSION(4-95)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR l SEQUENTIAL REVISION Watts Bar Nuclear Plant (WBN) Unit 1 05000390 NUMBER 3 OF 7 l
2002--
004 00 TEXT (If more space is required, use additional copies of NRC Formn 366A) (17)
C.
Dates and Approximate Times of Maior Occurrences:
September 21, 2002 l
11:00:20 EDT The 161 kV offsite power feed to CSST D was momentarily lost.
11:00:34 EDT 11:01 EDT 11:44 EDT 15:10 EDT The breaker at the hydro switchyard was reset to provide offsite power to CSST D.
Entered LCO 3.8.9 due to the loss of the offsite power feed to CSST D and the shedding of various plant components/systems.
The hydro switchyard components affected by the manipulation of the breaker are restored to their normal configuration.
Power was restored to the components/systems affected by the partial loss of offsite power and LCO 3.8.9 was exited.
D.
Other Systems or Secondary Functions Affected
The WBN onsite standby ac power system (diesel generators) is a safety-related system which is designed to supply power for ac-powered electrical devices essential to safety. The primary impact this event had on plant systems occurred when various non-essential components (loads) were shed as a result of the diesel generators supplying power to 6900V Shutdown Boards 13B-B and 2B-B. The shedding of the loads occurred as designed with one exception. Breaker 1-BKR-62-228/1 supplies power to a heater for the Boric Acid Tank and failed to open as part of the load shedding process. After identification, the breaker was configured open by the Operations staff until repairs were made. This problem was documented in the TVA corrective action program as problem evaluation report (PER) 02-013470-000.
E.
Method of Discovery
The plant responded as designed to the partial loss of the offsite power supply.U.S. NUCLEAR REGULATORY COMMISSION(4-95)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL REVISION Watts Bar Nuclear Plant (WBN) Unit 1 05000390 NUMBER 4 OF 7 l1 2002 --
004 00 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
F.
Operator Actions
Abnormal Operating Instruction (AOl) 35, 'Loss of Offsite Power,' directs the response to events like the one experienced on September 21, 2002.
The operations staff properly followed the controls defined in Section 3.2,
'Operator Actions (Loss Of One 161 KV Power Supply)to respond to the power interruption.
G.
Safety System Responses:
As designed, the 1 B-B Motor Driven Auxiliary Feedwater (AFW) Pump and the Turbine Driven AFW Pump started along with the four emergency diesel generators (DGs).
DGs 1 B-B and 2B-B connected and supplied power to 6.9 kV Shutdown Boards 1B-B and 2B-B.
Once this occurred and voltage returned to the shutdown buses, the automatic load sequence logic connected the essential loads in the proper sequence. In addition, the load shed logic removed (tripped) the non-essential loads to assure that the loading on each of the DGs was within the ratings of the generator.
One non-essential component (load) was not removed from the 1B-B DG.
This was due to the breaker feeding the Boric Acid Tank heaterfailing to open. This heater is rated at 22.5 kW and because it remained energized, the load to DG 1 B-B was increased by 22.5 kW. A review of the maximum steady state loading composite summary for the 1B-BDG found sufficient margin was available to support all required loads with the ratings of the generator not being exceeded.
Ill.
CAUSE OF THE EVENT
A.
Immediate Cause:
The cause of the momentary partial loss of offsite power is discussed below in Part B, 'Root Cause."
B.
Root Cause:
The momentary partial loss of offsite power was caused by the inadvertent manual operation of a breaker (Breaker 934) at the hydroelectric plant.U.S. NUCLEAR REGULATORY COMMISSION(4-95)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL REVISION Watts Bar Nuclear Plant (WBN) Unit 1 05000390 NUMBER 5 OF 7 2002--
004 00 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
C.
Contributing Factor:
Contributing to the cause of this event are the following three issues:
- 1.
On September 16, 2002, Breaker 968 was removed from service for a scheduled internal inspection. Dispatcher switching was performed as written to accomplish this task. However, the switching instructions for removing Breaker 968 from service set up the Bus 2-2 relaying scheme incorrectly. The resulting current imbalance was not detected until the hydro Operator placed generator Number 3 online on September 21, 2002. The current imbalance resulted in the operation of the differential relays on Bus 2-2 and a subsequent disagreement alarm in the hydro plant control room.
- 2.
The red (breaker closed/energized) indicator light for Breaker 934 was not working. This resulted in all three lights associated with the breaker not being lit during the time the disagreement alarm was sounding. At this time, the hydro plant operator assumed the disagreement light for Breaker 934 was burned out and he also thought that the disagreement lights had been cleared, but the audible alarm continued in the Control Room.
Based on this, the hydro plant Operator opened Breaker 934.
- 3.
Prior to opening Breaker 934, the hydro plant Operator did not take the required time to ensure that the bus feeding WBN was deenergized.
Once Breaker 934 was opened the operator reviewed the available indicators and realized that he hadinterrupted the 161 kV power feed to WBN.
He responded by quickly closing Breaker 934.
Had he reviewed other available indicators first, it would have been evident that Breaker 934 was closed and was not the cause of the disagreement alarm.
IV.
ASSESSMENT OF SAFETY CONSEQUENCES
The interruption in one of the 161 kV offsite power feeds from the hydro plant switchyard was very brief. Therefore, the response of WBN to the momentary partial loss of 161 kV power is the primary safety consideration.
As indicated previously, the plant systems/components responded as designed to the partial loss of 161 kV power. The one exception was the failure to open of the breaker feeding the Boric Acid Tank heater. This heater is rated at 22.5 kW and because it remainedenergized, the load toU.S. NUCLEAR REGULATORY COMMISSION(4-95)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL l REVISION Watts Bar Nuclear Plant (WBN) Unit 1 05000390 NUMBER 6 OF 7 l
2002--
004 00 TEXT (If more space Is required, use additional copies of NRC Form 366A) (17) diesel generator 1B-B was increased by 22.5 kW. A review of the maximum steady state loading composite summary for the 1 B-B diesel generator identified sufficient margin was available to support all required loadswith the ratings of the generator not being exceeded. Considering this, the impact of the event was minimal.
V.
CORRECTIVE ACTIONS
A.
Immediate Corrective Actions
- 1.
Refresher training was provided to six hydro plant Operators in the areas of:
a.
The significance of the loss of either of the WBN offsite power feeds.
b.
The need to verify that both the disagreement white light and the control panel meters indicate that a breaker has tripped.
c.
The expectation of the performance of a control board lamp walk down at the end of each shiftwas reinforced.
- 2.
Tape was installed on the control boards to outline the controls for the WBN offsite power breakers as a reminder to the operators that the manipulation of a breaker inside the tape could affectWWBN.
Note:
The Watts Bar hydro plant experienced a fire on September 27, 2002.
The fire damaged the electrical controls in the plant and resulted in the loss of both offsite 161 kV power feeds to WBN. The impact of the fire on WBN is being addressed in TVA's corrective action program as PER 02-013616. The fire event resulted in the declaration of a Notification of Unusual Event (NOUE) and will be reported under 10 CFR 50.73 as LER 2002-05.
B.
Corrective Actions to Prevent Recurrence:
NoneU.S. NUCLEAR REGULATORY COMMISSION(4-95)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL l REVISION Watts Bar Nuclear Plant (WBN) Unit 1 05000390 NUMBER l
7 OF 7 2002--
004 00 TEXT (If more space is required, use additional copies of NRC Form 366A) {17)
VI.
ADDITIONAL INFORMATION
A.
Failed Components:
There were no failed components involved in this LER.
B.
Previous LERs on Similar Events:
There have been no previous LERs for WBN that were caused by a loss of offsite power.
C.
Additional Information
None D.
Safety System Functional Failure Consideration:
This event is not considered a safety system functional failure in accordance with NEI 99-02.
E.
Loss Of Normal Heat Removal Consideration:
Because the event did not involve a reactor trip, it is not considered a scram with loss of normal heat removal in accordance with NEI 99-02.
VII.
COMMITMENTS
None.