ML12044A184
| ML12044A184 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 02/10/2012 |
| From: | Feintuch K Division of Operating Reactor Licensing |
| To: | Browning T, Byrne T Florida Power & Light Co |
| References | |
| Download: ML12044A184 (25) | |
Text
NRR-PMDAPEm Resource From: Feintuch, Karl Sent: Friday, February 10, 2012 12:53 PM To: Browning, Tony; Byrne, Thomas
Subject:
Operating Experience regarding Byron Loss-of-offsite-power event - Duane Arnold notification Attachments: Beaver Valley LER.PDF; Fitz LER.PDF; NMP LER.PDF; EN 7624 Byron 2.pdf; EN 7636 Byron.pdf (Intended for Tony; sent to Tom if Tony is traveling early next week)
Attached for your information are event notifications concerning the recent Byron loss of offsite power and related LERs at other plants. No action is required on your part, and the information is being provided for awareness purposes. As I understand it, INPO is also contacting licensees regarding these events.
Let me know if you have any questions.
Karl Feintuch USNRC 301-415-3079 1
Hearing Identifier: NRR_PMDA Email Number: 266 Mail Envelope Properties (Karl.Feintuch@nrc.gov20120210125300)
Subject:
Operating Experience regarding Byron Loss-of-offsite-power event - Duane Arnold notification Sent Date: 2/10/2012 12:53:02 PM Received Date: 2/10/2012 12:53:00 PM From: Feintuch, Karl Created By: Karl.Feintuch@nrc.gov Recipients:
"Browning, Tony" <Tony.Browning@fpl.com>
Tracking Status: None "Byrne, Thomas" <Thomas.Byrne@fpl.com>
Tracking Status: None Post Office:
Files Size Date & Time MESSAGE 499 2/10/2012 12:53:00 PM Beaver Valley LER.PDF 617750 Fitz LER.PDF 365676 NMP LER.PDF 246305 EN 7624 Byron 2.pdf 92446 EN 7636 Byron.pdf 102776 Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:
Recipients Received:
Power Reactor Event Number: 47624 Facility: BYRON Notification Date: 01/30/2012 Region: 3 State: IL Notification Time: 11:39 [ET]
Unit: [ ] [2] [ ] Event Date: 01/30/2012 RX Type: [1] W-4-LP,[2] W-4-LP Event Time: 10:01 [CST]
NRC Notified By: LEO WEHNER Last Update Date: 01/31/2012 HQ OPS Officer: JOHN KNOKE Emergency Class: UNUSUAL EVENT Person (Organization):
10 CFR Section: JAMNES CAMERON (R3DO) 50.72(a) (1) (i) - EMERGENCY DECLARED CYNTHIA PEDERSON (R3) 50.72(b)(2)(iv)(B) - RPS ACTUATION - CRITICAL BRUCE BOGER (ET) 50.72(b)(2)(i) - PLANT S/D REQD BY TS JEFFERY GRANT (IRD) 50.72(b)(3)(iv)(A) - VALID SPECIF SYS ACTUATION SIL MOUVONE (DOE)
DEBBY HASSEL (DHS)
LOU BURCKANT (FEMA)
MIKE BEVERLY (USDA)
Initial RX Current Unit SCRAM Code RX CRIT Initial PWR Mode PWR Current RX Mode Power 2 A/R Y 100 0 Hot Standby Operation Event Text UNUSUAL EVENT DUE TO LOSS OF OFFSITE POWER GREATER THAN 15 MINUTES At 1101 EST, Byron Unit-2 experienced a reactor trip due to RCP undervoltage. All rods fully inserted, MSIV's were manually closed and decay heat is being removed by Auxiliary Feedwater pumps running and steam leaving via atmospheric relief valves. The unit is currently in a natural circulation cooldown with the diesels supplying station emergency loads. Licensee will be cooling the plant down to Mode 5.
At 1118 EST, Byron declared an Unusual Event due to a loss of offsite power on Unit 2 from a faulted Station Auxiliary Transformer (SAT). The faulted SAT caused both 6.9 kV and 4.1 kV bus voltage to drop. Smoke was observed coming from the SAT with no visible flames being apparent.
This caused bus loads to trip without a complete loss of ESF busses 241 and 242. These buses were manually disconnected from the SAT, which transferred the load to the emergency diesel generators 2A and 2B. Both diesel generators started and loaded without incident. Offsite assistance was requested from the local fire department as a precaution.
The licensee is also declaring notification for 10 CFR 50.72(b)(3)(v)(D)
Unit 1 is not being affected by this event and remains at 100% power.
The licensee has notified the NRC Resident Inspector.
- UPDATE FROM GREG BALESTRIERI TO JOHN KNOKE AT 2119 EST ON 01/31/12 * *
"At 2000 CST on 1/31/12, Byron terminated their Unusual Event due to the Loss of Offsite Power to Unit 2. Switchyard repairs were completed and offsite power has been restored to essential busses 241 and 242 thru System Auxiliary Transformers 242-1 and 242-2. Unit 2 Emergency Diesel Generators have been shutdown."
The licensee is citing classification 10 CFR 50.72(c)(1)(iii)
The licensee has notified the NRC Resident Inspector. Notified R3DO (James Cameron), NRR EO (Louise Lund), IRD MOC (Scott Morris), DHS (Konopka) and FEMA (Hollis). Licensee may issue a press release.
Power Reactor Event Number: 47636 Facility: BYRON Notification Date: 02/03/2012 Region: 3 State: IL Notification Time: 22:10 [ET]
Unit: [1] [2] [ ] Event Date: 02/03/2012 RX Type: [1] W-4-LP,[2] W-4-LP Event Time: [CST]
NRC Notified By: MIKE LINDEMANN Last Update Date: 02/03/2012 HQ OPS Officer: DONALD NORWOOD Emergency Class: NON EMERGENCY Person (Organization):
10 CFR Section: JAMNES CAMERON (R3DO)
OTHER UNSPEC REQMNT SCRAM Initial Current Unit Code RX CRIT PWR Initial RX Mode PWR Current RX Mode 1 N Y 100 Power Operation 100 Power Operation 2 N N 0 Cold Shutdown 0 Cold Shutdown Event Text VOLUNTARY REPORT - DESIGN VULNERABILITY IN 4.16kV BUS UNDER-VOLTAGE SCHEME "On January 30, 2012, a design vulnerability was discovered at Byron and Braidwood stations in the Engineered Safety Feature 4.16kV bus under-voltage protection scheme for Byron Station Units 1 and 2. Specifically a voltage unbalance created by an open circuit of either the A or C phase from the offsite grid to the System Auxiliary Transformers (SAT) is not designed to actuate the protective relays on the 4.16kV safety bus that provides isolation from the offsite grid and the automatic start and loading of the emergency onsite diesel generators.
"Two under-voltage relays are provided on each 4.16kV safety bus, which are combined in a two out of two logic to generate a loss of power signal. The relays are sensing voltage between two phases (i.e., A&B and B&C). An open circuit condition on the C phase or the A phase would not satisfy the two out of two logic. This condition results in both 4.16kV safety buses remaining energized with a bus undervoltage situation and results in equipment protective devices actuating from over-current conditions.
"This configuration is a non-conforming condition in that the design of the under-voltage relays and logic was intended to identify degraded grid conditions, not loss of a single phase. With an open circuit on the A or C phase from the grid to the SATs, during normal operations, operators have to diagnose the condition and manually isolate safety buses from offsite power which would automatically start and load the emergency diesel generators. During a design basis event concurrent with an open circuit on A or C phase from the grid to the SATs, analysis performed to date indicates that starting of the ECCS loads would have caused the bus voltage to decrease sufficiently to actuate the under-voltage protective relays and restore cooling with emergency onsite power without challenging fuel design limits.
"The 4.16kV safety bus under-voltage protection scheme at Byron and Braidwood is believed to be a typical industry design. This design issue is being evaluated at the other Exelon stations. The results of this evaluation will be shared with the NRC. Therefore, this condition is being reported as a voluntary notification due to its potential generic industry applicability."
The licensee notified the NRC Resident Inspector.
Power Reactor Event Number: 47637 Facility: BRAIDWOOD Notification Date: 02/03/2012 Region: 3 State: IL Notification Time: 22:10 [ET]
Unit: [1] [2] [ ] Event Date: 02/03/2012 RX Type: [1] W-4-LP,[2] W-4-LP Event Time: [CST]
NRC Notified By: MIKE LINDEMAN Last Update Date: 02/03/2012 HQ OPS Officer: DONALD NORWOOD Emergency Class: NON EMERGENCY Person (Organization):
10 CFR Section: JAMNES CAMERON (R3DO)
OTHER UNSPEC REQMNT SCRAM Initial Current Unit Code RX CRIT PWR Initial RX Mode PWR Current RX Mode 1 N Y 100 Power Operation 100 Power Operation 2 N Y 100 Power Operation 100 Power Operation Event Text VOLUNTARY REPORT - DESIGN VULNERABILITY IN 4.16kV BUS UNDER-VOLTAGE SCHEME "On January 30, 2012, a design vulnerability was discovered at Byron and Braidwood stations in the Engineered Safety Feature 4.16kV bus under-voltage protection scheme for Braidwood Station Units 1 and 2. Specifically a voltage unbalance created by an open circuit of either the A or C phase from the offsite grid to the System Auxiliary Transformers (SAT) is not designed to actuate the protective relays on the 4.16kV safety bus that provides isolation from the offsite grid and the automatic start and loading of the emergency onsite diesel generators.
"Two under-voltage relays are provided on each 4.16kV safety bus, which are combined in a two out of two logic to generate a loss of power signal. The relays are sensing voltage between two phases (i.e., A&B and B&C). An open circuit condition on the C phase or the A phase would not satisfy the two out of two logic. This condition results in both 4.16kV safety buses remaining energized with a bus undervoltage situation and results in equipment protective devices actuating from over-current conditions.
"This configuration is a non-conforming condition in that the design of the under-voltage relays and logic was intended to identify degraded grid conditions, not loss of a single phase. With an open circuit on the A or C phase from the grid to the SATs, during normal operations, operators have to diagnose the condition and manually isolate safety buses from offsite power which would automatically start and load the emergency diesel generators. During a design basis event concurrent with an open circuit on A or C phase from the grid to the SATs, analysis performed to date indicates that starting of the ECCS loads would have caused the bus voltage to decrease sufficiently to actuate the under-voltage protective relays and restore cooling with emergency onsite power without challenging fuel design limits.
"The 4.16kV safety bus under-voltage protection scheme at Byron and Braidwood is believed to be a typical industry design. This design issue is being evaluated at the other Exelon stations. The results of this evaluation will be shared with the NRC. Therefore, this condition is being reported as a voluntary notification due to its potential generic industry applicability."
The licensee notified the NRC Resident Inspector.