05000331/LER-2007-009, Loss of Essential Bus Resulted in a Loss of Safety Function
| ML073480177 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 12/04/2007 |
| From: | Richard Anderson Duane Arnold |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NG-07-0983 LER 07-009-00 | |
| Download: ML073480177 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3312007009R00 - NRC Website | |
text
0 FPL Energy.,
Duane Arnold Energy Center FPL Energy Duane Arnold, LLC 3277 DAEC Road Palo, Iowa 52324 December 4, 2007 NG-07-0983 10 CFR 50.73 U.S. Nuclear Regulatory Commission c-AttW*:-Db-. nent-eontreI-Desk-Washington, D.C. 20555-0001 Duane Arnold Energy Center Docket 50-331 License No. DPR-49 Licensee Event Report #2007-009-00 Please find attached the subject Licensee Event Report (LER) submitted in accordance witb.10 CFR 50.73. This :letter makes no new commitments or changes to any existing commitments.
Richard L. Anderson Vice President, Duane Arnold Energy Center FPL Energy Duane Arnold, LLC cc:
Administrator,, Region Ill, USN RC Project Manager, DAEC,"USNRC Resident Inspector, DAECý, USNRC
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
, the NRC may (See reverse for required number of not conduct or sponsor, and a person is not required to respond to, the digits/characters for each block) information collection.
- 3. PAGE Duane Arnold Energy Center 05000 331 1
OF 4
- 4. TITLE Loss of essential bus resulted in a loss of safety function
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEUNIA 1E MONTH DAY YEAR NUMBER NO.
05000 FACILITY NAME DOCKET NUMBER 10 05 2007 2007 9
12 04 2007 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 1 E] 20.2201(b) 13 20.2203(a)(3)(i) 13 50.73(a)(2)(i)(C) 13 50.73(a)(2)(vii)
E] 20.2201(d) 13 20.2203(a)(3)(ii) 13 50.73(a)(2)(ii)(A) 13 50.73(a)(2)(viii)(A)
[]
20.2203(a)(1) 13 20.2203(a)(4) 13 50.73(a)(2)(ii)(B) 1] 50.73(a)(2)(viii)(B)
E1 20.2203(a)(2)(i) 13 50.36(c)(1)(i)(A) 13 50.73(a)(2)(iii)
[]
50.73(a)(2)(ix)(A)
- 10. POWER LEVEL 13 20.2203(a)(2)(ii) 13 50.36(c)(1)(ii)(A)
E] 50.73(a)(2)(iv)(A)
E] 50.73(a)(2)(x) 100 13 20.2203(a)(2)(iii) 13 50.36(c)(2)
[] 50.73(a)(2)(v)(A)
[]
73.71(a)(4) 1] 20.2203(a)(2)(iv)
E] 50.46(a)(3)(ii)
E] 50.73(a)(2)(v)(B) 13 73.71 (a)(5) 13 20.2203(a)(2)(v) 13 50.73(a)(2)(i)(A) 13 50.73(a)(2)(v)(C) 13 OTHER 13 20.2203(a)(2)(vi) 13 50.73(a)(2)(i)(B)
[
50.73(a)(2)(v)(D)
Specify in Abstract below or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code)
Bob Murrell, Engineering Analyst (319) 851-7900CAUSE MANUJ-SYSTEM COMPONENT FACUR SFACTUE REPORTABLE TO EPIX X
ED BKR W120 N
- 14. SUPPLEMENTAL REPORT EXPECTED C) YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
@ NO ABSTRACT (Limit to 1400 spaces, i e., approximately 15 single-spaced typewritten lines)
On 10/05/07 at 0408, with the plant at 100% power and in Day 5 of 8 Limiting Condition for Operation (LCO) for the 'A' Emergency Diesel Generator (EDG), a loss of 480 Volt AC essential bus 1 B42 occurred during a clearance application on breaker 1 B4234A. The loss of bus 1 B42 resulted in a loss of 'B' Emergency Service Water (ESW). The loss of 'B' ESW resulted in the 'B' EDG being incapable of performing its safety function. The loss of 'B' EDG resulted in a loss of the onsite emergency power safety function. At the time of this event, the 'A' ESW pump was inoperable, but available following pre-planned maintenance.
The primary cause or the event was an equipment failure related to an underlying equipment deficiency that was exacerbated by Operator action.
Essential bus 1 B42 was repaired and returned to service at 0715 on 10/05/07 after completion of maintenance.
NRC FORM 3EE (9-2007)
PRINTED ON RECYCLED PAPER NRC FORM 366 (9-2007)
PRINTED ON RECYCLED PAPERU.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3) 1 ER SEQETA NUMISER Duane Arnold Energy Center 05000331 YEAR EAL REVISIONUMBER 2007 009 00 2of4 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
I. Description of Event
On 10/05/07, with the plant at 100% power and in Day 5 of 8 Limiting Condition for Operation (LCO) for the 'A' Emergency Diesel Generator (EDG) (IEEE Code - EK),
a loss of 480 Volt AC essential bus 1 B42 (IEEE Code - ED) occurred during a circuit breaker 1 B4234A clearance application. This condition resulted in a loss of both on-site emergency AC power sources from 0408 till approximately 0715.
Specifically, while setting electrical isolation to support replacement of the 'B' H 2/0 2 Analyzer Vacuum Pump (IEEE Code - IK) a fault occurred on the Motor Control Center (MCC) dual breaker cubicle 1 B4234A/B. The fault resulted in an electric arc which produced an arc-blast propagating through the MCC cubicle and exiting at the bottom of the cubicle, which was at floor level. At the time of this event, the 'A' EDG was out of service for pre-planned maintenance. The loss of 480 Volt MCC 1 B42 resulted in a loss of 'B' Emergency Service Water (ESW) (IEEE Code - BI).
The loss of 'B' ESW resulted in the 'B' EDG being incapable of performing its safety function. The loss of 'B' EDG resulted in a loss of the onsite emergency power safety function. At the time of this event, the 'A' ESW pump was inoperable, but available following'pre-planned maintenance.
II. Assessment of Safety Consequences
As a result of this event, the plant entered multiple Technical Specification (TS)
Actions, including a loss of safety function condition due to both ESW pumps being TS inoperable. Note that at the time of this event, the 'A' ESW pump was inoperable, but available. TS Action 3.7.3 Condition B for both ESW subsystems inoperable required the plant to be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and Mode 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. This condition also resulted in an 8-hour immediate notification event under 10CFR 50.72 for an event or condition that alone could have prevented fulfillment of a safety function to mitigate the consequences of an accident due to both EDG's being unavailable for a period of approximately 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> and 7 minutes.
In conclusion, it has been determined that from 0408 till approximately 0715 on 10/05/07, a loss of both onsite emergency AC power sources occurred.
Specifically, at the time of the event, the 'A' EDG was out of service for preplanned maintenance. The loss of MCC 1 B42 resulted in a loss of 'B' ESW. The loss of 'B' ESW resulted in the 'B' EDG being incapable of performing its safety function, and therefore a loss of the onsite emergency power safety function.
This event resulted in no personnel injuries.U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME 1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
SEQUENTIAL REVISION SE N
ERUMBE Duane Arnold Energy Center 05000331 YEAR NUMBER NUMBER 2007 009 00 3of4 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
This event did result in a Safety System Functional Failure due to both EDG's being unavailable at the same time.
Ill. Cause of Event:
The 1B4234A/B MCC breaker cubicle is a dual breaker cubicle. On the morning of 10/05/07, two operators were dispatched to implement a clearance that would open
'A' breaker within the cubicle and leave the 'B' breaker energized. The actions of the operators assigned were in accordance with the site's accepted practices.
When the operators achieved the correct breaker configuration, the operators attempted to open the MCC cubicle door. The operators had not fully overridden the breaker position/cubicle door interlock for the 'B' breaker, and therefore, the MCC cubicle internals were still interlocked with the MCC cubicle door. The outward force exerted by the operators was sufficient in this instance to cause outward movement of the common breaker stabs in the rear of the MCC cubicle.
This movement resulted in sufficient disengagement between breaker cubicle stabs and bus stabs to create an arc on at least one phase. Neither operator present was injured.
Following an initial investigation and follow-up Root Cause Evaluation (RCE) into this event, it was determined that the primary cause of the event was an equipment failure related to an underlying equipment deficiency that was exposed by Operator action. Specifically, the most probable cause of the arc flash was due to the 'C' phase stab for MCC breaker cubicle 1B4234A/B becoming separated from the right
'C' phase bus work. Due to the extent of the damage to the bus, it was not possible to determine the exact cause of the equipment failure.
Contributing to the event was the station management team's' failure to effectively identify and resolve previously identified issues with MCC breaker cubicle 1 B4234A/B in the Corrective Action Program (CAP). Specifically, the CAP Screening process missed the underlying equipment deficiency of inadequate breaker stab to bus engagement as indicated by the intermittent effects of loads supplied by 1 B4234B during previous breaker manipulations. Station managers focused corrective actions on the long-term issue of operating the dual configuration breakers during clearance activities. In addition, the RCE determined the consequences of the event could have been mitigated if the station had maintained the protected equipment program in a manner more consistent with industry best practices.U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
Duane Arnold Energy Center 05000331 YEAR SEQUENTIAL REVISION 05031NUMBER NUMBER 2007 009 00 4of4 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
IV. Corrective Actions
Interim Actions:
An Operations Shift Order was issued documenting the new expectation that effective immediately dual breaker 480vac MCC cubicles would not be opened unless both MCC breaker handles are in the open position.
An Operations Shift Order was issued documenting the new expectation that effective immediately on-line risk management was being upgraded. Specifically, guidance has been generated to protect divisionalized safety equipment.
A review of the work schedule for the next 13 weeks was conducted to identify and remove any Protected Train conflicts.
Corrective Action to Repair Cause of Event:
Essential bus 1 B42 was repaired and returned to service at 0715 on 10/05/07 after completion of maintenance.
V. Additional Information
Previous Similar Occurrences:
A review of LERs over the previous 5 years revealed no similar occurrences.
EIIS System and Component Codes:
lK - Containment Environmental Monitoring System EK - Emergency Onsite Power System ED - Low Voltage Power System - Class 1 E BI - Essential Service Water
Reporting Requirements
This event is reportable under 10 CFR 50.72(b)(3)(v), 'Any event or condition that alone at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to (D) Mitigate the consequences of an accident."
Gý FPL Energy, Duane Arnold Energy Center FPL Energy Duane Arnold, LLC 3277 DAEC Road Palo, Iowa 52324
'2
- - i MAILE FROM
(-On U.S. Nuclear Regulatory Commission ATTN: Document Control Desk MS-0-PI-17 Washington, DC 20555-0001 II Ii