05000317/LER-2010-001-01, For Calvert Cliffs, Regarding Reactor Trip Due to Water Intrusion Into Switchgear Protective Circuitry
| ML101530461 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 05/27/2010 |
| From: | Trepanier T Constellation Energy Group, EDF Group |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 10-001-01 | |
| Download: ML101530461 (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 |
| 3172010001R01 - NRC Website | |
text
Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, Maryland 20657 CENG a joint venture of fl Constellation eDF V, Energy
ý CALVERT CLIFFS NUCLEAR POWER PLANT May 27, 2010 U.S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
SUBJECT:
Document Control Desk Calvert Cliffs Nuclear Power Plant Unit No. 1; Docket No. 50-317; License No. DPR 53 Licensee Event Report 2010-001, Revision 01 Reactor Trip Due to Water Intrusion into Switchgear Protective Circuitry The attached supplemental report is being sent to you as required by 10 CFR 50.73. Should you have questions regarding this report, please contact Mr. Douglas E. Lauver at (410) 495-5219.
Very truly yours, Thomas E. Trepanier Plant General Manager TET/CAN/bjd
Attachment:
As stated cc:
D. V. Pickett, NRC S. J. Collins, NRC Resident Inspector, NRC S. Gray, DNR
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 1 OF 005
- 4. TITLE Reactor Trip Due to Water Intrusion into Switchgear Protective Circuitry
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE 1
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR 05000 NUM BER NO.
5 0 Ij _
I I
pFACILITY NAME OOCKET NUMBER 02 18 2010 2010 - 001 -
01 05 27 2010 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
E-.20.2201(b)
El 20.2203(a)(3)(i)
[E 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
El 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
[E 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
[E 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL
[] 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
ED 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
[E 20.2203(a)(2)(iii)
El 50.36(c)(2)
[E 50.73(a)(2)(v)(A)
[E 73.71(a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5) 93 El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
[E 50.73(a)(2)(v)(C)
[E OTHER El 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
El 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)
C. A. Neyman, Senior Engineering Analyst 10-495-3507CAUSE SYSTEM COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT FACTURER TO EPIX FACTURER TO EPIX X
EA 64 W120 Y
- 14. SUPPLEMENTAL REPORT EXPECTED 15.SEXPECTED MONTH DAY YEAR SUBMISSION E] YES (If yes, complete 15. EXPECTED SUBMISSION DATE) 0 NO DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On February 18, 2010, at 8:24 a.m., Unit 1 experienced an automatic, reactor trip from 92.8 percent power. The 12B Reactor Coolant Pump (RCP) tripped and the Reactor Protective System actuated on Reactor Coolant System low flow. The 12B RCP tripped due to a phase to ground short near one of the current transformers for the 12B RCP bus 14P differential / ground current protection. The ground fault was not isolated close to the source due to a failed ground protection relay in breaker 252-2202 the feeder breaker from Service Transformer P-1 3000-2 to the Unit 1 RCP buses. This resulted in Service Transformer P-13000-2 being deenergized.
The loss of P-1 3000-2 resulted in a loss of the normal power supply to 14 4 kV bus. This caused the 1 B Emergency Diesel Generator to start and supply power to 14 4 kV bus.
The cause of the fault was a phase to ground short near one of the current transformers for the 12B RCP bus differential/ground current protection due to water intrusion. This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A) due to Reactor Protective System actuation and automatic start of the 1 B Emergency Diesel Generator. Corrective actions include revision to a relay test procedure and improved management of roof issues.
NRC FORM 366 (9-2007)
IU.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE SEQUENTIAL REV YEAR NUMBER NO.
Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 2010
-- 001 --
01 2
of 005
DESCRIPTION OF EVENT
A.
PRE-EVENT PLANT CONDITIONS Unit 1 was operating at 92.8 percent of rated thermal power on February 18, 2010, prior to the subject event.
B.
EVENT On February 18, 2010, at 8:24 a.m., Calvert Cliffs Nuclear Power Plant, Unit 1 experienced an automatic reactor trip from 92.8 percent power. The 12B Reactor Coolant Pump (RCP) tripped and the Reactor Protective System actuated on Reactor Coolant System low flow. The reactor trip circuit breakers opened as designed and all control element assemblies fully inserted as expected. Following the reactor trip, the main turbine automatically tripped. Decay heat was removed via normal methods through the turbine bypass valves to the condenser. Steam generator pressure did not reach the setpoints for opening the main steam safety valves. The steam generators remained on normal feed throughout the event. No power-operated relief valves or pressurizer safety valves lifted during the event. Containment atmosphere parameters were unaffected by the trip. Radiation levels were not affected by the trip.
A ground fault occurred in the electrical distribution system. The ground fault was not isolated close to the source due to a failed ground protection relay in breaker 252-2202, the feeder breaker from Service Transformer P-1 3000-2 to the Unit 1 RCP buses. This resulted in Service Transformer P-1 3000-2 being deenergized. The isolation of P-1 3000-2 was achieved in part by the isolation of the 500 kV switchyard red bus. The loss of P-1 3000-2 resulted in a loss of the normal power supply to 14 4 kV bus. This caused the 1B Emergency Diesel Generator (EDG) to start and supply power to 14 4 kV bus.
The loss of 14 4 kV bus also resulted in 120 volt instrument bus 1Y10 being deenergized. This resulted in the loss of letdown flow from the Chemical and Volume Control System. Prior to letdown flow restoration, pressurizer level exceeded the Technical Specification Limiting Condition for Operation (LCO) 3.4.9.a water level limit of 225 inches.
Following the reactor trip, the unit transitioned into a scheduled refueling outage.
Unit 2 experienced a reactor trip when Service Transformer P-1 3000-2 was deenergized.
Details of that event were submitted in a separate Licensee Event Report (LER 318/2010-001).
C.
INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO THE EVENT The following component was inoperable or failed at the time of the event: Breaker 252-2202.U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE SEQUENTIAL REV YEAR NUMBER N
NO.
Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 2010
-- 001 --
01 3
of 005 D.
DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES
The reactor trip occurred on February 18, 2010 at 8:24 a.m. following the 12B RCP trip.
Following the loss of 14 4 kV bus, the 1B EDG started and powered the 14 4 kV bus. At 2:08 p.m., normal power was restored to the 14 4 kV bus and the 1 B EDG was secured.
Operators implemented Emergency Operating Procedure (EOP)-0, Post-Trip Immediate Actions, and performed post-trip immediate actions.
Operators implemented EOP-1, Reactor Trip, 16 minutes after the reactor trip to perform post-trip recovery actions for an uncomplicated reactor trip. Attempts to restore Chemical and Volume Control System letdown flow began 49 minutes after the reactor trip. Due to closure of the excess flow check valve, letdown was not restored until 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and 51 minutes after the reactor trip.
At 12:00 p.m., while shifting steam seals from main steam to auxiliary steam, Reactor Coolant System temperature increased slightly. As a result, pressurizer level increased above the Technical Specification LCO 3.4.9.a upper limit of 225 inches for 7 minutes. This was due to the loss of Chemical and Volume Control System letdown flow following the reactor trip.
Operators transitioned from EOP-1 to Operating Procedure-5, Plant Shutdown from Hot Standby to Cold Shutdown, 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> and 14 minutes after the reactor trip.
On February 21 at 5:50 a.m., the 500 kV switchyard red bus was reenergized.
E.
OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED
No other systems or functions were affected.
F.
METHOD OF DISCOVERY
The event was self-revealing.
G.
SAFETY SYSTEM RESPONSES The Reactor Protective System and Emergency AC Power Supply System operated as required. There were no safety system functional failures.
II.
CAUSE OF EVENT
The event is documented in station condition report number CR-2010-001351. The 12B RCP tripped due to an electrical fault in a 13 kV system. The fault was caused by a phase to ground short circuit of one of the current transformers for the 12B RCP bus 14P differential / ground current protection. The short circuit was caused by water intrusion into the cubicle that contained the bus work and relay protective circuitry as a result of a roof leak.U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
__LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE in SEQUENTIAL R'EV YEAR NUMBER N"O.
.Calvert Cliffs Nuclear Power Plant, Unit 1 05000 31.7 2010
-- 001 --
01 4
of 005 Breaker 252-2202 failed to open due to a problem with its ground fault relay. The relay's magnetizing coil had shorted out the majority of the windings and would not allow the relay's induction disc to spin. Possible failure modes for the relay are:
- Aging degradation.
A high amount of current during the event.
- The windings may have shorted following its calibration and testing in 2008.
III.
ANALYSIS OF THE EVENT
This event resulted in valid actuations of the Reactor Protective System and the 1 B EDG. The actuations were not part of a pre-planned sequence during testing or reactor operation.
Therefore, this event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A). Immediate notification of this event (Event Number 45709) was made on February. 18, 2010 at 11:47 a.m.
in accordance with 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(b)(3)(iv)(A).
The Nuclear Regulatory Commission Performance Indicator for Unplanned Scrams per 7,000 Critical Hours increased to 0.9 and remains green. No other performance indicators were impacted.
There were no actual nuclear safety consequences incurred from this event. An estimated conditional core damage probability of 6.3E-06 and an estimated conditional large early release probability of 2.7E-07 were calculated for this event.
IV.
CORRECTIVE ACTIONS
A.
ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:
Following the reactor trip, the Unit 1 transitioned into a scheduled refueling outage. Following the completion of the refueling outage, Unit 1 was restarted and paralleled to the grid on March 23, 2010.
B.
ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE Repairs were performed to bus, current transformers and insulation in the 14P02 cubicle.
Repairs were performed on the 45 foot switchgrear room roof. The protective relay was replaced on breaker 252-2202 and proper operation was verified.
IU.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE SEQUENTIAL REV YEAR NUMBER NO.
Calvert Cliffs Nuclear Power Plant, Unit 1 05000317 2010
-- 001 --
01 5
of 005 Actions planned to prevent recurrence include:
- 1.
Revise relay calibration procedure to perform a final as-left pickup verification to ensure the relay was not damaged during maintenance.
- 2.
Implement improved processes for categorization, prioritization and management of roofing issues.
V.
ADDITIONAL INFORMATION
A.
FAILED COMPONENTS:
Breaker 252-2202 ground fault relay 2RY251G/B22-2 was manufactured by Westinghouse (EPIX Identification Number W120).
B.
PREVIOUS LERs ON SIMILAR EVENTS A review of Calvert Cliffs' events over the past several years was performed. No previous occurrences were identified involving a reactor trip due to water intrusion.