05000458/LER-2007-002, Regarding Unplanned Manual Reactor Scram Due to Loss of Cooling on No. 2 Main Transformer
| ML071840161 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 06/29/2007 |
| From: | Lorfing D Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| G9.25.1.3, G9.5, RBF1-07-0113, RBG-46709 LER 07-002-00 | |
| Download: ML071840161 (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)(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 |
| 4582007002R00 - NRC Website | |
text
SEn tergy Entergy Operations, Inc.
River Bend Station 5485 U.S. Highway 61 N St. Francisville, LA 70775 Tel 225 381 4157 Fax 225 635 5068 dlorfin@entergy.com David N. Lorfing Manager-Licensing June 29, 2007 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Licensee Event Report 50-458 / 07-002-00 River Bend Station - Unit 1 Docket No. 50-458 License No. NPF-47 File Nos.
G9.5, G9.25.1.3 RBG-46709 RBF1-07-0113 Ladies and Gentlemen:
In accordance with 10CFR50.73, enclosed is the subject Licensee Event Report.
This document contains no commitments.
Sincerely, DNL/dhw Enclosure
Licensee Event Report 50-458 / 07-002-00 June 29, 2007 RBG-46709 RBF1-07-0113 Page 2 of 2 cc:
U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011 NRC Sr. Resident Inspector P. 0. Box 1050 St. Francisville, LA 70775 INPO Records Center E-Mail Mr. Jim Calloway Public Utility Commission of Texas 1701 N. Congress Ave.
Austin, TX 78711-3326 Mr. Jeff Meyers Louisiana Department of Environmental Quality Office of Environmental Compliance P.O. Box 4312 Baton Rouge, LA 70821-4312
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06/30/2007
- 6-2004)
, 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 River Bend Station - Unit 1 05000-458 1 of 4
- 4. TITLE Unplanned Manual Reactor Scram Due to Loss of Cooling on No. 2 Main Transformer
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 05 04 2007 2007 - 002 -
00 06 29 2007 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
[l 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii) 1
[: 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)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii) 0l 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL [I 20.2203(a)(2)(ii)
E] 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
[] 50.36(c)(2)
[E 50.73(a)(2)(v)(A)
[E 73.71(a)(4)
[I 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5) 67 E3 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
[E 50.73(a)(2)(v)(C)
El OTHER E] 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)
David N. Lorfing, Manager - Licensing 225-381-4157MANU-REPORTABLE MANUý REPORTABLE
CAUSE
COMPONENT FACU-REPOA
CAUSE
SYSTEM COMPONENT FACTURER TO EPIX FACTURER TO EPIX (see Y
text)
YES
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR SUBMISSION El YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
E NO DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
At 1256 CDT on May 4, 2007, an unplanned manual reactor scram was initiated following the loss of cooling on the No. 2 main transformer. Reactor power at the time of the scram was approximately 67 percent. Following the scram, reactor water level briefly decreased below Level 3 as expected, resulting in the automatic closure of two containment isolation valves in the suppression pool cleanup system. This isolation was confirmed to have occurred as designed. Control of reactor pressure and water level was promptly established. No emergency coolant injection system actuation was required.
This event is being reported in accordance with 10CFR50.73(a)(2)(iv)(A) as a condition that resulted in the unplanned manual actuation of the reactor protection system.
The loss of cooling to the transformer resulted from an electrical fault in the cooling system control cabinet caused by rainwater intrusion. The cabinet was repaired and sealed, and preventative maintenance procedures are to be enhanced to prevent recurrence. The plant responded to the manual scram as expected, thus this event was of minimal safety significance.
NRC FORM 366 (6-2004)
PRINTED ON RECYCLED PAPERU.S. NUCLEAR REGULATORY COMMISSION (1-2001)
LICENSEE EVENT REPORT (LER)
FAILURE CONTINUATION
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL REVISION YEAR NUMBER NUMBER River Bend Station - Unit 1 05000-458 2007 002 00 2
OF 4
REPORTED CONDITION At 1256 CDT on May 4, 2007, an unplanned manual reactor scram was initiated following the loss of cooling on the No. 2 main transformer (**XFMR**).
Reactor power at the time of the scram was approximately 67 percent. Following the scram, reactor water level briefly decreased below Level 3 as expected, resulting in the automatic closure of two containment isolation valves in the suppression pool cleanup system. This isolation was confirmed to have occurred as designed. Control of reactor pressure and water level was promptly established. No emergency coolant injection system actuation was required.
This event is being reported in accordance with 10CFR50.73(a)(2)(iv)(A) as a condition that resulted in the unplanned manual actuation of the reactor protection system.
INVESTIGATION AND CAUSAL ANALYSIS Two Westinghouse main transformers (EL) convert the 22kv output of the main generator
(**GEN**) to 230kv for distribution on the electrical grid. Each transformer is rated for approximately 70 percent of the generator's maximum capacity. The transformers are cooled by oil circulating through the internal windings. The oil is pumped through external radiators, where fans provide forced air circulation. Power to the oil pumps and fans is supplied by switchgear in the plant, arranged in two independent systems that are each capable of providing 100 percent of the necessary cooling.
During the morning before the scram, heavy rainstorms were moving through the local area. At 1108, a ground fault alarm (**ALM**) was received in the main control room, in conjunction with the process computer point "480 BUS 1E GROUND FAULT." The 480 volt switchgear NJS-LDC1E supplies one source of the power to the main transformer cooling system. Operators were dispatched to investigate the cause of the alarm. At 1110, both the process computer points and the ground fault alarm cleared. At the same time, two additional process computer alarms actuated, along with a main control panel alarm, indicating that breakers supplying power to the No. 2 main transformer cooling system had tripped.
Operators began closely monitoring the oil and winding temperatures in the transformer, while attempting to restore power via the alternate supply. After implementing the procedures for reconfiguring the cooling power supply, it was determined that no oil pumps or radiator fans could be restarted. Meanwhile, an examination of the cooling system control cabinet mounted on the transformer found that a significant electrical fault had occurred inside the cabinet. The fault had damaged a terminal block (**DBLK**) in the cabinet, resulting in the inability to operate any of the pumps or fans.
At 1221, a power reduction was commenced to take the main generator and the main transformer out of service. Initial investigation by electrical engineers determined that the transformer is rated for a maximum of 30 minutes of operation at full load with noU.S. NUCLEAR REGULATORY COMMISSION (1-2001)
LICENSEE EVENT REPORT (LER)
FAILURE CONTINUATION
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL REVISION YEAR NUMBER NUMBER River Bend Station - Unit 1 05000-458 2007 002 00 3
OF 4
cooling in service. When this was communicated to the main control room crew, it was determined that the normal reactor shutdown procedure could not be conducted quickly enough to avoid overheating the transformer. The decision was made to manually actuate a reactor scram.
The fault in the control cabinet was determined to have been caused by water intrusion.
Sealant around electrical conduits penetrating the cabinet was found to be degraded, which allowed the entry of rainwater. Additionally, the insulating material under the terminal block mounting studs is made of a cellulose-based material which tends to absorb moisture. This condition likely contributed to the susceptibility for arcing across the terminal block. An examination of the control cabinet on the No. 1 main transformer found that the insulation was made of a laminated resin material, which is impervious to moisture. No record of any modification to the No. 2 transformer control cabinet was found, thus, the insulation material likely was part of the original installation.
Further examination of the control cabinet found evidence that water intrusion had likely occurred in the past. A review of preventive maintenance procedures for the main transformer determined that no specific instructions are provided for inspecting the control cabinet for signs of leakage. Additionally, no requirements existed to periodically replace the sealant around the cabinet penetrations.
The peak temperatures in the transformer oil and windings during the event remained below design limits. Oil samples found no unusual signs of degradation.
Analysis of the plant response to this event found that one process computer point alarm failed to actuate. This alarm would have indicated to the operators that a ground fault had also occurred on switchgear NJS-LDC1F. This switchgear is the second source of power to the cooling system on No. 2 main transformer. This process computer point alarm should have actuated, because the fault in the transformer control cabinet also affected that switchgear. The failure of this alarm, in conjunction with ambiguous wording of other process computer points, hindered the operators' response to the event, in that they initially believed that the alternate source of power was available.
CORRECTIVE ACTION TO PREVENT RECURRENCE Numerous actions are being taken to address the various factors that contributed to this event. All these actions are being tracked in the station's corrective action program.
All other large power transformers installed outdoors on the site were inspected for similar conditions. Only the No. 1 main transformer showed any evidence of minor water intrusion into the control cabinet. No other power transformers were found to have the same cellulose-based insulation in the control cabinets. Sealant was applied to penetrations on the control cabinets on the main transformers to ensure that they remain NRC FORM 3668 (1-2001)U.S. NUCLEAR REGULATORY COMMISSION (1-200 1)
LICENSEE EVENT REPORT (LER)
FAILURE CONTINUATION
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL REVISION YEAR NUMBER NUMBER River Bend Station - Unit 1 05000-458 2007 002 00 4
OF 4
watertight. The control cabinets on the main transformers were modified to replace the terminal block with in-line splices.
Preventive maintenance procedures for the main transformers are being revised to (1) periodically replace the conduit sealant, and, (2) specifically inspect for any evidence of water intrusion.
Actions are being developed to correct the deficiencies identified in the process computer alarm system.
PREVIOUS OCCURRENCE EVALUATION No scrams at River Bend Station in the last ten years have resulted from a loss of capacity of the main transformers.
SAFETY SIGNIFICANCE
The manual actuation of the reactor protection system was successful, and all reactor control rods were fully inserted. The automatic closure of the containment isolation valves in the suppression pool cleanup system occurred as designed when reactor water level briefly decreased below Level 3. No other actuations were required by that signal.
No emergency coolant injection systems or standby diesel generators were required to initiate during this event. Thus, this event was of minimal significance to the health and safety of the public.
(NOTE:
Energy Industry Component Identification codes are annotated as (**XX**).)
NRC FORM 3666 (1-2001)