05000260/LER-2002-002, Automatic Scram Resulting from Main Bank Transformer Bushing Fault
| ML022760066 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 09/25/2002 |
| From: | Bhatnagar A Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 02-002-00 | |
| Download: ML022760066 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2602002002R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 Ashok S. Bhatnagar Vice President, Browns Ferry Nuclear Plant September 25, 2002 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Mail Stop OWFN, P1-35 Washington, D. C. 20555-0001 10 CFR 50.73
Dear Sir:
TENNESSEE VALLEY AUTHORITY -
BROWNS FERRY NUCLEAR PLANT (BFN)
UNIT 2 -
DOCKET 50-260 -
FACILITY OPERATING LICENSE DPR LICENSEE EVENT REPORT (LER) 50-260/2002-002-00 The enclosed report provides details of an automatic scram which occurred on Unit 2. A fault in a main bank transformer bushing caused a main generator trip which directly resulted in the scram.
In accordance with 10 CFR 50.73(a)(2)(iv)(A), TVA is reporting this event as the valid actuation of the reactor protection system and of containment isolation valves in more than one system.
There are no commitments contained in this letter.
Sincerely, cc:
See page 2 Pn.tod c mcydd pap.
U.S. Nuclear Regulatory Commission Page 2 September 25, 2002 Enclosure cc (Enclosure):
(Via NRC Electronic Distribution)
Mr. Kahtan N. Jabbour, Project Manager U.S. Nuclear Regulatory Commission (MS 08G9)
One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 Mr. Paul E. Fredrickson, Branch Chief U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-8931 NRC Resident Inspector Browns Ferry Nuclear Plant P. 0. Box 149 Athens, Alabama 35611
Abstract
On July 27, 2002, a Unit 2 main generator trip, main turbine trip, and reactor scram occurred from 100% power.
All expected system responses were received, including the automatic opening of four safety-relief valves.
Actuation of primary containment isolation system groups 2, 3, 6, and 8 occurred due to the expected temporary lowering of reactor water level. This logic isolates shutdown cooling (if in service), isolates the reactor water cleanup system, isolates the normal reactor building ventilation, initiates the standby gas treatment and the control room emergency ventilation systems, and retracts traversing incore probes (if inserted). The normal heat rejection path for the reactor remained in service. Reactor water level was recovered to the normal operating range by the normal reactor water level control system. Neither the high pressure coolant injection nor reactor core isolation cooling systems were used during this event.
The generator tripped due to a ground fault on a main bank transformer bushing, which occurred due to thermal degradation of the paper insulation of the bushing's internal condenser. Corrective actions included replacement of all of the low-side bushings on the transformer and increased monitoring of generator neutral resistor voltage trends. All new bushings will be installed on Unit 2 and Unit 3 main bank transformers. TVA will re-evaluate the criteria used in determining bushing condenser replacement intervals, and the bushing maintenance practices will be revised accordingly.
NRC FORM 366 (7-2001)
(If more space is required, use additional copies of (If more space is required, use addibonal copies of NRC Forn 366A) (17)
C. Dates and Approximate Times of Maior Occurrences:
July 27, 2002 12:28 PM CDT 12:35 PM CDT 12:40 PM CDT 12:52 PM CDT 14:47 PM CDT Unit 2 generator trip, main turbine trip, and reactor scram occurred. Expected PCIS actuations occurred.
The PCIS actuation logic was reset. The SGT and CREV systems were secured and normal reactor building ventilation re-established.
Reactor protection system logic reset RWCU system returned to service.
Required four-hour and eight-hour reports were made via telephone to the NRC Operations Center.
D. Other Systems or SecondarV Functions Affected None
E. Method of Discovery
This event was identified through numerous indications and alarms in the control room.
F. Operator Actions
This event was an uncomplicated scram. All operator actions taken in response to the scram and in the recovery from the event were appropriate. These actions included the verification that the reactor had been successfully shut down, the expected system isolations and initiations had occurred, and accomplishing the subsequent restoration of these systems to normal alignments.
G. Safety System Responses All equipment operated in accordance with the plant design during this event.
The RPS logic responded to the turbine trip event per design to initiate the reactor scram. All control rods fully inserted into the core.
The PCIS logic responded per design to the expected lowered reactor water level by actuating the following isolation groups:
Group 2 - Residual Heat Removal shutdown cooling function isolation (not in service at the time of the event)
Group 3 - RWCU system isolation Group 6 - primary and secondary containment isolation, including the isolation of the normal reactor building ventilation and the initiation of the SGT and CREV systems Group 8 - withdrawal and isolation of the Traversing Incore Probes (the probes were not inserted at the time of this event)
(If more space is required, use additional copies of (If more space is required, use additional copies of (If more space is required, use additional copies of NRC Forn 366A) (17)
VII. ADDITIONAL INFORMATION
A.
Failed Components Main Bank Transformer low voltage bushing (ASEA GOH 150)
B.
Previous LERs on Similar Events None C.
Additional Information
None D.
Safety System Functional Failure Consideration:
This event does not involve a safety system functional failure which would be reported in accordance with NEI 99-02. The scram was caused by a malfunction of non-safety related equipment. All safety-related equipment performed in accordance with design in response to the event.
E.
Loss of Normal Heat Removal Consideration:
The main condenser was retained as the heat sink during this event, and the feedwater system continued to provide reactor vessel inventory make-up. Neither HPCI nor RCIC operated during this event. A momentary lift of four SRV's occurred at the time of the event to control the initial pressure transient, but the valves properly reseated. Other than in quenching the discharge from the short-term opening of the SRV's, the suppression pool was not used as a heat sink following this event. This event does not constitute a scram with a loss of normal heat removal which would be reported in accordance with NEI 99-02.
VilI. COMMITMENTS None