05000302/LER-2004-003
| Crystal River | |
| Event date: | 09-06-2004 |
|---|---|
| Report date: | 10-29-2004 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 41022 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration |
| 3022004003R00 - NRC Website | |
EVENT DESCRIPTION
At 17:10 on September 5, 2004, Crystal River Unit 3 (CR-3) declared an Unusual Event based on issuance of a Hurricane Warning for Citrus County by the National Weather Service. At 17:35, the NRC Operations Center was notified (Event Number 41022). Tropical storm force wind gusts and heavy rain were anticipated due to the projected path of Hurricane Frances.
On September 6, 2004, Progress Energy Florida, Inc., (PEF) CR-3 was in MODE 1 (POWER OPERATION) at approximately 97 percent RATED THERMAL POWER. The Train "A" Engineered Safeguards (ES) 4160 volt bus [EB, BU] was being supplied power from the Offsite Power Transformer (OPT) [EB, XFMR]. The Train "B" ES 4160 volt bus was being supplied power from the Backup ES Transformer (BEST) [EB, XFMR].
At 11:02 on September 6, 2004, a fault on the 230 kilovolt (kV) Brookridge transmission line [FK, CBL] resulted in the opening of Breakers 1690 and 1691 (see Figure 1) [FK, BKR]. Mechanical failure of an insulator string [FK, INS] resulted in a phase-to-ground fault when the transmission line dropped into the metal transmission tower [FK, TWR]. That transmission tower is located along the transmission corridor approximately two miles from the CR-3 switchyard. This removed one of the sources of power to the BEST and Startup transformer [EB, XFMR].
At 11:51, on September 6, 2004, a fault on the 230 kV switchyard south bus [FK, BU] resulted in the opening of Breaker 1692 (see Figure 1). A phase-to-ground fault on Breaker 3232 resulted in actuation of the primary and backup bus differential relaying schemes [FK, 87] resulting in the tripping of Breakers 3235, 3232, 3231, 1695, 1160, 1157, 4902 and 1692. This removed the remaining source of power to the BEST and Startup transformer. Improved Technical Specification (ITS) 3.8.1, Condition A, was entered for loss of the BEST.
Loss of the BEST resulted in an undervoltage condition on the Train "B" ES 4160 volt bus.
Emergency Diesel Generator EGDG-1B [EK, DG] started and loaded onto the Train "B" ES 4160 volt bus.
The OPT remained available throughout this event, providing offsite power to the Train "A" ES 4160 volt bus. Breaker 4902 was open as a result of the 230 kV switchyard south bus trip, but breaker 4900 remained closed and provided power from the 230 kV switchyard north bus.
Loss of the Startup transformer resulted in a loss of power to the CR-3 6900 volt, 4160 volt [EB BU] and 480 volt [ED, BU] unit busses.
Loss of the Startup transformer resulted in: opening of the reactor trip breakers [AA, BKR] and insertion of the control rods [AA, ROD] into the reactor core; tripping the four reactor coolant pumps (RCP-1A, -1B, -1C and -1D) [AB, P]; and, loss of power to the Main Turbine Lube Oil System [TD]. Subsequent tripping of the Main Turbine [TA, TRB] resulted in actuation of the Reactor Protection System (RPS) [JC].
Power was lost to both main feedwater pumps (FWP-2A and -2B) [SJ, P]. The Emergency Feedwater Initiation and Control system (EFIC) [JB] actuated upon loss of the RCPs and main FWPs. Diesel driven Emergency Feedwater Pump EFP-3 [BA, P] and steam driven EFP-2 started, providing flow to the Once Through Steam Generators (OTSGs) [AB, SG].
The Main Steam Isolation Valves [SB, ISV] were closed per procedure and the plant was stabilized in natural circulation using EFP-3 and the Atmospheric Dump Valves [SB, V].
Besides the 230 kV Brookridge transmission line fault, no structures, systems or components were inoperable at the start of the event that contributed to the event. No pertinent maintenance or surveillance activities were in progress. Plant systems operated normally during the reactor trip, with exception of the following:
The FWP-2B turbine emergency lubricating oil pump (FWP-5B) motor [LL, P] was noted as running with no indicated discharge pressure. FWP-2B experienced a four minute coastdown without lubricating oil. An investigation revealed incorrect termination of the motor power leads that resulted in FWP-5B rotating in the wrong direction. No damage to the FWP-2B turbine bearings was experienced.
The Annunciator Alarm System [IB] was overloaded due to multiple post trip alarms. The Annunciator Alarm System was reset. Approximately twenty minutes of alarm data was lost.
Actuation of the RPS and Emergency Feedwater (EFW) System [BA] are reportable to the NRC.
At 12:44, on September 6, 2004, a non-emergency four-hour notification and a non-emergency eight-hour notification was made to the NRC Operations Center (Event Number 41023) in accordance with 10CFR50.72(b)(2)(iv)(B) and 10CFR50.72(b)(3)(iv)(A), respectively. This report is being submitted pursuant to 10CFR50.73(a)(2)(iv)(A).
SAFETY CONSEQUENCES
Upon loss of the BEST, an undervoltage condition on the Train "B" ES 4160 volt bus resulted in the start and loading of Emergency Diesel Generator EGDG-1B. Loss of the Startup transformer resulted in opening the reactor trip breakers and insertion of the control rods into the reactor core; tripping the four reactor coolant pumps; and loss of power to the Main Turbine Lube Oil System.
Subsequent tripping of the Main Turbine resulted in actuation of the RPS. Loss of the RCPs and both main FWPs resulted in an automatic EFIC actuation. Valid actuation of the RPS and EFIC System occurred to shut down the reactor and maintain adequate OTSG levels. The diesel driven EFP-3 and steam driven EFP-2 started to provide flow to the OTSGs.
The Main Steam Isolation Valves were closed per procedure and the plant was stabilized in natural circulation using EFP-3 and the Atmospheric Dump Valves. Reactor operators properly executed the Emergency Operating Procedures for plant shutdown.
At 07:19 on September 7, 2004, off site power was returned to the BEST and the actions of ITS 3.8.1, Condition A, were exited.
Based on the above discussion, PEF concludes that the RPS and EFW System performed as designed and did not represent a reduction in the public health and safety. The OPT remained available throughout this event, providing power to the Train "A" Engineered Safeguards (ES) 4160 volt bus. Therefore, this event does not meet the Nuclear Energy Institute definition of a Safety System Functional Failure (NEI 99-02, Revision 2).
CAUSE
The cause for loss of the 230 kV Brookridge transmission line was mechanical failure of a vertical string of insulators on the "A" phase due to diameter loss and consequent failure of one of the carbon steel pins connecting the insulators to one another. The porcelain "ball and socket" insulators were stamped "LAPP 20000 1968," indicating that they were manufactured by the Lapp Insulator Company and were 1968 vintage. The diameter loss was caused by possible leakage current which led to spark erosion and severe electrochemical corrosion of the carbon steel pin.
Corrosion/erosion reduced the cross section of the carbon steel pin sufficiently to result in tensile overload. The passing of Tropical Storm Frances resulted in tropical storm force winds that placed additional stress on the carbon steel pin. A phase-to-ground fault occurred when the "A" phase transmission line dropped and came in contact with the metal transmission tower.
The tripping of the 230 kV switchyard south bus was due to a flashover ("B" phase-to-ground) on breaker 3232 due to contamination from wind and salt spray from the passing of Tropical Storm Frances. The bus differential relaying schemes functioned as designed based on the fault condition of the breaker and isolated the fault by opening breakers 3235, 3232, 3231, 1695, 1160, 1157, 4902 and 1692. Since the relaying functioned as designed to protect the adjacent equipment from the fault and the fault occurred as a result of Tropical Storm Frances, there were no inappropriate acts or equipment failures. Therefore, there is no corrective action to prevent recurrence of this condition.
CORRECTIVE ACTIONS
1. CR-3 Administrative Instruction Al-704, "Reactor Trip Review and Analysis," was performed.
2. The failed vertical string of insulators was replaced. Vertical and "V" string insulators on the 230 kV Brookridge transmission line towers located along the transmission corridor adjacent to the CR-3 access road were inspected. Thirteen additional vertical strings of insulators were subsequently replaced on the 230 kV Brookridge transmission line.
3. A 230 kV switchyard south bus reenergization plan was created and implemented. The primary purpose of this plan was to reveal internal breaker faults prior to bus restoration. No internal breaker faults were identified. The 230 kV switchyard south bus breakers were closed and the 230 kV switchyard south bus was restored on September 7, 2004.
4. Breaker 3232 was evaluated. Physical evidence was found to confirm that a flashover had occurred from the "B" phase to ground. A series of tests were performed on the breaker with results being acceptable. In addition, an internal inspection was performed on the "B" phase of the breaker with results being acceptable. A complete hot wash was performed on insulators and breakers on the 230 kV switchyard south bus prior to CR-3 restart. A visual inspection of other sections of the 230 kV switchyard buses was also performed. The determination was made that additional hot washing was not required.
5. Other actions associated with this event are being addressed in the CR-3 Corrective Action Program in Nuclear Condition Report 136752.
PREVIOUS SIMILAR EVENTS
No previous similar events involving loss of offsite power to the Startup transformer due to the loss of the 230 kV Brookridge transmission line and the 230 kV switchyard south bus have been reported to the NRC by CR-3.
ATTACHMENTS
Figure 1 - 230 kV Switchyard Simplified Drawing Attachment 1 - Abbreviations, Definitions, and Acronyms Attachment 2 - List of Commitments FIGURE 1 230 KV SWITCHYARD SIMPLIFIED DRAWING 3230 1158 1680 CR4 3E33 11� UNIT 4 *- CENTRAL CR FLORIDA*. HOLDER 4- -
- BROOM:RIDGESA) EAST*- -31E Ei 11[ I3ACKUP3234 3231 ES.11-qCR.1 XFMRHELPER OFFINTENEWCOOLING POWERBERRY 4-TOWERS XFMR VA. 1 1160 11 a ATTACHMENT 1
ABBREVIATIONS, DEFINITIONS AND ACRONYMS
Al� Administrative Instruction BEST� Backup Engineered Safeguards Transformer CFR� Code of Federal Regulations EFIC� Emergency Feedwater Initiation and Control EFW� Emergency Feedwater EGDG� Emergency Diesel Generator ES� Engineered Safeguards FWP� Feedwater Pump ITS� Improved Technical Specifications kV� kilovolt NEI� Nuclear Energy Institute NRC� Nuclear Regulatory Commission OPT� Offsite Power Transformer OTSG� Once Through Steam Generator PEF� Progress Energy Florida, Inc.
RCP� Reactor Coolant Pump RPS� Reactor Protection System NOTES:� Improved Technical Specifications defined terms appear capitalized in LER text {e.g., MODE 1} Defined terms/acronyms/abbreviations appear in parenthesis when first used {e.g., Reactor Building (RB)}.
ATTACHMENT 2
LIST OF COMMITMENTS
The following table identifies those actions committed to by PEF in this document. Any other actions discussed in the submittal represent intended or planned actions by PEF. They are described to the NRC for the NRC's information and are not regulatory commitments. Please notify the Supervisor, Licensing & Regulatory Programs of any questions regarding this document or any associated regulatory commitments.
RESPONSE COMMITMENT DUE DATE
SECTION
No regulatory commitments are being made in this submittal.