05000458/LER-2004-002, Regarding Automatic Reactor Scram and System Actuations Due to Insulator Flashover in Switchyard
| ML043420057 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 11/29/2004 |
| From: | Lorfing D Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| G9.25.1.3, G9.5, RBF 1-04-0224, RBG-46366 LER 04-002-00 | |
| Download: ML043420057 (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 |
| 4582004002R00 - NRC Website | |
text
~ Entergy Entergy Operations, Inc.
River Bend Station 5485 U. S. Highway 61 N St. Francisville, LA 70775 Fax 225 635 5068 November 29, 2004 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Licensee Event Report 50-458 / 04-002-00 River Bend Station - Unit 1 Docket No. 50-458 License No. NPF-47 File Nos.
G9.5, G9.25.1.3 RBG-46366 RBF1 0224 Ladies and Gentlemen:
In accordance with 10CFR50.73, enclosed is the subject Licensee Event Report.
Sincerely, 0 *(y David N. Lorfing Manager - Licensing (acting)
DNL/dhw enclosure IC
Licensee Event Report 50-458 / 04-002-00 November 29, 2004 RBG-46366 RBFI 0224 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. O. 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. Prosanta Chowdhury Louisiana Department of Environmental Quality Office of Environmental Compliance Surveillance Division Radiological Emergency Planning & Response Unit P.O. Box 4312 Baton Rouge, LA 70821-4312
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06/3012007 (6-2004)
, the NRC may dig its/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 Automatic Reactor Scram and System Actuations Due to Insulator Flashover in Switchyard
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEOULENTIAL REV MONTH DAY YEAR FACLITY NAME DOCKETNUMBER MOPE ATIN MOEA YEA NUMBER NO.
MOT A
ER05000 FACILITY NAME DOCKET NUMBER 10 01 2004 2004 - 002 -
00 11 29 2004 05000
- 9. OPERATING MODE THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check allthatapply) o 20.2201(b)
D 20.2203(a)(3)(i) 0 50.73(a)(2)(i)(C) 0 50.73(a)(2)(vii) 1 a
20.2201 (d) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A)
O 20.2203(a)(1) 0 20.2203(a)(4) 0 50.73(a)(2)(ii)(B) 3 50.73(a)(2)(viii)(B)
D 20.2203(a)(2)(i) 0 50.36(c)(1)(i)(A) 0 50.73(a)(2)(iii) 0 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL 0 20.2203(a)(2)(ii) 0 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A) 0 50.73(a)(2)(x) o 20.2203(a)(2)(iii)
D 50.36(c)(2) 0 50.73(a)(2)(v)(A) 0 73.71(a)(4) o 20.2203(a)(2)(iv) 0 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(B)
E 73.71(a)(5) 100 a 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C) 0 OTHER o 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B) a 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 (Indude Area Code)
David N. Lorfing, Manager -Licensing (acting) 225-381-4157MANUI-REPORTABLE CAS YTMCMOET MANU.
REPORTABLE
CAUSE
SYSTEM COMPONENT CA USECOMPONENTCOMPONENTOEIFACTURER TO EPIX C
FK INS BrassO
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR SUBMISSION El YES (if yes, complete 15. EXPECTED SUBMISSION DATE) 0 NO DATE ABSTRACT (Limit to 1400spaces, i.e., approximately 15 single-spaced typewritten lines)
On October 1, 2004, at 7:17 a.m., with the plant operating at 100% power, a loss of power to the Division 1 standby switchgear caused the automatic start of the Division 1 diesel generator.
Some non-safety switchgear were also deenergized by this event. At 7:30 a.m., an automatic reactor scram was initiated by a main turbine trip. Both of these events were caused by the flashover of high-voltage insulator strings in the station transformer yard. During the event, all main reactor feedwater pumps shut down, main condenser vacuum was lost, and the standby service water system initiated. The reactor core isolation cooling (RCIC) turbine steam supply valve isolated during the pressure transient associated with the main turbine trip. Operators manually started the high pressure core spray (HPCS) system to provide water to the reactor. A momentary low reactor water level caused a primary containment isolation signal. This is being reported in accordance with 10CFR50.73(a)(2)(iv)(A) as an event that resulted in the automatic actuation of the reactor protection system, Division 1 diesel generator, and standby service water system; an automatic Isolation of primary containment; and the manual actuation of the RCIC and HPCS systems. There were no safety systems out of service at the time of the first event. Mitigating safety systems responded as designed. This event is bounded by the River Bend safety analysis, and was thus of minimal safety significance.
NRC ORM366(6-2041PRITEDON RCYCED APE 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 YER SEQUENTIAL I REVISION YEAR NUMBE NUMBER River Bend Station Unit 1 105000-458 2004 002 00 2
OF 4
REPORTED CONDITION On October 1, 2004, at 7:17 a.m., a flashover occurred in the 230kV station transformer yard across a post insulator (**INS**). This caused the loss of Reserve Station Service (RSS) No. 1, which interrupted power to the Division 1 standby bus. The Division 1 diesel generator (**DG**) started automatically, and restored power to the bus. This event also interrupted power to the "A" reactor protection system (RPS) bus. Operators responded to this event by restoring power to the "A" RPS bus and resetting the half scram. An actuation of Division 1 containment isolation valves occurred due to loss of power to the affected isolation control circuitry, and restoration procedures were initiated.
At 7:30 a.m., a second flashover occurred across a 230kV post insulator on the main generator line, resulting in a main generator trip and main turbine trip. The main turbine trip initiated the reactor scram as designed.
The main generator trip combined with the loss of RSS no. 1 resulted in the trip of two main condensate pumps and one main feedwater pump. The remaining two feedwater pumps tripped on low suction pressure following the loss of the condensate pumps. Ten main steam safety relief valves (SRVs) actuated automatically during the pressure transient resulting from the main turbine trip. SRVs were subsequently cycled manually to control reactor pressure and to aid in achieving cold shutdown.
The reactor core isolation cooling (RCIC) turbine steam supply valve (**ISV**)
automatically isolated during the pressure transient associated with the main turbine trip. Operators manually started the high pressure core spray system (HPCS) to provide makeup water for the reactor. Low reactor water level (Level 2) was reached for approximately one minute due to the pressure transient associated with the manual closure of an SRV. This occurred approximately 42 minutes after the scram. The Level 2 condition also initiated general containment isolation signals and the trip of the "B" reactor recirculation pump. The "A" reactor recirculation pump had tripped due to the loss of power.
The standby service water system actuated as designed due to a low pressure signal resulting from the loss of power to the normal service water pumps. Two of the three main condenser circulating water pumps in service before the event shut down due to loss of power. The output of the remaining pump was short-cycled through the discharge of the idle pumps due to the loss of power to their discharge valves, diverting flow from the main condenser. It was not possible to maintain main condenser vacuum, and the operators manually closed the outboard main steam isolation valves, and then cycled SRVs as needed to control reactor pressure.
Following the scram, it was determined that the isolation signal to the RCIC turbine steam supply valve was not valid, and efforts were begun to restore the system toU.S. NUCLEAR REGULATORY COMMISSION (1-2001)
LICENSEE EVENT REPORT (LER)
FAILURE CONTINUATION
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL I REVISION YEAR NUMBER NUMBER River Bend Station Unit 1 05000-458 2004 002 00 3
OF 4
service. RCIC was placed in its standby condition at 8:24 a.m. It was later started in the recirculation mode to assist in reactor pressure control.
When efforts to restore the main condenser to service were not successful, a reactor cooldown was initiated. Cold shutdown was reached at 11:35 p.m. that evening.
CAUSAL ANALYSIS The flashover on the insulators in the transformer yard was caused by the presence of contaminants in conjunction with a heavy fog at the time of the event. The contaminants on the insulators were the result of a buildup over time of solids carried by cooling tower drift. This buildup was worsened by the abnormally low rainfall in the three months preceding the event which resulted in little or no natural cleaning of the insulators.
The cooling tower drift was determined to be higher than normal due to degradation of the fasteners which hold the drift eliminators in place, and subsequent failure of a portion of the drift eliminators on two of the four cooling towers. The failed drift eliminators were towards the top of the towers which has the greatest impact on drift carryover.
The automatic isolation of the RCIC turbine steam supply valve resulted from a false high flow signal in the leak detection instrumentation which monitors the steam flow for indication of a line break outside the primary containment. The specific transmitter
(**FT**) involved is in the Division 2 isolation circuitry. At the time of the main turbine trip, the associated steam pressure transient caused this instrument to exceed its trip setpoint. The redundant Division 1 channel also sensed the pressure transient, but with a lower magnitude and opposite polarity, and thus did not trip. The Division 1 signal was affected by the presence of a small amount of non-condensable gasses in the high side sensing line which caused the magnitude of the transient to be reduced and the polarity to be reversed, i.e. the sensed pressure transient was in the negative or decreasing direction. The most likely cause of the Division 2 trip was the presence of a partial blockage in the low-pressure sensing line, which had the effect of delaying the sensed pressure transient in the low side of the transmitter. The high side of the transmitter sensed the pressure transient before the low side, resulting in an apparent high flow signal. The low side sensing line tap for these transmitters is located on the bottom side of the flow elbow used for sensing the steam flow. This piping configuration makes this installation more susceptible to debris introduction into the sensing line. It is postulated that debris was partially blocking the orifice in the low side sensing line resulting in a delay in the hydraulic pressure transient sensed by the low side of the transmitter.U.S. NUCLEAR REGULATORY COMMISSION (1-2001)
LICENSEE EVENT REPORT (LER)
FAILURE CONTINUATION
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR l SEQUENTIAL I REVISION River Bend Station Unit 1 05000-458 2004 002 00 4
OF 4
IMMEDIATE CORRECTIVE ACTIONS
The insulators in the transformer yards where the RSS no. 1 and main generator lines terminate were either cleaned, or, for those damaged by the event, replaced as necessary.
The sensing lines for the RCIC high steam flow transmitters were high velocity flushed and the high points were vented to remove any blockage and non-condensable gases.
The calibration of the transmitters was checked, and they were found to be operating correctly.
CORRECTIVE ACTIONS TO PREVENT RECURRENCE Degraded drift eliminators in the cooling towers were replaced during the subsequent refueling outage that began on October 21, 2004. Additionally, insulators in the RSS no.
2 transformer yard were replaced.
Dummy insulators were mounted in several areas near the switchyard to allow monitoring for deposition of residue carried by cooling tower drift.
Regarding the trip of the RCIC steam supply valve, maintenance procedures have been revised to assure that the sensing lines on the affected high steam flow instruments are flushed during every cold shutdown.
PREVIOUS OCCURRENCE EVALUATION No previous reactor scrams or actuations of standby diesel generators have been caused at River Bend by the insulator flashover mechanism that initiated this event.
SAFETY ANALYSIS
This event is bounded by the main generator load reject scenario, as documented in the River Bend Updated Safety Analysis Report.
The invalid automatic isolation of the RCIC turbine steam supply isolation valve at the time of the main turbine trip is not safety significant, as the RCIC system is not credited for mitigation of any analyzed event. All other safety systems operated as designed.
Although reactor water level reached Level 2 for approximately one minute, a significant margin to the top of active fuel was maintained.
(NOTE: Energy Industry Component Identification codes are annotated as (**XX**).)