05000374/LER-2004-001, Regarding Reactor Protection Bus B Trip and Inoperable Automatic Depressurization Valves Due to Equipment Failure
| ML040970454 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 03/26/2004 |
| From: | Landahl S Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 04-001-00 | |
| Download: ML040970454 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3742004001R00 - NRC Website | |
text
Exebnsm Exelon Generation Company, LLC LaSalle County Station 2601 North 21'Road Marseilles, IL 61341-9757 www.exeloncorp.com Nuclear March 26, 2004 10 CFR 50.73 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 LaSalle County Station, Unit 1 Facility Operating License No. NPF-18 NRC Docket No. 50-374
Subject:
Licensee Event Report In accordance with 10 CFR 50.73(a)(2)(iv)(A) and (a)(2)(vii), Exelon Generation Company, (EGC), LLC, is submitting Licensee Event Report Number.04-001-00, Docket No.050-374.
Should you have any questions concerning this letter, please contact Mr. Glen Kaegi, Regulatory Assurance Manager, at (815) 415-2800.
Respectfully, Susan Landahl Plant Manager LaSalle County Station
Attachment:
Licensee Event Report cc:
Regional Administrator - NRC Region IlIl NRC Senior Resident Inspector - LaSalle County Station tn S
Abstract
At 2334 hours0.027 days <br />0.648 hours <br />0.00386 weeks <br />8.88087e-4 months <br /> on 2/1/04, the 2B Reactor Protection System (RPS) Motor-Generator (MG)
Set output breaker (EPMA D) tripped, resulting in a loss of the 'B' RPS bus.
The loss of the 'B' RPS bus resulted in a half-scram and 'B' side Group 1 (except Main Steam Isolation Valves), 2, 3, 4, 5, 6, 7 and 10 containment isolations.
The Group 10 isolation isolated the Instrument Nitrogen (IN) compressor and caused the rupture disk to rupture.
While the rupture disk was being replaced, nitrogen pressure to four Automatic Depressurization System (ADS) accumulators dropped below the Technical Specification required 150 psig, causing them to be declared inoperable.
The cause of the RPS MG Set output breaker trip was an erratic voltage regulator gain potentiometer.
The cause of the inoperability of multiple ADS valves was that the pressure regulator for the backup compressed gas bottle system was unable to maintain the required 150 psig ADS accumulator supply header pressure under low load conditions.
Corrective actions included replacing the RPS MG set voltage regulator, replacing the IN rupture disk and returning the IN compressor to service.
A long term corrective action for the IN pressure regulator will be evaluated.
NRC FORM 366 (7-2001)
(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 Form 366A)
- 2. The potentiometers on the 1A, 1B, and 2A RPS MG set voltage regulators will be wiped, and the voltage regulators calibrated (AT#198850-24).
- 3. Procedure LES-RP-101 "Inspection of Reactor Protection Motor-Generator Sets" will be revised to wipe the voltage regulator potentiometers prior to performing the four year load test (AT#198850-25).
- 4. A Training Request will be issued to evaluate whether a knowledge deficiency exists in Maintenance regarding the difference between burnishing and filing relay contacts (AT# 198850-26).
- 5. Plant Engineering will evaluate upgrades to the IN pressure regulator to prevent future occurrences (AT# 198871-04).
F.
PREVIOUS OCCURRENCES
LER 374/88-010 Unit Shutdown Due to Automatic Depressurization System Nitrogen Backup Pressure Regulator Failure This LER documented a previous occurrence of the IN regulator IN035 failing to maintain 150 psig in the ADS accumulator header.
Corrective actions were to inspect the regulator and to replace the stem assembly.
Additionally, a surveillance procedure was developed to cycle the regulator on a refuel basis.
Until this event, there have been no reportable events of this nature in the past 16 years.
G.
COMPONENT FAILURE DATA
General Electric, Voltage Regulator Circuit Board, Model# 3300A03B0061 General Electric CRl20A Relay Target Rock, Pressure Regulator, Model# 77U401