05000443/LER-2003-002
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 40286 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 4432003002R00 - NRC Website | |
1. Description of Event At approximately 1948 hours0.0225 days <br />0.541 hours <br />0.00322 weeks <br />7.41214e-4 months <br /> on October 31, 2003, with the plant operating in Mode 1 at 100% power, Seabrook Station experienced an automatic reactor trip following a transfer of the 70 Main Feed Pump (MFP) [SJ] from the "Manual" to "Automatic' mode of operation. At the time of the reactor trip, plant personnel were troubleshooting the Emergency DC Lube Oil Pump (DC Pump) for the "A" MFP. The Emergency DC Lube Pump was experiencing numerous Intermittent starts. in order to assist in the performance of troubleshooting activities, the 'A" MFP slave controller was placed in the manual mode of operation. When the slave controller was returned to the automatic mode of operation, the 'A" MFP control valves closed and the pump coasted down_ Due to the reduced feedwater flow, steam generator levels decreased over an approximately forty-eight second period until an automatic trip occurred when the lo-to level setpoint (25%) was actuated.
Plant systems responded normally as a result of the reactor trip. The Emergency Feedwater (EFW) [BA] system actuated as designed to restore steam generator water levels. All control rods fully inserted. No primary or secondary relief valves lifted. This event was reported to the NRC at 2115 on October 31, 2003 (Event Number 40286) pursuant to the requirements of 10 CFR 50.72(b)(2)(tv)(8) and 10 CFR 50.72(b)(3)(1v)(A). This event is also reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A).
II. Cause of Event
The cause of the plant trip was a loss of the 'A MFP when its controller was placed in the automatic mode of operation from the manual mode of operation. The loss of the "A" MFP was due to a degraded circuit board/component in the "A" MFP General Electric MDT-20 Governor Speed Controller. The failed circuit board, in response to a signal change such as what is experienced when switching from manual to auto control, produced an output to drive the "A MFP control valves closed which is not a normal response.
Ill. Analysis of Event There were no adverse safety consequences as a result of this event. The Feedwater system is designed to supply feedwater to the steam generators to maintain the proper steam generator levels during steady-state and transient conditions. The feedwater flow from the two variable speed, horizontal, turbine-driven steam generator feedwater pumps combines into a common header that feeds two parallel high pressure heaters. The outlets of the high-pressure heaters combine into a common header. From this common header, an individual feedwater line supplies each steam generator.
The loss of normal feedwater results in a reduction of the capability of the secondary system to remove heat generated in the reactor core. In the event that the Feedwater system becomes unavailable, the Emergency Feedwater (EFW) system is designed to provide the emergency supply of feedwater. The EFW system is actuated automatically on loss of offsite power, lo-lo level in any of the steam generators, safety injection signals, or an Anticipated Transient Without Scram (ATWS) mitigation system actuation signal to remove sufficient heat to prevent over-pressurization of the Reactor Coolant System, and to allow for eventual system cool-down. The loss of normal feedwater is classified as an American Nuclear Society (ANS) Condition II event, a fault of moderate frequency and is a condition analyzed in Chapter 15 of the Seabrook Station Updated Final Safety Analysis Report.
During this event, the loss of the "A' MFP resulted in a reduced feedwater flow, which caused steam generator levels to rapidly decrease to the lo-lo setpoint resulting in a reactor trip. Plant systems responded normally as a result of the reactor trip. The Emergency Feedwater (EFW) system actuated as designed to restore steam generator water levels. All control rods fully inserted and no primary or secondary relief valves lifted.
IV. Corrective Actions
The failed circuit board in the A' MFP Genera! Electric MDT-20 Governor Speed Controller was replaced.
V. Additional Information
None VI. Similar Events This is the first event of this type within the past two years. Previous reactor trips due to lo-lo steam generator levels were described In LERs 90-025-00, 92-017-00, 93-01-00, 97-012-00 and 00-004-00. A review of the causes, failures, and sequence of these events indicates that they are unrelated to this event.
NRC FORM 365.4 (I.2e31)