ENS 45180
ENS Event | |
|---|---|
20:09 May 19, 2009 | |
| Title | Invalid Feedwater System Actuation While Shutdown |
| Event Description | On 5-19-09 ONS [Oconee Nuclear Station] Unit 3 was in Mode 3 during startup from a refueling outage. At 1609 EDT the 3A Motor Driven Emergency Feedwater Pump (MDEFWP) unexpectedly started when the control switch was placed in the AUTO2 position as part of system alignment prior to unit startup. Investigation found that the impulse line for the hydraulic oil pressure switch on the operating 3A Main Feedwater Pump was clogged, causing sensed pressure to read below setpoint. Repositioning the control switch enabled the 3A MDEFWP auto start circuitry, which immediately actuated due to the pre-existing false low pressure indication. Several other redundant indications validated that the pressure signal to the pressure switch was false and that actual hydraulic oil pressure remained above the pressure switch setpoint. Although the pressure switch did see low pressure in the impulse line, the actuation is considered invalid since the signal was based on a false reading that did not represent actual plant conditions.
Therefore this report is being made under 10 CFR 50.73(a)(1) and 50.73 (a)(2)(iv)(A). Per NUREG-1022, Rev. 2 the following information is requested: A) The specific train(s) and system(s) that were actuated. 3A Motor Driven Emergency Feedwater Pump (MDEFWP) which feeds the 3A Steam Generator (SG). B) Whether each train actuation was complete or partial. The train actuation was considered complete. The pump started per the signal and operated as required/expected in response to the signal. This pump is the only component in the train which receives a specific signal as part of the actuation circuitry. C) Whether or not the system started and functioned successfully. The 3A MDEFWP started and the system functioned successfully. The EFW control valve (3FDW-315) is set to control at 30 inches (SG startup level) versus 25 inches for Main Feedwater control. Therefore the SG level increased and the train then controlled at approximately 30 inches while an investigation determined the reason for the actuation (as explained above). The 3A MDEFWP was stopped at 2050 EDT and returned to normal status. Initial Safety Significance: Due to low feedwater demand at the time, there was little impact on the unit. Since the SG level was maintained above the normal control system setpoint, Main Feedwater flow was automatically reduced to compensate for the EFW flow. The 3A MDEFWP and associated pressure switch/actuation circuit were declared inoperable during pump shutdown and restoration to normal. Corrective Action(s): After troubleshooting identified the clogged impulse line, it was isolated and cleared. The 3A MD EFWP and the associated pressure instruments were returned to service. The licensee notified the NRC Resident Inspector. |
| Where | |
|---|---|
Oconee  South Carolina (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation | |
| Time - Person (Reporting Time:+1028.17 h42.84 days <br />6.12 weeks <br />1.408 months <br />) | |
| Opened: | Randy Todd 16:19 Jul 1, 2009 |
| NRC Officer: | Mark Abramovitz |
| Last Updated: | Jul 1, 2009 |
| 45180 - NRC Website | |
Unit 3 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Hot Standby (0 %) |
| After | Hot Standby (0 %) |
WEEKMONTHYEARENS 480302012-04-23T00:58:00023 April 2012 00:58:00
[Table view]10 CFR 50.73(a)(1), Submit an LER Keowee Hydro Power Station Automatically Started Based on an Invalid Signal ENS 465442010-11-18T07:45:00018 November 2010 07:45:00 10 CFR 50.73(a)(1), Submit an LER Invalid Actuation of Motor Driven Emergency Feedwater System ENS 451802009-05-19T20:09:00019 May 2009 20:09:00 10 CFR 50.73(a)(1), Submit an LER Invalid Feedwater System Actuation While Shutdown ENS 431462006-12-09T02:43:0009 December 2006 02:43:00 10 CFR 50.73(a)(1), Submit an LER Invalid Efw Actuations Due to an Issue in Sg Dryout Protection Circuit ENS 416492005-04-29T05:05:00029 April 2005 05:05:00 10 CFR 50.73(a)(1), Submit an LER Emergency Hydro Generators Auto Start - Unknown Cause ENS 406862004-03-20T19:59:00020 March 2004 19:59:00 10 CFR 50.73(a)(1), Submit an LER Invalid Actuation of the Motor Driven Emergency Feedwater Pumps 2012-04-23T00:58:00 | |