ENS 40305
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ENS Event | |
|---|---|
04:15 Nov 10, 2003 | |
| Title | Sequoyah Unit 2 Auxiliary Feedwater Actuation During Outage |
| Event Description | On 11/9/03 at 2315 [EST], with Unit 2 in Mode 3 in preparation for a Refueling Outage, an unanticipated ESF actuation occurred. With one Main Feedwater Pump (MFP) reset and one MFP tripped per the General Operating Procedures, Main Condenser Vacuum was being broken. Low Condenser vacuum caused the trip of the reset MFP. The signal for trip of two MFPs caused an Aux Feedwater (AFW) start. AFW was in service in manual control per procedure when the start signal was received; however, the start signal caused the Level Control Valves (LCVs) to reposition to their accident position.
The licensee notified the NRC Resident Inspector.
On November 9, 2003, after the planned Unit 2 reactor shutdown for refueling outage number 12, an auxiliary feedwater system start signal was initiated. During the shutdown, the auxiliary feedwater pumps (AFW) were started and both main feedwater pumps (MFP) had been tripped. Following transition from emergency operating procedure to the normal plant shutdown procedure, the feedwater isolation signal and one MFP trip were reset to allow shutdown of the turbine-driven pump, in accordance with plant procedures. As a result of the reactor coolant temperature decreasing below 540 degrees Fahrenheit, emergency boration was performed, and subsequently, control room personnel closed the main steam isolation valves (MSIVs) to limit cooldown of the RCS. After closure of the MSIVs, Operations personnel broke main condenser vacuum in accordance with plant procedures. The operators knew by their procedure that this would result in a low-condenser vacuum trip signal to the reset MFP trip bus and, with both MFPs trip bus tripped, the logic would be completed for initiation of an AFW start signal. The procedure states 'Breaking main condenser vacuum will cause loss of main feed pump turbine condenser vacuum to both MFPs resulting in an ESF actuation.' On November 10, 2003, at 0039 Eastern standard time, NRC was notified in accordance with 10 CFR 50.72 (b)(3)(iv)(A) of the ESF actuation (event notification 40305). 10 CFR 50.72 and 50.73 requires reporting of any event or condition that results in valid actuation of any of the systems listed in paragraph (b)(3)(iv)(B) except when the actuation results from and is part of a pre-planned sequence during testing or reactor operation. NUREG 1022 states that the intent is to require reporting of actuations of systems that mitigate the consequences of significant events. The breaking of the condenser vacuum was driven by plant conditions. However, the start signal to the AFW system was not to mitigate an event for the condition the plant was in (i.e., both MFPs had been secured and decay heat was being controlled by AFW in accordance with normal operating procedures) and is therefore considered a preplanned event. Based on the above information, the initiation of the AFW start signal is not reportable and the notification is being withdrawn. The licensee has notified the NRC Resident Inspector. Notified R2DO(Ayres) |
| Where | |
|---|---|
Sequoyah  Tennessee (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(iv)(A), System Actuation | |
| Time - Person (Reporting Time:+-3.6 h-0.15 days <br />-0.0214 weeks <br />-0.00493 months <br />) | |
| Opened: | Bill Harris 00:39 Nov 10, 2003 |
| NRC Officer: | Jeff Rotton |
| Last Updated: | Jan 5, 2004 |
| 40305 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Hot Standby (0 %) |
| After | Hot Standby (0 %) |
WEEKMONTHYEARENS 577792025-06-24T07:51:00024 June 2025 07:51:00
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50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip Due to Negative Rate Trip Following Rapid Turbine Load Reduction ENS 469912011-06-26T20:14:00026 June 2011 20:14:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip Due to Turbine Trip ENS 464922010-12-20T05:50:00020 December 2010 05:50:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Manual Reactor Trip Due to a Fire in the Main Generator Bus Duct ENS 464242010-11-17T03:10:00017 November 2010 03:10:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Manual Reactor Trip Based on Decreasing Steam Generator Level ENS 455202009-11-26T07:42:00026 November 2009 07:42:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Manual Trip Due to Loss of Vacuum on Turbine Driven Feedwater Pump ENS 450972009-05-27T23:04:00027 May 2009 23:04:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Reactor Trip from Power Range High Neutron Flux Rate ENS 450452009-05-07T02:56:0007 May 2009 02:56:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Manual Reactor Trip Due to Feed Regulating Valve Failure ENS 450292009-04-29T01:59:00029 April 2009 01:59:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Manual Reactor Trip Initiated as a Result of a Loss of Condensate Flow ENS 449342009-03-26T08:52:00026 March 2009 08:52:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip and Aux Feed Water Start Due to Loss of an Off Site Power Source ENS 449352009-03-26T08:52:00026 March 2009 08:52:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip and Aux Feed Water Start Due to Loss of an Off Site Power Source ENS 446492008-11-09T23:21:0009 November 2008 23:21:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Reactor Trip Breakers Opened Manually Due to Indicated Dropped Control Rod ENS 439092008-01-17T00:25:00017 January 2008 00:25:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Manual Reactor Trip Due to Lowering Steam Generator Level ENS 432332007-03-13T19:27:00013 March 2007 19:27:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Manual Reactor Trip Due to "a" Main Feedwater Pump ENS 431152007-01-23T17:44:00023 January 2007 17:44:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Reactor Trip Due to Feedwater Regulating Valve Failure ENS 424442006-03-22T21:24:00022 March 2006 21:24:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Turbine Trip / Reactor Trip Caused by Main Generator Trip ENS 415832005-04-09T15:11:0009 April 2005 15:11:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip on Turbine Trip Due to Low Auto Stop Oil Pressure on Pressure Switches ENS 414372005-02-24T02:06:00024 February 2005 02:06:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip on Low-Low Steam Generator Level ENS 405892004-03-15T20:18:00015 March 2004 20:18:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip Due to Main Generator Electrical Fault Signal ENS 404752004-01-25T08:16:00025 January 2004 08:16:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Unplanned Auto Start of Turbine Driven Auxiliary Feedwater Pump ENS 403052003-11-10T04:15:00010 November 2003 04:15:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Sequoyah Unit 2 Auxiliary Feedwater Actuation During Outage ENS 401132003-08-28T20:04:00028 August 2003 20:04:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Alert Declared Due to Reactor Protection System Failure 2025-06-24T07:51:00 | |
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