ENS 45850
ENS Event | |
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23:17 Apr 16, 2010 | |
Title | Loss of Cooling Accident Signal Due to High Drywell Pressure Signal |
Event Description | On April 16, 2010 at 1917 hrs., Unit 1 received an ECCS [emergency core cooling system] loss of cooling accident (LOCA) signal on high drywell pressure. Based on plant data, drywell pressure reached a maximum pressure of approximately 1.25 psig, which is below the LOCA and RPS [reactor protection system] signal actuation pressure of 1.85 psig. At this time, the cause of the drywell pressure increase is under investigation. RPS logic did not initiate due to drywell pressure not reaching the actuation setpoint of 1.85 psig. Although the ECCS logic prematurely actuated, the signal is being treated as 'valid' for the ECCS actuation until further investigation is completed. All expected ECCS actions occurred as a result of the signal. The LOCA logic has been reset and all affected systems have been returned to normal or standby configuration.
As a result of the LOCA system actuations, several cooling tower fans tripped and condenser vacuum began to decrease. Reactor power was reduced to approximately 86 percent as a result of decreasing condenser vacuum. Power is being maintained at approximately 86 - 88 percent at this time. There are no other plant issues or concerns at this time. The licensee notified the NRC Resident Inspector. According to the licensee, normal drywell operating pressure is .5 to 1.2 psig. Prior to the event, drywell pressure had been steady at approximately 1.0 psig. Current drywell pressure is .6 psig. According to the licensee, ECCS systems that started (but did not inject) included: Core Spray pumps, Residual Heat Removal pumps, High Pressure Coolant Injection pump, and the Diesel Generators. An event review team is assessing this event to determine the root cause.
On April 16, 2010, Hatch Unit 1 received a LOCA ECCS initiation from a high drywell pressure signal. Based on the information available at that time, a notification was made to the NRC assuming the signal to be valid until further investigation could be completed. After further review, the determination has been made that the initiation signal originated from a faulted ATTS [Analog Transmitter Trip System] card and not from a valid high drywell pressure condition. Based on this information, this condition did not require an NRC notification in accordance with 10CFR50.72 and, as such, is being retracted through this updated response. The licensee notified the NRC Resident Inspector. Notified the R2DO (Hopper) |
Where | |
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Hatch Georgia (NRC Region 2) | |
Reporting | |
10 CFR 50.72(b)(3)(iv)(A), System Actuation | |
Time - Person (Reporting Time:+2.2 h0.0917 days <br />0.0131 weeks <br />0.00301 months <br />) | |
Opened: | Al Manning 01:29 Apr 17, 2010 |
NRC Officer: | Donald Norwood |
Last Updated: | Apr 17, 2010 |
45850 - NRC Website
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Unit 1 | |
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Reactor critical | Critical |
Scram | No |
Before | Power Operation (100 %) |
After | Power Operation (86 %) |
WEEKMONTHYEARENS 570212024-03-11T17:37:00011 March 2024 17:37:00
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ECCS Discharge Manual Reactor Scram After Feed Pump Trip ENS 443372008-07-04T12:39:0004 July 2008 12:39:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Scram on Turbine Trip ENS 440462008-03-07T19:46:0007 March 2008 19:46:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation, 10 CFR 50.72(b)(2)(iv)(A), System Actuation - ECCS Discharge Automatic Reactor Scram with Hpci/Rcic Actuation Due to Loss of Condensate Feedwater ENS 435522007-08-07T19:06:0007 August 2007 19:06:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Reactor Scram on Low Reactor Water Level Following Partial Loss of Condensate Feedwater Flow ENS 420962005-10-29T17:25:00029 October 2005 17:25:00 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 Unusual Event - Main Transformer Fire ENS 417252005-05-23T21:47:00023 May 2005 21:47:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Manual Scram Due to Condenser Hotwell Chemistry ENS 410702004-09-25T05:06:00025 September 2004 05:06:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Group 2 Containment Isolation Actuation ENS 405652004-03-03T18:45:0003 March 2004 18:45:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Swing Diesel Generator Auto Started from a Bus Undervoltage Valid Signal 2024-03-11T17:37:00 | |