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Event Notification Report for February 16, 2021 - Texas- NRC: Emergency Class: Non Emergency

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  • Event Notification Report for February 16, 2021 - Texas- NRC: Emergency Class: Non Emergency

    U.S. Nuclear Regulatory Commission
    Operations Center

    Event Text
    EN Revision Imported Date: 2/16/2021


    "At 0526 [CST] on 02/15/2021, Unit 1 automatically tripped due to low steam generator levels. The low steam generator levels were due to loss of Feedwater pumps 11 and 13 (cause unknown).

    "Auxiliary Feedwater and Feedwater Isolation actuated as designed. All Control and Shutdown Rods fully inserted. No primary or secondary relief valves opened. There were no electrical problems. Normal operating temperature and pressure (NOT/NOP) is 567 degrees F and 2235 psig.

    "There were no significant TS LCOs entered.

    "This event was not significant to the health and safety of the public based on all safety systems performed as designed. Unit 2 was not affected. Decay heat removal is being controlled via Steam Dumps. [Auxiliary Feedwater is supplying water to the Steam Generators.] Offsite power is in the normal electrical lineup.

    "The NRC Resident inspector has been notified."

    Unit 2 was not affected and remains at 100% power.
    __________________________________________________ _______________________________________

    South Texas Project Unit 1 tripped at 0537 on Feb 15, 2021

    February 15, 2021
    By Rod Adams

    In addition to those other electricity supply system issues, at 0537 central time, there was an unscheduled trip at South Texas Project Unit 1. That nuclear generating plant usually produces 1350 MW of electricity.

    Vicki Rowland, the lead for Internal Communications at the STP Nuclear Operating Company provided the following narrative about the unit’s operating status.
    On Monday, Feb. 15, 2021, at 0537, an automatic reactor trip occurred at South Texas Project in Unit 1. The trip resulted from a loss of feedwater attributed to a cold weather-related failure of a pressure sensing lines to the feedwater pumps, causing a false signal, which in turn, caused the feedwater pump to trip. This event occurred in the secondary side of the plant (non-nuclear part of the unit). The reactor trip was a result of the feedwater pump trips. The primary side of the plant (nuclear side) is safe and secured.

    STP values safety over production, so our first priority is the safety of our teammates, especially regarding the freezing weather and road conditions.

    Secondarily our priority is the operating unit. Unit 2 is operating at 100 percent power. We evaluated Unit 2 and have confirmed that we do not have the same issues that caused the feedwater pump trips in Unit 1.

    STP crew members are safely working to promptly return Unit 1 to the grid. We are validating the issues that caused the feedwater pumps to trip and will take the necessary actions to prevent reoccurrence.

    STP has operated very reliably with only two reactor trips in the past several years. On May 1, 2016, the South Texas Project Unit 1 automatic reactor trip due to a main generator lock. Prior to that on Jan. 8, 2013, Unit 2 experienced an automatic reactor trip from full power caused by a main transformer fire.

    Update: (Feb 16, 2021 1345) Some people have wondered how “pressure sensing lines” for a feed water pump could have been affected by cold outside air temperatures. There are no turbine halls at STP, both of steam turbines are out in the open air. I’m sure there is a design reason for this choice, but it isn’t apparent. Here is a satellite photo of the site from Google Maps. End Update