8 janvier 2013
Le 8 janvier à 16h40, l’unité 2 de la centrale de South Texas s’est arrêté en urgence. L’alimentation électrique principale a été perdue suite à un incendie ou une explosion sur un transformateur principal d’alimentation du réacteur.
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En plus de la perte du transformateur principal, plusieurs lignes de distribution électrique secourues et non secourues ont été perdues. Le générateur diesel de secours a pris le relais d’alimentation de quelques uns des circuits électriques perdus. Les pompes de refroidissement du circuit primaire ayant perdues leurs alimentations électriques, le refroidissement s’effectue par convection naturelle ! Les soupapes ont relâché à l’atmosphère la vapeur liée à l’excès d’énergie (ndr : passage en quelques minutes d’une puissance de près de 4 000 MW thermiques à quelque kW ). Une situation critique a été déclarée. L’unité 1 n’a pas été affectée par cette évènement.
Facility : SOUTH TEXAS - Region : 4 State : TX Unit : [2] Date : 01/08/2013 Notification Time : 18:15 [ET] - Event Date : 01/08/2013 - Event Time : 16:40
Emergency Class : UNUSUAL EVENT
EMERGENCY DECLARED RPS ACTUATION - CRITICAL
Initial PWR Initial RX Mode 100 % Current PWR Current RX Mode Power Operation 0 % Hot Standby
Event Text
UNUSUAL EVENT DECLARED DUE TO MAIN TRANSFORMER FIRE
"Fire in Unit 2 main transformer 2A. Reactor trip. Two train of offsite power lost to Unit 2."
"An Unusual Event was declared based on EAL HU-2 - Fire or explosion in protected area or switchyard which affects normal plant operations."
At 1655 CST, South Texas Unit 2 declared an Unusual Event due to a main transformer fire. Unit 2 tripped from 100% power and is currently at 0% power in Mode 3. The transformer fire is out. In addition to the loss of the main transformer, several safety related electrical busses and non-safety electrical busses lost offsite power. The appropriate emergency diesel generators started and powered the safety related busses. Unit 2 is currently stable and on natural circulation due to the loss of power to the reactor coolant pumps. Auxiliary feedwater is functioning as required and decay heat is being removed through the steam generator atmospheric relief valves. Unit 1 was unaffected by the event.
The licensee notified the NRC Resident Inspector.
Notified DHS SWO, FEMA, DHS NICC and NuclearSSA via email.
* * * UPDATE FROM RICK NANCE TO BILL HUFFMAN AT 2055 EST ON 1/8/2013 * * *
"On January 8, 2013, at 1640 CST, a failure of the Unit 2 Main Transformer occurred which resulted in a Unit 2 automatic trip. The failure of the main transformer resulted in a fire and damage to the transformer. The onsite fire brigade responded to the fire. The fire was declared under control at 1649 CST and declared out at 1656 CST. No offsite assistance was required.
"An Unusual Event was declared at 1655 CST for initiating condition HU-2 (Fire or explosion in protected area or switchyard which affects normal plant operations) due to the main transformer fire.
"Due to the site electrical lineup at the time, the loss of the main transformer resulted in a loss of power to 4160 ESF buses 2A and 2C, and associated Standby Diesel Generators 21 and 23 started as required and loaded on to their respective buses. 4160 ESF bus 2B remained energized from offsite power during this event and Standby Diesel Generator 22 did not start since an undervoltage condition did not exist on its ESF bus.
"All three (3) motor-driven and the steam-driven Auxiliary Feedwater Pumps started as required. The Main Steam Isolation Valves were closed in accordance with procedure to limit plant cooldown. Decay heat is being removed via Auxiliary Feedwater with Steam Generator Power Operated Relief Valves.
"Following the reactor trip, Pressurizer Power Operated Relief Valve 656A momentarily lifted and re-closed.
"There were no personnel injuries and no radiological release as a result of this event. A press release has been issued.
"The plant is currently stable in Mode 3 and the cause of the event is under investigation.
"The Unusual Event was terminated at 1947 CST on 1/8/2013."
The licensee notified the NRC Resident Inspector.
Notified R4DO (Gaddy), NRR (Leeds), R4 (Reynolds), IRD (Gott), NRR EO (Hiland). Notified DHS SWO, FEMA, USDA, HHS, DOE, DHS NICC, EPA, and NuclearSSA via email.
Source : https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2013/20130109en.html
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