10 septembre 2014
Une mise à jour de requalification a été effectuée le 10 septembre 2014, soit un an après la survenue du problème.
Type : PWR - Puissance : 2 568 MWth - Première divergence : 09/1974
Available in english only.
Rappel : le cœur du réacteur étant critique, le système de contrôle de l’eau a été placé en manuel pour tenter de stabiliser le flux d’alimentation dont l’oscillation a, malgré tout, continué à croître. Cet arrêt manuel aurait été réalisé en anticipation d’un arrêt automatique du réacteur. Après l’arrêt du réacteur, l’engagement de 4 soupapes a échoué. La pression, qui a été abaissée selon les procédures, a permis d’activer les soupapes et le réacteur a été stabilisé.
Event Number : 49471
Facility : OCONEE
State : SC
Unit : [3]
RX Type : [3] B&W-L-LP
Event Date : 10/24/2013 - Event Time : 05:53
Emergency Class : NON EMERGENCY 10 CFR Section : 50.72(b)(2)(iv)(B) - RPS ACTUATION - CRITICAL
Initial PWR : 100 % Current PWR : 100%
Event Text
MANUAL REACTOR TRIP FROM FULL POWER DUE TO FEEDWATER SYSTEM OSCILLATIONS
"At 0553 EDT on 10/24/2013, Oconee Unit 3 was manually tripped due to oscillations in the feedwater system in anticipation of an automatic reactor trip. At 0549 EDT, Unit 3 began experiencing small feedwater oscillations. The feedwater control system was placed in manual in an attempt to stabilize feedwater flows. Feedwater oscillations continued to grow in magnitude and at 0553 EDT, a manual trip was directed to prevent an automatic reactor trip.
"Due to an RPS actuation, this event is being reported as a 4 and 8 hour Non-Emergency per 10 CFR 50.72 (b)(2)(iv)(B) and 10 CFR 50.72 (b)(3)
"Following the reactor trip, four main steam relief valves failed to reseat. Procedure guidance was utilized to reduce main steam system pressure by approximately 30 psig to reseat the main steam relief valves. All main stream relief valves are now reseated. All other post trip conditions were normal and all other systems performed as expected. Unit 3 is currently in Mode 3 and stable.
"Operations have been stabilized on Unit 3. A post-trip investigation is in progress, per site procedures and directives."
The licensee has notified the NRC Resident Inspector.
* * * UPDATE FROM BOB MEIXELL TO DONALD NORWOOD AT 1439 ON 9/10/14 * * *
"Duke Energy reviewed NRC Event Number 49471 against NUREG 1022, Rev 3, section 3.2.6, "System Actuation" and determined this event should have been reported only per 10 CFR 50.72 (b)(2)(iv)(B), RPS Actuation (while critical). Thus, Duke Energy is revising NRC Event Number 49471 to remove the 8-hour report criteria 10 CFR 50.72 (b)(2)(iv)(A). The NRC Resident Inspector was notified of this revised report.
"This update has no effect on safety significance."
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2014/20140911en.html#en49471
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