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Uncontrolled withdrawal of a control rod without SCRAM

Reaktivitätseintrag bei unkontrolliertem Herausziehen eines Regelstabes ohne SCRAM
T. Abou-El-Maaty
From the journal Kerntechnik

Abstract

In the present work, the thermal-hydraulic analysis of reactivity-induced transients in a Low Enriched Uranium (LEU) core of a typical material test research reactor is conducted using the previous program developed Khater et al. The analysis was done for the uncontrolled withdrawal of a control rod under scram-disabled conditions. The initiating event reactivity was considered with and without influence of the reactivity efficiency curve (“S” curve). The results of the transient calculations are analyzed and compared with each other. In the transient without the “S” curve influence, a high primary peak power of 406.18 MW is attained and a clad melt down is occurring after 1.85 s. In the transient with the “S” curve influence, a super prompt highly critical situation is produced (1.762 $ at 0.895 s) with a very high primary peak power of 801.05 MW at 0.912 s. A fast clad melt down is resulting in the hot channel at 1.088 s and a stable film boiling is occurring. This study shows that the influence of the reactivity efficiency curve results in higher peaks in power and temperatures (fuel, clad and coolant) with a fast clad melt down than that of a linear assumption.

Kurzfassung

In der vorliegenden Arbeit wurden die reaktivitäts-induzierten Transienten in einem Kern mit niedrig angereichertem Uran eines typischen Materialtest-Forschungsreaktors mit Hilfe des zuvor entwickelten Rechencodes ETRR2-RIA thermohydraulisch analysiert. Die Analyse wurde für den Fall eines unkontrollierten Herausziehens eines Regelstabes ohne SCRAM durchgeführt. Die bei diesem Ereignis freigesetzte Reaktivität wurde mit und ohne den Einfluss der Reaktivitätsleistungskurve (“S“-Kurve) betrachtet. Die Ergebnisse der Transientenberechnung werden analysiert und miteinander verglichen. Bei der Transiente ohne “S“-Kurven-Einfluss wird eine promptkritischer Zustand (1,762 $ bei 0,895 s) mit einer sehr hohen primären Leistungsspitze von 801,05 MW nach 0,912 s erzeugt. Dies verursacht ein schnelles Schmelzen der Hüllrohre im Heißkanal nach 1,088 s und ein stabiles Filmsieden. Diese Studie zeigt, dass der Einfluss der Reaktivitätsleistungskurve zu höheren Leistungs- und Temperaturspitzen (Brennstoff, Hüllrohre und Kühlmittel) mit einem schnelleren Schmelzen der Hüllrohre führt als dies bei einer linearen Annahme der Fall ist.

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Received: 2007-3-20
Published Online: 2013-04-05
Published in Print: 2007-11-01

© 2007, Carl Hanser Verlag, München