Abstract
The progression of a severe accident in a CANDU type reactor is slow because the core is surrounded by a large quantity of heavy and light water which acts as a heat sink to remove the decay heat. Therefore, the source term formation is a complex and long process involving fission products transport and releasing in the fuel matrix, thermal hydraulics of the transport fluid in the primary heat system and containment, deposition and transport of fission products, chemistry including the interaction with the dousing system, structural materials and paints, etc. The source term is strongly dependent on initial conditions and accident type. The paper presents chemistry aspects for a severe accident in a CANDU type reactor, in terms of the retention in the primary heat system. After releasing from the fuel elements, the fission products suffer a multitude of phenomena before they are partly transferred into the containment region. The most important species involved in the deposition were identified. At the same time, the influence of the break position in the transfer fractions from the primary heat system to the containment was investigated.
Kurzfassung
Die Abfolge bei einem schweren Unfall in einem CANDU-Reaktor ist langsam, da der Kern mit großen Mengen leichten und schweren Wassers umgeben ist, das als Wärmesenke für die Zerfallswärme dient. Deshalb ist die Quelltermbildung ein komplexer und langwieriger Prozess der Transport und Freisetzung von Spaltprodukten, Thermohydraulik der Transportflüssigkeit im primären Wärmetransportsystem und im Containment, Deposition und Transport von Spaltprodukten, chemische Aspekte, einschließlich der Wechselwirkung mit dem Löschwassersystem, dem Strukturmaterial, den Anstrichen, usw. Der Quellterm ist stark abhängig von den Anfangsbedingungen und der Art des Unfalls. In der vorliegenden Arbeit werden chemische Aspekte bei einem schweren Unfall in einem CANDU-Reaktor dargestellt in Form der Retention im primären Wärmetransportsystem. Nach Freisetzung aus den Brennelementen durchlaufen die Spaltprodukte eine Reihe von Prozessen bis ein Teil ins Containment überführt wird. Die wichtigsten Phänomene bei der Deposition werden aufgezeigt. Gleichzeitig wurde der Einfluss der Bruchstelle in den Übertragungsanteilen vom primären Wärmetransportsystem zum Containment untersucht.
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