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Simmer model of a low-enriched uranium non-power reactor


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Titre de la revue : Nuclear Engineering and Design Volume : 238 N° : 1 Pagination : 41-48 Date de publication : 01/01/2008

Type de document > *Article de revue

Mots clés > accident dislocation coeur, SIMMER

Unité de recherche > IRSN/DSR/SEGRE

Auteurs > BIAUT Guillaume, TOBITA Yoshiharu, WILHELM Dirk

Date de publication > 01/01/2008

Résumé

IRSN has started using the coupled neutronics-fluid dynamics code SIMMER [1] to study core-disruptive accidents induced by insertions of large reactivities to produce very short period power excursions in fuel plate-type and water-moderated experimental research reactors. Until now, French safety analyses retain a bounding thermal energy released and mechanical yields, deduced from analysis of destructive in-pile test programs, to study the behavior of such reactors and design their structures and containment. Contrary to this approach, the present research program aims at modeling the design basis accident of research reactors with a low enriched fuel using a CFD code. The objective is to analyze the effects of reactivity feedbacks and how they would limit the generated thermal energy released in the fuel. These aspects require a close coupling of the neutronics to the fluid dynamics analysis. The consequences of the nuclear power excursion, the changes of state of the fuel and the coolant, and ultimately the mechanical energy released are calculated by SIMMER. For large step-wise reactivity introductions, the Doppler effect and, at a lower extent, the fuel element thermal dilatation, which generates locally a decrease of the moderator to fuel ratio, limit the power excursion before the energy released is high enough to melt a large part of the fuel. Moreover, it has been shown that imposing an external reactivity as a step-wise or time dependent reactivity introduction yields results quite different from those of the physical movement of control rods.