Investigation of core deformation reactivity model improvement in plant dynamics analysis code during ULOHS test of U.S. experimental fast reactor EBR-II

Sodium-cooled fast reactors have intrinsic safety features decreasing reactor power during the increase of the core inlet temperature by the feedback reactivity due to the core deformation. It is necessary for the composition of the core highly of secure to understand the influence of the safety features with high accuracy. In this paper, to enable the plant dynamics analyses taking account of the thermal stratification in the cold pool, the 1D-CFD coupling method in which CFD was applied to the cold pool was applied to the ULOHS (Unprotected Loss Of Heat Sink) test performed in the experimental fast reactor EBR-II in the U. S. and the evaluation of the core inlet temperature could be improved. By using this 1D-CFD coupling method, sensitivity analyses concerning the core bowing reactivity were carried out with the aim of improving the evaluations of the core deformation reactivity. Through the numerical analyses, the applicability of the core bowing reactivity model to the test could be indicated. (author)