Conceptual design for Japan sodium-cooled fast reactor. (2) Thermal-hydraulic design for reactor upper sodium plenum in JSFR

A conceptual design study for Japan Sodium-cooled Fast Reactor (JSFR) is being carried out in the framework of the 'Fast Reactor Cycle Technology Development (FaCT)' project. The present study focused on thermal-hydraulic issues in the reactor upper plenum. The first issue is thermal striping which might influence integrity of the lower part of the upper internal structure. The second is vortex cavitation which might influence integrity of the hot leg pipes. The third is cover-gas entrainment which might cause reactivity disturbance of the core. In this study, design measures to mitigate the thermal striping and the vortex cavitation and to prevent the gas entrainment have been proposed, and three-dimensional thermal-hydraulic analyses in the upper plenum have been performed to evaluate the measures. The effectiveness of the measures was well shown by the analyses to be reflected to the reactor vessel design of JSFR. (author)