Thermal-hydraulic analysis on Ex-Vessel fuel Storage Tank of MONJU at severe accident

In this paper, results of a thermal-hydraulic analysis on the Ex-Vessel fuel Storage Tank (EVST) of the fast breeder reactor MONJU at severe accident is described. Safety evaluations on this facility have ever been performed by using a one-dimensional flow network code. However, validation on a model of this code has been needed, because EVST has plenums and asymmetry equipment. Therefore we performed a CFD analysis under a condition of station blackout (SBO) in order to clarify the circulation flow rate and multidimensionality of the EVST. As a result, the following points were confirmed: 1) Circulation flow rate is maintained half of a flow rate at the rated operation condition at the minimum. 2) Thermal stratification arises in the lower plenum at SBO. 3) Circumferential distribution of flow rate at the lower plenum is made uniform at the inlet of the rotating rack. 4) Thermal-hydraulic behavior in the rotating rack is almost one-dimensional. (author)