The pool-type reactor encloses primary pumps and IHXs located around the core barrel in a reactor vessel. Consequently, the reactor vessel diameter tends to be larger than that of loop-type reactor. From the viewpoint of commercialization in the future, the vessel diameter and its weight including sodium coolant will increase further. Moreover, the seismic loading conditions imposed on design works of the SFR concept are very severe for large vessel. For the heavy weight large vessel under severe seismic conditions, the buckling evaluation on the cylindrical part of the vessel is significant for a feasibility study. In this paper, the prospects are described in terms of seismic design to prevent buckling of the reactor vessel based on parameter studies with diameters of the vessel. In addition, the seismic isolation device which will be effective as a countermeasure is proposed in order to secure a margin against buckling of a large reactor vessel.