Role and approach to the recriticality elimination with utilizing the in-pile test reactor of the IGR research graphite reactor

A basic concept of the recriticality-free core is to prevent any large-scale molten fuel compaction that might induce super-prompt criticality and this is achieved by assuring sufficient early fuel discharge from the core in case of fuel melting. For this purpose, a function of Controlled Material Relocation (CMR) is required, when the fuel assembly becomes molten and begins to propagate to the neighboring subassemblies. A simples design to realize CMR is proposed as FAIDUS, i.e., Fuel Assembly with Inner Duct Structure, core concept, where the inner duct has a role to enhance the axial discharge capability of molten fuel from the core. The advantage of FAIDUS is that the behavior of molten fuel discharge can be rather one-dimensional and thus this mechanism can be demonstrated in the experiment