Fuel Arraying and Rod Dimensioning of FCM replacement fuel for LWRs

After Fukushima accident, necessity of developing an accident-tolerant fuel for existing LWRs has been raised. The joint R and D project (US-DOE funded) on the FCM replacement fuel for LWRs has been recently begun at KAERI. FCM refers to the fully ceramic micro-encapsulated fuel which is compacted hundreds of TRISO particles into ceramic conductive matrix pellet. The project aims to show the fuel feasibility and compatibility with existing LWR cores (OPR1000). They require new design to compensate the low fissile inventory of particle-based fuel and comprehensive qualification of neutronic, thermal hydraulics and mechanical aspect. Figure 1 shows the overall concept of the FCM replacement fuel. For a particle-based fuel, a thick coated layer surrounding UO2 kernel retains released fission gas within the fuel particle element and significantly reduce fissile inventory per unit fuel volume. On the consideration of low fissile inventory and high enrichment cost, FCM fuel will be a fat fuel with tight inter-rod spacing. Thus, this paper introduces some technical issues related to fuel arraying (fuel lattice formation) and fuel rod dimensioning (fuel rod diameter) of FCM replacement fuel for LWRs, based on the experience of developing dual-cooled annular fuel for existing LWRs