Neutronic design and evaluation of a PWR fuel assembly with accident tolerant-Fully Ceramic Micro-Encapsulated (AT-FCM) fuel

Fully Ceramic Micro-Encapsulated (FCM) fuel has greater capability of fission product retention and oxidation resistance. Presence of an additional fission product barrier in the form of strong SiC layer, make it an attractive option to be used as PWR fuel. In present studies, PWR fuel assemblies are transformed from standard 17 × 17 into new designs of 15 × 15 and 13 × 13 arrays with increased rod diameter but the same assembly dimension. These assemblies contain TRISO type fuel embedded in SiC matrix. For full implementation of the accident tolerant fuel concept, this study also investigates on the replacement of conventional Zircaloy-4 cladding with SS-304 and FeCrAl to minimize the hydrogen production due to interaction of water with cladding at high temperatures. Both are found to be feasible as a clad, however the neutronic penalty associated with SS-304 is very high, ultimately leading to shorter cycle length. A preliminary study of burnable poisons i.e. Erbia and Gadolinia as QUADRISO particles shows that the Erbia is preferable material due to its good depletion performance. In new assembly designs, temperature coefficients of reactivity (Doppler & Moderator) are negative through the life cycle of FCM fuel. Pin power peaking factors are less than 1.10 at BOC and RCCA worth is higher compared with reference assembly. Transuranic production is almost two to three times lower, compared with reference UO₂ fuel assembly. This is very important aspect of FCM fuel from proliferation point and viewed as an additional advantage.