Fast reactor modular island cores

As the most essential characteristics of fast breeder reactors must be safety as well as economy, a modular island core concept is proposed, to nullify the sodium voiding effect, while keeping neutronic performances of conventional homogeneous cores (high unitary power, high burn-up). In fact, very low or even negative sodium voiding effects are obtained, but mainly to the detriment of the core size, the length of the operating fuel cycle (about one year) and the fuel enrichment level. The two best modular island cores are composed of seven homogeneous modules and three heterogeneous modules. The most efficient coupling zone is made up of two rows of fertile blankets and one row of highly concentrated boron shielding. (author)