Core characteristics of breeding BWR for BARS (BWR with advanced recycle system)

An innovative BWR core has been proposed which aims at a breeding ratio of 1.0 or more as well as a negative void coefficient. This core is composed of two types of MOX fuel assemblies. One has a triangular tight lattice of fuel pin where the active core height is 1.6 m. The ratio of the flow area to the fuel area is about 0.5. The other type has the same lattice, but the core height is 0.8 m and a neutron-streaming channel is provided above the core region where no fuel pin is arranged in order to enhance the negative void reactivity coefficient. Our analysis shows that this type of core has a breeding ratio of 1.04 and a void coefficient of -1 x 10-4 Δk/k per 1% void increase when the thermal output was 3926 MW. It is also indicated that the core characteristics including breeding ratio are hardly influenced by the rare earth elements and minor actinides that are contained in MOX fuels fabricated with the dry-oxide-fuel-reprocessing. (author)