Fuel and core design studies on metal fuel sodium-cooled fast reactor (3). Joint research report for JFY2007 and 2008

A metal fuel core has specific features, in comparison with a mixed oxide fuel core, on higher heavy metal density, harder neutron spectrum, and more efficient neutron utilization. These features are strengthened when applying enlarged applicable design envelops of metal fuel specifications, sodium void reactivity, and, bundle pressure drops. A joint study on 'Reactor Core and Fuel Design of Metal Fuel Core of Sodium-cooled Fast Reactor' has been conducted by the JAEA and the CRIEPI, and this report shows the studies on (1) Applicable design envelopes of metal fuel specifications, (2) Conceptual core designs, and, (3) Safety features of metal fuel core. As for the metal fuel specifications, 1) fuel with lower Zr content limit of 3 wt% is assessed to be feasible, and 2) design parameter ranges on Pu enrichment, Miner Actinide content, fuel smear density, and, fuel stack length are proposed for conceptual design studies. The conceptual core designs for realizing specific features of 1) high breeding ratio (∼1.40) without employing blankets, and 2) reduced (∼12%) Pu-fissile inventory with high breeding ratio (∼1.37) are presented. A simplified model of FBR deployment scenario is developed - under the scenario requiring large share of FBR fleet, deployment terms of the high breeding concept and the reduced Pu-fissile inventory concept are shortened ∼14% and ∼19%, respectively. For the safety study, severe event after the ULOF is estimated based on existing analyses. The event would be terminated in the early stage instead of the high peak power, because the moderated linear heat power of the designed metal fuel results in so-called extrusion fuel breach mode. (author)