Convex core concept for fast reactors: 新道ブログ

When the conventional fast spectrum core is melted down, a large positive reactivity is inserted due to the decrease of average distance among the fissile nuclides which reduces the neutron leakage from the core and increase the fission reaction rate. The measure to prevent this positive reactivity was to install a fuel flow hole for the melted fuel to the outside of the core region. However the hole inversely affects core performances and provides difficuties to the core design. In order to solute this problem, a radial flow of melted fuel due to the leveling in the core is utilized. This idea was inspired when a concave core was researched in June, 2015. It was found that the slumping reactivity of the concave core, where the height of the outer core is more than that of the inner core, was larger than that of the conventional cylindrical core. Then I wondered how about the convex core, where the inner core is higher than the outer core. The Monte Carlo calculation result for a large fast reactor, where the inner core height is 100cm and the outer is 50 cm, and the levelized melted core height is 51 cm, was negative, about -2$.