Reevaluation of Burnable Poison Effects in a VHTR

For a safe and reliable operation of the block-type VHTR (Very High Temperature Reactors), a burnable poison (BP) is inevitable to reduce the burnup reactivity swing and to control the core power distribution. The objective of this work is to find a promising BP material and to optimize the BP design in terms of the core performances. A 600MWth VHTR core, which was modified from the GT-MHR design, is considered for the neutronic study. A sintered mixture of BP and a carbon matrix is adopted for the BP application since it provides a residual reactivity and is less costly, as compared with the coated particle type one. Our previous work showed that B4C provides a better performance than Er2O3, Gd2O3. In this work, a more comprehensive evaluation is implemented for more BP materials and a physics study is done to minimize the reactivity swing