Neutronic design of advanced sodium cooled TRU burner cores using moderator rods and absorber region

In this paper, 400MWe sodium cooled fast reactor cores having high TRU burning rate are designed and neutronically analyzed. In particular, new fuel assembly concept having a thick duct is used in central region of the cores to achieve the power flattening under a single TRU contents in charging fuel by reducing fuel volume fraction in the central core region and the use of this new fuel assembly also increases TRU burning rate by reducing conversion ratio. To further increase TRU burning rate, B₄C absorber regions are considered to be placed in the axially central parts of all fuel rods and their combined effects with 12 ZrH_1.8 moderator rods per one fuel assembly on the core performances are analyzed in detail. The results show that the use of B₄C absorber in axially central region of core effectively reduces the sodium void worth and significantly increases TRU burning rate and that its combined use with ZrH_1.8 moderator rods leads to further improvements of core performances including TRU burning rate, sodium void worth, and Doppler coefficient. (author)