Neutronic Design of the Pb-ahtr

This study (1) investigates the neutronic characteristics of the Pebble Bed Advanced High Temperature Reactor (PB-AHTR); (2) compares the PB-AHTR neutronic performance against those of the alternative design options of He-cooled high temperature reactors using either pebble (PBMR) or prismatic (VHTR) fuel and against a liquid-salt cooled design version of the latter (LS-VHTR); (3) studies the possibility of incinerating TRU in the PB-AHTR feeding TRU from LWRs spent fuel. It is found that the optimal features a graphite-to-heavy metal ratio of ~360 and its reactivity coefficients are all negative. A comparison with the helium-cooled pebble-bed reactor and with a prismatic-fuel reactor that is cooled with either flibe or helium is also presented. It is found that the PB-AHTR offers similar discharge burnup as the other three designs. As compared to the gas-cooled pebble bed, the PB-AHTR uranium loading and energy generated per pebble are ~2.5 times higher. When loading TRU in the pebbles it is found that they can reach a burnup as high as 685 GWd/tHM and the core average reactivity coefficients are all negative. About 70% of the initial load of HM is incinerated in a single pass.