High Flux Particle Bed Reactor Systems for Rapid Transmutation of Actinides and Long Lived Fission Products

An initial assessment of several actinide/LLFP burner concepts based on the Particle Bed Reactor (PBR) is described. Core configurations consisting of 72-85 Pu fuelled “driver,” and ~42 actinide loaded “target” PBR fuel elements in a low temperature D₂O, or beryllium carbide moderator/reflector are examined. Direct cooling of the HTGR BISO/TRISO type particles by radial flow of pressurized helium gas through the fuel bed allows high power densities (~5 MW/l), and high flux levels (~1.0E16 n/cm²-sec). As a result, up to ~50 % of the actinides in the target elements are burned in a postulated 20 day cycle.

The PBR based actinide burner concept possesses a number of safety and economic benefits relative to other reactor based transmutation approaches. These include a low inventory of radionuclides (~5% of that in a commercial LWR), and high integrity, coated fuel particles which can withstand extremely high temperatures, while still retaining virtually all fission products. This ensures large thermal margins under normal operating conditions, and minimizes the potential source term in postulated accidents. In addition, the pressure tube design and the possibility of on-line refueling offer further potential safety and economic advantages.