Very-high-flux research reactors based on particle fuels

A new approach to high-flux research reactors is described, the VHFR (Very-High-Flux Reactor). The VHFR fuel region(s) are packed beds of HTGR-type fuel particles through which coolant (e.g. D2O) flows directly. The small particle diameter (typically of the order of 500 microns) results in very large surface areas for heat transfer (approx. 100 cm2/cm3 of bed), high power densities (approx. 10 megawatts per litre), and minimal ΔT between fuel and coolant (approx. 10K) VHFR designs are presented which achieve steady-state fluxes of approx. 2x1016 n.cm-2.s-1. Deuterium/beryllium combinations give the highest flux levels. Critical mass is low, approx. 2 kg 235U for 20% enriched fuel. Refuelling can be carried out continuously on-line, or in a batch process with a short daily shutdown. Fission product inventory is very low, approx. 100 to 300 grams, depending on design. (author)