The political claim for conversion of the neutron source FRM II to or below 50% enrichment lasts now for at least 1½ decades. All promises to solve the issue were done with expectations for new highest density UMo fuels to come in time. Qualification of a new UMo fuel for high power research reactor conversion in Europe and the US is instead expected with a timeframe of still more than a decade from now on (till 2030).
The compact fuel element of FRM II actually uses U3Si2 fuel of up to uranium densities of 3gU/cc at maximum 93% enrichment. This work reflects several MEU options for the FRM fuel element with different fuels, and finally with this U3Si2 backup fuel, which is rather well qualified since the ‘90s to achieve high burn up or fission density levels in high flux reactors till density of 4.8 gU/cc. One can further suppose most reserved plate dimensions in thickness values and width, the current ones and allow no change with inner and outer core radii.
The final statement of this work is, that one could stay fine with an enrichment of 50% or marginally below for a fuel element of FRM II at identical geometry (except longer plates) in the actual central channel, what would reduce adaptations at the reactor to a minimum. The solution could be without real loss for the user community or any reactor performance thanks to main gains due to an outer boron coat [RRFM-16] at the element.
Dr. Markos Skoulatos