2017 | AFC ACCOMPLISHMENTS 182 Figure 2. Example fuel designs for (a) a once-through fuel system; and (b) a design when fuel recycling is anticipated. Accomplishments: The major accomplishment was to refocus the test program on once- through fuel systems and fuel designs for enhanced actinide utilization. For a once-through fuel system, the elimination of bond sodium suggests that an annular fuel geometry is preferred with either a mechanical bond or with a narrow helium-filled gap between the fuel and cladding to assure the transport of thermal energy from the fuel into the coolant. The focus of development will be on designs appropriate for the second generation, sodium-free fuel system associated with theVersatileTest Reactor. For this application, burnup requirements are expected to be on the order of 10 at.%, so designs that use well-studied fuel alloys of either U-10Zr or U-20Pu-10Zr combined with a smear density of 75 percent are expected to be sufficient.