2017 | AFC ACCOMPLISHMENTS 183 For a design that involves recycling of the fuel, high burnup designs provide substantial economic benefits, which in turn implies low smear densities to accommodate the accumulation of fission products. In this case, the presence of bond sodium provides significant benefit in terms of heat transfer and results in little additional cost to recycle the fuel. Unfortunately, the fabrication of annular fuel in a hot cell is judged to be difficult, while slotted fuel designs [1] can likely be manufactured by casting (see Figure 2 for a schematic). Concerns associated with slotted fuel designs include distortion of the fuel pin because of the non-uniform pressure exerted by the fuel onto the cladding and the potential for increased axial growth when compared to an annular design. However, once the fuel has swelled into the available void space (typically by 1-2 atom% burnup), the effect of the initial fuel geometry should be minimal. For a given fuel alloy composition, decreasing smear density also necessarily reduces the inventory of fissile material contained within the fuel rod.To offset this reduction, the behavior of pure uranium or uranium- plutonium alloys will be explored. However, given that a major benefit of U-10Zr is its increased resistance to fuel-clad chemical interaction, these fuel designs will require the development of liner or coating technologies to protect the clad from the fission products that accumulate as the fuel is burned. An alternative to both annular and slotted fuel designs would be to fabricate porous metallic fuel. If sodium bond was used in conjunction with fuel with elongated porosity, one potential advantage is that bond sodium could potentially be infiltrated into the fuel during fabrication and thereby reduce the uncertainty regarding the amount of sodium in the fuel during the course of irradiation. For the present time, however, annular fuel is the default geometry for once-through fuel systems and slotted designs are assumed to be more appropriate for the recycled fuel designs. Fabrication and testing of these fuel systems will be the focus of the program in the coming years. The testing program has been re-focused to support the Versatile Test Reactor and on fuel designs that will be able to achieve substantially higher burnups without a reduction in heavy metal inventory.