b'Figure 2. Calculated evolution of fission rate and burnup over the first 7 cycles of irradiation for the U3Si2 disk specimens for different RAC locations indicated in the legend.is welded in a helium-argon mixtureis expected to start irradiation in early (bottom). Figure 2 shows the calcu- calendar year 2021 and finish irradia-lated burnup and fission rate evolutiontion during the fall of the same year. for the U 3 Si 2specimens over the firstFigure 3 shows temperature contour 7 cycles of irradiation. The numbersplots (in C) for a U 3 Si 2specimen and (RAC) indicated in the legend indicateits surrounding capsule components. the radial position (R=1, facing awayTemperature variations within the fuel from the HFIR core), the axial targetspecimens are calculated to be 5C. position (A=2, core midplane), and theFigure 4 shows calculated average fuel capsule position (C) within the target,and TM temperatures at beginning of numbered 16 from bottom to top.cycle (BOC) and end of cycle (EOC) The fission rates appear to approach afor cycles 1, 4, and 12. As expected, the steady-state value in the range of 100average fuel temperatures are constant W/g after reaching an equilibriumto within 40C by cycle 4 once between breeding and burning of Puequilibrium fission rates have been isotopes. The first (higher burnup)achieved. The calculated TM tempera-target is expected to finish irradia- tures are 30C lower than the fuel tion in early calendar year 2022. Thetemperatures. Irradiation of U 3 Si 2will second (lower burnup) target hasprovide new data regarding the irradia-not yet been inserted due to limitedtion performance of a candidate ATF position availability in HFIR. This targetto complement current ATF-1 integral 90 2020|AFC ACCOMPLISHMENTS'