2018 | AFC ACCOMPLISHMENTS 134 on the size of the gap between the rodlet and capsule and the composi- tion of the gas in that gap. Fill gases can be varied from 100% helium for a higher conductivity gas gap to 10% helium in 90% argon if lower conductivity gas is required. As built calculations using the final as-built dimensions and fuel compositions indicated that two of the five capsules would run excessively hot in the reactor, leading to likely failure. In order to mitigate this risk a swaging process was developed to reduce the size of the rodlet-capsule gas gap.The swaging process successfully reduced the capsule diameter while not impacting the rodlet on both capsules while maintain design tolerances. Based on the re-worked dimensions calculations showed that one capsule, IRT1-C3, would still run too hot. This capsule was disassembled using standard machining techniques and the rodlet recovered. Based on as built dimensions and fuel compositions a new, higher conductivity, fill gas was specified.Table 2 shows the fill gas compositions of all capsules. It was originally planned to insert all five capsule in reactor cycle 164A (June 2018), however, because IRT1-C3 had to be re-built it was inserted a cycle later in 164B (September 2018). In conclusion, five AFC-OA drop in style irradiation tests were fabricated using U-TRU feedstock recovered from recycled used MOX fuel.