Although the overall conversion experience was positive, the converted reactor core behaved somewhat differently than the calculated core. In particular, the converted reactor was substantially less reactive than was calculated. The reason for this difference is still not fully understood. In the near term, the UWNR staff is pursuing a plan to shuffle the core and reduce the number of reflectors. This will cause a slight reduction of the neutron flux in some positions; however, the reshuffling should increase the flux in other positions. This reshuffling would take the core from the “X” configuration of 21 fuel assemblies and 14 reflectors to a “+” configuration of 21 fuel assemblies and 6 reflectors (see Figure 3-2).

Overall, the conversion-related work enabled a widespread upgrade in UWNR staff’s analysis capabilities, and it has also provided opportunities for further analysis. For example, experimental research is ongoing to better understand natural circulation heat transfer in TRIGA-relevant conditions, and the fresh LEU core provides a wide variety of benchmark data for continuing to improve analytical capabilities.