There are remaining fuel development and fabrication challenges asso­ciated with producing the UMo monolithic LEU fuel that will be required to convert HFIR:

• Fuel development is still under way, and the results will affect the final LEU fuel design. A fuel irradiation test series is currently ongoing at Idaho National Laboratory (INL); ORNL expects that this testing (which includes fuel failure testing) will guide safety and other calculations. The analysis of the fission product release from these tests will be most helpful.

• Fuel fabrication methods still need to be developed for producing variable radial and axial fuel thicknesses. In addition, the safety analyses rely on precise manufacturing tolerances, so for HFIR more than other reactors, fuel fabrication will need to be very precise.

• Criticality testing of the fuel will need to be completed. A facility will need to be identified for this purpose.

• Reactor startup testing will need to be conducted both at low power (to validate the analyses) and at full power (to demonstrate fuel performance and the preservation of key mission capabilities).

• Finally, ORNL will need to plan and assess the impacts of initial commissioning as well as the transition from HEU operation to full LEU operation.