Prior to beginning the conversion analysis, some safety analysis param­eters at MITR were not well known, particularly for the finned cladding.

To complete the safety analysis, further information is being gathered on the following three topics:

• Finned channel hydraulic pressure drop. A flow experiment has been built, measurements have been made, and a finned channel correla­tion[65] describing the relationship between the pressure drop and the flow rate has been developed.

• Adequacy of the onset of nucleate boiling (ONB) correlation for finned channels.[66] For this purpose, the MITR boiling flow loop is being constructed to measure ONB for the LEU channel geometry and validate the Bergles-Rohsenow ONB correlation[67] [68] [69] for finned channels. This facility will be operational later this year.

• Oxide distribution in the finned cladding. The current burnup limit of 1.7 x 1021 fissions per cubic centimeter is based on an even 50 microm­eter-thick aluminum oxide distribution on the cladding. However, particu­larly within the finned region, the actual oxide distribution is unknown. MITR is currently using an eddy current probe for fin-tip measurements of oxide thickness. This thickness will then be compared with the operational history of the fuel element. Finally, a selected fuel element will be shipped to Idaho National Laboratory for evaluation of the oxide distribution in the areas between the fins.