Critical mass experiments to be conducted at HAPO will require dilute and concentrated plutonium solutions. Since very high plutonium concentrations (~2,000 g/l) cannot be attained in pumpable solutions, solid plutonium compounds will be utilized for this phase of the work. Mixtures of plutonium oxide and polyethylene, methyl methacrylate or paraffin compacted in containers have been considers for use in highly-concentrated plutonium systems of known hydrogen to plutonium atomic ratio (H/Pu).

During the period when the writer mixing fuel element was being evaluated, a small Litton glass lathe and a General Electric Fillerarc welder were used to weld the mixing spool to the fuel element. Due to the condition of these units and to the numerous difficulties encountered with them, it was deemed necessary to design and procure a semi automatic welding unit which could weld in excess of three hundred fuel elements per day.