A number of equipment revisions have been recommended by the Engineering Department for conversion of Recuplex to a manufacturing facility. These revisions include three items affecting the critical mass safety of the solvent extraction system: replacement of the bottom disengagement section of the H-3 stripping column with an always safe unit; replacement of the H-9 and H-10 intercolumn, organic phase surge tanks with always safe tanks; and replacement of the colorimetric plutonium monitors in the aqueous and organic raffinate streams with units insensitive to stream contaminants. This memorandum is intended to clarify the needs for these equipment revisions in achieving a safe and flexible operating system and to indicate the relative effects of revising each of the various equipment pieces separately. The general bases for the present criticality control measures in the solvent extraction system are reviewed briefly prior to discussion of the individual revisions.