Types of solvent extraction contactors in general commercial use for nonnuclear applications include [LI, М3, T2]:

1. Spray columns

2. Baffle-plate columns

3. Perforated-plate columns

4. Columns packed with Raschig rings or Berl saddles

5. Mixer-settlers

Some of this conventional equipment has been applied to the solvent extraction purification of natural uranium and thorium. All of these conventional gravity column contactors are less compact than is desirable for reprocessing irradiated reactor fuel. The height of a vertical — column gravity contactor equivalent to a single equilibrium stage of contacting is about 60 to 120 cm, so very tall columns would be needed for the 10 or more theoretical stages needed for some of the separations in fuel reprocessing.

The need for compact contactors in reprocessing irradiated reactor fuel, as well as the need for many stages and small inventory in purifying special organic materials and pharmaceutical products, has stimulated the development of solvent extraction contacting equipment with reduced holdup, reduced stage height, or both. Most of these devices have in common the input of mechanical energy to promote contacting of phases, separation of phases, and/or counter­current flow. Contactors that have been used in reprocessing irradiated reactor fuel are listed in Table 4.12, adapted from a compilation by Davis and Jennings [D1 ]. Additional high- performance contactors that have been used in some nuclear applications and in the pharmaceutical industry include the Fenske-Long extractor, a vertical stack of mixer-settlers, and the Podbielniak centrifugal extractor [Т2].

The contactors used in nuclear applications are described in the following sections.