Reactor Research Exchange Program. Components to be used in the JUPITER semi-industrial experimental plant which will have a daily throughput of 2 kg (Th,U)O/sub 2/ are described. A slab vessel was developed for use in the dissoIution of (Th,U)O/sub 2/ particles. Laboratory tests on dissolution of the particles and adjustment of the feed solution were conducted. An apparatus for continuous dissolution tests and an air-pulsed mixer-settler for extraction are also described. (JGB)