[en] A pilot unit for the treatment of spent solvent was built and operated to demonstrate the feasibility of the EUROWATT process and to treat all the spent organic solvents in storage on the Eurochemic site. A battery of mixer-settlers adapted to the process was tested. A prototype pyrolyser was developed and worked perfectly during the whole operating time of the unit. The present report describes the different parts of the apparatus, the controls and safety devices. The radioactive spent solvents have been treated in eight campaigns lasting one week each. Comments are given on the results obtained during operation. Finally, some improvements to the facility are suggested. (author)