[en] The vapor compression evaporator plant with a capacity of 3 m³/hr was installed at the Japan Atomic Energy Research Institute, Oarai Establishment in March of 1978. After completion, in order to asertion both the characteristic inherent in the plant and the optimum operating condition, a series of tests were conducted using both non-radioactive liquid and a radioactive solution which were prepared for these purposes. As a final step we ran the facility to gain experience in the operation and maintenance of the plant using real liquid radioactive waste. The items ascertaind through conducting these tests, the operation and maintenance of the facility were as follows; (1) the designed treatment capacity of 3 m³/hr was attained; (2) the controllability of the plant was satisfactory down to the half capacity (1.5 m³/hr); (3) the decontamination factor was greater than 10³; (4) the evaporation factor which has strong bearings on the operating cost was 14 times as high as a common single-effect evaporator, therfore, only one-fourteenth the energy is needed as a heat source to run the plant; (5) scales on the heat transferring region could be entirely removed with a chemical agent; and (6) after having processed actual radioactive liquid waste of 3,000 m³, on main component of the plant showed any sign of deterioration. The results obtained showed that the vapor multi-effect compression evaporator is one of the most promising ways for radioactive liquid waste treatment. (author)