Abstract: An improved technique employing first and second flash vaporization stages for purifying radioactive liquids is described. The liquid is first flash-evaporated in the first vaporization stage and the resulting vapor is conducted to a first direct condenser. Enriched liquid obtained from the second vaporization stage is applied via a circulating pump to the first direct condenser to condense by contact the vapor from the first vaporization stage and to form a mixture with this condensate. The resulting mixture is thus flash-evaporated in the second vaporization stage. A portion of the enriched liquid obtained from the second vaporization stage is withdrawn from the loop formed by said second vaporization stage, said circulating pump, said first direct condenser, and the connecting conduits therebetween for further processing, e.g., recycling to the first vaporization stage, or for discharging.