Abstract: Liquid-containing radioactive wastes are bound into thermoplastic material by introducing particles of thermoplastic material at a non-sticking temperature into a kneading machine, heating the thermoplastic material in the absence of radioactive wastes to at least 100.degree. C., adding the liquid-containing wastes to the heated thermoplastic material, mixing and concurrently increasing the temperature of the mixture to a temperature of about 200.degree. C. or more to vaporize liquid in the mixture, maintaining the mixture at a vaporization temperature to dry to the mixture, releasing evolved vapors and discharging the dried mixture from the kneading machine. Difficulties due to clogging of the kneading machine and fluctuations in the consistency of the dried end product are minimized.