Abstract: The invention is directed to an apparatus for washing a solvent in the recessing of irradiated nuclear fuel. The solvent is washed with an aqueous solution in a mixer-settler having at least one stage which includes a mixing chamber and a settling chamber. The pH is measured by a sensor adjacent stirring means in the mixing chamber and is coupled to a controller controlling metering of the washing solution. The pH of the dispersion in the mixing chamber is measured and an amount of washing solution is added which influences the pH toward the desired operational value. Various recycling means and weir overflow means also influence pH control and the washing operation.

Abstract: The invention is directed to a method for electrochemically decomposing iganic material contained in an aqueous radioactive waste solution. The solution is concentrated by evaporation in order to reduce its volume for further treatment as a waste solution. In order to achieve a more effective decomposition of inorganic compounds in the aqueous radioactive solution, an electrolytic process is performed during evaporation of the waste solution with the electrolytic process effecting the electrochemical decompostion. An apparatus for carrying out the method includes an evaporator for accommodating the waste solution and the evaporator is configured as an electrolytic cell.