Abstract: Process for separating the noble fission gases xenon and krypton from a prepurified waste gas from a nuclear plant. The prepurified waste gas is brought into contact with liquid Cl.sub.2 CF.sub.2 as an absorption agent in a first column at an operating pressure which is less than or equal to normal pressure, whereby Xe, Kr, N.sub.2 O, CO.sub.2, O.sub.2 and N.sub.2 are absorbed by the agent. Subsequently, the liquid absorption agent containing the absorbed gases is heated to substantially the boiling temperature of Cl.sub.2 CF.sub.2 at the operating pressure for vaporizing part of the liquid absorption agent and desorbing the absorbed Kr, N.sub.2 and O.sub.2 to thereby separate the Kr and Xe from one another. The desorbed Kr, N.sub.2 and O.sub.2 gases are separated from the vaporized absorption agent. The liquid absorption agent which has not been vaporized is treated to recover Xe, N.sub.2 O and CO.sub.2. Waste gas containing Kr, N.sub.2 and O.sub.