DEVELOPMENT OF A CRYOGENIC KRYPTON-SEPARATION SYSTEM FOR THE OFFGAS OF REPROCESSING PLANTS.

The concept of cryogenic rare gas separation from reprocessing offgas pursued at present at the Kernforschungszentrum Karlsruhe (KfK) is discussed and compared with other offgas purification flowsheets. The KfK concept includes: separation of O//2 and residual NO//x by catalytic reduction with H//2, adsorptive retention of H//2O, CO//2, NH//3 etc. and cryogenic distillation of first N//2-Kr-Xe, then Kr-Xe mixtures. Some features pertinent to this flowsheet which were studied experimentally either on a laboratory or semiworks scale, are described including the following: desublimation of Xe in the first column, coadsorption of Kr at and its selective desorption from the adsorption bed, purification of the Xe product, poisoning of the reduction catalyst and methanization of CO//2. It is shown that all of these features, despite being capable of causing malfunctions of the process, can be controlled by proper process design and operational conditions in a way not to impair with a good Kr decontamination factor.