Patent Number: 
Section: claims

1. A process for treating a gas stream, which comprises the steps of:passing the gas stream over a first catalytic adsorber module in a first purification stage for oxidation of entrained impurities;mixing in molecular or atomic oxygen into the gas stream;passing the gas stream with the mixed-in oxygen over an oxidation catalyst in a second purification stage; andpassing the gas stream leaving the oxidation catalyst over a second catalytic adsorber module in a third purification stage for reducing excess oxygen. 2. The process according to claim 1, which further comprises using a Cu/CuO mixture as a catalytic adsorber material both in the first catalytic adsorber module and in the second catalytic adsorber module. 3. The process according to claim 1, which further comprises determining an index for a proportion of entrained impurities in the gas stream on a basis of which an amount of the oxygen mixed into the gas stream is set, before the gas stream enters the first catalytic adsorber module. 4. The process according to claim 1, which further comprises setting a temperature of the gas stream to from about 400° C. to 450° C. at a point where the gas stream enters the oxidation catalyst. 5. The process according to claim 1, which further comprises preheating the gas stream before the gas stream enters the oxidation catalyst using a recuperative heat exchanger receiving the gas stream leaving the oxidation catalyst. 6. The process according to claim 1, which further comprises setting a temperature of the gas stream to about 250° C. at a point where the gas stream enters the first catalytic adsorber module. 7. The process according to claim 1, which further comprises preheating the gas stream before the gas stream enters the first catalytic adsorber module using a recuperative heat exchanger receiving the gas stream leaving the second catalytic adsorber module. 8. A method of operating a nuclear power station, which comprises the steps of:passing a substrearn of a helium cooling gas stream over a first catalytic acisorber module in a first purification stage for oxidation of entrained impurities;mixing in molecular or atomic oxygen into the substream of a helium cooling gas stream;passing the gas stream with the mixedin oxygen over an oxidation catalyst in a second purification stage; andpassing the gas stream leaving the oxidation catalyst over a second catalytic adsorber module in a third purification stage for reducing excess oxygen. 9. The method according to claim 8, which further comprises determining an index for a proportion of possibly entrained oxygen in the gas stream leaving the second catalytic adsorber module and positions of the first and second catalytic adsorber elements in a flow path of the gas stream are exchanged after a prescribed limit for the, index has been exceeded. 10. A gas treatment system, comprising:at least tPo catalytic adsorber modules disposed in series relative to a gas stream;an oxidation catalyst disposed between said catalytic adsorber modules in a gas flow direction; anda feed unit for feeding molecular or atomic oxygen disposed upstream of said oxidation catalyst. 11. The gas treatment system according to claim 10, further comprising:a sensor sensing a proportion of entrained impurities in the gas stream and disposed upstream of a first, one of said catalytic adsorber modules; anda controlled parameter transducer assigned to said feed unit and having an input side connected to said sensor. 12. The gas treatment system according to claim 10, wherein said catalytic adsorber.modules each contain a Cu/CuO mixture as a catalytic adsorber material. 13. The gas treatment system according to claim 10, further comprising an intermediate heating system disposed upstream of said oxidation catalyst. 14. The gas treatment system according to claim 13,further comprising an outflow line for conducting the gas stream from said oxidation catalyst;further comprising an inflow line; andwherein said intermediate heating system contains a recuperative heat exchanger having a primary side connected into said outflow line for receiving the gas stream from said oxidation catalyst and a secondary side connected into said inflow line for receiving the gas stream to 1Se sent to said oxidation catalyst. 15. The gas treatment system according to claim 10, further comprising a heating system installed upstream of a first, of said catalytic adsorber modules. 16. The gas treatment system according to claim 15,further comprising a gas discharge line connected to a second one of said catalytic adsorber modules;further comprising a gas feed system for said first catalytic adsorber module; andwherein said heating system has a recuperative heat exchanger having a primary side connected into said gas discharge line for receiving the gas stream from said second catalytic adsorber module and a secondary side connected into said gas feed system for feeding the gas stream to said first catalytic adsorber module. 17. The gas treatment system according to claim 10, further comprising a joint switching system for directing a flow of the gas stream for said catalytic adsorber modules. 18. The gas treatment system according to claim 10, further comprising a pressure vessel functioning as a common outer housing, said catalytic adsorber modules and said oxidation catalyst disposed in said pressure vessel. 19. The gas treatment system according to claim 10, wherein the gas treatment system is connected to a helium cooling gas circuit of a nuclear plant.