Patent Number: 
Section: claims

1. A nuclear plant, comprising:a containment shell;a shut-off valve disposed outside of said containment shell;at least one pressure relief line passing out of said containment shell and sealed by said shut-off valve, and through said pressure relief line a pressure relief flow can flow during relief operation when said shut-off valve is open, said pressure relief line having an inlet mouth;a gas flow treatment device, disposed within said containment shell, and disposed upstream from said pressure relief line on an inlet side, said gas flow treatment device having a lateral casing and a chimney-shaped flow duct, enclosed by said lateral casing, and having a lower inflow opening and an upper inflow and outflow opening formed therein, said gas flow treatment device disposed upstream from said shutoff valve; anda first group of catalytic elements for eliminating at least one of hydrogen or carbon monoxide disposed in said chimney-shaped flow duct above or in a region of said lower inflow opening, and said inlet mouth of said pressure relief line disposed above said first group of catalytic elements and below said upper inflow and outflow opening in said lateral casing such that in an event of a critical fault or emergency with release of at least one of the hydrogen or the carbon monoxide in said containment shell, during convection operation preceding the relief operation, when said shut-off valve is closed said chimney-shaped flow duct is flowed through from bottom to top by a gas mixture present in said containment shell by a principle of natural convection, and during the relief operation the gas mixture flows into said chimney-shaped flow duct from below and from above by a principle of forced overflow and flows away via said pressure relief line as the pressure relief flow. 2. The nuclear plant according to claim 1, further comprising a second group of catalytic elements for eliminating at least one of the hydrogen or the carbon monoxide in said chimney-shaped flow duct and disposed above said inlet mouth of said pressure relief line and below or in a region of said upper inflow and outflow opening of said chimney-shaped flow duct. 3. The nuclear plant according to claim 2, further comprising a through-flow limitation device disposed in said pressure relief line, and adjusted in relation to a power of said first and second group of catalytic elements such that during the relief operation a concentration of at least one of the hydrogen or the carbon monoxide in a region of said inlet mouth of said pressure relief line is less than 50% of a corresponding concentration in the region of said lower inflow opening of said chimney-shaped flow duct. 4. The nuclear plant according to claim 3, wherein said through-flow limitation device is adjusted and a shape of said chimney-shaped flow duct selected in such a way that a mass flow occurring in said pressure relief line during the relief operation is at most 100% of a mass flow in said chimney flow duct during the convection operation. 5. The nuclear plant according to claim 3, wherein said through-flow limitation device is adjusted and a shape of said chimney-shaped flow duct selected in such a way that a flow speed onto said first and second groups of catalytic elements during the relief operation is less than 5 m/s. 6. The nuclear plant according to claim 2, wherein said first and second groups of catalytic elements are configured in such a way, as regards an operating temperature thereof during the relief operation, that said first and second groups of catalytic elements act as igniters at a hydrogen concentration of more than 7 vol. % in an incoming gas mixture. 7. The nuclear plant according to claim 1, wherein said gas flow treatment device is disposed in a lower third, in relation to a total height of said containment shell. 8. The nuclear plant according to claim 1, wherein said gas flow treatment device is disposed set apart from primary convection paths in a region of low hydrogen concentration in partially enclosed spaces. 9. The nuclear plant according to claim 7,wherein said gas flow treatment device is one of a plurality of gas flow treatment devices for the pressure relief flow, disposed in the lower third in relation to the total height of said containment shell;further comprising a plurality of catalytic recombiners, disposed positioned above and not acting directly on the pressure relief flow, for eliminating at least one of the hydrogen or the carbon monoxide; andwherein said gas flow treatment devices together bring about less than 20% of a total available recombination power. 10. The nuclear plant according to claim 1, wherein an air exchange number in said containment shell of L <0.3 h is achieved during the convection operation. 11. The nuclear plant according to claim 1, further comprising a cooling device, disposed inside said containment shell, for the pressure relief flow and is connected into said pressure relief line. 12. The nuclear plant according to claim 11, wherein said cooling device is configured for convective re-cooling by way of the gas mixture located in said containment shell and/or by evaporation cooling. 13. The nuclear plant according to claim 11, wherein said cooling device is configured, in terms of cooling power thereof, to cool the pressure relief flow from an input temperature in a range of approximately 400 to 500 ° C. to an output temperature in a range of approximately 150 to 300 ° C. 14. The nuclear plant according to claim 1, wherein said containment shell has a lead-through and said pressure relief line has a thermal protection cladding in a region of said lead-through through said containment shell. 15. The nuclear plant according to claim 1, wherein said first group of catalytic elements is constructed from palladium, on metal substrates having a ceramic coating, and said first group of catalytic elements contain a precious metal proportion of more than 0.2 wt. % based on said substrates. 16. The nuclear plant according to claim 1, further comprising at least one of filters or scrubbers for purifying the pressure relief flow and for activity re-cooling and disposed in a portion of said pressure relief line disposed outside of said containment shell. 17. The nuclear plant according to claim 2, further comprising a through-flow limitation device disposed in said pressure relief line, and adjusted in relation to a power of said first and second group of catalytic elements such that during the relief operation a concentration of at least one of the hydrogen or the carbon monoxide in a region of said inlet mouth of said pressure relief line is less than 30% of a corresponding concentration in the region of said lower inflow opening of said chimney-shaped flow duct. 18. The nuclear plant according to claim 3, wherein said through-flow limitation device is adjusted and a shape of said chimney-shaped flow duct selected in such a way that a mass flow occurring in said pressure relief line during the relief operation is less than 80% of a mass flow in said chimney-shaped flow duct during convection operation. 19. The nuclear plant according to claim 1, wherein an air exchange number in said containment shell of L <0.1 h is achieved during the convection operation. 20. The nuclear plant according to claim 1, wherein said first group of catalytic elements is constructed from palladium on metal substrates having a ceramic coating, and said first group of catalytic elements contain a precious metal proportion of more than 0.5 wt. % based on said substrates. 21. The nuclear plant according to claim 1, wherein said first and second groups of catalytic elements are constructed from at least one precious metal selected from the group consisting of palladium, platinum, and vanadium on at least one of ceramic substrates or on metal substrates having a ceramic coating, and said first and second groups of catalytic elements contain a precious metal proportion of more than 0.2 wt. % based on said substrates. 22. The nuclear plant according to claim 1, wherein said first and second groups of catalytic elements are constructed from at least one precious metal selected from the group consisting of palladium, platinum, and vanadium on at least one of ceramic substrates or on metal substrates having a ceramic coating, and said first and second groups of catalytic elements contain a precious metal proportion of more than 0.5 wt. % based on said substrates.