Patent Number: 
Section: claims

1. An exhaust stack of a nuclear containment building comprising:a system configured to passively filter radioactive materials from a flow, the system including,a perforated deflector shield configured to remove particulates of the radioactive materials from the flow by mechanical action; andone or more radionuclide removal devices configured to remove radioactive aerosols, reactive radioactive gases, or radioactive aerosols and reactive radioactive gases from the flow, the radionuclide removal devices including,a perforated plate defining a first section and a second section, the second section downstream of the first section, the perforated plate having a generally conical shape, a vertex of the perforated plate being downstream of and positioned above a base of the cone, the base of the cone defining an inlet through which the flow enters the first section before moving generally upwardly into the second section, and the perforated plate configured to remove water from the flow by mechanical action, andfilter media in the second section, the system being a passive system, such that the system is configured to operate independent of operator action. 2. The exhaust stack of claim 1, wherein the radioactive materials comprise one or more of reactive gaseous radioactive materials, liquid radioactive materials, and particulate radioactive materials. 3. The exhaust stack of claim 1, wherein in a direction of the flow, the perforated deflector shield precedes the perforated plate. 4. The exhaust stack of claim 1, wherein in a direction of the flow, the perforated deflector shield precedes the one or more radionuclide removal devices. 5. The exhaust stack of claim 1, wherein the perforated deflector shield mechanically removes the particulates of the radioactive materials from the flow using gravitational settling. 6. The exhaust stack of claim 1, wherein in the perforated plate, mixing of the flow reduces thermophoretic forces within the flow. 7. The exhaust stack of claim 1, wherein heat rejection from the flow reduces thermophoretic forces within the flow. 8. The exhaust stack of claim 1, wherein mixing of the flow reduces thermophoretic forces within the flow. 9. The exhaust stack of claim 1, wherein in the at least one of the one or more radionuclide removal devices, heat rejection from the flow improves capture by reducing thermophoretic forces within the flow. 10. The exhaust stack of claim 1, wherein the filter media comprises one or more of activated alumina (Al2O3), activated charcoal, organic wax, and plastic. 11. The exhaust stack of claim 1, wherein the filter media comprises one or more high-efficiency particulate air (HEPA) filters. 12. A method for passively filtering radioactive materials from a flow in an exhaust stack of a nuclear reactor containment building, the method comprising:mechanically removing particulates of the radioactive materials from the flow using a perforated deflector shield;mechanically removing water from the flow using a perforated plate, the perforated plate defining a first section and a second section, the second section downstream of the first section, the perforated plate having a generally conical shape, a vertex of the perforated plate being downstream of and positioned above a base of the cone, the base of the cone defining an inlet through which the flow enters the first section before moving generally upwardly into the second section, and the perforated plate configured to remove water from the flow by mechanical action; andremoving radioactive aerosols, reactive radioactive gases, or radioactive aerosols and reactive radioactive gases from the flow using filter media. 13. The method of claim 12, wherein the mechanically removing of the particulates of the radioactive materials from the flow precedes the mechanically removing of the water from the flow. 14. The method of claim 12, wherein the mechanically removing of the particulates of the radioactive materials from the flow precedes the removing of the radioactive aerosols, reactive radioactive gases, or radioactive aerosols and reactive radioactive gases from the flow using the filter media. 15. The method of claim 12, wherein the mechanically removing of the water from the flow precedes the removing of the radioactive aerosols, reactive radioactive gases, or radioactive aerosols and reactive radioactive gases from the flow using the filter media.