Forced gas flow canister dehydration
The present invention provides a method and system for ensuring that cavities used to store radioactive elements are adequately dried without intrusive measuring. In one aspect the invention is a system for drying a cavity loaded with radioactive elements, the loaded cavity having a free volume (V F ), a starting vapor pressure (vP S ), and a cavity pressure (P C ), the system comprising: a non-reactive gas source adapted to supply a non-reactive gas to the system; means to cool a non-reactive gas to a temperature (T C ) thereby drying the non-reactive gas; means to flow the dry non-reactive gas to the cavity, the flow means adapted to introduce the dry non-reactive gas to the cavity at a flow rate R for a period of time (t); and means to remove wet non-reactive gas from the cavity; wherein the non-reactive gas source, the cooling means, the flow means, the removal means, and the cavity are fluidly coupled; wherein T C and R are controlled to achieve a desired vapor pressure (vP D ) in the cavity in time t.
1. A system for drying a cavity loaded with radioactive elements, the loaded cavity having a free volume (V F ), a starting vapor pressure (vP S ), and a cavity pressure (P C ), the system comprising:
a non-reactive gas source adapted to supply a non-reactive gas to the system;
means to cool a non-reactive gas to a temperature (T C ) thereby drying the non-reactive gas;
means to flow the dry non-reactive gas to the cavity, the flow means adapted to introduce the dry non-reactive gas to the cavity at a flow rate R for a period of time (t);
means to remove wet non-reactive gas from the cavity;
wherein the non-reactive gas source, the cooling means, the flow means, the removal means, and the cavity are fluidly coupled;
wherein T C and R are controlled to achieve a desired vapor pressure (vP D ) in the cavity in time t.
2. The system of claim 1 wherein the flow rate R is a mass flow rate or a volumetric flow rate.
3. The system of claim 1 further comprising means to heat the dry non-reactive gas to a temperature (T H ), the heating means fluidly coupled to the system downstream of the cooling means and upstream of the cavity, wherein T H is controlled to achieve the desired vapor pressure vP D .
4. The system of claim 3 wherein when vP D is about 3 Torrs, V F is about 300 cubic feet, P C is about 50 pounds per square inch, and vP S is about 87 Torrs; and wherein R is a volumetric flow rate set at about 78.125 cubic feet per minute, T H is set at about 300 degrees Fahrenheit, and T C is set at or below about 21 degrees Fahrenheit; time t is about 22.5 minutes.
5. The system of claim 3 wherein the non-reactive gas is helium and when vP D about 3 Torrs, V F is about 300 cubic feet, P C is about 50 pounds per square inch, and vP S is about 87 Torrs; and wherein R is a mass flow rate set at about 2.5 pounds per minute, T H is set at about 300 degrees Fahrenheit, and T C is set at or below about 21 degrees Fahrenheit; time t is about 22.5 minutes.
6. The system of claim 3 wherein the means to heat the dry non-reactive gas is an auxiliary heater.
7. The system of claim 1 wherein the flow means is a gas circulator.
8. The system of claim 1 wherein the cooling means comprises a condenser module fluidly coupled upstream to a demoisturizer module, the demoisturizer module adapted to freeze dry the non-reactive gas so that the non-reactive gas that exits the demoisturizer module is at temperature T C .
9. The system of claim 1 wherein the system is adapted to re-circulate the wet non reactive gas that is removed from the cavity through the system.
10. The system of claim 1 wherein the non-reactive gas is nitrogen, carbon dioxide, light hydrocarbon gases, or an inert gas selected from the group consisting of helium, argon, krypton, and xenon.
11. The system of claim 1 wherein the desired vapor pressure vP D in the cavity is at or below about 3 Torrs.
12. The system of claim 11 wherein the temperature T C is at or below about twenty-one degrees Fahrenheit.
13. The system of claim 11 wherein the cavity has a top and a bottom, wherein the system is adapted to supply the dry non-reactive gas to the cavity at or near the bottom of the cavity and further adapted to remove the wet non-reactive gas from the cavity at or near the top of the cavity.
14. A system for drying a cavity loaded with radioactive elements to a desired degree of dryness in terms of a desired vapor pressure (vP D ), the loaded cavity having an inlet, an outlet, a free volume (V F ), a starting vapor pressure (vP S ), and a cavity pressure (P C ), the system comprising:
a source of non-reactive gas;
a cooling apparatus fluidly coupled between the gas source and the inlet of the cavity, the cooling apparatus adapted to cool the non-reactive gas from the gas source to a temperature (T C ) thereby drying the non-reactive gas;
means for flowing the non-reactive gas from the gas source, through the cooling apparatus and through the cavity, the non-reactive gas entering the cavity via the inlet and exiting the cavity via the outlet;
a controller means adapted to: (1) flow the non-reactive gas that exits the cooling apparatus through the cavity at a flow rate R for a period of time (t), wherein T C and R are controlled to achieve the desired vapor pressure (vP D ) in the cavity after time t; or (2) flow the non-reactive gas that exits the cooling apparatus through the cavity so that the free volume V F of the cavity turns over X times, wherein T C and X are controlled to achieve the desired vapor pressure (vP D ) in the cavity.
15. The system of claim 14 further comprising means for fluidly coupling the gas source to the outlet of the cavity so that the wet non-reactive gas exiting the cavity flows back into the gas source.
16. The system of claim 14 further comprising:
means to heat the non-reactive gas that exits the cooling apparatus to a temperature (T H ), the heating means fluidly coupled between the cooling apparatus and the inlet of the cavity; and
wherein T H is controlled to achieve the desired vapor pressure vP D .
17. The system of claim 16 wherein the heating means is an auxiliary heater and the flow means is a gas circulator.
18. The system of claim 14 wherein the cooling means comprises a condenser module and a demoisturizer module, the condenser module fluidly coupled upstream of the demoisturizer module, the demoisturizer module adapted to freeze dry the non-reactive gas so that the non-reactive gas that exits the demoisturizer module is at the temperature T C .
19. The system of claim 14 wherein the non-reactive gas is nitrogen, carbon dioxide, light hydrocarbon gases, or an inert gas selected from the group consisting of helium, argon, krypton, and xenon.
20. A system for drying a cavity loaded with radioactive elements to a desired degree of dryness in terms of a desired vapor pressure (vP D ), the loaded cavity having an inlet, an outlet, a free volume (V F ), a starting vapor pressure (vP S ), and a cavity pressure (P C ), the system comprising:
a source of non-reactive gas fluidly coupled to the inlet of the cavity;
means for drying the non-reactive gas to a desired dryness level prior to entering the inlet;
means for flowing the non-reactive gas from the gas source, through the drying means and through the cavity;
a controller means adapted to: (1) flow the non-reactive gas that exits the drying means through the cavity at a flow rate R for a period of time (t), wherein the dryness level and R are controlled to achieve the desired vapor pressure (vP D ) in the cavity after time t; or (2) flow the non-reactive gas that exits the drying means through the cavity so that the free volume V F of the cavity turns over X times, wherein the dryness level and X are controlled to achieve the desired vapor pressure (vP D ) in the cavity.