Method of storing high level radioactive waste

Abstract

A method of storing high level radioactive waste, and specifically a method of adjusting or controlling the temperature of ventilation air flowing through a storage cavity of a ventilated system. The method includes positioning a metal canister containing high level radioactive waste in a storage cavity of the ventilated system. The ventilated system includes a cask body, a cask lid, a plurality of inlet ducts, and at least one outlet duct so that ventilation air can flow from atmosphere into the storage cavity where it is heated and then back out to the atmosphere. The method includes progressively reducing a cross-sectional area of one or more of the inlet ducts and/or the outlet duct over time so that a rate at which the ventilation air is heated within he storage cavity is maintained above a predetermined threshold to mitigate the risk of stress corrosion cracking in the metal canister.

What is claimed is: 
     
         1 . A method of storing high level radioactive waste comprising:
 a) positioning a metal canister containing high level radioactive waste in a storage cavity of a ventilated system comprising a cask body, a cask lid positioned atop the cask body, at least one outlet duct extending from a top of the storage cavity to an ambient atmosphere, and a plurality of inlet ducts, each of the inlet ducts having a cross-sectional area and the at least one outlet duct having a cross-sectional area;   b) convectively flowing ventilation air from the ambient atmosphere into a bottom of the storage cavity through the inlet ducts, the ventilation air being heated at a heating rate and rising from the bottom of the storage cavity to the top of the storage cavity, the ventilation air exiting the storage cavity through the at least one outlet duct;   c) positioning a first air flow adjustment member in at least one of: (1) one or more of the plurality of inlet ducts; or (2) the at least one outlet duct to reduce the cross-sectional area of the at least one of the one or more of the plurality of inlet ducts or the at least one outlet duct to maintain the heating rate of the ventilation air above a predetermined threshold; and   wherein the first air flow adjustment member is selected to reduce the cross-sectional area of the at least one of the one or more of the plurality of inlet ducts or the at least one outlet duct by a predetermined percentage based on a first set of conditions measured at time T 1 .   
     
     
         2 . The method according to  claim 1  wherein the first set of conditions comprises the heating rate of the ventilation air in the storage cavity, ambient temperature, and decay heat of the high level radioactive waste in the metal canister. 
     
     
         3 . The method according to  claim 1  further comprising, prior to step c), performing a computational fluid dynamics simulation to calculate a percentage of the cross-sectional area of the one or more of the plurality of inlet ducts and a percentage of the cross-sectional area of the at least one outlet duct that should be closed to maintain the heating rate of the ventilation air above the predetermined threshold, and selecting one or more air flow adjustment members from a set of air flow adjustment members for positioning in the at least one of the one or more of the plurality of inlet ducts or the at least one outlet duct to reduce the cross-sectional areas of the inlet ducts and the cross-sectional area of the at least one outlet duct by the calculated percentage. 
     
     
         4 . The method according to  claim 1  further comprising:
 d) removing the first air flow adjustment member from at least one of the one or more of the plurality of inlet ducts and/or the at least one outlet duct in which it is positioned; 
 e) positioning a second air flow adjustment member in at least one of: (1) one or more of the plurality of inlet ducts; or (2) the at least one outlet duct to maintain a heating rate of the ventilation air above the predetermined threshold; and 
 wherein the second air flow adjustment member is selected to reduce the cross-sectional area of the at least one of the one or more of the plurality of inlet ducts or the at least one outlet duct by a predetermined percentage based on a second set of conditions measured at time T 2  that is after time T 1 . 
 
     
     
         5 . The method according to  claim 4  wherein the first air flow adjustment member reduces the cross-sectional area of the at least one of the one or more of the plurality of inlet ducts or the at least one outlet duct in which it is positioned by a first percentage and wherein the second air flow adjustment member reduces the cross-sectional area of the at least one of the one or more of the plurality of inlet ducts or the at least one outlet duct in which it is positioned by a second percentage that is greater than the first percentage. 
     
     
         6 . The method according to  claim 1  wherein the first air flow adjustment member comprises a plurality of open cell portions, and wherein a combined cross-sectional area of the plurality of open cell portions is less than the cross-sectional area of the at least one of the one or more of the plurality of inlet ducts or the at least one outlet duct in which the first air flow adjustment member is positioned. 
     
     
         7 . The method according to  claim 1  further comprising positioning an air flow adjustment member into each of the plurality of inlet ducts to reduce the cross-sectional area of each of the plurality of inlet ducts. 
     
     
         8 . The method according to  claim 1  further comprising positioning the first air flow adjustment member in the at least one outlet duct to reduce the cross-sectional area of the at least one outlet duct. 
     
     
         9 . The method according to  claim 1  wherein step b) includes bifurcating the ventilation air flowing through each inlet duct around a cylindrical member positioned in the inlet duct. 
     
     
         10 . The method according to  claim 9  wherein the cylindrical member is configured and arranged to block a straight line of sight through each inlet duct from ambient to the the storage cavity of the cask body. 
     
     
         11 . A method of storing high level radioactive waste comprising:
 a) positioning a metal canister containing high level radioactive waste in a storage cavity of a ventilated system comprising a cask body, a cask lid positioned atop the cask body, at least one outlet duct extending from a top of the storage cavity to an ambient atmosphere, and a plurality of inlet ducts, the plurality of inlet ducts having a combined cross-sectional area and the at least one outlet duct having a combined cross-sectional area;   b) convectively flowing ventilation air from the ambient atmosphere into a bottom of the storage cavity through the inlet ducts, the ventilation air being heated at a heating rate and rising from the bottom of the storage cavity to the top of the storage cavity, the ventilation air exiting the storage cavity through the at least one outlet duct; and   c) modifying at least one of: (1) the combined cross-sectional area of the plurality of inlet ducts; or (2) the combined cross-sectional area of the at least one outlet duct over time to maintain the heating rate of the ventilation air above a predetermined threshold.   
     
     
         12 . The method according to  claim 11  wherein step c) comprises reducing, without later increasing, the at least one of the combined cross-sectional area of the plurality of inlet ducts or the combined cross-sectional area of the at least one outlet duct.