Method and apparatus for dehydrating high level waste based on dew point temperature measurements

1. A method of drying a cavity loaded with high level waste (“HLW”) comprising:

a) flowing a non-reactive gas through the cavity;

b) repetitively measuring dew point temperature of the non-reactive gas exiting the cavity;

c) upon the dew point temperature of the non-reactive gas exiting the cavity being measured to be at or below a predetermined dew point temperature, activating a timer set for a predetermined period of time;

d) continuing to repetitively measure the dew point temperature of the non-reactive gas exiting the cavity while the timer is activated;

e) wherein if during the performance of step d) the dew point temperature of the non-reactive gas is measured to rise above the predetermined dew point temperature prior to the predetermined period of time expiring, deactivating and resetting the timer and returning to step b); and

f) wherein if during the performance step d) the predetermined period of time expires without the dew point temperature of the non-reactive gas being measured to rise above the predetermined dew point temperature, discontinuing the flow of the non-reactive gas and sealing the cavity.

2. The method of claim 1 wherein step (a) comprises flowing the non-reactive gas through the cavity at a predetermined flow rate.

3. The method of claim 2 wherein the cavity has a volume and the predetermined flow rate is chosen so that the volume of the cavity is turned over 25 to 50 times per hour.

4. The method of claim 1 wherein the predetermined dew point temperature is selected to correspond to a desired vapor pressure within the cavity.

5. The method of claim 1 wherein the predetermined dew point temperature is in a range of approximately 20 to 26.degree. F., and the predetermined time is in a range of approximately 25 to 35 minutes.

6. The method of claim 5 wherein the predetermined dew point temperature is approximately 22.9.degree. F. and the predetermined time is approximately 30 minutes.

7. The method of claim 1 wherein step a) comprises drying the non-reactive gas that exits the cavity after the dew point temperature is measured; and re-circulating the dried non-reactive gas through the cavity.

8. The method of claim 7 wherein step a) comprises drying the non-reactive gas with a desiccant.

9. The method of claim 7 wherein step a) comprises drying the non-reactive gas by chilling the non-reactive gas.

10. The method of claim 1 wherein the non-reactive gas is nitrogen, carbon dioxide, light hydrocarbon gases, or a noble gas selected from the group consisting of helium, argon, neon, radon, krypton, and xenon.

11. The method of claim 1 wherein the predetermined dew-point temperature is selected to correspond to a vapor pressure of 3 Torr or less in the cavity.

12. The method of claim 1 wherein step a) comprises drying the non-reactive gas that exits the cavity after the dew point temperature is measured; re-circulating the dried non-reactive gas through the cavity; wherein the predetermined dew-point temperature is selected to correspond to a vapor pressure of 3 Torr or less in the cavity; and flowing the non-reactive gas through the cavity at a predetermined flow rate that results in a volume of the cavity being turned over 25 to 50 times per hour; wherein the non-reactive gas is helium; wherein the cavity is formed by a canister and is loaded with spent nuclear fuel, the canister positioned in a cask.

13. A method of preparing spent nuclear fuel rods for dry storage, the method comprising:

a) providing a container having a cavity containing wet spent nuclear fuel rods;

b) draining bulk water from cavity;

c) flowing a non-reactive gas through the cavity;

d) repetitively measuring dew point temperature of the non-reactive gas exiting the cavity; and

e) upon the dew point temperature of the non-reactive gas exiting the cavity being measured to remain at or below a predetermined dew point temperature, activating a timer set for a predetermined period of time and continuing to repetitively measure the dew point temperature of the non-reactive gas;

f) wherein if the dew point temperature of the non-reactive gas is measured to rise above the predetermined dew point temperature prior to the predetermined period of time expiring, deactivating and resetting the timer and returning to step b); and

g) wherein if the predetermined period of time expires without the dew point temperature of the non-reactive gas being measured to rise above the predetermined dew point temperature, discontinuing the flow of the non-reactive gas and sealing the cavity.

14. The method of claim 13 further wherein step c) comprises flowing the non-reactive gas through the cavity at a predetermined flow rate that turns a free volume of the cavity over 25 to 50 times per hour.

15. The method of claim 13 wherein the container is a metal canister.

16. The method of claim 13 wherein step c) comprises drying the non-reactive gas that exits the cavity after the dew point temperature is measured; and re-circulating the dried non-reactive gas through the cavity.

17. The method of claim 13 wherein the predetermined dew point temperature is selected to correspond to a desired vapor pressure within the cavity.

18. The method of claim 13 wherein the container is a metal canister and positioned within a cask.