SYSTEM AND METHOD FOR PREPARING A CONTAINER LOADED WITH WET RADIOACTIVE ELEMENTS FOR DRY STORAGE

• US 20090158614A1
• Filed: 12/22/2008
• Published: 06/25/2009
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: Holtec International, Inc.
• Original Assignee: Holtec International, Inc.
• Inventors: Singh, Krishna P., Griffiths, John D.
• Granted Patent: US 8,561,318 B2
• Time in Patent Office: Days
• US Class Current: 34/474
• CPC Class Codes: F26B 21/08 Humidity
• CPC Class Codes: F26B 21/14 using gases or vapours other than air or steam , e.g. inert gases
• CPC Class Codes: F26B 5/04 by evaporation or sublimation of moisture under reduced pressure, e.g. in a vacuum F26B11/049 and F26B17/128 take precedence
• CPC Class Codes: F26B 5/12 by suction
• CPC Class Codes: G21C 19/32 Apparatus for removing radioactive objects or materials from the reactor discharge area, e.g. to a storage place; Apparatus for handling radioactive objects or materials within a storage place or removing them therefrom disposal of waste material G21F9/00
• CPC Class Codes: G21F 5/005 Containers for solid radioactive wastes, e.g. for ultimate disposal
• CPC Class Codes: G21F 5/008 Containers for fuel elements
• CPC Class Codes: G21F 5/06 Details of, or accessories to, the containers
• CPC Class Codes: G21F 9/28 Treating solids
• CPC Class Codes: G21F 9/34 Disposal of solid waste
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors

Abstract

A system and method for preparing a container holding high level radioactive waste for dry storage. In one aspect, the invention is a method of preparing a canister having a cavity loaded with wet radioactive elements for dry storage, the method comprising: (a) providing a gas circulation system comprising a condensing module, a desiccant module, a gas circulator module; (b) connecting the gas circulation system to the canister so as to form a hermetically sealed closed-loop path that includes the cavity; (c) filling the hermetically sealed closed-loop path with a non-reactive gas; (d) circulating the non-reactive gas through the hermetically sealed closed-loop path until the condensing module is no longer removing substantial amounts of water from the circulating non-reactive gas, wherein the desiccant module is sealed off from the hermetically sealed closed-loop path during step (d); and (e) adding the desiccant module to the hermetically sealed closed-loop path and continuing to circulate the non-reactive gas through the hermetically sealed closed-loop path, the desiccant module dehumidifying the circulating the non-reactive gas. In another aspect, a system and method is disclosed wherein the second phase of drying is performed by a vacuum module rather than the desiccant module to achieve the desired dryness level, the vacuum module being switched into the closed loop after the first phase of drying is completed.

Claims

1. A method of preparing a canister having a cavity loaded with wet radioactive elements for dry storage, the method comprising:

(a) providing a gas circulation system comprising a condensing module, a desiccant module, a gas circulator module;

(b) connecting the gas circulation system to the canister so as to form a hermetically sealed closed-loop path that includes the cavity;

(c) filling the hermetically sealed closed-loop path with a non-reactive gas;

(d) circulating the non-reactive gas through the hermetically sealed closed-loop path until the condensing module is no longer removing substantial amounts of water from the circulating non-reactive gas, wherein the desiccant module is sealed off from the hermetically sealed closed-loop path during step (d); and

(e) adding the desiccant module to the hermetically sealed closed-loop path and continuing to circulate the non-reactive gas through the hermetically sealed closed-loop path, the desiccant module dehumidifying the circulating the non-reactive gas.

2. The method of claim 1 further comprising:

continuing step e) until a desired vapor pressure is achieved in the cavity of the canister.

3. The method of claim 1 further comprising:

f) repetitively measuring dew point temperature of the circulating non-reactive gas as it exits the cavity during step e); and

g) upon the dew point temperature of the circulating non-reactive gas exiting the cavity being measured to be at or below a predetermined dew point temperature for a predetermined time, discontinuing the flow of the non-reactive gas and sealing the cavity.

4. The method of claim 1 wherein it is determined that condenser is no longer removing substantial amounts of water from the circulating non-reactive gas by monitoring a moisture accumulator.

5. The method of claim 1 wherein it is determined that condenser is no longer removing substantial amounts of water by measuring the dew point temperature of the circulating non-reactive gas exiting the cavity during step d).

6. The method of claim 1 wherein the addition of the desiccant module to the hermetically sealed closed-loop path in step e) is achieved by manipulating two three-way valves.

7. A system for preparing a canister having a cavity loaded with radioactive elements for dry storage, the apparatus comprising:

a gas circulation system comprising a source of a condenser module, a desiccant module, a gas circulator module;

the gas circulation system adapted to form a hermetically sealed closed-loop path when operably connected to the cavity of the canister to be prepared for dry storage; and

means for adding and removing the desiccant module as part of the hermetically sealed closed-loop path.

8. The system of claim 7 wherein the means for adding and removing the desiccant module comprises two three-way valves.

9. The system of claim 7 further comprising dew point temperature measuring means located upstream of the condensing module and downstream of the cavity.

10. The system of claim 9 further comprising:

a controller operably coupled to the dew point temperature measuring means;

wherein the dew point temperature measuring means is adapted to create signals indicative of the measured dew point temperature of the non-reactive gas and transmit the signals to the controller; and

wherein the controller is adapted to analyze the signals and upon determining that the signals indicate that the measured dew point temperature is at or below a predetermined dew point temperature for a predetermined time, the controller is further adapted to (i) cease flow of the non-reactive gas through the cavity; and

/or (2) activate a means for indicating that the cavity is dry.

11. The system of claim 7 a pressurized non-reactive gas reservoir fluidly coupled to the gas circulation system, a valve located between the non-reactive gas reservoir and the gas circulation system.

12. The system of claim 7 further comprising a controller operably coupled to the means for adding and removing the desiccant module, the controller adapted to add the desiccant module as part of the hermetically sealed closed-loop path upon determining that the condensing module is no longer removing substantial amounts of water during operation.

13. A method of preparing a canister having a cavity loaded with wet radioactive elements for dry storage, the method comprising:

(a) providing a gas circulation system comprising a condensing module, a vacuum module, a gas circulator module;

(b) connecting the gas circulation system to the canister so as to form a hermetically sealed closed-loop path that includes the cavity;

(c) filling the hermetically sealed closed-loop path with a non-reactive gas;

(d) circulating the non-reactive gas through the hermetically sealed closed-loop path until the condensing module is no longer removing substantial amounts of water from the circulating non-reactive gas, wherein the vacuum module is sealed off from the hermetically sealed closed-loop path during step (d);

(e) discontinuing the circulation of the non-reactive gas through the hermetically sealed closed-loop path;

(f) fluidly coupling the vacuum module to the cavity and fluidly isolating the cavity and the vacuum module; and

(g) applying a vacuum pressure to the cavity via the vacuum module so as to create a sub-atmospheric pressure within the cavity until a desired vapor pressure is achieved in the cavity of the canister.

14. The method of claim 13 further comprising:

(h) back-filling the cavity with dry non-reactive gas; and

(i) sealing the cavity.

15. The method of claim 13 wherein it is determined that condenser is no longer removing substantial amounts of water from the circulating non-reactive gas by monitoring a moisture accumulator.

16. The method of claim 13 wherein it is determined that condenser is no longer removing substantial amounts of water by measuring the dew point temperature of the circulating non-reactive gas exiting the cavity during step d).