Method for treating mixed radioactive waste

• US 5,745,861 A
• Filed: 03/11/1996
• Issued: 04/28/1998
• Est. Priority Date: 03/11/1996
• Status: Expired due to Fees

• Current Assignee: Quantum Catalytics LLC
• Original Assignee: Molten Metal Technology Incorporated
• Inventors: Snider, James W., Bell, Jimmy T.
• Primary Examiner(s): MAI, NGOCLAN THI
• Application Number:
  US08/613,924
• Time in Patent Office: 778 Days
• Field of Search: 210/682, 210/688, 588/201, 588/1, 588/20, 423/210.5, 423/DIG. 12, 423/6, 423/7
• US Class Current: 588/1
• CPC Class Codes: G21F 9/02 Treating gases
• CPC Class Codes: G21F 9/12 by absorption; by adsorption; by ion-exchange
• CPC Class Codes: G21F 9/14 by incineration; by calcination, e.g. desiccation
• CPC Class Codes: G21F 9/302 in an inorganic matrix
• CPC Class Codes: Y10S 423/12 Molten media

Abstract

Mixed radioactive wastes, such as those that include a radioactive component and a dissolved salt component, are treated by directing the waste through at least one ion-exchange medium that binds at least a portion of the radioactive component. A liquid discharge stream from which the radioactive component has been separated, and which includes the dissolved salt component, is directed into a molten bath that causes at least a portion of at least one dissolved salt component of the liquid discharge stream to be reductively vaporized and thereby form at least one vaporized product. A gaseous discharge stream is generated by the molten bath that includes at least one vaporized product. In one specific embodiment, the mixed radioactive waste includes radioactive cesium as the radioactive component and sodium nitrate as the dissolved salt component.

Claims

1. A method for treating a mixed radioactive waste that includes a radioactive component and a dissolved salt component, comprising the steps of:

a) directing the waste through at least one ion-exchange medium that binds at least a portion of the radioactive component, thereby forming a liquid discharge stream that includes the dissolved salt component; and

b) directing said liquid discharge stream into a molten bath that causes at least a portion of at least one dissolved salt component of the liquid discharge stream to be reductively vaporized and thereby form a gaseous discharge stream that includes at least one vaporized product.

2. The method of claim 1, wherein the waste is directed through at least two ion-exchange media to form the liquid discharge stream.

3. The method of claim 2, wherein the ion-exchange media each preferably bind a distinct radioactive component.

4. The method of claim 3, wherein the waste is directed through at least one electrochemical ion-exchange medium.

5. The method of claim 4, wherein the waste is directed through an electrochemical ion-exchange medium following direction of the waste through a chemical ion-exchange medium.

6. The method of claim 5, further including the step of evaporating at least a portion of a liquid component of the liquid discharge stream before said liquid discharge stream is directed into the molten bath.

7. The method of claim 6, further including the step of exposing the liquid discharge stream to electrodeposition, whereby at least one heavy metal component is separated from the liquid discharge stream.

8. The method of claim 7, wherein said electrodeposition causes separation of technetium from the liquid discharge stream.

9. The method of claim 1, wherein the liquid discharge stream is directed into a molten bath that includes an iron component.

10. The method of claim 1, wherein the liquid discharge stream is directed into a molten bath that includes a nickel component.

11. The method of claim 1, wherein the liquid discharge stream is directed into a molten bath that includes copper.

12. The method of claim 1, wherein an ion-exchange medium through which the radioactive waste is directed selectively binds a cesium component of the radioactive waste.

13. The method of claim 1, wherein an ion-exchange medium through which the radioactive waste is directed selectively binds a strontium component of the radioactive waste.

14. The method of claim 12, wherein selective binding of cesium includes exposure of the radioactive waste to electrochemical ion exchange.

15. The method of claim 1, further including the step of combining a dissociation product of the gaseous discharge stream with a reactant, whereby the dissociation product and the reactant react to form a reaction product.

16. The method of claim 15, wherein the dissociation product and the reactant are combined by scrubbing the gaseous discharge stream with a liquid that includes the reactant.

17. The method of claim 16, wherein the reactant includes water.

18. The method of claim 17, wherein the gaseous discharge stream includes sodium as a dissociation product, whereby reaction with said water reactant causes formation of sodium hydroxide as a reaction product that is a component of a scrubber liquid discharge stream.

19. The method of claim 15, wherein the reactant includes oxygen.

20. The method of claim 19, wherein the gaseous discharge stream includes carbon monoxide that contains carbon¹⁴ as a dissociate product, whereby reaction with said oxygen reactant causes formation of carbon dioxide that contains said carbon¹⁴.

21. The method of claim 20, further including the step of reacting said carbon dioxide with sodium hydroxide to thereby form sodium carbonate that includes the carbon¹⁴.

22. The method of claim 21, further including the step of solidifying the sodium carbonate.

23. The method of claim 1, further including the step of filtering the radioactive waste to thereby form a sludge component and supernate component.

24. The method of claim 23, further including the step of settling the radioactive waste prior to directing the radioactive waste through said ion-exchange medium, whereby a supernate and a sediment are formed, said supernate being subsequently directed through said ion-exchange medium and said sediment being directed into the molten bath that causes at least one radioactive organic component of the sediment to dissociate and form radioactive carbon.

25. The method of claim 24, further including the step of directing an oxygen source into the molten bath, whereby the oxygen source reacts with the radioactive carbon to form radioactive carbon monoxide that is discharged from the molten bath as a component of a gaseous discharge stream.

26. The method of claim 25, wherein supernate discharged from the ion-exchange medium is the oxygen source that is directed into the molten bath.

27. The method of claim 26, wherein the gaseous discharge stream includes sodium, and further including the steps of:

a) combining the gaseous discharge stream with water, whereby the water reacts with the sodium to form sodium hydroxide that separates from the gaseous discharge stream;

b) combining the gaseous discharge stream with an oxygen source, whereby the oxygen source reacts with radioactive carbon monoxide in the gaseous discharge stream to form radioactive carbon dioxide; and

c) combining the radioactive carbon dioxide with the sodium hydroxide, whereby the radioactive carbon dioxide reacts with the sodium hydroxide to form a radioactive sodium carbonate precipitate.

28. The method of claim 27, further including the step of solidifying the radioactive sodium carbonate.

29. The method of claim 23, further including the step of directing at least a portion of said sludge component into a molten bath.

30. The method of claim 29, further including the step of separating a vaporizable portion from the sludge component before directing said sludge component into the molten bath.

31. The method of claim 30, further including the step of combining the vaporizable portion with the supernate.

32. The method of claim 31, further including the step of directing the combined vaporizable portion and supernate through an ion-exchange medium.

33. The method of claim 30, further including the steps of converting the sludge component into a sludge particulate that can be suspended by a gas to form a suspended particulate stream.

34. The method of claim 33, further including the step of combining the sludge particulate with a gas stream to form a suspended particulate stream.

35. The method of claim 27, further including the step of directing the gaseous discharge stream, from which carbon dioxide has been removed by reaction with sodium hydroxide, into a molten bath.

36. The method of claim 35, wherein the liquid discharge stream is directed into a first molten bath and wherein the gaseous discharge stream, from which carbon dioxide has been removed by reaction with sodium hydroxide, is directed into a second molten bath.

37. The method of claim 36, further including the step of scrubbing the gaseous discharge stream, from which carbon dioxide has been removed by reaction with sodium hydroxide, to thereby form a second scrubber liquid discharge stream.

38. The method of claim 37, wherein the second scrubber liquid discharge stream is formed by scrubbing the gaseous discharge stream with water.

39. The method of claim 38, wherein the radioactive waste material causes the second scrubber liquid discharge stream to include at least one member selected from the group consisting of cesium hydroxide, sodium hydroxide, lead hydroxide, potassium hydroxide, lead and mercury.

40. The method of claim 39, further including the step of filtering the second scrubber liquid discharge stream to thereby form a filtrate that includes at least one of cesium hydroxide and sodium hydroxide and to form a residue that includes at least one of lead and mercury.

41. The method of claim 40, further including the step of combining the filtrate with the supernate.

42. The method of claim 41, further including the step of separating a vaporizable portion from the residue.

43. The method of claim 42, wherein the vaporizable portion of the residue is separated from the residuing by vaporizing said portion.

44. The method of claim 43, further including the step of fixing the residue.

45. The method of claim 44, wherein said residue is fixed by mixing the residue with a sulfur polymer cement.

46. The method of claim 36, further including the step of directing a portion of the first molten bath to the second molten bath.

47. The method of claim 36, further including the step of directing a carbon source into the second molten bath.

48. A method for treating a radioactive waste that includes a radioactive component, a metal component, and a dissolved salt component, comprising the steps of:

a) settling the radioactive waste to form a supernate layer that includes the radioactive component and the dissolved salt component, and a sludge layer that includes the heavy metal component;

b) directing the supernate layer through at least one ion-exchange medium that binds at least a portion of the radioactive component, thereby form a liquid discharge stream that includes the dissolved salt component;

c) directing said liquid discharge stream into a first molten bath, said first molten bath causing at least a portion of at least one dissolved salt component of the liquid discharge stream to dissociate and form at least one dissociation product, whereby a gaseous discharge stream is formed that includes at least one said dissociation product; and

d) directing said sludge layer into a second molten bath, whereby at least a portion of the metal component vaporizes and is discharged from second molten bath.

49. The method of claim 48, further including the steps of:

a) separating a vaporizable portion from the sludge layer before directing said sludge layer into the molten bath; and

b) combining the vaporizable portion with the supernate layer.

50. The method of claim 49 wherein the supernate includes a radioactive carbon component and a sodium carbonate component, whereby a gaseous discharge stream generated by the first molten bath includes a sodium component, further including the steps of:

a) directing an oxygen source into the molten bath, whereby the oxygen source reacts with a radioactive carbon component to form radioactive carbon monoxide that is discharged from the molten bath as a component of the first gaseous discharge stream;

b) combining the gaseous discharge stream with water, whereby the water reacts with the sodium to form the gaseous discharge stream; and

c) combining the gaseous discharge stream with an oxygen source, whereby the oxygen source reacts with carbon monoxide in the gaseous discharge stream to form radioactive carbon dioxide.

51. The method of claim 50, further including the step of combining the radioactive carbon dioxide with the sodium hydroxide, whereby the radioactive carbon dioxide reacts with the sodium hydroxide to form a radioactive sodium carbonate precipitate.

52. The method of claim 51, further including the steps of:

a) directing the gaseous discharge stream, from which carbon dioxide has been removed by reaction with sodium hydroxide, into the second molten bath; and

b) directing at least a portion of the first molten bath into the second molten bath.

53. The method of claim 51, further including the steps of:

a) scrubbing the gaseous discharge stream, from which carbon dioxide has been removed by reaction with sodium hydroxide, with water to form a second scrubber liquid discharge stream that includes at least one component of the radioactive waste, said component selected from the group consisting of cesium in the form of cesium hydroxide, sodium in the form of sodium hydroxide, lead and mercury;

b) filtering the second scrubber liquid discharge stream to thereby form a filtrate that includes at least one of cesium hydroxide and sodium hydroxide and to form a residue that includes at least one of lead and mercury;

c) combining the filtrate with the supernate; and

d) fixing the residue.