Not Applicable
1. Field of Invention
The present invention relates generally to the treatment of radioactive waste and in particular to the separation of tritium from radioactive waste materials.
2. Description of the Related Art
Tritium is a radioactive isotope of hydrogen with a half-life of approximately 12.3 years. As tritium is both a radioactive contaminant and a potentially useful material for numerous scientific and commercial applications, the generation of tritium in pressurized water reactors (PWRs) is a matter of vital interest. Normal reactor operations produce quantities of tritiated water. In particular, the use of boron as a moderator within reactor systems naturally leads to the production of tritium and to the presence of tritium-containing water molecules both within the water used for cooling the reactor and within water used in storage pools for radioactive waste materials.
Available public water treatment processes remove many radioactive contaminants but are ineffective for tritium. Tritium is one of several radioactive isotopes that, over time, concentrate in organic systems and enter the food chain, possibly with adverse environmental and public health effects. Tritium contamination of the groundwater in the vicinity of nuclear power stations, including PWRs, has led to public outcry and negative publicity for the nuclear power industry. This could be particularly important, for example, at the site of a nuclear incident. Clearly, it would be advantageous to have methods, systems and apparatuses for the separation and concentration of tritium from light water used in PWRs and from water and liquids isolated from radioactive waste materials. (Herein, “light water” is used to refer to tritiated water, and especially HTO, and in opposition to “heavy water,” or D2O, which is used in other nuclear applications.) The capability to separate tritium from reactor water and from radioactive waste materials is important for clean, safe, and secure radioactive waste management, which in turn is important for the safe and cost-effective use of nuclear power.
Disclosed herein are systems, methods, and apparatuses for separating tritium from radioactive materials and the water from nuclear reactors. In particular, the present general inventive concept, in some of its several embodiments, includes system and processes for high throughput treatment of water from reactor systems to concentrate and separate tritium from the reactor water. Of particular interest here is the development of a high throughput, low concentration system for volume reduction, as opposed to a low throughput, high concentration system for tritium product generation. Some embodiments of the present general inventive concept involve the reaction of tritiated hydrogen gases with water in the presence of a catalyst (often a palladium catalyst) in a catalytic exchange column, yielding a more concentrated and purified tritiated water product.
In some of its various embodiments, the present general inventive concept includes an advanced tritium system (ATS) for the separation of tritium. An ATS receives water from a light water reactor or from radioactive waste treatment system. When it enters the ATS, the water contains tritium isotopes, primarily in the form of tritiated water (e.g. HTO), where at least one of the protonic hydrogen atoms of the water molecule has been replaced by a tritium atom. The water with tritiated water passes into an electrolyzer—generally an alkaline electrolyzer, although other electrolyzers are contemplated—where the tritiated water is broken up by electrolysis into a combination of oxygen gas (O2) and hydrogen gas comprising a number of hydrogen isotopes and isotope combinations (e.g. H2, HT, T2). The oxygen gas is diverted and discharged from the ATS, while the hydrogen gas with tritium is directed to a gas purifier, where various contaminants entrained in the gas, such as KOH or another substance from the electrolyzer, are removed from the gas. The hydrogen gas passes from the gas purifier into a catalytic exchange column; in some embodiments, the hydrogen gas leaving the gas purifier first passes through a heater or a humidifier, or both, before entering the catalytic exchange column. Within the catalytic exchange column, tritium is separated from protonic hydrogen. Hydrogen gas, including gas molecules with tritium constituents, enters the bottom of the catalytic exchange column and rises through the height of the catalytic exchange column. Generally, the hydrogen gas with tritium has been heated before it enters the catalytic exchange column. Substantially simultaneously, purified (distilled or at least deionized) water from a purified water source is fed into the top of the catalytic exchange column and allowed to trickle down. The catalytic exchange column is packed with granulated palladium or a similar catalyst. When the rising hydrogen gas with tritium encounters the falling purified water in the presence of the catalyst within the catalytic exchange column, the hydrogen gas with tritium and the purified water react to yield tritiated water (e.g., HTO) and hydrogen gas that is substantially free of tritium isotopes (i.e., “detritiated hydrogen”). The detritiated hydrogen is vented from the catalytic exchange column, while the tritiated water exits the catalytic exchange column and proceeds to a holding tank. This concentrated, substantially pure hydrogen can then be used as a fuel source. In many embodiments, the tritiated water in the holding tank is fed back into the electrolyzer in order to repeat the process of electrolysis and catalytic tritium separation, thereby yielding a tritiated water product with a higher concentration of tritium. Otherwise, the tritiated water proceeds from the holding tank to storage or other disposition (e.g., waste stabilization and disposal). Passing tritiated water from a nuclear reactor, or from radioactive waste, through an ATS such as the one illustrated in
In some embodiments of the present general inventive concept, a system for high throughput separation and concentration of tritium from tritiated waste water in light water nuclear reactors includes an electrolysis system to etectrolyze tritiated waste water to produce oxygen gas, hydrogen gas and tritium gas, a heater to heat water vapor, a liquid phase catalytic exchange column to receive a mixture of hydrogen gas and tritium gas from said electrolysis system and heated water vapor from said heater, said liquid phase catalytic exchange column including a catalyst to retain tritium gas from said mixture as said mixture passes through said liquid phase catalytic exchange column, a deionized water source to provide deionized wash water to said liquid phase catalytic exchange column in order to remove said tritium from said catalyst, so that said deionized wash water and said tritium emerge from said liquid phase catalytic exchange column as a concentrated tritium waste product a gaseous exhaust subsystem to carry away hydrogen gas and water vapor as gaseous exhaust from said liquid phase catalytic exchange column.
In some embodiments, said catalyst includes palladium.
In some embodiments, said catalyst includes palladium coated with a hydrophobic material.
In some embodiments, said catalyst includes palladium coated with a hydrophobic polymer.
In some embodiments, said catalyst includes palladium coated with a fluoropolymer.
In some embodiments, said catalyst includes palladium coated with a polytetrafluoroethylene.
Some embodiments further include a tritium monitor to monitor the tritium content of the gaseous exhaust within said gaseous exhaust subsystem.
Some embodiments further include a condenser to condense at least some of the gaseous exhaust.
Some embodiments further include a stabilization subsystem for treating said concentrated tritium waste product.
In some embodiments of the present general inventive concept, a method for high throughput separation and concentration of tritium from tritiated waste water in light water nuclear reactors includes electrolyzing tritiated water to produce hydrogen and tritium gas, combining hydrogen and tritium gas produced by electrolysis with heated water vapor to produce a mixture, passing the mixture through a liquid phase catalytic exchange column that includes a catalyst configured to retain tritium from the mixture, passing deionized wash water through said liquid phase catalytic exchange column to remove the tritium from said catalyst, collecting the tritium and the deionized wash water as a high activity tritium waste product, and expelling water vapor and hydrogen gas as effluent.
In some embodiments, said catalyst includes palladium.
In some embodiments, said catalyst includes palladium coated with a hydrophobic material.
In some embodiments, said catalyst includes palladium coated with a hydrophobic polymer.
In some embodiments, said catalyst includes palladium coated with a fluoropolymer.
In some embodiments, said catalyst includes palladium coated with a polytetrafluoroethylene.
In some embodiments, a method further includes monitoring the tritium content of the effluent with a tritium monitor.
In some embodiments, a method further includes condensing at least some of the effluent.
In some embodiments, a method further includes stabilizing the high activity tritium waste product.
The above-mentioned and additional features of the invention will become more clearly understood from the following detailed description of the invention read together with the drawings in which:
The present general inventive concept, in some of its embodiments, includes processes and methods for the separation, isolation, or removal (collectively “separation”) of tritium from radioactive waste. In particular, the present general inventive concept, in some of its several embodiments, includes systems and processes for high throughput treatment of water from reactor systems to concentrate and separate tritium from the reactor water.
Turning to the figures,
From the liquid/solid separation system 30, liquid wastes that are substantially free of solid waste material proceed 38 to a liquid processing system 40. In some embodiments, such as the one illustrated in
Passing tritiated water from a nuclear reactor, or front radioactive waste, through an ATS such as the example illustrated in
Some embodiments of the present general inventive concept include using an ATS to concentrate tritium in reactor water into a small volume of concentrated tritiated water.
A number of catalysts are contemplated for use in the LPCE column 230. In some embodiments, the catalyst is generally a TEFLON®-coated palladium catalyst, or a catalyst that includes palladium coated with or mixed with a fluorinated polymer, or a catalyst that includes palladium coated with or mixed with a hydrophobic polymer, or a similar catalyst. Other catalysts are contemplated by the present general inventive concept, and the present general inventive concept is not limited to the illustrated example embodiment catalysts.
As noted, the protonic hydrogen gas produced by electrolysis and passed through the LPCE column 230 generally is expelled along with water vapor as gaseous exhaust 232, as shown in
Multiple options exist for the further disposition of the tritium after is separated and concentrated by the ATS as in the illustrated embodiment in
Thus, in some of the several example embodiments of the present general inventive concept, systems, methods, and processes for a high throughput, low concentration processing of low activity tritiated light water include the electrolysis of at least some of the tritiated water to produce hydrogen and tritium gas. The hydrogen and tritium gas produced by electrolysis are combined with heated water vapor and passed through a LPCE column, which generally includes a catalyst that includes palladium coated with a hydrophobic polymer. As the hydrogen and tritium gas, along with heated water vapor, rise through the LPCE column, the tritium is retained on the catalyst. Deionized wash water passes down the column (i.e., in the opposite direction of the flow of the hydrogen gas and heated water vapor) and carries the retained tritium out of the LPCE column. The tritium, combined with the deionized wash water, is thereby collected as a high-activity tritium waste product with substantially less volume than the original volume of low activity tritiated light water. The water vapor and hydrogen gas, substantially free of tritium, are exhausted as effluent. Some embodiments of the present general inventive concept include various treatments of the hydrogen effluent.
Generally, in some example embodiments of the present general inventive concept, the molar gas flow rate of the hydrogen and tritium gas, along with heated water vapor, rising through the LPCE column is greater than the molar liquid flow rate of the deionized wash water travelling down through the LPCE columns.
In some example embodiments of the present general inventive concept, the composition or component ratio of the mixture of hydrogen gas and water vapor is adjusted to comply with emission guidelines while still maximizing throughput.
The present general inventive concept is not limited to the illustrated embodiments.
While the present general inventive concept has been illustrated by description of some embodiments, and while the illustrative embodiments have been described in detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.
This Application is a continuation-in-part of U.S. application Ser. No. 13/079,331, filed Apr. 4, 2011, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application 61/320,5.15, filed Apr. 2, 2010.
Number | Date | Country | |
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61320515 | Apr 2010 | US |
Number | Date | Country | |
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Parent | 13079331 | Apr 2011 | US |
Child | 13863206 | US |