Gas phase oxidative separation of ruthenium from used nuclear fuel

Abstract

A method of partitioning ruthenium from used nuclear fuel that includes dissolving a used nuclear fuel in a dissolution acid to form a main process stream and an undissolved solid composition comprising ruthenium and one or more additional fission products, heating the undissolved solid composition into an operating temperature range in a gaseous oxidizing environment such that at least some of the ruthenium oxidizes and phase separates, thereby forming a ruthenium containing gas and capturing the ruthenium containing gas.

Description

Atty. Docket No. SHINE5-45284.601GAS PHASE OXIDATIVE SEPARATION OF RUTHENIUM FROM USED NUCLEAR FUELCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application 63 / 685,021 filed August 20, 2024, the contents of which are incorporated by reference in its entirety.BACKGROUND

[0002] The present disclosure relates generally methods and systems of processing used nuclear fuel.SUMMARY

[0001] According to one embodiment of the present disclosure, a method of partitioning ruthenium from used nuclear fuel includes dissolving a used nuclear fuel in a dissolution acid to form a main process stream and an undissolved solid composition comprising ruthenium and one or more additional fission products, heating the undissolved solid composition into an operating temperature range in a gaseous oxidizing environment such that at least some of the ruthenium oxidizes and phase separates, thereby forming a ruthenium containing gas and capturing the ruthenium containing gas.

[0002] According to another embodiment of the present disclosure, a method of partitioning ruthenium from used nuclear fuel includes dissolving a used nuclear fuel in a dissolution acid to form a main process stream and an undissolved solid composition comprising ruthenium and one or more additional fission products, positioning the undissolved solid composition in an oxidation unit, wherein the oxidation unit comprises a gas outlet fluidly coupled to an off-gas capture unit and a gas inlet fluidly coupled to an oxidizing gas source, directing one or more oxidizing gases through the gas inlet and into the oxidation unit to form a gaseous oxidizing environment, heating the undissolved solid composition into an operating temperature range in the gaseous oxidizing environment such that at least some of the ruthenium oxidizes and phase separates, thereby forming a ruthenium containing gas, and capturing the ruthenium containing gas.Aty. Docket No. SHINE5-45284.601

[0003] According to yet another embodiment of the present disclosure, a method of partitioning ruthenium from used nuclear fuel includes dissolving a used nuclear fuel in a dissolution acid to form a main process stream and an undissolved solid composition comprising ruthenium and one or more additional fission products, positioning the undissolved solid composition in an oxidation unit, forming a pressurized gaseous oxidizing environment in the oxidation unit, wherein the pressurized gaseous oxidizing environment induces ruthenium oxidation in the undissolved solid composition such that at least some of the ruthenium oxidizes and phase separates, thereby forming a ruthenium containing gas, and capturing the ruthenium containing gas.

[0004] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0005] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 schematically depicts an embodiment of a fuel processing system comprising a shearing system, a voloxidation system, a dissolution system, a ruthenium separation system, and a solvent extraction system, according to embodiments disclosed and described herein; and

[0007] FIG. 2 schematically depicts an embodiment of a ruthenium separation system, according to one or more embodiments disclosed and described herein.Atty. Docket No. SHINE5-45284.601DETAILED DESCRIPTION

[0008] Reference will now be made in detail to embodiments of used nuclear fuel processing that includes the partitioning of ruthenium from used nuclear fuel during a used nuclear fuel separation and recycling process. Used nuclear fuel processing starts by shearing fuel rods to expose the fuel pellets, which are then oxidized into a used nuclear fuel powder. Cladding material is then separated from the used nuclear fuel powder. Next, the used nuclear fuel powder is dissolved in a dissolution acid, such as nitric acid, forming a main process stream. The main process stream contains the majority of the initial used nuclear fuel and includes uranium and plutonium, as well as minor actinides, lanthanides, and fission products. This main process stream is then further processed using a number of techniques, for example, uranium / plutonium co-extraction processes to partition used nuclear fuel into uranium, uranium / plutonium, neptunium, technetium, minor actinides (e.g., americium and curium), lanthanides, and fission products using liquid-to-liquid extraction, ion exchange extraction, and combinations thereof.

[0009] However, not all the used nuclear fuel powder dissolves. Instead, some of the initial used nuclear fuel remains in particle form, referred to herein as an “undissolved solid composition.” For example, about 5% of the initial used nuclear fuel remains in particle form. The undissolved solid composition includes a number of fission products, such as ruthenium, technetium, palladium, molybdenum, zirconium and rhodium. Current used nuclear fuel separation and recycling processes treat the undissolved solid composition as high-level waste, which is immobilized, for example, in borosilicate glass or ceramic. However, some of the fission products in the undissolved solid composition - particularly ruthenium - are present at a relatively high concentration and are high value materials that, if partitioned from the remainder of the undissolved solids, can be sold for use in a variety of industries.

[0010] The fuel processing system of the present disclosure includes a ruthenium separation system, which may be used to partition ruthenium from the undissolved solid composition using a continuous oxidation reaction and gas phase conversion process. Ruthenium can exist in several oxidation states (0 through VIII) and has a tendency for hydrolysis and the formation of many complex compounds, which can lead to problems related to ruthenium's removal from liquid radioactive materials or even its accurate compositional determination. Because of theseAty. Docket No. SHINE5-45284.601 qualities of ruthenium, separation of ruthenium typically requires strict optimization of different chemical and physical conditions during separation of each species. The ruthenium separation system and the method of its operation described herein overcome some of the challenges of separating ruthenium from used nuclear fuel, allowing for the recycling of this useful material, and incentivizing the reprocessing of used nuclear fuel, thereby reducing the longevity and longterm radiotoxicity of nuclear waste, and improving reprocessing economics. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

[0011] Referring now to FIG. 1, a fuel processing system 100 is schematically depicted. The fuel processing system 100 is configured to process used nuclear fuel, for example, to partition and recycle components of used nuclear fuel. The used nuclear fuel described herein may comprise uranium dioxide (UO2) nuclear fuel. As depicted in FIG. 1, the fuel processing system 100 comprises a fuel rod shearing system 102, a vol oxidation system 104, a dissolution system 106, and a solvent extraction system 108 and a ruthenium separation system 200. As shown schematically in FIG. 1, the solvent extraction system 108 comprises several subsystems each configured to selectively extract different subsets of the elements present in used nuclear fuel. For example, the solvent extraction system 108 may comprise a uranium extraction subsystem 110 configured to selectively extract or co-extract uranium, plutonium, neptunium, and technetium from a main process stream, a fission product extraction subsystem 158, configured to selectively extract cesium and strontium from the main process stream, an actinide extraction subsystem 160 configured to selectively extract minor actinides and lanthanides from the main process stream, and a downstream metal extraction subsystem 190 configured to selectively extract noble metals from the main process stream. The solvent extraction system 108 is described in more detail in PCT Application. No. PCT / US24 / 29747, herein incorporated by reference in its entirety.

[0012] Referring still to FIG. 1, the fuel rod shearing system 102 is configured to separate the end fittings of a nuclear fuel rod bundle of used nuclear fuel and to cut the used nuclear fuel rods into segments sized to facilitate voloxidation of the materials inside the cladding of the nuclear fuel rods. Indeed, the fuel rod shearing system 102 is configured to shear used nuclear fuel rods to expose pellets of used nuclear fuel and separate cladding hulls. The fuel rod shearing systemAtty. Docket No. SHINE5-45284.601102 comprises one or more shearing devices. The vol oxidation system 104 comprises a voloxidation furnace and an off-gas system. The off-gas system is fluidly coupled to the voloxidation furnace and is configured to capture gases released by heating the used nuclear fuel pellets and hulls in the voloxidation furnace. In operation, the voloxidation furnace heats the sheared pellets and hulls to a temperature in a range of from 300° C to 650° C. In some embodiments, NO2, O2, air, and H2O are present in the voloxidation furnace during the heating process. Voloxidation converts the uranium dioxide (UO2) of the used nuclear fuel pellets to triuranium octoxide (UsOs) or uranium trioxide (UO3). Voloxidation also alters the crystal structure of the used nuclear fuel pellets. Without intending to be limited by theory, the conversion of UO2 to U3O8 or UO3 causes the used nuclear fuel to undergo a structural change in which its crystal form changes from a cubic structure to an orthorhombic structure. This structural change also converts the used nuclear fuel material from solid pellets and pellet fragments to a coarse powder form. This increase in surface area and the altered uranium oxidation state caused by voloxidation results in a nuclear fuel material that dissolves more readily in acid (e.g., in nitric acid) in the subsequent dissolution process performed by the dissolution system 106.

[0013] During voloxidation, the change in crystal structure of the used nuclear fuel and the elevated temperature causes additional volatile fission products (e.g., separation products) to be released for collection, such as tritium and iodine (e.g.,129I). During voloxidation, tritium is released as tritiated water (HTO) which may be captured on a hydrophilic sorbent such as molecular sieves, zeolite beds, or a combination thereof.129I is also released during the voloxidation, especially when NO2 is utilized, and may be captured using a zeolite bed, caustic scrubber, molecular sieves, or a combination thereof. Other volatile fission products, such as xenon (Xe), krypton (Kr), e g.,85Kr, and carbon-14 (14CO2) are removed both during voloxidation and the subsequent dissolution process. The14CO can be captured using caustic scrubbers, molecular sieves, zeolite beds, or a combination thereof. The Kr and Xe are also released during dissolution and may be captured on a chilled adsorbent material, such as a zeolite, charcoal, a metal organic framework material.

[0014] Referring still to FIG. 1, the dissolution system 106 comprises a dissolution tank for dissolving the now powdered used nuclear fuel in a dissolution acid (e.g., a first dissolutionAtty. Docket No. SHINE5-45284.601 acid), such as nitric acid. In some embodiments, the dissolution system 106 also comprises a buffer tank, which may be fluidly coupled to the dissolution tank. After voloxidation, the used nuclear fuel powder and hulls are transferred to the dissolution tank of the dissolution system 106 and dissolved in the dissolution acid, clarifying the dissolved used nuclear fuel from undissolved metallics, such as cladding dust and fission product particles and inclusions. These undissolved metallics form the undissolved solid composition, which comprises ruthenium and one or more additional fission products, such as palladium, technetium, molybdenum, rhodium, and zirconium. The undissolved solid composition may next be transferred to the ruthenium separation system 200 for additional processing and partitioning, and the dissolved used nuclear fuel may be transferred to the solvent extraction system 108 for additional processing and partitioning.

[0015] The solvent extraction system 108 may comprise several subsystems each configured to partition selective portions of the used nuclear fuel for storage or further processing. For example, the uranium extraction subsystem 110, the fission product extraction subsystem 158, the actinide extraction subsystem 160, and the downstream metal extraction subsystem 190 may each comprise one or more extraction banks and is configured to selectively extract or co-extract materials of used nuclear fuel, such as uranium, plutonium, neptunium, technetium, strontium, cesium, lanthanides, and actinides using liquid-liquid extraction techniques. Each extraction bank comprises a plurality of mixing devices, which may be fluidly coupled to one another and arranged in series. The plurality of mixing devices may comprise centrifugal contactors, pulse columns, mixer settlers, or combinations thereof. In some embodiments, centrifugal contactors are useful because their compact size allows for the use of smaller hot cells, reducing the capital cost required for facility construction. In operation, the mixing devices induce reactions between elements in an acidic liquid (i.e., in an aqueous phase) and elements in an organic liquid (i.e., in an organic phase).

[0016] As described in detail in PCT Application. No. PCT / US24 / 29747, portions of the used nuclear fuel partitioned using the solvent extraction system 108 are captured in either an aqueous phase, that is, together with an acidic liquid or in an organic phase, that is, together with an organic material. The portions (e.g., elements) of used nuclear fuel captured in aqueous phase may then be solidified, removing the aqueous phase, for example, vaporizing the aqueous phase,Atty. Docket No. SHINE5-45284.601 forming an oxidizing gas. The aqueous phase may comprise nitric acid such that the oxidizing gas formed when solidifying partitioned elements of used nuclear fuel comprises nitric acid vapor. As depicted in FIG. 1, the solvent extraction system 108 may be fluidly coupled to the ruthenium separation system 200 by a gas source pathway 232, this facilitates use of one or more oxidizing gases formed when partitioning portions of used nuclear fuel, for example, using liquid-liquid extraction techniques, to be used when partitioning ruthenium from the undissolved solid composition using the ruthenium separation system 200.

[0017] Referring also to FIG. 2, the ruthenium separation system 200 comprises an oxidation unit 210, an off-gas capture unit 220 fluidly coupled to the oxidation unit 210, for example, to a gas outlet 212 of the oxidation unit 210, by an off-gas pathway 222, and an oxidizing gas source 230 fluidly coupled to the oxidation unit 210 by the gas source pathway 232. The oxidation unit 210 further comprises a solid input 213 for positioning the undissolved solid composition in the oxidation unit 210 and a solid output 214 for removing a retained solid composition from the oxidation unit 210. While the solid input 213 and solid output 214 are shown in FIG. 2 as separate ports, it should be understood that embodiments are contemplated with a single port for loading and unloading solid material.

[0018] In some embodiments, the oxidation unit 210 is configured to generate heat. For example, the oxidation unit 210 may comprise a furnace, a rotary kiln, a fluidized bed combustion system, or the like. A rotary kiln is useful because it facilitates homogeneous mixing of particles, allowing for easier release of gases. In operation, heating that occurs in the oxidation unit 210 may be direct-fired heating or indirect heating. In some embodiments, the oxidation unit 210 is confirmed to generate a high-pressure environment. For example, the oxidation unit 210 may include a high-pressure chamber. In some embodiments, the oxidation unit 210 is configured to generate both heat and a high-pressure environment, for example, the oxidation unit 210 may comprise a high-pressure heating system, such as a pressurized furnace, a pressurized rotary kiln, a pressurized fluidized bed combustion system, or the like. The ruthenium separation system 200 may further comprise a milling unit 240, a dissolution unit 250, a precalciner unit 260, and a gamma radiation source 270.Atty. Docket No. SHINE5-45284.601

[0019] After the undissolved solid composition is partitioned from the remainder of the used nuclear fuel, the undissolved solid composition may be positioned in the oxidation unit 210. In some embodiments, in the oxidation unit 210, the undissolved solid composition is heated into an operating temperature range in a gaseous oxidizing environment, such that at least some of the ruthenium present in the undissolved solid composition oxidizes and phase separates, thereby forming a ruthenium containing gas. The ruthenium containing gas formed by phase separation in the oxidation unit 210 flows from the gas outlet 212 of the oxidation unit 210, through the offgas pathway 222, and is captured in the off-gas capture unit 220. The ruthenium containing gas may comprise RuC gas, RuCh gas, RuCh gas, RuO gas, Ru gas, H2RUO5 gas, or a combination thereof. Indeed, the oxidation process of ruthenium is Ru - RuO? -> RuOa -> RuO4 in continuous oxidation in the operating temperature range.

[0020] In some embodiments, the operating temperature range is from 100 °C to 1500 °C, for example, from 100 °C to 1450 °C, 100 °C to 1400 °C, 100 °C to 1350 °C, 100 °C to 1300 °C, 100 °C to 1250 °C, 100 °C to 1200 °C, 100 °C to 1150 °C, 100 °C to 1100 °C, 100 °C to 1050 °C, 100 °C to 1000 °C, 100 °C to 950 °C, 100 °C to 900 °C, 100 °C to 850 °C, 100 °C to 800 °C, 100 °C to 100 °C, 100 °C to 700 °C, 100 °C to 650 °C, 100 °C to 600 °C, 100 °C to 550 °C, 100 °C to 500 °C, 100 °C to 450 °C, 100 °C to 400 °C, 100 °C to 350 °C, 100 °C to 300 °C, 100 °C to 250 °C, 100 °C to 200 °C, 200 °C to 1100 °C, 200 °C to 1050 °C, 200 °C to 1000 °C, 200 °C to 950 °C, 200 °C to 900 °C, 200 °C to 850 °C, 200 °C to 800 °C, 200 °C to 750 °C, 200 °C to 700 °C, 200 °C to 650 °C, 200 °C to 600 °C, 200 °C to 550 °C, 200 °C to 500 °C, 200 °C to 450 °C, 200 °C to 400 °C, 200 °C to 350 °C, 200 °C to 300 °C, 400 °C to 1100 °C, 400 °C to 1050 °C, 400 °C to 1000 °C, 400 °C to 950 °C, 400 °C to 900 °C, 400 °C to 850 °C, 400 °C to 800 °C, 400 °C to 750 °C, 400 °C to 700 °C, 400 °C to 650 °C, 400 °C to 600 °C, 150 °C to 1500 °C, 200 °C to 1500 °C, 250 °C to 1500 °C, 300 °C to 1500 °C, 350 °C to 1500 °C, 400 °C to 1500 °C, 450 °C to 1500 °C, 500 °C to 1500 °C, 550 °C to 1500 °C, 600 °C to 1500 °C, 650 °C to 1500 °C, 700 °C to 1500 °C, 750 °C to 1500 °C, 800 °C to 1500 °C, 850 °C to 1500 °C, 900 °C to 1500 °C, 950 °C to 1500 °C, 1000 °C to 1500 °C, 1050 °C to 1500 °C, 1100 °C to 1500 °C, 1150 °C to 1500 °C, 1200 °C to 1500 °C, 1250 °C to 1500 °C, or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints. Without intending to be limited by theory, at atmospheric pressure, oxidation of rutheniumAty. Docket No. SHINE5-45284.601 begins at a temperature of greater than 400 °C in air and can convert different chemical forms of Ru to its highest oxidation state (to RuC , which is volatile).

[0021] In some embodiments, a maximum temperature in the operating temperature range is 1500 °C or less, for example, 1500 °C or less, 1450 °C or less, 1400 °C or less, 1350 °C or less, 1300 °C or less, 1250 °C or less, 1200 °C or less, 1150 °C or less, 1100 °C or less, 1050 °C or less, 1000 °C or less, 950 °C or less, 900 °C or less, 850 °C or less, 800 °C or less, 750 °C or less, 700 °C or less, 650 °C or less, 600 °C or less, 550 °C or less, 500 °C or less, 450 °C or less, 400 °C or less, 350 °C or less, 300 °C or less, 250 °C or less, 200 °C or less, 150 °C or less, 100 °C or less or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints. The temperature may be ramped from a starting temperature (e.g., room temperature) to the maximum temperature at a temperature ramp rate in a range of from 5 °C / min to 20 °C / min, for example, 6 °C / min, 8 °C / min, 10 °C / min, 12 °C / min, 14 °C / min, 16 °C / min, 18 °C / min or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints, the undissolved solid composition may be heated in the operating temperature range for an oxidation period, which may be in a range of from 1 hour (hr) to 5 hrs, such as from 2 hrs to 4 hrs, for example, 1 hr, 1.25 hrs, 1.5 hrs, 2.75 hrs, 2 hrs, 2.25 hrs, 2.5 hrs, 2.75 hrs, 3 hrs, 3.25 hrs, 3.5 hrs, 3.75, hrs, 4 hrs, 4.25 hrs, 4.5 hrs, 4.75 hrs, 5 hrs, or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints.

[0022] The gaseous oxidizing environment comprises at least 1 ppm of oxygen containing gas. The gaseous oxidizing environment may be formed in the oxidation unit 210 by directing one or more oxidizing gases into the oxidation unit 210. For example, one or more oxidizing gases may be directed from the oxidizing gas source 230, through the gas source pathway 232, and into the oxidation unit 210. The one or more oxidizing gases may enter the oxidation unit 210 through the gas inlet 211. The one or more oxidizing gases comprise O2, NOX(e.g., NO2, N2O, or a combination thereof) HNO3 vapor, or a combination thereof. Without intending to be limited by theory, HNO3 vapor is a stronger oxidizing agent than NOX, which is a stronger oxidizing agent than 02. Thus, gaseous oxidizing environments that effectively oxidize ruthenium may have varying amounts of oxygen containing gases, depending on the relative composition of the gaseous oxidizing environment. For example, in some embodiments, the gaseous oxidizingAty. Docket No. SHINE5-45284.601 environment comprises HNO3 vapor, NOXor a combination of HNO3 vapor and NOXin a range of from 1 ppm to 100 ppm, for example, 1 ppm to 75 ppm, 1 ppm to 50 ppm, 1 ppm to 25 ppm, 10 ppm to 100 ppm, 25 ppm to 100 ppm, 25 ppm to 75 ppm, 5 ppm to 100 ppm, 15 ppm to 100 ppm, 20 ppm to 100 ppm, 30 ppm to 100 ppm, 40 ppm to 100 ppm, 50 ppm to 100 ppm, 10 ppm to 90 ppm, 20 ppm to 80 ppm, 30 ppm to 70 ppm, 40 ppm to 60 ppm, or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints. In some embodiments, the gaseous oxidizing environment comprises HNO3 vapor, NOx or a combination of HNO3 vapor and NOXof at least 1 ppm, at least 2 ppm, at least 5 ppm, at least 10 ppm, at least 20 ppm, at least 25 ppm, at least 40 ppm, at least 50 ppm, at least 75 ppm, at least 100 ppm, at least 150 ppm, at least 200 ppm, at least 250 ppm, at least 300 ppm, at least 400 ppm, at least 500 ppm, at least 750 ppm, at least 1000 ppm, at least 2000 ppm, or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints.

[0023] In some embodiments, the oxidizing gas source 230 may comprise one or more gas tanks housing oxidizing gases. In some embodiments, as depicted in FIG. 1, the oxidizing gas source 230 may be the solvent extraction system 108 of the fuel processing system 100. HNO3 vapor and NOx may be formed by heating concentrated nitric acid. In operation, oxidation is further induced by increasing the amount of oxidizing gas in the oxidation unit 210. As the oxidation level of ruthenium increases, the boiling point and sublimation point of the ruthenium decreases. As one example, the gaseous oxidizing environment comprises 50 ppm of HNO3 vapor, NOX, or a combination thereof, and the maximum temperature of the operating temperature range is 650 °C. As another example, the gaseous oxidizing environment comprises at least 25 ppm of HNO3 vapor, NOx, or a combination thereof, and the maximum temperature of the operating temperature range is 800 °C or less. Moreover, certain ruthenium oxides have lower boiling points and sublimation points than the other fission product oxides and metals in the undissolved solid composition, facilitating separation of ruthenium from the remaining undissolved solid composition.

[0024] For example, the melting point of ruthenium metal is 2550 °C, the boiling point of ruthenium metal is 4100 °C. The boiling and sublimation point of ruthenium (IV) oxide (RuCh) is 1200 °C and the decomposition point is 1400 °C. The melting point of RuC is 25.5 °C, theAty. Docket No. SHINE5-45284.601 boiling point of R11O4 is 40 °C. As noted above, the one or more additional fission products of the undissolved solid composition may include palladium, molybdenum, zirconium and rhodium. The melting point of palladium metal is 1555 °C and the boiling point of palladium metal is 2963 °C. The melting point of PdO is 750 °C, and the decomposition point of PdO is 1150 °C, at which the PdO decomposes into O2 and Pd metal. The melting point of molybdenum metal is 2623 °C and the boiling point of molybdenum metal is 4639 °C. The melting point of MoO2 is 1100 °C. The melting point of MoO3 is 795 °C and the sublimation point of MoO3 is 1155 °C. The melting point of technetium metal is 2157 °C and the boiling point of technetium metal is 4265 °C. The melting point of TcO? is 1100 °C. The melting point of TC2O7 is 119.5 °C and the boiling point of TC2O7 is 310.6 °C. The melting point of URU3 is 1938 °C. The melting point of zirconium metal is 1852 °C and the boiling point of zirconium metal is 4377 °C. The melting point of ZrCF is 2715 °C and the boiling point of ZrCh is 4300 °C. The melting point of rhodium metal is 1964 °C and the boiling point of rhodium metal is 3696 °C. The melting point of RhCh is 1050 °C. The melting point of RI12O3 is 1100 °C.

[0025] Thus, by heating and gas phase converting ruthenium oxide at or below 1500 °C (or lower in some highly oxidizing environments), the amount of unwanted fission products (e.g., palladium, molybdenum, zirconium, and rhodium) that are released together with the ruthenium is minimized. Indeed, when heating the undissolved solid composition in the gaseous oxidizing environment, at least some of the one or more additional fission products are retained in the gaseous oxidizing environment, for example, in the oxidation unit 210, forming a retained solid composition. The retained solid composition comprises a higher weight percentage of the one or more additional fission products than the undissolved solid composition. For example, the one or more additional fission products may be present in the retained solid composition at a weight percentage of 80% or greater, for example, 82% or greater, 84% or greater, 85% or greater, 86% or greater, 88% or greater, 90% or greater, 92% or greater, 94% or greater, 95% or greater, 96% or greater, 98% or greater, 99% or greater, or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints.

[0026] Referring again to FIG. 2, the gamma radiation source 270 may be positioned between the oxidation unit 210 and the oxidizing gas source 230, along the gas source pathway 232, such that gamma radiation generated and output by the gamma radiation source 270 irradiates the oneAtty. Docket No. SHINE5-45284.601 or more oxidizing gases traveling along the gas source pathway 232 from the oxidizing gas source 230 to the oxidation unit 210, for example, before the one or more oxidizing gases enter the oxidation unit 210. The gamma radiation source 270 may comprise cobalt-60, cesium-137, or any other gamma emitting material, or any combination thereof. In operation, irradiating the one or more oxidizing gases with gamma radiation forms one or more free radicals of oxygen and at least a portion of the one or more free radicals of oxygen enters the oxidation unit 210. Without intending to be limited by theory, the presence of free radicals of oxygen forms a more intense oxidizing environment, facilitating oxidation reactions with ruthenium at lower temperatures.

[0027] Referring still to FIG. 2, in embodiments in which the oxidation unit 210 is configured to generate a pressurized gaseous oxidizing environment, oxidation and phase separation of the ruthenium may be induced in the pressurized gaseous oxidation environment at lower temperatures when compared to environments at atmospheric pressure. For example, a temperature in the pressurized gaseous oxidizing environment is 300 °C or less, such as 250 °C or less, 200 °C or less, 150 °C or less, 125 °C or less, 100 °C or less, 90 °C or less, 80 °C or less, 75 °C or less, 70 °C or less, 60 °C or less, 50 °C or less, 45 °C or less, 40 °C or less, or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints. After positioning the undissolved solid composition in the oxidation unit 210, a pressurized gaseous oxidizing environment may be formed in the oxidation unit 210, for example, by directing one or more oxidizing gases into the oxidation unit 210 to a pressure above atmospheric pressure. For example, one or more pumps may be fluidly coupled to the gas source pathway 232 to pump the one or more oxidizing gases into the oxidation unit and generate the pressurized gaseous oxidizing environment. In some embodiments, the undissolved solid composition is subjected to the pressurized gaseous oxidation environment such that at least some of the ruthenium present in the undissolved solid composition oxidizes and phase separates, thereby forming a ruthenium containing gas. The ruthenium containing gas formed by phase separation in the oxidation unit 210 flows from the gas outlet 212 of the oxidation unit 210, through the off-gas pathway 222, and is captured in the off-gas capture unit 220. In some embodiments, the gas outlet 212 is closable. For example, the gas outlet 212 may be closed when forming for a period of time while the pressurized gaseous oxidizing environment isAtty. Docket No. SHINE5-45284.601 present in the oxidation chamber and thereafter opened to facilitate flow of the ruthenium containing gases formed in the pressurized gaseous oxidizing environment t the off-gas capture unit 220.

[0028] The pressurized gaseous oxidizing environment comprises a pressure of greater than 1 atmospheres, for example, 1.1 atmospheres or greater, 1.2 atmospheres or greater, 1.25 atmospheres or greater, 1.3 atmospheres or greater, 1.4 atmospheres or greater, 1.5 atmospheres or greater, 1.6 atmospheres or greater, 1.7 atmospheres or greater, 1.75 atmospheres or greater, 1.8 atmospheres or greater, 1.9 atmospheres or greater, 2 atmospheres or greater, 2.25 atmospheres or greater, 2.5 atmospheres or greater, 2.75 atmospheres or greater, 3 atmospheres or greater, 3.25 atmospheres or greater, 3.5 atmospheres or greater, 3.75 atmospheres or greater, 4 atmospheres or greater, 4.25 atmospheres or greater, 4.5 atmospheres or greater, 4.75 atmospheres or greater, 5 atmospheres or greater, 6 atmospheres or greater, 8 atmospheres or greater, or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints. For example, the pressurized gaseous oxidizing environment comprises a pressure in a range of from greater than 1 atmosphere to 8 atmospheres, such as from greater than 1 atmosphere to 5 atmospheres, from greater than 1 atmosphere to 4 atmospheres, from greater than 1 atmosphere to 3 atmospheres, from 1.1 atmospheres to 5 atmospheres, from 1.25 atmospheres to 5 atmospheres, from 1.5 atmospheres to 5 atmospheres, from 2 atmospheres to 5 atmospheres, from 1.1 atmospheres to 3 atmospheres, from 1.25 atmospheres to 3 atmospheres, from 1.5 atmospheres to 3 atmospheres, from 2 atmospheres to 4 atmospheres, or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints.

[0029] Referring again to FIGS. 1 and 2, in some embodiments, prior to heating the undissolved solid composition in the oxidation unit 210, the undissolved solid composition may be positioned in the milling unit 240, where the undissolved solid composition is milled, reducing the average particle size of the undissolved solid composition, increasing the surface are of the undissolved solid composition. The milling unit 240 configured to reduce the particle size of the undissolved solid composition, increasing the surface area of the undissolved solid composition and may comprise a horizontal grinding mill, a stirred mill, high pressure grinding rolls, or any other know or yet to be developed milling device.Aty. Docket No. SHINE5-45284.601

[0030] In some embodiments, prior to heating the undissolved solid composition in the oxidation unit 210, the undissolved solid composition may be positioned in the dissolution unit 250 for a secondary dissolution step. In the dissolution unit 250, a portion of the one or more additional fission products of the undissolved solid composition are dissolved using a second dissolution acid. The second dissolution acid may comprise the same acid as the first dissolution acid used in the dissolution system 106 to dissolve the bulk of the used nuclear fuel. For example, the first dissolution acid and the second dissolution acid may each comprise nitric acid. However, the second dissolution acid comprises a higher molar concentration than the first dissolution acid. For example, the second dissolution acid may comprise nitric acid with a molar concentration of4 molar or greater, for example, in a range of from 4 molar (M) to 8 M, for example, 4 M, 4.5 M,5 M, 5.5 M, 6 M, 6.5 M, 7 M, 7.5 M, 8 M, or any range having any two of these values as endpoints, or any value in a range having any two of these values as endpoints. In some embodiments, the portion of the one or more fission products dissolved using the second dissolution acid is molybdenum. The sublimation point of molybdenum trioxide (MoOa) is 1155 °C and the sublimation point of ruthenium(IV) oxide (RuCh) is 1200 °C. Thus, removing molybdenum using a second dissolution step minimizes the amount of molybdenum that phase separates together with ruthenium when heating the undissolved solid composition in the oxidation unit 210. In some embodiments, the secondary dissolution step may be done after milling the undissolved solid composition and before heating the undissolved solid compositing in the oxidation unit 210.

[0031] In some embodiments, prior to heating the undissolved solid composition in the oxidation unit 210, the undissolved solid composition may be positioned in the precalciner unit 260, which heats the undissolved solid composition into a pretreatment range to dry the particles of the undissolved solid composition, which may still be wet after removal from the dissolution unit 250. The pretreatment operating range comprises a maximum temperature that is lower than a maximum temperature of the operating temperature range. In some embodiments, the pretreatment range is 75 °C to 200 °C, 100 °C to 150 °C, or the like, for example, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C, 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, or any range having any two of these values as endpoints, or any value in a range having anyAtty. Docket No. SHINE5-45284.601 two of these values as endpoints. In some embodiments, the pretreatment heating step may be done after the secondary dissolution step and before heating the undissolved solid compositing in the oxidation unit 210.

[0032] While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

[0033] As utilized herein, the terms “approximately,” “about,” “substantially”, and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. Indeed, such terms refer to the subsequently listed property or measurement within normal manufacturing tolerances and imperfections in the relevant field. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical values or idealized geometric forms provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the disclosure as recited in the appended claims.

[0034] The term “coupled” and variations thereof, as used herein, means the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent or fixed) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members coupled directly to each other, with the two members coupled to each other using a separate intervening member and any additional intermediate members coupled with one another, or with the two members coupled to each other using an intervening member that is integrally formed as a single unitary body with one of the two members. If “coupled” or variations thereof are modified by an additional term (e.g., directly coupled), the genericAtty. Docket No. SHINE5-45284.601 definition of “coupled” provided above is modified by the plain language meaning of the additional term (e g., “directly coupled” means the joining of two members without any separate intervening member), resulting in a narrower definition than the generic definition of “coupled” provided above. Such coupling may be mechanical, electrical, or fluidic.

[0035] References herein to the positions of elements (e.g., “top,” “bottom,” “above,” “below”) are merely used to describe the orientation of various elements in the FIGURES. It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the present disclosure.

[0036] Although the figures and description may illustrate a specific order of method steps, the order of such steps may differ from what is depicted and described, unless specified differently above. Also, two or more steps may be performed concurrently or with partial concurrence, unless specified differently above. Such variation may depend, for example, on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations of the described methods could be accomplished with standard programming techniques with rule-based logic and other logic to accomplish the various connection steps, processing steps, comparison steps, and decision steps.

Claims

Atty. Docket No. SHINE5-45284.601CLAIMSWhat is claimed is:

1. A method of partitioning ruthenium from used nuclear fuel, the method comprising: dissolving a used nuclear fuel in a dissolution acid to form a main process stream and an undissolved solid composition comprising ruthenium and one or more additional fission products; heating the undissolved solid composition into an operating temperature range in a gaseous oxidizing environment such that at least some of the ruthenium oxidizes and phase separates, thereby forming a ruthenium containing gas; and capturing the ruthenium containing gas.

2. The method of claim 1, wherein the ruthenium containing gas comprises RuCL gas, RuCh gas, RUO2gas, RuO gas, Ru gas, H2RUO5 gas or a combination thereof.

3. The method of claim 1, wherein when heating the undissolved solid composition in the gaseous oxidizing environment, at least some of the one or more additional fission products are retained in the gaseous oxidizing environment, forming a retained solid composition, wherein the retained solid composition comprises a higher weight percentage of the one or more additional fission products than the undissolved solid composition.

4. The method of claim 3, wherein the one or more additional fission products are present in the retained solid composition at a weight percentage of 90% or greater.

5. The method of claim 3, wherein the one or more additional fission products are present in the retained solid composition at a weight percentage of 95% or greater.

6. The method of claim 1, wherein a maximum temperature in the operating temperature range is 1500 °C or less.Aty. Docket No. SHINE5-45284.6017. The method of claim 1, wherein a maximum temperature in the operating temperature range is 1200 °C or less.

8. The method of claim 1, wherein a maximum temperature in the operating temperature range is 1000 °C or less.

9. The method of claim 1, wherein a maximum temperature in the operating temperature range is 800 °C or less.

10. The method of claim 1, wherein a maximum temperature in the operating temperature range is 600 °C or less.

11. The method of claim 1, wherein the gaseous oxidizing environment comprises one or more oxidizing gases.

12. The method of claim 11, wherein the one or more oxidizing gases comprise O2, NOX, HNO3 vapor, or a combination thereof.

13. The method of claim 12, wherein the one or more oxidizing gases comprise 1 ppm to 100 ppm of HNO3 vapor, NOXor a combination of HNO3 vapor and NOX.

14. The method of claim 12, wherein the one or more oxidizing gases comprise at least 40 ppm of HNO3 vapor, NOXor a combination of HNO3 vapor and NOX.

15. The method of claim 12, wherein a maximum temperature in the operating temperature range is 800 °C or less and the one or more oxidizing gases comprise at least 25 ppm of HNO3 vapor, NOx or a combination of HNO3 vapor and NOX.

16. The method of claim 1, wherein the dissolution acid comprises a first dissolution acid and the method further comprises, prior to heating the undissolved solid composition, dissolving a portion of the one or more additional fission products of the undissolved solid composition in aAtty. Docket No. SHINE5-45284.601 second dissolution acid, wherein the second dissolution acid comprises a higher molar concentration than the first dissolution acid.

17. The method of claim 16, wherein the first dissolution acid and the second dissolution acid each comprise nitric acid and the second dissolution acid comprises a concentration in a range of from 4 to 8 molar.

18. The method of claim 16, wherein the portion of the one or more additional fission products comprises molybdenum.

19. The method of claim 1, further comprising, prior to heating the undissolved solid composition, milling the undissolved solid composition thereby increasing a total surface area of the undissolved solid composition.

20. The method of claim 1, wherein dissolving the used nuclear fuel in the dissolution acid comprises dissolving a used nuclear fuel powder in the dissolution acid, and the method further comprises, prior to dissolving the used nuclear fuel powder, heating one or more used nuclear fuel pellets to form the used nuclear fuel powder.

21. The method of claim 20, wherein heating the one or more used nuclear fuel pellets comprises heating the used nuclear fuel pellets to a temperature in a range of from 300° C to 650° C in an environment comprising NO2, O2, air, and H2O.

22. The method of claim 20, wherein heating the one or more used nuclear fuel pellets removes one or more volatile fission products from the used nuclear fuel.

23. The method of claim 22, further comprising capturing the one or more volatile fission products.

24. The method of claim 22, wherein the one or more volatile fission products removed from the used nuclear fuel comprise tritium, xenon, iodine,14CC>2, and krypton.Atty. Docket No. SHINE5-45284.60125. The method of claim 1, further comprising, prior to heating the undissolved solid composition into the operating temperature range, heating the undissolved solid composition into a pretreatment temperature range, wherein the pretreatment operating range comprises a maximum temperature that is lower than a maximum temperature of the operating temperature range.

26. The method of claim 1, wherein the gaseous oxidizing environment is present in an oxidation unit comprising a gas inlet fluidly coupled to an oxidizing gas source, and the method further comprises directing one or more oxidizing gases through gas inlet and into the oxidation unit to form the gaseous oxidizing environment.

27. The method of claim 26, further comprising irradiating the one or more oxidizing gases with gamma radiation prior to the one or more oxidizing gases entering the oxidation unit.

28. The method of claim 27, wherein irradiating the one or more oxidizing gases forms one or more free radicals of oxygen and the at least a portion of the one or more free radicals of oxygen enter the oxidation unit.

29. The method of claim 28, wherein a maximum temperature in the operating temperature range is 800 °C or less.

30. The method of claim 28, wherein a maximum temperature in the operating temperature range is 600 °C or less.

31. A method of partitioning ruthenium from used nuclear fuel, the method comprising: dissolving a used nuclear fuel in a dissolution acid to form a main process stream and an undissolved solid composition comprising ruthenium and one or more additional fission products; positioning the undissolved solid composition in an oxidation unit; wherein the oxidation unit comprises:Atty. Docket No. SHINE5-45284.601 a gas outlet fluidly coupled to an off-gas capture unit; and a gas inlet fluidly coupled to an oxidizing gas source; directing one or more oxidizing gases through the gas inlet and into the oxidation unit to form a gaseous oxidizing environment; heating the undissolved solid composition into an operating temperature range in the gaseous oxidizing environment such that at least some of the ruthenium oxidizes and phase separates, thereby forming a ruthenium containing gas; and capturing the ruthenium containing gas.

32. The method of claim 31, wherein the ruthenium containing gas is captured in the off-gas capture unit.

33. The method of claim 31, wherein the ruthenium containing gas comprises Ru04 gas, RuCh gas, RUO2gas, RuO gas, Ru gas, I URuO gas, or a combination thereof.

34. The method of claim 31, wherein the one or more oxidizing gases comprise O2, NOX, HNO3, or a combination thereof.

35. The method of claim 34, wherein the one or more oxidizing gases comprise 1 ppm to 100 ppm of HNO3 vapor, NOXor a combination of HNO3 vapor and NOX.

36. The method of claim 34, wherein the one or more oxidizing gases comprise at least 40 of HNO3 vapor, NOXor a combination of HNO3 vapor and NOX.

37. The method of claim 34, wherein a maximum temperature in the operating temperature range is 800 °C or less and the one or more oxidizing gases comprise at least 25 ppm of HNO3 vapor, NOXor a combination of HNO3 vapor and NOX.

38. The method of claim 31 , wherein the one or more oxidizing gases are directed into the oxidation unit from an oxidizing gas source.Atty. Docket No. SHINE5-45284.60139. The method of claim 38, wherein the oxidizing gas source comprises solvent extraction subsystem of a fuel processing system, wherein the solvent extraction subsystem is configured to partition one or more elements in used nuclear fuel using a liquid-liquid extraction process in which the one or more oxidizing gases are formed when solidifying a partitioned element of used nuclear fuel.

40. The method of claim 38, wherein the oxidizing gas source comprises a tank housing the one or more oxidizing gases.

41. The method of claim 31, wherein the oxidation unit comprises a rotary kiln.

42. The method of claim 31, wherein the dissolution acid comprises a first dissolution acid and the method further comprises, prior to positioning the undissolved solid composition in the oxidation unit, dissolving a portion of the one or more additional fission products of the undissolved solid composition in a second dissolution acid, wherein the second dissolution acid comprises a higher molar concentration than the first dissolution acid.

43. The method of claim 42, wherein the first dissolution acid and the second dissolution acid each comprise nitric acid and the second dissolution acid comprises a concentration in a range of from 4 to 8 molar.

44. The method of claim 43, wherein the portion of the one or more additional fission products comprise molybdenum.

45. The method of claim 31, further comprising, prior to heating the undissolved solid composition, milling the undissolved solid composition using a milling unit, thereby increasing a total surface area of the undissolved solid composition.

46. The method of claim 31 , further comprising, prior to heating the undissolved solid composition into the operating temperature range, heating the undissolved solid composition into a pretreatment temperature range, wherein the pretreatment operating range comprises aAty. Docket No. SHINE5-45284.601 maximum temperature that is lower than the maximum temperature of the operating temperature range.

47. The method of claim 46, wherein heating the undissolved solid composition into the pretreatment temperature range is performed in a precalciner unit, prior to positioning the undissolved solid composition in the oxidation unit.

48. The method of claim 46, wherein the maximum temperature in the pretreatment temperature range is 150 °C or less.

49. The method of claim 31, wherein when heating the undissolved solid composition in the gaseous oxidizing environment, at least some of the one or more additional fission products are retained in the oxidation unit, forming a retained solid composition, wherein the retained solid composition comprises a higher weight percentage of the one or more additional fission products than the undissolved solid composition.

50. The method of claim 49, wherein the one or more additional fission products are present in the retained solid composition at a weight percentage of 90% or greater.

51. The method of claim 49, wherein the one or more additional fission products are present in the retained solid composition at a weight percentage of 95% or greater.

52. The method of claim 31, wherein a maximum temperature in the operating temperature range is 1500 °C or less.

53. The method of claim 31, wherein a maximum temperature in the operating temperature range is 1200 °C or less.

54. The method of claim 31, wherein a maximum temperature in the operating temperature range is 1000 °C or less.Atty. Docket No. SHINE5-45284.60155. The method of claim 31, wherein a maximum temperature in the operating temperature range is 800 °C or less.

56. The method of claim 31, wherein a maximum temperature in the operating temperature range is 600 °C or less.

57. The method of claim 31, further comprising irradiating the one or more oxidizing gases with gamma radiation prior to the one or more oxidizing gases entering the oxidation unit.

58. The method of claim 51, wherein the gamma radiation is generated by a gamma source comprising cobalt-60, cesium- 137, or a combination thereof.

59. The method of claim 58, wherein irradiating the one or more oxidizing gases forms one or more free radicals of oxygen and the at least a portion of the one or more free radicals of oxygen enter the oxidation unit.

60. The method of claim 58, wherein a maximum temperature in the operating temperature range is 800 °C or less.

61. The method of claim 58, wherein a maximum temperature in the operating temperature range is 600 °C or less.

62. The method of claim 31, wherein dissolving the used nuclear fuel in the dissolution acid comprises dissolving a used nuclear fuel powder in the dissolution acid, and the method further comprises, prior to dissolving the used nuclear fuel powder, heating one or more used nuclear fuel pellets to form the used nuclear fuel powder.

63. The method of claim 62, wherein heating the one or more used nuclear fuel pellets comprises heating the used nuclear fuel pellets to a temperature in a range of from 300° C to 650 °C in an environment comprising NO2, O2, air, and H2O.Aty. Docket No. SHINE5-45284.60164. The method of claim 62, wherein heating the one or more used nuclear fuel pellets removes one or more volatile fission products from the used nuclear fuel.

65. The method of claim 62, further comprising capturing the one or more volatile fission products.

66. The method of claim 64, wherein the one or more volatile fission products removed from the used nuclear fuel comprise tritium, xenon, iodine,14CC>2, and krypton.

67. A method of partitioning ruthenium from used nuclear fuel, the method comprising: dissolving a used nuclear fuel in a dissolution acid to form a main process stream and an undissolved solid composition comprising ruthenium and one or more additional fission products; positioning the undissolved solid composition in an oxidation unit; forming a pressurized gaseous oxidizing environment in the oxidation unit, wherein the pressurized gaseous oxidizing environment induces ruthenium oxidation in the undissolved solid composition such that at least some of the ruthenium oxidizes and phase separates, thereby forming a ruthenium containing gas; and capturing the ruthenium containing gas.

68. The method of claim 67, wherein the pressurized gaseous oxidizing environment comprises a pressure of 1.5 atmospheres or greater.

69. The method of claim 67, wherein the pressurized gaseous oxidizing environment comprises a pressure of 2 atmospheres or greater.

70. The method of claim 67, wherein the pressurized gaseous oxidizing environment comprises a pressure in a range of from greater than 1 atmosphere to 3 atmospheres.

71. The method of claim 67, wherein a temperature in the pressurized gaseous oxidizing environment comprises 100 °C or less.Atty. Docket No. SHINE5-45284.60172. The method of claim 67, wherein a temperature in the pressurized gaseous oxidizing environment comprises 50 °C or less.

73. The method of claim 67, wherein the pressurized gaseous oxidizing environment comprises one or more oxidizing gases.

74. The method of claim 73, wherein the one or more oxidizing gases comprise O2, NOX, HNO3 vapor, or a combination thereof.

75. The method of claim 74, wherein the one or more oxidizing gases comprise 1 ppm to 100 ppm of HNO3 vapor, NOXor a combination of HNO3 vapor and NOX.

76. The method of claim 74, wherein the one or more oxidizing gases comprise at least 40 ppm of HNO3 vapor, NOXor a combination of HNO3 vapor and NOX.

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