Medical Isotope Production Without Highly Enriched Uranium (2009) / Chapter Skim
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7 Conversion to LEU-Based Production of Molybdenum-99: Technical Considerations
7 Conversion to LEU-Based Production of Molybdenum-99: Technical Considerations
Pages 90-100
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From page 90... ...
TARGET DESIGN AND PROCESSING As noted in Chapter 1, almost all of the Mo-99 produced for medical use in the world today is made using HEU targets. These targets consist of an HEU "meat," usually a uranium oxide or uranium metal alloy, contained within a metal or metal alloy cladding (Chapter 2)
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From page 91... ...
Direct Replacement of the HEU in the Target with LEU HEU and LEU have essentially the same physical and chemical properties, so the direct replacement of HEU by LEU in the target meat would pose no particular target design, fabrication, or testing challenges. The LEU target would have the same geometry, heat transfer, and chemical processing properties as the equivalent HEU target and could be irradiated and processed in essentially the same manner.
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From page 92... ...
Also, space limitations in the reactor target irradiation positions might preclude the use of substantially larger targets. Increase the Mass of U-235 in the Target by Changing the Composition of the Target Meat The HEU targets used for most current Mo-99 production are u ranium-aluminum alloys (Table 2.2)
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From page 93... ...
showing the irradiated LEU foil target being removed from the target cladding in preparation for dissolution. SOURCES: Courtesy of George Vandergrift, Argonne National Laboratory, and the University of Missouri, respectively.
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From page 94... ...
: Gram for gram, uranium foil targets can produce as much or more Mo-99 than currently used HEU targets under the same irradiation conditions. The uranium foil is potentially compatible with the alkaline and acidic dissolution processes that are currently employed by large-scale producers. The foils used for this development work have been produced by Argonne National Laboratory by hot and cold rolling and by the Korea Atomic Energy Research Institute (KAERI, South Korea) using a casting method (Kim et al., 2004)
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From page 95... ...
(4) The fluoride ion dissolves uranium silicide but complicates waste treatment and disposal because of its corrosive nature.
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From page 96... ...
: Irradiated HEU targets are dissolved in acidic or alkaline solutions, and Mo-99 is recovered through a series of chemical processing steps followed by sorption onto an alumina column or other media. Over the years, Mo-99 producers have added proprietary improvements to their processes to reduce processing time, reduce product impurities, and improve Mo-99 recovery.
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From page 97... ...
Development work on LEU targets would be initially aimed at producing designs that mimic (to the extent feasible given the forgoing discussion on target design options) the characteristics of currently utilized HEU targets.
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From page 98... ...
Such testing allows LEU target m aterials to be evaluated using conventional wet-laboratory facilities. B ecause target irradiation times for Mo-99 production are short and U-235 burn-ups in the targets are low, unirradiated LEU targets have essentially the same material and chemical properties as irradiated LEU targets.
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From page 99... ...
FINDINGS Several important technical considerations for converting Mo-99 production from HEU targets to LEU targets were described and discussed in this chapter. Based on this information, the committee finds that: • There are three basic approaches for converting HEU targets to LEU: Direct replacement of HEU in the target with LEU; increasing the mass in U-235 in the target by increasing target size; or increasing the mass of U-235 in the target by changing target composition.
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From page 100... ...
• R&D will be essential for making wise selections about conversion approaches. Most of the needed R&D can be carried out using cold testing and radioactive tracer testing at full scale and at relatively low cost in conventional laboratory facilities.
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