Apr 27, 2020
Reducing waste and time – Novel approach allows for rapid isotope production for medical diagnostics
Life Sciences, Chemical Process, Physical Sciences, Energy and Environment
- ⁹⁹ᵐTc as one of the most important medical radioisotopes
- Novel dry-chemical separation of molybdenum and uranium
- More environmentally friendly production with less toxic waste
Dr. M. Charlotte Hemmer
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With its wide application range in nuclear medicine, technetium-99m (⁹⁹ᵐTc) is one of the most important medical radioisotopes. Used by doctors and scientists for diagnostic and research purposes into organ structures and function, ⁹⁹ᵐTc arises through the ß-decay of its parent isotope molybdenum-99 (⁹⁹Mo) which is a fission byproduct of the neutron irradiation of targets enriched in uranium-235 (235U) in nuclear reactor. Due to its short half-life of 66 hrs, ⁹⁹Mo production has to happen on a regular basis and is tightly scheduled to ensure continuous availability and not risk interruptions impacting patient care. ⁹⁹ᵐTc is directly extracted on-site in hospitals in specialized generators from a decaying sample of ⁹⁹Mo. By emitting γ-rays, it can then be used for radiodiagnostics after injection into patients. Significant global efforts are underway to ensure a reliable continuous supply chain of ⁹⁹Mo and ⁹⁹ᵐTc. In addition, the call for a more environmentally friendly solution has intensified in the last years as the target conversion from highly to low enriched uranium comes at the cost of a significant increase in radioactive waste. Following neutron irradiation, uranium targets have to be dissolved to recover and purify ⁹⁹Mo. Depending on the uranium target used, the dissolution process involves the use of an alkaline or acid solution. In both cases, the waste management presents a considerable problem, since the accumulating waste from ⁹⁹Mo production contains ca. 97% of the enriched uranium from the original targets¹.
The present innovation describes a dry-chemical process allowing for the rapid separation of molybdenum from uranium by converting them to their corresponding metal hexafluorides. The multi-stage process originates with a gas phase mixture of MoF6 and UF6 which is fed into a liquid or supercritical fluid phase to dissolve both metal fluorides. By photoreduction UF6 is precipitated to its pentafluoride UF5. Separating UF5 as a solid phase yields a solution containing the desired MoF6. The solvent itself is highly volatile, allowing for its evaporation after the separation process. Alternatively, the separation process can be achieved via a gas phase mixture containing MoF6, UF6and a fluorine atom scavenger mixed in gaseous form. The inventive separation has the advantage over the established wet chemical separation by producing smaller quantities of acidic radioactive waste which results in a costly and elaborate disposal.
- Rapid dry chemical separation of molybdenum and uranium
- Reduced acidic waste production compared to wet chemical procedure
- Opportunity to use separation approach for recycling of unspent uranium from uranium-molybdenum alloys currently under development
Proof of concept