Belgian and Dutch researchers have developed a new method for producing medical radioisotopes without the use of enriched uranium.
Using electron accelerators, the scientists can apply an electron beam at energy densities several orders of magnitude higher than that of the sun’s core to isotopes. The isotopes break down into radioisotopes with little long-lived radioactive waste left over, according to Physics World
Developing this technique is the SMART project, an international collaboration made up of the Belgian Institute of Radio Elements (IRE) and Dutch companies Demcon and ASML. They say that using this alternative approach will relieve dependency on nuclear reactors, with several aging and unable to keep up with demand.
The idea is based on the use of accelerated electron beams to generate extreme ultraviolet light for lithography applications. The SMART project is scaling up the technology for large-scale radioisotope production and upon achieving certain milestones, aims to create a commercial production facility.
To start, it will use its technique to convert non-radioactive molybdenum-100 (Mo-100) into molybdenum-99 (Mo-99), the nuclear parent of Technetium-99m (Tc-99m). Tc-99m is the most commonly used medical radioisotope in the world and part of tens of millions of procedures annually to diagnose heart disease, cancer and other diseases. The researchers recently showed that their Mo-100 target could withstand prolonged exposure to the extreme intensity of the irradiation.
Using the ELBE superconducting electron accelerator at the German research lab, Helmholtz Zentrum Dresden-Rossendorf, they performed the tests on a 1:1000 scale, compared with the intended size for Mo-99 production. The power density deposited in the target is nine orders of magnitude higher than that of the sun’s core. This places the radiation environment on par with a reactor vessel wall in a nuclear plant for over 10 years.
They exposed a millimeter-sized molybdenum target to a 30 kW electron beam for 115 hours straight, the time required to produce isotopes. To cool and prevent the target from evaporating under that exposure, the researchers used liquid sodium due to its high specific heat capacity and conductivity. The substance proved to be an effective coolant, with the target surviving five consecutive days of extreme radiation.
“Not only is the liquid sodium extremely challenging to work with, it is also used in one of the most extreme conditions that we can ever produce on Earth,” lead engineer Bas Vet, of Demcon, told Physicsworld.
The researchers plan to scale up the final industrial proportions and have included specifics for the target, its environment, the cooling and the system that processes the irradiated target in the final factory design.
They hope to have the factory built and operational by 2028.
The majority of Mo-99 is produced from high-enriched uranium at five nuclear research reactors in the world, and smaller amounts are produced from low-enriched uranium in at least three. Efforts to reduce highly enriched uranium and radioactive waste left over are underway. The Technical University of Munich in Germany is currently building an Mo-99 irradiation facility at its reactor, FRM II that is designed for targets with low-enriched uranium
. Since it will be using less enriched uranium plates, it will irradiate at least twice as many to meet worldwide demand for Tc-99m. It also has developed a new method for extracting Mo-99 without the use of aqueous chemistry to decrease waste.
The U.S., now able to meet sufficient Mo-99 demand with its domestic source, announced in February that it will no longer ship
highly enriched uranium overseas. This, it says, will help decrease the substance worldwide and assuage concerns that it could be used to build nuclear weapons, which are enriched with more than 93% of U235. HEU contains 20% or more U235.