A 2013 report from the American Association for the Advancement of Science’s Center for Technology, Science, and Security Policy addresses the accessibility of medically useful radioactive isotopes in the context of nuclear nonproliferation. According to the report, construction of nuclear reactors, regardless of their purpose, would be a step away from international nonproliferation and would create new national security risks. The report examines the dangers of constructing reactors capable of uranium enrichment and then provides an alternative to reactors in the form of accelerator-driven isotope creation.
To fully understand the policies surrounding nuclear proliferation, you really need to understand the basis of nuclear enrichment. Naturally occurring uranium contains two isotopes, the highly reactive but relatively rare U-235 and the more common but more stable U-238. Uranium enrichment involves the process of stripping away U-238 so that only the fission-ready U-235 remains. The terms which we often hear regarding enrichment, such as depleted uranium, low enriched uranium, or highly enriched uranium, refer to the fraction of the sample which is made up of U-235. Highly enriched uranium is internationally defined by the range from 20% to 100% U-235, with the upper bounds of that, particularly 90% and above, being what is typically used in nuclear weapons.
According to the article, power reactors use 3.5% low enriched uranium and medical isotope production requires 19.75% enrichment, with some isotopes even requiring highly enriched uranium in those dangerous ninety percent ranges. The main issue is that having the capacity to enrich to even 3.5% uses the same centrifuge set-up as enriching to 90% and upwards. Thus, having the ability to enrich to light, power-producing levels (or medium, medically-relevant levels) also carries the ability to create weapons grade uranium.
So, to avoid the proliferation of nuclear arms capable nations, the report suggests accelerator-based technology as a replacement. By using particle accelerators, those isotopes necessary for medical treatments and diagnostic tests can be produced without the need for building reactors or for the centrifuges used in enriching uranium. These treatments and tests include procedures like the targeted doses of radiation used in treating cancer and even your everyday x-rays.
Now, accelerators can be used to produce Plutonium-239 (Pu-239), another highly reactive compound. Pu-239 is created when U-238 captures a neutron. Yet the costs of repurposing a medical-grade accelerator for this purpose and maintaining that process long enough to obtain a weapons-level amount of Pu-239 makes it an incredibly impractical process. As such, accelerators would appear to provide a safe and cost-effective alternative to reactors.
According to the report, most any commonly used medical isotopes can be produced with a particle accelerator without prohibitive cost. The authors examine a wide range of isotopes and explain both how they are used and how they can be produced with a particle accelerator. In particular, they used Molybdenum-99/Technetium-99m as a representative case to calculate cost and proliferation risk for other compounds, finding that any serious effort to obtain a dangerous amount of reactive isotopes would take so long and be so obvious to other nations that accelerators don’t really pose much of a threat.
By and large, particle accelerator based isotope production presents a cost-effective and non-proliferative alternative to nuclear reactors, which nations such as the United States would see as being very beneficial given the recent attempt by Iran to start a nuclear power program. So far as keeping serious nuclear technology to a global minimum is concerned, particle accelerators do seem to solve the otherwise difficult to address issue of accessing medically necessary compounds.
Original article: http://www.aaas.org/cstsp/files/AAAS_CSTSP_Medical_Isotope_Report.pdf