Transmutation is a technological ‘solution’ sometimes proposed to deal with high level, long lived waste. The aim is to use reactors, spallation technology or particle accelerators to generate beams of neutrons or charged particles to transform long lived radionuclides into shorter lived or stable isotopes. For example, neutron bombardment of radioactive iodine-129 results (indirectly) in its conversion to stable, non-radioactive xenon. And neutron bombardment of plutonium and neptunium leads to their fission which converts them into shorter-lived radionuclides.
Problems with transmutation include the following (Zerriffi and Makhijani, 2000; Ansolabehere et al., 2003):
* The technology is immature and its future is uncertain.
* It is useful only for certain types and forms of waste. It does not do away with the need for long-term management (storage or disposal) of the resulting wastes.
* It may require the use of reactors (with the attendant proliferation, public health and environmental risks).
* It may require reprocessing (with the attendant proliferation, public health and environmental risks) to separate waste streams prior to selective treatment. Failure to separate/partition can lead to unwanted outcomes such as conversion of stable isotopes into radioactive isotopes.
The MIT Interdisciplinary Study concludes that: “Decisions about partitioning and transmutation must … consider the incremental economic costs and safety, environmental, and proliferation risks of introducing the additional fuel cycle stages and facilities necessary for the task. These activities will be a source of additional risk to those working in the plants, as well as the general public, and will also generate considerable volumes of non-high-level waste contaminated with significant quantities of transuranics. Much of this waste, because of its long toxic lifetime, will ultimately need to be disposed of in high-level waste repositories. Moreover, even the most economical partitioning and transmutation schemes are likely to add significantly to the cost of the once-through fuel cycle.” (Ansolabehere et al., 2003.)
Another novel technology is ‘pyroprocessing’, which would be used on conjunction with fast neutron reactors (but could not be used in conjunction with conventional reactors). Spent fuel is dissolved in a chemical bath, electrodes are inserted to selectively concentrate plutonium and other transuranics which can then be recycled as fast reactor fuel. This process is preferable to conventional reprocessing as it does not involve plutonium separation, and the mix of transuranics (including plutonium) could not be used in weapons (unless it was further processed to separate the plutonium). The waste stream of fast reactors coupled with pyroprocessing would be fission products, most of which are short-lived. (Hannum et al., 2009.)
Pyroprocessing has been demonstrated on a pilot scale but considerable further work needs to be done. In 2009, South Korea announced its intention to embark on a R&D program to assess the viability of operating reactors in conjunction with pyroprocessing by the year 2028. That is almost 20 years − just to assess the viability of the concept.