To reduce the problems associated with very long-term storage, it has been proposed that the long-lived actinides (such as Np-237, Am-241, Am-243, Cm-244) are removed from the waste and transmuted (“incinerated”) into shorter-lived or stable isotopes using:
- An accelerator-driven system (ADS) — a sub-critical reactor driven by a spallation neutron source.
- A fast reactor — which has a harder neutron spectrum capable of fissioning the minor actinides.
The idea is to convert long-lived isotopes (with half-lives of thousands to millions of years) into isotopes with half-lives of decades or less, dramatically reducing the time for which the waste must be isolated.
This concept remains largely at the research and development stage, although several countries (France, Japan, Belgium) have active programmes.