Helium-cooled reactor technologies for accelerator transmutation of nuclear waste

Helium-cooled reactor technologies offer significant advantages in waste transmutation. They are ideally suited for use with fast, thermal or epithermal neutron energy spectra. They can provide a relatively hard thermal neutron spectrum for transmutation of fissionable materials such as 239Pu using ceramic-coated particles, a graphite moderator, and a non-fertile burnable poison. These features (1) allow deep levels of transmutation with minimal or no intermediate reprocessing, (2) facilitate passive decay heat removal via heat conduction and radiation, (3) allow operation at relatively high temperatures for a highly efficient generation of electricity, and (4) discharge the transmuted waste in a form that is highly resistant to corrosion for long times. They also provide the hardest possible fast neutron environment since the helium coolant is essentially transparent to neutrons and does not degrade neutron energies. This facilitates transmutation of actinides that have low fission-to-capture ratios in the thermal neutron energy range. In this paper, we report work on the development of two concepts using helium-cooled reactor technologies for transmutation. Both concepts make use of thermal and fast energy spectra. (author)