HLW after the separation of U, Pu and Np contains two major radionuclide groups: fission products and TRU elements. The later ones are the most dangerous and should be separated in the special actinide fraction. This process has been realized at PA “Mayak”.
The composition of the actinide fraction depends on a separation method:
A. Radionuclides of Am and Cm with minor amounts of U, Np and Pu.
B. Radionuclides of Am and Cm with minor amounts of U, Np and Pu and also REEs.
C. Radionuclides of Am and Cm with minor amounts of U, Np and Pu and also REEs and perhaps some amount of Zr.
The fraction with composition A can be burned off in fast reactors whereas the fractions with compositions B and C should be immobilized in stable matrices. Alpha-Activity of actinide fraction is subsequently determined by 244Cm, 241Am, 244Am, 239Pu and 242Pu during a long-term storage. The storage time depends on conditions and can reach several hundreds of thousands years. The main requirements to matrices are chemical and radiation resistances. The fraction with composition B can be incorporated in perovskite ceramics whereas in case of composition C the additional zirconolite and/or pyrochlore phases are necessary.