Fabrication and characterization of inert matrix and thoria fuel for actinides transmutation

In using nuclear energy in the uranium fuel cycle, Plutonium (Pu) and so-called minor actinides (MAs) such as neptunium (Np), americium (Am) and curium (Cm) are produced in addition to the fission products. The strategies currently pursued involve the partitioning of uranium and plutonium by the reprocessing of spent fuel elements for use as Pu-U/mixed oxide fuel (MOX) or the direct final disposal of the spent fuel elements after interim storage. In contrast to the predominantly short-lived fission products (<300 years), the long-lived MAs as well as Pu dominate the toxicity potential of the waste over long periods (> 104 years). The selective partitioning of MAs from the fission products and separate treatment can considerably improve long-term safety. At present, strategies are being discussed world-wide to 'burn' the MAs as well as Pu in special reactors, i.e. using thorium based fuels, or accelerator-driven subcritical systems and thus transmute them into short-lived fission products. (orig.)