The main reason for reprocessing is to separate the remaining uranium and plutonium in the fuel from fission products and transuranic elements other than plutonium, so that these materials can be reused as material for new

14.3 Relative radiotoxicity of the different components in spent nuclear fuel from a light water reactor irradiated to 41 MWd/kg U with respect to the radiotoxicity of the corresponding uranium ore (NEA, 1999c).

fuel (plutonium mixed with uranium in Mixed Oxide (MOX) fuel and reprocessed uranium re-enriched in so called ‘reprocessed uranium’ (REPU) fuel). In this process also the volume of high-level waste and the long-term toxicity is reduced. By more advanced reprocessing, that is not yet in use, it could also be possible to remove the transuranic elements and some long-lived fission products from the waste, thus further reducing the radiotoxicity. The intention would then be to burn (nuclear incineration) the removed components in a fast neutron reactor or another fast flux nuclear facility, e. g. an accelerator driven reactor (ADS).[84]

The waste from the reprocessing includes the high-level waste containing the fission products and transuranic elements other than plutonium, the metal components of the fuel element (fuel cladding, end pieces and spacers), and secondary process and maintenance waste. In the end decom­missioning waste will also be generated.

The solution of fission products and transuranic elements is concentrated and then mixed with glass-forming components and melted to become a glass matrix (vitrification), which is poured into a metal container that is subsequently sealed and kept clean on the outside. This is the main HLW. Most of the radioactivity of the fuel remains in the HLW.

The metal components of the fuel element are further cleaned to mini­mize the remaining fuel oxide in this waste stream. After compaction or cementation the metal components are filled in tight containers similar to the HLW and handled in a similar way as HLW or ILW.

The process and maintenance waste is physically similar to such waste from a nuclear power plant (see Section 14.2.4). There is, however, an important distinction as the fuel is dissolved in the reprocessing plant and the systems and components are exposed directly to the fuel material. Some of this waste could thus contain significant amounts of long-lived radionu­clides and would therefore be classified as ILW.

Reprocessing of one year’s fuel from a 1000 MWe LWR will generate 2-3 m3 of vitrified HLW and some 10 m3 of ILW and LLW. Some ILW and LLW will also be generated in the MOX fabrication facility.