16.1.1 Technical targets

Clearly, the overall aim of reprocessing is to recover uranium and plutonium efficiently from spent fuel while meeting safety targets and limiting environmental impact.

Some specific technical targets follow.

Recovery efficienciesfor uranium andplutonium

The efficiency of recovery for uranium and plutonium must be as high as possible (> 99%) in order to reduce the amount of these long-lived elements within the waste streams. As an example the efficiencies in La Hague reprocessing plant (France; AREVA) are around 99.88% for uranium and plutonium.

Specificationsfor reprocessed uranium

Reprocessed uranium is generally delivered as a concentrated solution (200-400 g/l) of uranyl nitrate for further conversion into oxides (UO2 or U3O8) or tetra — or hexafluoride depending upon subsequent use (storage, fuel manufacture or re-enrichment).

Standards are driven by re-enrichment and include norms regarding chemical and radiochemical impurities (less than 3000 ppm of volatile compounds at 850 °C other than uranium).

The specific в activity from fission products must be less than 18 500Bq/gU. The a activity, other than uranium, must be less than 250Bq/gU.

Reprocessed uranium includes all uranium isotopes from 232 to 238 except 237, which decays quickly to neptunium-237. These isotopes have a long half-life (>105 years) except for uranium-232, which has a half-life of 70 years. Through successive a and в decays, uranium-232 produces very hard and intense Y emitters.

The presence of these isotopes in smaller, though significant amounts has adverse effects in neutronic terms. Consequently, the uranium-232 and -236 isotopes must be particularly considered in calculation of enrichment levels.