Lower waste volumes

European reprocessing companies have invested heavily in reducing the volume of low and intermediate wastes associated with reprocessing, leading to a three-fold reduction over the past 15 years.¹ However, even today the total volume of conditioned and packaged reprocessing waste is about 20 m³/tHM, while the volume of conditioned and packaged spent fuel is about 2 m³/tHM.² Although the volume of vitrified high-level waste from reprocessing is lower than the volume of spent fuel, intermediate-level wastes must also be disposed of in a repository adding considerably to total repository waste volumes resulting from reprocessing. Cogema and BNFL have announced further waste volume reductions in the future. However their figures still ignore low level wastes which account for about half of total reprocessing waste management and disposal costs.

What advantages do smaller volumes bring? They clearly reduce storage and transport costs, but the benefits in terms of repository safety are less clear. The design and performance of a repository is primarily dependent on the heat output of the waste placed inside it. Although glassified HLW has a slightly reduced heat rate because it does not contain plutonium, this will not affect waste storage or repository design. Moreover, the decay heat associated with actinides in spent MOX fuel is an order of magnitude higher than for spent uranium fuel.

Lower toxicity

A general index of radiotoxicity is often used by reprocessors to argue that the removal of plutonium from the high level waste stream significantly improves long term safety of the repository. However, safety assessments for a variety of repository designs and geological environments show that spent fuel can, in principle, be disposed of as safely as vitrified high-active reprocessing waste. The German repository concept assumes, for instance, that spent fuel and vitrified HLW will be disposed of in the same repository. Spent fuel is at least as good a matrix for fission and actinide products as glass, and new research into ceramic waste forms suggests that it may be better.^{3 Repository safety assessments show that long-term safety depends on the mobilisation of radioactivity. Studies of plutonium mobilisation suggest that it will not move far out of the near-field of the repository under most conditions. Removing plutonium does not therefore bring great improvements to long-term safety which is determined more by the prevalence of nuclides like neptunium-237, technetium-99 and iodine-129. These occur in the same amounts in spent fuel and reprocessing waste.}

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1. Cogema, 'Reprocessing-Recycling: the Industrial Stakes', presentation, Bonn, May 1995.
2. G. Kessler, 'Direct disposal Versus Multiple Recycling of Plutonium', paper presented at the German RSK/Japanese NSC Meeting, Tokyo, November 1992.
3. 3 W. Lutze and E.C. Ewing (eds), Radioactive Waste Forms for the Future, North Holland, Amsterdam, 1988.