Radiotoxicity has been used as a measure of the potential benefit of TRU transmutation. If 99.5-99.9% recovery of TRUs is assumed, it can be shown that, compared to a closed or open cycle PWR, use of P&T causes the radiotoxicity of buried highly active materials (essentially the losses at reprocessing) to be reduced by about two orders of magnitude after several hundred years. By comparing the calculated radiotoxicity with the ‘reference level’ it can be seen that, with P&T, the buried material is less radiotoxic than the initial uranium ore after approximately three hundred years. In comparison, with a once-through (direct disposal) fuel cycle it takes more than 1-200000 years to achieve this. A typical example is given in Fig. 17.7.

The upper curve in Fig. 17.7 represents the natural reduction in radiotoxicity with time for the direct disposal of spent LWR-UOX fuel, at a burn-up of 51 GWd/ MTIHM (once-through cycle). The middle curve corresponds to the multi­recycling of Pu in a fast reactor so that FPs plus MAs plus Pu losses at reprocessing are sent to a geological disposal. The lowest curve corresponds to the multi­recycling of both Pu and MAs in a fast reactor so that only FPs plus Pu+MA losses at reprocessing are sent for geological disposal. In all reprocessing cases, the recovery factor is assumed to be 99.9%. This factor is already reached at industrial scale in the case of Pu (e. g. at the La Hague plant in France) and it has been reached at laboratory scale (or pre-industrial scale) in the case of MAs (e. g. at the ATALANTE facility in France43).

As indicated above, one interesting result shown in Fig. 17.7 is that, if Pu+MA are multi-recycled and only losses at reprocessing are sent to a geological disposal together with FPs, the radiotoxicity of the disposed material reaches the level of the radiotoxicity of the initial uranium ore, after only few hundred years, while in the case of direct disposal of the irradiated fuel, it takes 2-300 000 years to get the same result.