One of the side results of reprocessing activities is generation of high-level radioactive waste. This is the concentrate of the aqueous side streams from nuclear fuel reprocessing. Besides this major source of HLW there may be some other wastes that fell into this category12 but their volume contributions would be lower and the conditioning and packaging may differ in each specific case. The reprocessing waste consists of fission products and minor actinides but contains also the remnants of U and Pu isotopes (up to 1%). 1 3 Reprocessing waste is typically vitrified and stored until final disposal facilities become available. Figure 15.17 shows an

example of vitrified HLW conditioned and packaged in a metal canister for disposal. Until final disposal the HLW is stored in storage facilities. A photo of such storage facility in La Hague is shown in Fig. 15.18. A schematic of the vitrification process and interim storage of HLW in La Hague is shown in Fig. 15.19.15 The canisters with vitrified waste are stored stacked on top of each other in vaults that contain a number of channels. The photo in the Fig. 15.18 shows the tops of the vaults.

One of the advantages of vitrified waste is that the leaching rate is very low even if the containers and overpack were damaged. Disposal of HLW will be in the deep geological repositories similar to or using the same technology as for spent fuel disposal. There are several design concepts for disposal of HLW at various levels of development but they are in most cases tied to the concept for spent fuel disposal as they require a similar geological environment.

As the majority of major actinides are removed from the HLW its radiotoxicity is also lower and it takes a shorter period of time to reach the baseline radiotoxicity of uranium ore as shown in Fig. 15.20. This level of radiotoxicity of uranium ore may be considered as a reference to the natural background. The radiotoxicity of spent fuel is almost an order of magnitude larger to begin with and in addition it takes almost two orders of magnitude less time for HLW to reach the radiotoxicity of uranium ore.

As the radiotoxicity of HLW is after some 400 years dominated by actinides (tails of major actinides from reprocessing and minor actinides), efficient removal of actinides by partitioning and transmutation would simplify the disposal requirements but those technologies are still under development.

Air cooling

Dust removal

Heat and activity will decrease naturally over time

Sampling

Interim storage

Decontamination

Supply

15.19 Vitrification process and interim storage for HLW in La Hague, France.

15.20 Relative radiotoxicity of spent fuel and HLW over time.

458 Nuclear fuel cycle science and engineering