26 D.F. McGinnes

French vitrification Process

Fig. 2.14. An example of the vitrification process (image courtesy of AREVA-NC).

stainless steel containers and stored. The advantage of using glass as a matrix for HLW conditioning is that, if correctly formulated (i.e., no soluble phases are permitted to form), the radionuclides are contained within the glass and any release is subsequently a very slow process (Nagra, 1994).

2.5.2.5. Spent fuel

SF already represents a reasonably stable waste form. Conditioning of the spent fuel involves placing it in a metallic canister. As noted above, canisters currently under development are, e.g., a copper canister with a cast iron insert that is planned to be used in Sweden (Werme, 1998). Other designs under consideration in other countries include the use of stainless steel containers, which also offer a sufficient level of long-term corrosion resistance and stability compared to the copper/cast iron design, ceramics, titanium, etc. (see Chapter 5 for more details).

2.5.3. Process qualification/product quality

Before any wastes can be conditioned for storage/final disposal, it is necessary to obtain approval from the competent authorities to ensure that the resulting product will be suitable. As an example, the procedure currently in place in Switzerland will now be reviewed (note that while this varies in the details from country to country, the basic procedure is the same):

1.Initial research and development, including small-scale tests

2.Assessment by the disposal organisation (Nagra)

3.Authorisation by the regulator (HSK) to move to pilot plant/prototype testing

4.Production of 1:1 scale packages, check of QA procedures

5.Assessment by the disposal organisation