This appendix is based upon an article written by H Nifenecker and G Ouzounian (ANDRA, * France).

Deep disposal of nuclear wastes can be considered a reference strategy against which transmutation-incineration options can be evaluated. Here we give a simple account of the kind of performance which can be expected from a well conceived deep underground disposal site.

First, we give a sketchy description of what an underground disposal facility could be.’f Then, we will give the bases on which computation of the diffusion of radioactive elements through geological layers rest. Finally, we will give results in the case of clay. Of course, such theoretical cal­culations must be validated in the most realistic manner possible. Experimen­tal studies in underground laboratories have been described by one of the authors in the July 1999 issue of the SFP* journal [175].