Actinide migration: from basic studies to performance assessment how to fix research priorities

Full text of publication follows: Most safety or performance evaluations, recently carried out in several countries (Switzerland, France, Belgium, Sweden) tend to minimize the importance of actinides in the long-term safety. Soluble long-lived fission products dominate the dose rate at the outlet, either in normal or reference scenarios, or in most degraded scenarios. Low solubility of actinides in neutral to alkaline conditions, low redox potentials and high sorption explain such results. Moreover, the role played by colloidal transfer is estimated to be minor, considering the efficient filtration of colloids by compacted clays or clayey host rocks. However, several research institutions and laboratories develop intensive research programs on actinide chemistry and colloid-facilitated migration of actinides. This somewhat contradictory situation deserves some comments and clarification. The distance between science and performance assessment may be an explanation, but, in order to insure the credibility of the whole research process on high level waste deep disposal, one needs to enlighten the research strategies and needs. A description of degraded scenarios in which actinides could be durably oxidized is proposed, together with a qualitative evaluation of their occurrence possibilities. In a similar manner, some details about the incidental conditions during which actinides could escape the near field through colloidal migration are given, together with their relevance and probabilities. This kind of studies will help in the prioritization of research projects, connected to waste disposal in deep rock formations. Alternatively, most research efforts on colloidal migration of actinides are applicable to surface conditions (shallow fracture systems, rivers and lakes), whereas colloid characterization is also essential to understand hydrolysis and solubility of tetravalent and trivalent actinides. (authors)