Technical and economic aspects of retrievability in spent nuclear fuel disposal. A literature survey

This literature research collects cost and feasibility aspects of retrievability of spent nuclear fuel disposal. The Finnish plan for the final disposal of spent nuclear fuel includes some features favouring retrievability, like modularity of disposal plan, good corrosion resistance of copper canisters and long estimated lifetime of disposal shafts and tunnels. Possible political and technical arguments for retrievability are collected and the possible actions taken after retrieving (opening of copper canisters, transportations and interim storage) are looked into. In the Finnish disposal plan retrieving is possible in each stage of repository development. Technical feasibility of retrieving is presented before sealing of a disposal hole, after filling and sealing of a disposal tunnel and after final closure of the repository. Many features of the disposal concept (hydrogeological conditions, radioactive radiation and heat generation of the spent fuel, and properties of bentonite) affect the feasibility and cost of retrieving. Questions dealing with nuclear material safeguards, monitoring and continuity of knowledge should be taken into account when retrievability is being considered. Different ways used for expressing the cost of retrieving, are currency unit, delay of the scheduled disposal project and percentages of the actual disposal cost. Estimated costs for two different cases of retrievability, immediate closure and postponed closure of repository, are presented. Cost estimates, made in Finland, are quite rough, but the Swedish cost calculation example of immediate closure case is interesting because of similarity of Finnish and Swedish disposal concepts. There are also examples of cost, based on research and development work enhancing retrievability. It is noticed that there are only few exact cost estimations relating to retrievability. The reasons might be the improbability of actual retrieving and the fact that retrieving, if materialised, will take place far in the future. (orig.)