Lessons from nature : the behaviour of technical and natural barriers in the geological disposal of spent nuclear fuel

This work deals with the study of the long-term performance of materials and elements involved in the near- and far-field of an underground nuclear waste repository. Materials and elements occurring in nature are similar, or at least analogous, to the materials and elements manufactured or processed by man. Also, natural processes may be similar to those envisaged as occurring in a nuclear waste repository. This similarity makes it possible to study the behaviour of those materials in nature and to compare it with the behaviour of the manufactured materials to be used in a repository. As many materials and elements have been in the natural environment for long time periods (thousands to million of years), the data obtained can be extrapolated to estimate the future evolution of similar components in a nuclear waste repository. Thinking by analogy is the process of comparison, with those materials, elements and environments used to perform the studies that allow the comparison to be regarded as natural analogues. The Hyrkkölä U-Cu mineralisation (SW Finland) was studied as an analogue to the behaviour of copper canisters in crystalline bedrock. This analogue could also address the interaction between copper corrosion products and uranium. Copper sulphides are shown to retain up to 25% of uranium as U (IV) even if oxidizing conditions prevail. Furthermore, uranium was observed in smectite (main component of bentonite) associated with native copper and cuprite, which constitutes an analogue to the behaviour of the repository near-field materials in a natural oxidizing environment. In addition to the Hyrkkölä analogue, the issue of irreversible sorption or uranium immobilization is also addressed, in the studies of the boulder rock near Hämeenlinna. The behaviour of U, Th, and rare earth elements (REE) as analogues to the long-lived actinides is also evaluated in groundwater and rock samples at Olkiluoto (SW Finland). U and Th were shown to be released more easily from clean fracture surfaces than from fracture surfaces covered with calcite or kaolinite. From the studies presented here, it may be seen that the Hyrkkölä analogue has been applied so far in safety assessments, mainly to demonstrate the canister lifetime and to a lesser extent to confirm the interactions between copper corrosion products and uranium. Up to the present, the issues of irreversible sorption or immobilization and the analogy between REE and actinides have not been taken into account in safety assessments. The results of the studies presented here indicate strong prospects that these issues could be new and powerful tools indispensable to safety assessments. More research and understanding is required, however, to form them into operational tools for this application.

Department dc:contributor.department

Department of Materials Science and Rock Engineering

Grantor dc:publisher

Helsinki University of Technology

Year dc:date.issued

2002

Author dc:creator

• Marcos, Nuria

Contributors dc:contributor

• Aalto-yliopisto
• Aalto University

Language dc:language.iso

en

Repository record dc:identifier.uri

https://aaltodoc.aalto.fi/handle/123456789/2244

OAI record oai:identifier

https://aaltodoc.aalto.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Aaaltodoc.aalto.fi%3A123456789%2F2244