What issues are tackled by the project?

The project addresses the issues of geochemical barriers in operation during the deposition of burn-up nuclear fuel. Burnt-up nuclear fuel from nuclear power plants consists of more than 95 % of carbon dioxide (UO2). A wide variety of radioactive isotopes with half-lives ranging from several years to more than tens of thousands of years remain in the nuclear fuel. Aside from physical barriers (products of engineering such as steel or copper containers, bentonite or concrete), the rock and groundwater will play a deciding role as other types of barriers in the geological environment. The types of rocks, their mineral composition and mechanical characteristics together with groundwater, whose composition is given by the rock composition and flow regime, will decide the durability of engineered barriers throughout the duration of the nuclear fuel storage. Simultaneously, rock type, mineral composition, and mechanical characteristics of rocks together with groundwaters determine the migration capability of radionuclides out of which uranium is the most crucial one in a long-term point of view.

For safety reasons, the burnt-up fuel must be isolated from the surrounding environment in this period. During the construction, operation and closure of the deep nuclear repository will undergo several changes in conditions which will impact the engineered barriers, construction materials and the geological environment.

Nuclear power plants (NPP) in the Czech Republic do not possess any deep nuclear repositories. The Dukovany NPP and the Temelín NPP possess medium-term repositories only meant for used fuel (so-called interim repositories).

The Rožná uranium deposit represents a unique opportunity to study uranium migration in a real geological environment under conditions which are comparable with the conditions of the planned deep nuclear repository of burnt-up fuel. The deposit site has been open for sixty years and is accessible from the surface down to the depth of 1200 metres. The Rožná mine is planned to be sealed in 2019.

The results brought by the project will enable the specification of the required characteristics of engineered barriers and the disposal site design as a whole. The results will then represent an invaluable foundation of the subsequent locality selection safety analysis and disposal site implementation in the Czech Republic.

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