Geological final disposal

In 2000, the Finnish Government made a decision-in-principle, according to which “out of the investigated final disposal options, final disposal deep in bedrock, i.e. geological final disposal, offers the best and most realistic possibilities to isolate high-level nuclear waste from the biosphere, i.e. the human habitat”. In Finland, final disposal means deposition in crystalline bedrock, which constitutes the majority of Finnish bedrock. Finnish bedrock is among the oldest in the world.

All variations of geological final disposal have in common the fact that nuclear waste is stored deep underground. Geological final disposal is planned, for example, in Germany in salt dome and in France in mudstone. All geological environments have special characteristics to be taken into account in final disposal. In crystalline bedrock, it is water. Therefore, it has been clearly defined in studies at which depth the disposal canisters must be placed in order to ensure bedrock conditions favourable for the engineered release barriers, especially for the canister. The deposition holes will be drilled into the most solid rock zones, where water seepage from rock crevices is as small as possible.

Alternatives to geological final disposal were investigated before the Finnish Government’s decision-in-principle. As theoretical alternatives, many methods were proposed, such as sending into space and burying in polar glaciers or benthal deposits of the oceans. These options were investigated, but many problems were identified with their practical application.

Reprocessing of spent fuel has also been investigated, but recycling is technically demanding and expensive. Moreover, the end result of reprocessing would still be radioactive waste to be disposed of. Storing spent nuclear fuel in interim storages in the wait for a technologically superior recycling solution has also been considered in some parts of the world. It has been decided in Finland that the solution will not be passed on to the next generations, but that the implementation of final disposal of spent nuclear fuel will begin during this decade.

In Finland, however, a back door is left open to technological progress: spent nuclear fuel must be retrievable from the repository if a new treatment method is invented for it. The easiest way to do this is within the next 100 years, while the production phase of final disposal is still ongoing. At the end of this period, the facility will be closed for good, after which retrieving the canisters from the repository will be more challenging. In view of this phase, it has been tested, for example, what kinds of methods can be applied to remove swollen bentonite from around a canister.