Construction of the first underground nuclear waste repository in the UK is expected to begin in 2025, Radioactive Waste Management Directorate (RWMD) mangaging director Bruce McKirdy has revealed.
The repository could start storing waste by 2040.
“This is for intermediate level waste, with the assumption that high level waste will be placed in 2075,” said McKirdy, who was outlining the strategy at the NCE “New Nuclear” conference in Birmingham earlier this month.
The store will hold waste at depths of between 200m and 1km, sealed within containers and barriers to ensure radioactive contamination does not occur.
For example, intermediate level waste can be grouted into steel drums before it is stored.
The drums may then be chemically conditioned with a buffer material to inhibit the solubility of radio-nuclides such as plutonium.
The depth of geological cover will also ensure passive safety. Mass backfill and engineered seals will also be constructed once the repository is filled.
Local communities will have to volunteer sites for the store. This approach is being pursued because attempts to identify sites without the support of locals - including sites in the UK and Canada - have failed, while effots to create community backed sites in Sweden and Finland have succeeded.
To date the RWMD has received expressions of interest from three local authorities in Cumbria. The British Geological Survey is now studying the suitability of the geology.
Three types of rock are considered the most appropriate for a nuclear repository. The first - high strength rock - includes granite and is desirable because of its low permeability. Sites chosen for radioactive waste disposal in Finland and Sweden are within areas of granite.
Lower strength sedimentary rock is also favoured. This is physically uniform, so any flow of water occurs through the overall rock mass.
Switzerland’s Opalinus clay geological disposal concept is designed for this type of rock.
Finally, evaporates may also be suitable.
This rock may contain water that has been trapped since formation, but which is isolated from water flow that could dissolve it.
In the United States this type of rock is used for the Waste Isolation Pilot Plant in New Mexico, which has been used for more than a decade. Germany has also developed a concept for this type of rock.