North Dakota site chosen for test of nuclear waste disposal concept developed in Sheffield
The US Department of Energy (DOE) is investigating a safer, faster and cheaper method of disposing of high-level nuclear waste than the conventional mined repository planned for implementation in several countries, including the UK. Known as deep borehole disposal, the concept has been developed in the UK in the Department of Materials Science and Engineering.
The DOE has selected a Battelle Memorial Institute-led team to drill a test borehole to over 16,000 feet in the crystalline basement rock formation near Rugby, North Dakota, as the next stage of proving the deep borehole concept.
The Sheffield Deep Borehole Disposal Research Group, in collaboration with Sandia National Laboratories, is currently developing a program of research and development for the field test which will include key issues such as how to prevent groundwater corrosion of the waste packages and how to seal the borehole to prevent any escape of the radioactive waste.
No active waste is planned to go into the test borehole but if the field test is successful, the USA hopes to dispose of its ‘hottest’ and most radioactive waste – left over from cold war plutonium production and currently stored at Hanford in Washington State – in a similar borehole.
The Sheffield group calculate that all of the UK’s high level nuclear waste from spent fuel reprocessing could be disposed of in just six boreholes 5km deep, fitting within a site little larger than a football pitch.
In March three members of the Sheffield group will be presenting papers on deep borehole disposal at ‘Waste Management 2016’ in Phoenix, Arizona. Professor Fergus Gibb, Dr Karl Travis and John Beswick (of Marriott Drilling) will talk on technical options, the Hanford wastes and borehole construction respectively. This is the first time this prestigious meeting has included a session on borehole disposal and indicates the importance the US attaches to the new concept.
Deep borehole disposal (DBD) has a number of advantages over the current solution envisaged for all UK nuclear waste, which is in a mined repository at around 500m depth: DBD is effectively ‘pay-as-you-go’ disposal. A mined repository can cost from hundreds of millions to tens of billions of dollars to construct before any waste can be disposed of; DBD costs a few tens of millions of dollars per borehole.
There are more geological sites suitable for DBD as the granitic layer that is required can be found at appropriate depths under much of the continental crust.
A borehole could be drilled, filled and sealed in less than five years, compared to the current timescale for a UK mined repository, which is to open in 2040 and take its first waste between 2075 and 2140 (although a site has not yet been agreed). As DBD disposes of nuclear waste at greater depths and with greater safety and because there are more potential sites available, it should be easier to obtain public and political acceptance of the technology. DBD has limited environmental impact and does not require a huge site: the holes are a maximum 0.6m in diameter and can be positioned just a few tens of metres apart. Once a borehole is complete, all physical infrastructure on the surface can be removed.
While seismic activity might damage the containers within the borehole, fracture the surrounding rock and disrupt some of the nearest barriers in the borehole, it would still not destroy the isolation of the waste or make it possible for radioactivity to reach the surface or any ground water.
The demonstration borehole in the USA will be drilled just under half a metre in diameter and trials will be conducted to ensure waste packages can be inserted into the borehole and recovered if required. Drilling is scheduled to begin in September 2016, with initial results within a year. If these results are positive, disposal of the Hanford waste capsules would then take place in another borehole, just 0.2 to 0.3m in diameter.