Saturday, July 31, 2021

Nuclear Theddlethorpe 02

If the proposal to create a Deep Geological Facility (GDF) for high level nuclear waste at the former gas terminal at Theddlethorpe is to be opposed effectively then one must concentrate of arguments that will sway the opinions of Radioactive Waste Management, planning inspectors and politicians, locally and nationally.

Concerns about safety, however natural, heartfelt and understandable, are unlikely to influence decision makers because the industry will be able to assure government that the project can be completed safely.

Which leaves the two issues that could determine the future of the project:

1. the suitability of the site for a major industrial development, and

2. the suitability of the geology for a nuclear depository.

1. Industrial Development

The gas terminal was built on a greenfield site in a rural area on agricultural land with the assumption that, on decommissioning, it would be returned to its former state. It must, therefore, now be regarded as if the gas terminal had never existed, a greenfield site. In such an area, and lacking major road and any rail connection, the site would never normally be considered for a major industrial project. Such development would more likely be directed to a large brownfield site such as an ex-steelworks. Scunthorpe comes to mind as having a large redundant site with a railway running through it, nearby motorway links and a large, skilled potential labour force. I mention Scunthorpe as the underlying geology is similar to Theddlethorpe's. If any decision maker should balk at locating the facility in an urban area it might suggest that they do not have confidence in the safety of their project.

The scale of the project is, perhaps, under appreciated by many. It is doubtful whether the footprint of the Conoco gas terminal is large enough to accommodate the GDF and the timescale has not been much talked about. It would probably take more than a decade to develop the facility and then the work of emplacing waste might continue for a hundred years before it is finally sealed and the surface ground returned to its previous state.

2. Geology

Underlying a few metres of superficial marine and glacial deposits is some 200 metres of the Chalk. This is a very permeable rock, about as much use as a wet sponge for sealing nuclear waste. Below the Cretaceous rocks lies the Jurassic, of which the Ancholme Group is probably the rocks of interest. The objective would be to find a thick and homogenous layer of clay, sufficiently impervious to radionucleotide migration to prevent leakage for hundreds of thousands of years after the initial protection of the copper containment vessels has broken down after many millennia.

The Ancholme Group is a complex series of mostly clays but with sandstone and other more permeable horizons. A sufficiently thick clay layer needs to be found.
The Ampthill Clay Formation is the shallowest such layer and is just over 100 metres thick here. Below this lies the 20m thick West Walton Formation and below that the Oxford Clay Formation. This is the same layer as the Callovo-Oxfordian in which the French plan to deposit their high level nuclear waste in the CIGEO facility. But in our area the Oxford Clay is only about 30 metres thick.

The underlying Lias Group of the Lower Jurassic is a rather mixed bag of rocks and probably does not present a good location for nuclear waste disposal but below this in the Upper Triassic is the Mercia Mudstone Group. This is a sequence some 250 to 300 metres thick and may be the most likely location for a waste facility. (Some folk will recall the 1980s and Fulbeck site that targeted these rocks.)

That's a brief and sketchy summary of Theddlethorpe geology. For a much more detailed account, and the one that will be used as the introduction to the topic by decision makers, see the British Geological Survey's National Geological Screening:
Eastern England region, Minerals and Waste Programme, Commissioned Report CR/17/092

If the UK Government chooses a soft-rock Geological Disposal Facility, such as Theddlethorpe's geology allows, the closest exemplar is the French CIGEO facility but note that French law currently requires that the disposal remains potentially reversible, allowing the material to be retrieved by a future generation. This is in contrast to the approach in Finland where the policy is to seal the waste permanently. Theirs is a hard rock solution with the waste buried in caverns dug some 500 metres down into granite. 

In the UK we have not yet had the important debate about whether to adopt the French or the Finnish philosophy. They are fundamentally different. The choice is still to be made between soft rock, in which case Theddlethorpe is in the frame, and hard rock, where we have to turn to Cumbria, or better still, Scotland, for a site.

One further aspect, which has been acknowledged by Radioactive Waste Management, is that the sedimentary rocks of Lincolnshire contain hydrocarbons, oil and gas. While our current civilisation, wary of climate change, may choose to leave them in the ground, a future civilisation, say 1000 years hence, might be tempted to extract this valuable resource. Do we have an ethical duty to keep it free from nuclear contamination?

Further reading: Deep Time Reckoning by Vincent Ialenti.


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