Sandy S. Answering some questions is going to get more difficult for me. I last taught this subject bqck in 2011, and since then gave away my research and reference materials. I never expected to need them again. So for the most part I'm relying on memory. This is, I think fairly good, but some of the more technical details, like the half lives of specific actinides, have gone and I will need to consult. So, on the basis of my memory alone:

1) How likely is a leak from this type of repository? Answer, as far as we can predict, zero probability. The waste will be encased in borosilicate glass. Roman glass, not specifically made to contain nuclear waste, has lasted 2000 years without deteriorating. The glass will be placed in specially designed low corrosion stainless steel containers predicted not to corrode for 100,000 years. The Swedes use copper containers that should be effective for one million years. Most experts reckon these barriers are overkill, the geological barrier, if well chosen, is the only containment necessary.

2) When it does [leak] how likely is it that the leaked material will reach water that we would have access to? Answer, so long as the geological setting is appropriate, never. I suppose one could never rule out the remote possibility that a descendant might deliberately drill down into contaminated formation waters. However the repository would be located where no known geologic resources were present. So why would a future descendant drill so deeply?

The intention of geological storage is to remove the waste from contact with the biosphere for a length of time ncessary for radiation levels to decline to those within the original uranium ore. For the longer lasting actinides this will be closer to 100,000 years, not 10,000 years. By the shorter time span the high level waste would have become low level waste ( but I need to check this).

Channel tunnel style space bored under the sea off Dorset or similar.

A tunnel boring machine making a figure of 8 tunnel, glass / metal encased, accessible for maintenance long into the future in case glass embedding develops an unknown failure mechanism.

It would cost a large amount of money, but for all of our active material and possibly other countries as well, for a suitable price, we might even break even.

As a resident of Cumbria, I would be very interested in Alan Kendall's views about the geology of West Cumbria in terms of the Government's apparent determination to bury radioactive waste here.

I am very reluctantly in favour of nuclear fuel as a necessary producer of essential energy, now that the eco-fascists have gone a long way to destroying conventional reliable fuel generation and replaced it with intermittent, expensive and unreliable wind and solar. Something reliable needs to fill the gap, and nuclear is all I can think of if we are not to be allowed to burn fossil fuels and the lights are not to go out.

My equally reluctant conclusion is that nuclear waste should be buried very deep under lock and key and in as safe a way as possible, in as geologically appropriate a location as possible. There is an ongoing debate as to whether Cumbria (west Cumbria in particular) has geology which is suitable. If it is suitable, I could live with that, but if it is not suitable, I think it should be buried elsewhere. The Government seems to be determined to bury it here in Cumbria, relying on the fact that west Cumbria is economically depressed and heavily dependent on the huge sums of money poured annually into the decommissioning of Sellafield (and because therefore some - the jobs-dependent - residents are sympathetic to all things nuclear). Small details (like "is the geology of Cumbria appropriate for burying nuclear waste?") don't seem to enter the equation, so far as Westminster is concerned.

So, I should be very interested in the views of a disinterested geologist, especially in view of an early comment by Alan that his own home area probably has the most appropriate geology. Please shed light on this for me, Mr K. Many thanks, in anticipation.

Mark Hodgson. I have not studied the geology of west Cumbria, so what I write now is solely based on book learning. Your area may be suitable but it's certainly not the best site. I think you are correct in your belief that the government favours the area because residents are used to nuclear power and reprocessing and therefore are the most likely population to accept a nuclear waste repository. However, another aspect is that the area is already a site of surface waste storage, so that this waste need not be transported to a more distant site.

When the British Geological Survey first reviewed the UK in terms of suitability for waste storage they came up with about five or six different types of geological settings that would be suitable. One of these was where very old rocks (which would host the repository) had been covered by layers of much younger rocks that included water bearing strata. If the old, tight rocks never reached the surface, there would be no opportunities for water to be transmitted through them. Groundwaters instead would travel only through the shallower aquifers. This is the situation near Thetford.

West Cumbria is somewhat similar in that old rocks are overlain by much younger strata that include good aquifer sandstones. However these old rocks do not remain buried. Towards the lakes they rise up and are exposed at the surface. The fear is that fractures in the old rocks will allow water to pass from the lakes area down beneath the younger strata to the repository site. Since the entire reason for disposal by geological burial is to keep the waste away from flowing groundwaters, the setting in Cumbria is not ideal. Those who support building the repository in Cumbria argue that the scenario I have outlined is theoretical and no evidence exists to prove such water movement through the fractures, or even that a continuous network of fractures actually exists.

Thank you Alan - very much appreciated.

One further point, if I may trouble you again: we have had some minor earth tremors in this area in recent years. One a few years ago was the only one I have experienced in this country that was serious enough to be noticed - it was late one evening as we were going to bed, and it felt as though a vehicle had crashed into the house. Question: are earth tremors random in their distribution over the UK, or are they more frequent in some areas than in others? Follow-up question: in the context of burying nuclear waste, does it matter?

Thanks again.

Alan Kendall
Out of curiosity are you familiar with the situation at Oklo Mine, Gabon?

I have only read brief descriptions but as I understand it the nuclear reaction involved groundwater being boiled off in cycles. It was a long time ago but the material was still active and I assume that the groundwater was still in the area. It would be interesting to know how radio-active the water was in a long lived (1.7 billion years) stable highly radio-active environment.

Interesting discussion with particular thanks to Alan K for his knowledge and expertise. I seem to recall that in his talk to the Heartland Institute Patrick Moore indicated that there may be ways of using nuclear waste in the future?

Dung

If you drop plutonium into a subduction zone, will it subsequently emerge from the associated volcanoes?

Not to worry EM rates of motion in subduction zones are only a few centimetres a year and the magmas are generated a depths of 10-50km. Also because the plates descend at a shallow angle, when the magma rises vertically it won't pass through any plutonium.

Sandy S. I am, but clearly not as up.to date as you are. I just spent a couple of very pleasant hours reading up the latest developments. I wasn't aware, for instance, of the cycling hypothesis, where studies of xenon isotopes indicate 30 minutes of criticality followed by 2hours 30 mins of cooling, over and over for hundreds of thousands of years, 1.7 billion years ago. Not only that, but the boiling water would probably have erupted as a very predictable geyser, like Old Faithful in Yellowstone Park. It's science like that, achieving what at first sight would seem to be unachievable knowledge, that makes my now much reduced scientific life so pleasurable. Thank you for bringing it to my attention. It's made my day.

More to the point the natural reactors at Oklo are important to the subject of geological storage of nuclear waste because it can be shown there that long-lived radioactive actinides and transuranic materials that formed 1.7 billion years ago, have not migrated away from the reactor sites, despite these materials being in contact with grounwaters. The Oklo example demonstrates the super long term viability of storing similar materials (nuclear waste). Waste repositories of course will be located where there will be no grounwater access.

Alan Kendall
Thanks for taking the time to look into it, it's one of the joys of this blog the diverse stuff that comes up requiring further reading.

It's also thanks to the BBC I was aware of the Oklo reactors. Because of that knowledge the nuclear waste storage problems with leaks and groundwater seemed to me potentially a bit overplayed. What was going on for longer than homo-sapiens have been around was a nuclear reactor venting boiling water and steam direct from the fission reactor. Then for 1.7 billion years the water must have surrounded the waste material. I also find it interesting how they came to the initial conclusion there'd been a reactor in operation.