Instant Genius - The race to bury nuclear waste in hidden bunkers, with Lewis Blackburn

Episode Date: June 25, 2023

As the UK builds more nuclear reactors, there is an increasing pressure to find somewhere to put the waste. But what actually is nuclear waste? Does it actually look like a bright green sludge? Where does currently go? To answer these questions I’m joined by Dr Lewis Blackburn, nuclear materials scientist at the University of Sheffield. He talks about the incredible research going into sealing, burying and locking away nuclear waste, the relationship between nuclear and space (and why we can’t just fire off our nuclear waste on a rocket), and the vast timescales when it comes to nuclear waste that go beyond human lives, including the people working on them. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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So you can experience exceptional sound at home. Music just as the artist intended. Visit name audio.com to learn more. From BBC Science Focus, this is instant genius, a bite-sized masterclass in podcast form. I'm Noah Leach, news editor at BBC Science Focus magazine. If I say nuclear waste, what do you think of? For many people, the term brings up apocalyptic wastelands. For some, a cartoonish bright green sludge and three-eyed fish.

But what actually is nuclear waste? Where does it go? Is it safe for people and the environment? To answer these questions, I'm joined by Dr. Lewis Blackburn, nuclear material scientist at the University of Sheffield. He talks about the incredible and urgent research going into sealing, burying and locking away nuclear waste, the relationship between nuclear waste and space, and why we can't just fire off our nuclear waste on a rocket, and the vast time scales when it comes to nuclear waste that go well beyond human lives, including the people working on it. So Lewis, what is nuclear waste?

So a lot of people probably have this idea in their head that nuclear waste is a green goo that sits in large barrels, that's sort of seen power plants. And that isn't necessarily true. So nuclear waste actually encompasses a very wide variety of materials. It isn't one thing. There isn't such a thing as just a generic nuclear waste.

So the International Atomic Energy Agent say the IAEA generally classified nuclear waste into four different categories. And these are determined by what we call half-life. So essentially, how long the material would be radioactive for and radioactivity. So how radioactive a certain isotope that's contained within the waste is. So these categories are very low-level waste, low-level waste, intermediate-level waste, and then high-level waste. So high level of nuclear waste is the material that really needs to be isolated from the environment for a very long time. And this is generally, when we talk about high level waste, what we're talking about is either spent nuclear fuel.

So that is nuclear fuel that's been sat in a reactor, undergoing fission to generate electricity for several years in some instances. This material is then removed from a reactor where it can either be stored for a very long time and then disposed of as well. waste or it can be what we call reprocessed. So the reprocessing of spend nuclear fuel is a very important process because what we can do is take the reusable uranium and the plutonium that's formed in the spent nuclear fuel. These can essentially be chemically recovered by using a series of aqueous chemical extractions. After we reprocess the fuel, what we're left with is all the nasties that are left at the end. That's referred to as the high-level waste.

And what happens in most countries where they do these processes is that that is then converted into a glass. All the leftover products, so a lot of long-lived radioisotopes, so things like technetium, trace amounts of things like curium and amorycium, and then a lot of activation products and corrosion products, a lot of chromium and iron and nickel. These are essentially contained in sort of a slurry of nitric acid. So that type of nuclear waste looks like your sort of stereotypical cartoon image of nuclear waste, sort of like a green goo type material. What happens is this is dried.

Obviously, each step I talk about here is quite a long process. So I'm kind of giving you the main points. The material is dried and then it's poured into big containers, these big melters. And glass forming additives are added. So things like silica. boron, aluminium, etc. These all, when melted together, will make the nuclear waste, so the high-level nuclear waste, each of those atoms will basically incorporate into the structure of the glass. And the reason we use glass is that glass is a very durable material.

So there are several analogs that exist in nature, and there are, you know, there's thousands of years of human history that tells us that when we make glass, so when we melt things and quench them, cool them really quickly to form glasses, that they can actually sit in the environment and be quite stable for very long periods of time. So this gives us confidence that when we put nuclear waste into glass, it will last long enough in the environment, such that by the time it starts to dissolve, all the radioactivity should have essentially decayed away. So we talk about intermediate level waste, we're talking about materials that aren't necessarily the most damaging in terms of what would be their environmental impact, but there's quite a lot of it, and some of it is fairly radioactive.

So intermediate level waste looks like things more like irradiate graphite that's been sat in the reactors, the metal cladding that comes off of the fuel that's sheared off. So again, very heterogeneous. It isn't necessarily one thing. It could be sort of contaminated bricks. It could be contaminated, say, graphite, so the swarf, the metal cladden that comes off of the the tubes that hold the fuel pins, things like that. And the sort of baseline treatment for a lot of those materials is to essentially grout them in cement, pour them into giant drums, sort of 200-liter drums at a time,

and these are basically added with different cementitious groutes. As a reason for that is that that's suitable enough to contain the waste and condition it for the time periods that are needed. We know quite a lot about cement chemistry. Cement is generally quite cheap material to produce. Again, humans are very good at producing cement. So a lot of the research that goes on at the moment is studying the interactions of, for example, fuel-cladding materials with cement. And what we know is that the mobility of things like trace amounts of uranium in cement is enough to contain them.

Then we come to things like low-level nuclear waste and very low-level nuclear waste. So these are materials that are generally very difficult to categorize because they could be comprised of. almost anything. It could be generally things like gloves and, you know, lab equipment, glassware, anything that has become in contact with trace amounts of radioactive material that puts it above the threshold for being clasped as radioactive. So that's kind of the broad level description of what nuclear waste is. Nuclear waste isn't necessarily one thing at all. It could be a wide spectrum of materials, all of which needs some kind of conditioning or some kind of stabilisation what we call immobilisation before they are disposed of.

The green slurry that is turned into glass, are we talking about sheets of glass or pellets? What can we imagine when we're thinking of what's actually going to be disposed of? So we're talking about sort of large canisters that are sort of cylindrical, basically large cylindrical blocks of glass that are contained within sort of stainless steel containers. So they're poured in as a, as a, as a, as a, melt. So they're not pellet size. These glass containers are more on the order of probably around the same size to maybe a little bit smaller than your average garden waste bin.

So the steps that you've talked about there, you've mentioned that these things take a lot of time. And obviously with nuclear waste, we are talking a huge half-life, as you call it. So could you explain what a half-life actually is and how long into the future these materials are going to take to decay. So the concept of half-life is how long it takes half of the radioactivity associated radioactivity of material to decay. So there are three modes generally, three modes of radioactive decay, and these are alpha, beta and gamma decay. It's important to remember that when we're talking about something like high-level nuclear waste, you're talking about most elements in the periodic table are in this mixture.

And each of those elements have stable isotopes, that they have configurations of protons and neutrons in electrons that are stable, which means they don't undergo radioactive decay. Once they've been through a nuclear reactor and they've been baked in neutrons for a very long time, a lot of those elements will have formed unstable configurations of electrons, protons and neutrons. What that means is they basically have excess energy that they need to get rid of. And the way that atoms do this is by radioactive decay. So, for example, if we have something like uranium,

which is a heavy, the heavier elements generally tend to undergo alpha decay. An isotope of uranium, for example, uranium 238 will generally, or uranium 235, for example, what will happen is it will let go of alpha particles. And these then basically acts as the way that energy is released from the atom. So as I said, most elements in the periodic table are in the high level nuclear waste, and a lot of those elements will have unstable configurations of electrons, neutrons, and protons, which means it's very difficult to say how long it needs to last, because the varying proportions of those elements will be different.

However, we're talking on the order of around 100,000 years for all of the radioactivity, or most of the radio activity to have reached a safe level. And the sort of safe level that we're referring to is the sort of philosopher behind this is the uranium from which the original fuel was derived has an associated background activity. We're trying to get to the level where once the waste is completely disintegrated or, you know, once the waste is compromised in a disposal environment, the radio activity associated with it will be of the same order of magnitude

as the original uranium which was used to produce the fuel. That's kind of like the life cycle analysis of this material. But yeah, we're talking on the order of 100,000 years to a million years in the future which is obviously an extremely long and difficult amount of time to really prepare for

because we don't know what society will look like, we don't know what the earth will look like. In 100,000 years, will humans still be around? You know, what are the difficulties in the long term with planning for disposed of nuclear fuels and nuclear waste this far into the future? There are many difficulties associated with that. So for context, for listeners, the oldest pyramid is about 4,500 years old. So we're talking facilities that need to be, will need to be the longest serving human structures ever by a really long way.

So what are those risks? and challenges, what are you having to take into account when these facilities are being designed? So when we're talking about a facility, what we're generally referring to is what's called a geological disposal facility. So geological disposal is the preferred method of long-term isolation of nuclear waste from the environment in every country that has nuclear waste. The sort of international consensus is that this is the most scientifically mature, and feasible route to long-term environmental isolation. And what we mean by environmental isolation is we can put this material essentially

in a specially engineered underground facility where it will remain undisturbed for, again, periods of 100,000 years or longer. So there are many, many different engineering and scientific challenges with that, as you can imagine. foremost is how do we choose where this site will be, how do we choose how deep it will be, what waste needs to go in there, what waste doesn't need to go in there.

You've got to think about cost, manpower, time. It could take 50 to 100 years to build a site like this. It will, without a doubt, it would be the largest infrastructure project that the UK will undertake for a very long time, if not the largest infrastructure project, simply because there are so many variables and the end goal is so important.

We can't get this wrong. And there is a large amount of industrial and academic research that's going on right now to look at every single aspect of designing this facility. So the research, for example, that we do at the University of Sheffield is if you think of this as like a timeline, the research we're doing is right at the start. So how can we get the properties of the waste,

mobilization correct. So we're looking at things like designing sort of specialist glass compositions and special ceramic compositions that we can test in a laboratory and we can extrapolate out and say we know that on a lab scale in a controlled environment, the material is so durable, you know, ex-durability. We can then extrapolate that out and say, knowing what we know about how nuclear waste evolves in the groundwater environment, this is how long to the future it will last. Obviously there are things like the geological aspects, so we have to choose areas of rock

that have got a very well-defined sort of structure and properties. We need to know about how water flows through the rocks, the sort of hydraulic and sort of mechanical properties of all the surrounding bedrock. However, so these areas to sort of climate change-driven

catastrophes, you know, how likely are earthquakes, there are many different geological aspects and that's possibly the most important. of all the aspects, choosing an area, choosing a site that is, you know, sort of mechanically and hydraulically stable enough to handle a very large underground excavated project. And I suppose a lot of listeners are thinking, well, what does this even look like?

So what it kind of looks like as a concept at the moment is a surface site, probably a kilometre squared with like, you know, sort of surface buildings, access shafts down to a depth between 200 and 700. meters and then essentially lots and lots of excavated vaults underground where there will be individually placed canisters of, for example, intermediate level waste or sort of sementitious drums. And then on the other side, they'll be sort of higher heat generating waste, so things like spend nuclear fuel or glass product that we talked about earlier, and then potentially even

immobilized plutonium products as well. And again, these will all be individual sort of casks that will be sort of buried in specific vaults. And then in the long run, once all the waste has been placed, all the vaults will be backfilled with some kind of buffer material. So this could be something like a cement, or it could be something such as a material called bentonite, which is kind of like a clay. These will all be backfilled, and then all the surface facilities will be backfilled to the top. and it's very likely that the surface facilities will then be sort of decommissioned and it will essentially be sort of restored back to

you know so it'll be like a plane site there shouldn't really be anything there there are philosophical arguments that happen a lot as to you know should we mark where this facility will be should we put signs saying stay away how do you communicate to any species that might be on the planet in 100,000 years don't come here, don't dig here, because what you'll find is a large amount of highly radioactive material. That's a question that I can't answer, and many people are still thinking about how do we mark a facility like this.

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name audio creates systems that deliver exceptional sound and unforgettable listening experiences at home. Try it for yourself at a focal powered by name boutique. Visit focal powered by name.com for more information. So we've been talking about underground facilities. That seems to be the kind of the way to do it. But what are some of the other ideas that humans have had so far in terms of getting rid of nuclear waste? Have any others been serious contenders?

So for a while in the 70s and 80s, there was basically some dumping in the sea of some intermediate and low-level waste materials. And this obviously was not a good or sustainable long-term option because although the sea and the earth's oceans are extremely very large. Having corroding containers of radioactive material at the bottom of the North Sea essentially is not a good idea. And this, you know, obviously received significant public backlash at the time. And, you know, it still is sort of a large issue. But, you know, glad to say that direct disposal of sort of conditioned waste in the sea

does not happen anymore. there have been some more extreme ideas that have been proposed. I suppose the most sort of popular one of people like to discuss is the idea of basically firing it into the sun or shoving it off into space. While in principle, you know, having waste not on the earth is sort of the best solution in a sense because if it's not here, then we don't have to deal with it. Sending things off to space obviously requires significant propulsion in the form of like a rocket. and I think we're all aware that one thing that rockets do fairly frequently is explode on the launch pad.

I can't remember the statistic off the top of my head, but I imagine it's a large enough risk that it should be not considered whatsoever. A large amount of rockets have exploded on a launch pad. And reusable rocket technology and things like this, they are getting better, no doubt. If you look at sort of a track record in the last 10 years compared to the 70s, 80s, in 90s, for example, of sort of of space manned and unmanned space launches, no doubt we're getting better at building rockets and they are safer

and they explode far less frequently. But you can envisage a scenario with, you know, a large payload of radioactive waste sat on the top of a rocket, it explodes on the launch pad, and then what you have is all of those radioactive elements that we want to isolate from the environment,

all the iodine and cesium and technetium and plutonium, all the things that are very dangerous to the environment and to humans, all this material would essentially be dispersed in the atmosphere and wind currents and, you know, sort of weather cycles would then carry that material all over and it would contaminate the wider environment,

whether this is by sort of settling down onto sort of soils and sort of integrating its way into the sort of food chain by being, you know, consumed by different animals and then, you know, sort of bioaccumulation, whether, you know, contaminates, water supplies, you know, it gets into drinking water, things like that. These are all the things that we don't want to happen. And this is why the geological disposal approach, whereby waste is conditioned

appropriately in a suitable, what we call a waste form. So when we convert waste, for example, if when we turn high-level nuclear waste into a glass, what we're doing is making what's called a waste form. And the glass is the waste form itself. So what we're trying to do is stop that happening. So we don't want things like, take plutonium, for example, plutonium 239 as a half-life, I think, of 24,000 years. An extremely long period of time, you know, plutonium is dangerous in wildlife, sort of food chains. It's just generally bad for the environment.

We don't want it to contaminate drinking water. We don't want it to sort of contaminate the atmosphere because it's radio toxic. So it has an associated toxicity with it. it so you know you could damage basic cells and life forms it's obviously a highly controlled substance you know certain types of plutonium are fissile which means that they're capable of sustaining a chain reaction which essentially means that you know certain types of plutonium could be used to produce weapons in large enough quantities so these are the considerations as to why we want to have all the waste contained in a stable matrix that can sit underground in a specially

engineered facility for a period exceeding 100,000 years. And geological disposal is the only feasible scientific way to do that at present. Now, whether in future, you know, far enough down the line in things like space elevators become sort of feasible, whereby they design these large structures that can essentially act as an elevator shaft. So if you basically don't have to put a propulsion, you don't have to put a rocket underneath nuclear way to send it into space. Whether that would ever be a feasible option, I'm not sure.

I know I've done some reading on this subject, and I know that to build something like a space elevator, the sort of technology needed to build on big enough to actually sort of ensure that anything that goes up, it would go out into space and not come back down. The materials that are needed are sort of like these copper or carbon nanotube materials, and they're extremely difficult to produce.

And I think it's probably a bit of a pipe dream. We can't wait long enough for that to happen. You know, nuclear waste is a clear and present danger to society and the environment now. And the approach of kicking the can down the road, which is what's being done, you know, for the last sort of 50 or 60 years in not only this country and in most countries, you know, but especially in the US and the UK, our nuclear programs in their infancy did not consider enough the long-term repercussions of generating large volumes of nuclear waste. So now it's our time. So this current generation of scientists and engineers, it's our responsibility now to clean this mess up essentially and to convince the public and the government

that geological disposal of waste is a safe, long-term, viable option and a suitable strategy for taking this highly active material and ensuring that it can't contaminate the last. around us and can't basically pose a risk to wildlife and ecology in general. So where is our nuclear waste in the UK currently going then? The volumes of nuclear waste are present, what's predicted to arise could essentially fill sort of like a Wembley Stadium-sized volume. There was a lot of nuclear waste and there's a lot more future horizons that will be produced.

The nuclear infrastructure in the UK is only set to expand. So at present, I believe that they're at 15 operasies. nuclear reactors. There are plans outlined to build more. So the Hinkley Point C reactor is well under construction and there will be likely quite a few more reactors that are produced. So at present spent nuclear fuel when it comes out of a reactor is cooled, basically put into giant swimming pools essentially because it's really, really, really hot and it's really, really radioactive. So by putting it in a cooling pond for a couple of years, you allow that initial residual heat, to decay away and some of the radioactivity associated with the really short-lived

sort of decay products that form, the front-end activity can decrease a little bit. And then what happens is all the spent fuel is basically packaged and sent to Sellerfield, which is in Cumbria and sort of north and northwest of England. This is where the reprocessing happens. So this is where the spent fuel is dissolved and essentially turn to. end into high-level waste. At present, generally, like, a large amount of the nuclear material that's in this country is at the Sellerfield site.

The actual logistics of waste transport and waste transfer are not something that I sort of know too much about. I imagine some of the actual practices are, you know, for security reasons, probably not widely available. But generally, most of the high-level waste is exported off the sites to Sellerfield, which is essentially the holding pen. And as you can imagine, obviously, there were large volumes of of waste sort of at the field awaiting a long-term repository. So at present, the government is basically exploring different siting options as to where we're going to actually build

the geological repository. What are some of those options? If we have a repository, or when we have a repository in the UK, where is it likely to be? So as of 2023, there are sort of two areas of the country that are under consideration for the construction of geological repository, one of which is in Cumbria and one of which is near Lincolnshire. In terms of how far along these siting processes are, so in the UK, we operate what's called sort of a volunteerist approach. So in order for a site to be considered, a willing community has to basically form a partnership with essentially the siting people, the branch of government that is responsible for sighting this place.

And it's a volunteerist approach, so it has to kind of have full support from the local community. Both of these sort of siting processes are still relatively in their infancy. Again, I'm not involved in the siting process, so I'd be hesitant to say how far along they actually are. But in terms of, you know, some goalposts that have sort of been set, the roadmap that's been set out by the government, it's hoped that in the next sort of two to three decades,

that there is some serious progress made on construction and sort of getting the waste packages sort of ready to be disposed of properly. The entire process of, you know, basically the first spade in the ground to complete closure of the facility, estimates vary. It's likely to take, could take up to 100, years for this to happen. So the people that are working on this project now, the people that are working, you know, in all areas of the siting process, whether that's the fundamental chemistry

of the materials right at the beginning, all the way down to, you know, the people that are liaising with the local communities and local partnerships. All of us, there are many of us that will see very likely that none of us will see the actual closure of the facility. And I know that's That's quite important. I think, you know, what we're doing is starting a process that, you know, many of us won't see till the end. But it's important that, you know, us as our generation of scientists and engineers, we're the ones that will really be responsible for constructing a facility that really will last,

you know, 100,000 years and keep nuclear waste safe from the environment. It is a large responsibility. So that's why it's important that we have appropriate funding and appropriate research development, you know, really strong links between the end user and, you know, the academic and industrial sectors. So, for example, some of the work we're doing at Sheffield now is looking at the viability of studying how waste forms and contain simulent nuclear waste will interact with different types of groundwater that might be found at each of these sites. So it's important to remember as well that the repository will be underground, obviously, forever,

but it will eventually basically decay away. It will, you know, over a million years to two million years, you know, there will be seismic changes. Water will penetrate this facility eventually. So what we're trying to do essentially is demonstrate that by the time water starts to dissolve away the glass and dissolve away the ceramics are used to encapsulate the nuclear waste, by the time that happens, the activity will be low enough

such that it doesn't really matter anymore. And are there any facilities already in existence anywhere in the world? I mean, which countries are ahead of the game? So Finland is by far ahead of the game. So Finland has the Enkalo repository, which is the world's only operational, deep, geological repository that has a license to dispose of spent nuclear fuel. So the Finns are really leading the way in terms of geological repositories. the US has had problems citing its repository for a very long time.

There was a very large project to basically scope out an area of land that was called Yucca Mountain. This site had decades of research poured into it and was ultimately cancelled. The French and Germans are kind of still in their siting process, but I believe the French have a site kind of decided. again, the UK is still in the sighting process. But to give you a solid answer, yes, Finland is the only country that really is making strides. And I believe they've just had their licence accepted to start disposing of real spent nuclear fuel. I've been to the facility.

I was lucky enough to go maybe four years ago now. And it really is an extremely large and incredible infrastructure project. It really is. What innovations or kind of promising new technologies are searching for better ways to dispose of nuclear waste or improve the kind of designs that we have? So there are certain reactor types that have been proposed that could essentially take nuclear waste and sort of re-burn it essentially. We could do things like fabricate mixed oxide fuels that use sort of waste plutonium. I'm hesitant to use the term waste because there's still an argument as to whether plutonium is a resource or a waste. but you know there's always the opportunity to reuse these materials but i think it's important to

to remember that there is there'll never be any kind of process or sort of any kind of reactor cycle that doesn't produce waste they all produce waste it's just what the chemical composition and physical properties of that waste are that would be you know sort of changed we can use things like plutonium and amorycium to make radio acetope thermal generators, which are generally referred to as space batteries. So for fueling long space missions where we need to keep components warm and keep them powered, something like a plutonium, radio acetope thermal generator, and RTG would be a good use of something like a waste plutonium products as a valuable resource for fueling certain types of long-term space missions.

There are many different sort of reactor concepts and designs that could take spent fuel and burn them for longer, but it's important to remember there will always be waste at the end. And what we need to do is be confident that no matter what type of waste we produce, we have a safe, capable method to convert it and immobilize it into a stable waste form that could be disposed of in a geological setting. You've been listening to Material Scientist and engineer Lewis Blackburn talking about the future of nuclear waste.

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