Nuclear energy is always in the news, but how much do you know about nuclear fission and what happens to nuclear waste? To find out, Naked Scientists Anna Lacey and Dave Ansell visit Sizewell B power station in Suffolk, and studio guest Ian Farnan from Cambridge University discusses nuclear waste disposal and why current methods might not contain the radiation as long as we thought. But as clinical radiologist Anant Krishnan explains, radiation plays a crucial role in medicine, including allowing us to see broken bones and killing off tumours. Sticking with uses of radiation that save lives, Anna and Dave find out how a smoke detector works in Kitchen Science.
In this episode
The humble aspirin is a bit of a wonder-drug. Not only can it cure aches and pains, but some research has shown that it might help to prevent certain types of cancer, including bowel cancer. Now Cancer Research UK has opened a clinical trial to test whether the drug can prevent oesophageal cancer - that's cancer of the gullet/food-pipe. This type of cancer is on the risk in the UK, and we have one of the highest rates of the disease in Europe. The researchers are recruiting 5,000 men and women across the UK who suffer from a condition known as Barrett's oesophagus. This is an illness in which acid reflux from the stomach back up into the gullet causes cells to change their identity, and become more "stomach-like". Having Barrett's oesophagus can increase your risk of oesophageal cancer - in fact, having the condition makes you fifty times more likely to get oesophageal cancer, although only around one in a hundred people with the condition will go on to get cancer. The clinical trial, known as ASPECT, will test whether the combination of aspirin and an acid-blocking anti-ulcer drug called esomeprazole can prevent cancer from developing in people with Barrett's oesophagus. They think it might work by damping down acid production and long-term low-level inflammation that is believed to contribute to cancer. The ASPECT team are looking for people who want to take part in the trial. The best way to find out more is to ask your GP, call the Cancer Research UK nurse team on 0207 061 8355, or look at the charity's patient information website, which is
Tongue to Talk About
Scientists have found the animal with the world's most powerful tongue. It's not a whale, an elephant or even a cow, it's the giant palm salamander, Bolitoglossa dofleini, which lives on the forest floors of Central America and whose tongue packs an 18 kilowatt per kilogram punch. This is twice the power of the existing holder of the tongue title, a Colorado river toad called Bufo alvarius. Stephen Deban, from the University of South Florida, made high-speed video recordings of the animals' tongues in action, but these revealed that their tongues flicked out far faster than could be achieved by muscle contraction alone. To find out what was going on the team attached electrodes to the tongue and recorded the muscle cells' electrical firing pattern. Surprisingly they found that the tongue muscles contract for far longer (over 100 times longer) than the duration of muscle cell activity. This suggests that the tongue must be storing up energy. Deban thinks that lengths of collagen wound around the muscles are acting like a stretched elastic band. When released these collagen fibres snap back on themselves, just as a bow string fires an arrow, suggests Deban.
Proteins Produce Prematurity
Research presented at a scientific conference in the US has suggested a way that protein analysis could be used to predict premature births. The researchers have been studying inflammatory proteins found in amniotic fluid, the liquid that surrounds a baby in the womb. Signs of inflammation are found in around half of all women who give birth prematurely. Although there are many proteins in this fluid, not all of them are actually medically meaningful. The team studied amniotic fluid samples taken from more than 120 women who had gone into hospital for a premature birth. They found that women with a particular abnormal collection of proteins were more likely to have infection and inflammation in their placenta and umbilical cord - making them more likely to give birth prematurely. This was only a small study, so the next step will be to try and set up a larger trial. But this could provide a way of working out which mums and babies are at risk of premature birth and infection, so they can be monitored and treated appropriately.
Storm Clouds Gathering on Climate Change Horizon
If you can't take the heat you move into the shade, right? But what about if that means the entire Earth? Well that's the strategy being put forward on a planetary scale by Iowa State University researcher Curtis Struck, who suggests that one way to cool an overheated-Earth would be to mine dust from the moon and use it to build artificial cloud cover in space. Writing in the Journal of British Interplanetary Society, Struck points out that dust particles from the moon are just the right size to scatter sunlight. Positioning the particles at two locations along the Moon's orbit would produce a pair of stable clouds that would pass in front of the sun once a month, cutting sunlight by twenty hours per month and helping to cool the planet. But not everyone thinks it's a good idea; some critics are concerned that the particles could act like mirrors and reflect more light onto the Earth during the times when they are not directly in front of the Sun.
- How a Nuclear Power Station Works
How a Nuclear Power Station Works
with Anna Lacey, Dave Ansell, Colin Tucker and Matt Lunn
Kat - Now we've just been hearing about radiation in your own home, but what about the stuff that creates radioactivity: nuclear reactions? Earlier this week we sent the Naked Scientists Anna Lacey and Dave Ansell to Sizewell B nuclear power station in Suffolk, which is one of the nineteen nuclear reactors in the UK and currently supplies around 3% of the UK's electricity needs. They went along in their sturdy protective gear to find out what's inside a power station and how it actually works.
Anna - I've managed to get through security and I'm now fully kitted out in blue overalls and a nice hard hat. But before I go and have a look around the power plant, the first questions should really be: what is nuclear energy? Well in the case of the power plant here at Sizewell, it's all about a fission reaction. To do that, you have to split the nucleus of an atom like uranium in two, and it's this splitting it in half gives off loads of energy. But to find out a little bit more about how that really works, I'm here with Dave. So Dave, how do we go about splitting an atom in two?
Dave - Well as the name suggests, nuclear energy is all about the nucleus of an atom. Now the nucleus of an atom is made up of two kinds of particles: you've got protons which are positively charged and repel each other quite strongly, and you've got neutrons that don't have any charge at all and kind of sit there. Both neutrons and protons are attracted together over very short distances by something called the strong nuclear force. This acts like glue and sticks neighbouring ones together. This means that a very big nucleus, something like uranium which is the heaviest nucleus you can find naturally, you've got 92 protons that are repelling each other. That's almost overcoming the attraction of the glue. All you've got to do is give it a bit more energy by throwing in a slow neutron into the middle of that to give it enough energy to split it into two and break that glue connection. Once that's broken, you've got two halves of a nucleus, which are repelling each other really strongly. They fly apart and release an immense amount of energy. Luckily, it also releases two or three neutrons which can fly off and hit another uranium atom which will split and release others. This gives you a chain reaction and you can release an immense amount of energy.
Anna - Ok thanks for that Dave. Well now we've heard about some of the science behind splitting atoms, let's talk to somebody who works with this kind of stuff every single day. So I'm here with Colin Tucker and he's a physicist and nuclear safety engineer, I think that's right isn't it Colin, here at Sizewell. So Colin, what is it that we're actually looking at here?
Colin - You're stood outside the reactor building, which is the big white dome that people see when they walk up and down the coast here in Suffolk. That's 72 metres high and it makes people think that maybe we've got a big reactor here; we haven't. The reactor's only four metres across and it's buried right down in the basement of that building.
Anna - So what kind of energies are we talking about being produced here at Sizewell B?
Colin - In that reactor, which as I say is only about four metres across, we're generating 3500 million Watts of heat. So it's about a million electric kettles-worth in that small volume. We use that heat to heat water, about 20 tonnes of water a second. We heat it up to more than 300 degrees Celcius. What do we do that for? Well we can then use that water to heat up some more water at a lower pressure and make steam, about 2 tonnes of steam a second. That travels from the big white building across to the right here into the turbine hall where it spins our turbines at 3000 times per minute. At the back end of those turbines are the generators, and that's what we're here for. Nuclear power stations exist to generate electricity and that's what we do, day in day out.
Anna - That sounds fantastic. Can we go and see it?
Colin - We can go and have a look at the turbine hall, certainly.
Anna - We are now in the turbine hall and as you can probably hear it's insanely noisy. What we have is an enormous open building with lots of metal floors round the edge, one of which I'm standing on. And down in the middle is a whole series of turbines, and this is what Colin was talking about. The steam comes into here and it turns the turbines that generate electricity. But we can't really talk in here so we're going to go outside now and take out our earplugs... Ok then Colin, so we're now outside the turbine hall because it's a bit too noisy to be talking to you in there. How is this different to what's going on inside a coal-fired power station? Is there a difference?
Colin - Very little difference between this and a coal-fired power station. The steam conditions are a little bit different and some of the bits of the turbines are a little bit different, but if you walked into a coal-fired station such as something like Drax, you'll just see a row of turbines that looks just like these.
Anna - So the only difference really is what you're putting in at the beginning. Is it coal or is it going to be uranium?
Colin - Absolutely. We just use the uranium as a heat source. That's all it's there for.
Anna - So are you pumping in uranium fuel all the time? Are you always constantly having to stoke up the turbines so to speak?
Colin - No we replace about a third of the fuel with new fuel every 18 months. So we run for sixteen and a half months continuously at Sizewell B at full power continuously 24 hours a day. At the end of that we shut it down, do a lot of maintenance, testing and a lot of inspections and we replace about a third of the fuel.
Anna - So I suppose the next question is what are we going to do with all the waste and it's a question a lot of people are very very concerned about. So we've got another person here called Matt Lunn. Matt can you tell me, what do you do here at Sizewell?
Matt - My job is to advise the management on the safety of the use of ionising radiation and also to advise on the protection of the environment.
Anna - Well it sounds like you're the person we need to be around to make sure we're nice and safe. We're going to go off now I believe, to see what happens to the waste and where it all goes.
Matt - We're currently in the spent fuel building, which is next to the reactor building and what you're looking at here is a deep pool of water about the size of a five-a-side football pitch. It's about fourteen metres deep and in that pool we've got our spent fuel.
Anna - So you just said about spent fuel there. What is spent fuel?
Matt - Spent fuel is basically a fuel assembly where we've burnt a certain proportion of the fuel. However we can't burn the rest because of a build up of what are called fission product poisons. During the fission process, the uranium splits and it splits into roughly two halves, and they're called fission products. However those fission products are actually much better at absorbing neutrons than the actual uranium itself and therefore what happens is that the nuclear reaction dies out. Effectively 96% of the actual useable fuel is actually unburned.
Anna - Ok well we've got all this fuel left over and it's in a big pool of water. Why is it that you're storing the radioactive waste under water?
Matt - The fission products inside the fuel give off intense radiation, and water is a good shield, it's cheap and it also has a cooling effect as well.
Anna - So how does the water shield you from the radiation?
Matt - Basically the gamma rays just bounce off the water molecules and eventually dissipate their energy in the water.
Anna - What are you going to do with it after that?
Matt - Unlike the earlier power stations, our spent fuel is designed to be stored underwater, and we can actually store it here until the end of the station life and beyond, and that's the current strategy. The options for dealing with it in the long term are either reprocessing like we do at Sellafield or you can bury the fuel in casks deep underground. Unfortunately the United Kingdom doesn't have a final repository for spent fuel at the moment. Therefore we'll just continue to store this either underwater or eventually in special casks above ground.
Anna - Well we've now come to the end of our tour of the nuclear power station. Thanks very much to Matt and to Colin for showing us round and getting us past security. But Colin finally, we're standing now next to the National Grid building, which is where all the power from the power station goes into fuel our homes. Do you think that nuclear power is going to be a big contributor to our electricity needs in the future?
Colin - Absolutely. At the moment we generate about 20% of the electricity used in the UK. We're a very very low carbon emmiter in terms of the generation that we produce and on a large scale. What are we going to do as these power stations get older? We're going to have to replace them with something. To replace them with renewables on such a large scale is going to wreck the landscape. We're going to have to have some renewables and some nuclear. It's a very exciting time to be working in the industry because everyone now is seriously looking at new build again and I'm sure that in a few years' time we'll see more of these being built.
- Storing Nuclear Waste
Storing Nuclear Waste
with Ian Farnan
Chris - Now we were talking about Sizewell there. It's not a very big reactor: four metres by four metres they said. That sounds tiny, but they said there's a huge amount of radioactive waste. How much?
Ian - I'm not exactly sure how much is stored at Sizewell. In fact all the nuclear waste that's produced at Sizewell is currently on site there so the UK doesn't actually deal with that waste at the moment.
Chris - How much have we got stockpiled at the moment? We heard earlier how there are 19 functional power stations in this country and a number have been shut down.
Ian - The majority of our waste, the volume is 470 000 cubic metres. To put that in perspective, only a few per cent of that radioactivity is in the vast volumes there and I think 98 or 99% of the radioactivity is in a much smaller volume, and that's what we call high level waste. This is the really really dangerous stuff.
Chris - How dangerous and why?
Ian - It emits beta and gamma radiation. It's extremely harmful and you cannot approach it. It takes many years to cool down and so Anna at Sizewell will have seen the spent fuel ponds. When the fuel rods are removed from the nuclear reactor, they're placed underwater and left to cool for long periods of time. Other reactors leave the rods there for maybe 10 or 15 years and then pull them out into something called dry casks. But it takes about that period of time before you can store them out of the water.
Chris - But storing them: how long are we going to have to store them for before they're considered safe again?
Ian - In the UK we have actually taken many of our nuclear fuel rods and reprocessed them. And in that process you separate out into two main types of waste. You have what's called the fission products which is half of the heavy element or the two halves that have split apart, and then you get the remaining uranium, which is depleted uranium, and plutonium that is generated in the nuclear reactor. So you've got these two parts. The fission products themselves are dangerous for about three hundred years, so the principle elements would have half lives of about thirty years, so ten half lives would be three hundred years. There are a few other problematic elements in there; technicium is one which we will hear about and has medical uses but it exists there and is quite long-lived.
Chris - But some of this waste that we're talking about we say that it needs ten half lives to be safe and that's 300 000 years.
Ian - No, 300 000 years would be something like plutonium 239.
Chris - Which we're producing in these things.
Ian - Yes so there's two types of waste: there's the waste that we call the fission products and in the UK we've separated the plutonium and the uranium from the fission products so the fission products are ok in 300 years. The plutonium and uranium are on much longer time scales.
Chris - So at the moment we've got a considerable amount of material that could be radioactive for a third of a million years.
Ian - Exactly.
Chris - How do we store that?
Ian - In July the government commission called CoRWM reported and said that we should build what's called a geological repository. What they said was that we should dig a hole between 200 and 1000 metres deep. It will be a bit like a mine, so a shaft will go down and then you'll cut out drifts into the surrounding rock and then you'll place canisters of material.
Chris - So does this just mean you put some stuff in a barrel and bury it?
Ian - No. The fission products themselves are treated with some oxides, heated up, and formed into glass. Those are then poured into cans, extremely strong cans, and they're stored at Sellafield at the reprocessing site.
Chris - Now is that stuff stable for a third of a million years?
Ian - That stuff doesn't necessarily need to be stable for a third of a million years because it only contains the fission products.
Chris - But I'm talking about the ones that need storing for a third of a million years, Ian.
Ian - So that material is stored at Sellafield and we've not decided what to do with that yet. Well we've decided what we're going to do with 5%. 5% of that and 100 tonnes of plutonium has been set aside as not useful as a future nuclear. This really depends, Chris, on decisions on whether we build new nuclear power stations and whether those nuclear power stations will then be licensed to burn what we call mixed oxide fuel: uranium plus plutonium. So depleted uranium and then the fissile material will be plutonium.
Chris - But what I'm getting at Ian is how do we work out a safe way to store that stuff with this incredibly long half life that needs a long time in the ground to calm down?
Ian - Well what we're trying to do is to develop some mineral-based ceramics which in a similar way to forming the glass, we mix oxides and we form something which is like a mineral. There are certain minerals that occur on the earth that have been proven to hold uranium and thorium for billions of years in some cases, and so those are the kinds of models for the kinds of materials we want to use. So we would like to isolate these very long-lived isotopes into a mineral before storing it, and hopefully that mineral will be sufficiently durable that it would not decay or be damaged by the radioactive decay that occurs inside it.
Chris - Is that true? Does it?
Ian - We haven't yet found one that's going to last for 300 000 years.
Chris - How long does it last?
Ian - Well the particular case we looked at recently lasted for about 1400 years.
Chris - So that's a fraction of what you need. So at the moment what you're saying is that we have this high level waste and we've got nothing that we can actually do that's going to be a safe long-term prospect for it.
Ian - It's a question of confidence. We know that this material will degrade because of its own internal radiation. Whether that amorphous material will then be dissolved by water is not very well understood.
Chris - Why does it get damaged? Why does it fall apart over time?
Ian - What happens is that there's an alpha particle emitted from heavy nuclei like plutonium and that heavy nucleus then recoils a bit like a howitzer that's just fired a shell. That skittles into all the other atoms and knocks them all over the place, and basically you no longer have a very well-described very durable material at that point because the atoms are all in very high energy positions. They're all knocked out of their usual positions and so could be attacked more readily by water.
Kat - So the challenge is to find something stable. We've had a suggestion here from Keith in Watford who says that nuclear waste could be encased in glass and shot into space. Is there any other way of sensibly getting rid of nuclear waste without putting it somewhere on the planet?
Chris - Yeah David in Chelmsford says why don't we dump it on the moon?
Ian - I think the Committee on Radioactive Waste Management, which delivered its report last July did consider very quickly putting things in space; firing them into the sun is another option. A feasibility request went to NASA and they could only guarantee, I think, 1 in 35 launches wouldn't result in an explosion, so the idea is that it would be too dangerous to do that.
Chris - It would be similar to what happened with Chernobyl basically in terms of the amount of contamination.
Ian - You would deliver it into the stratosphere and it would be spread around the world.
Kat - That just sounds terrible. So more research is needed quite urgently.
Ian - I think that the research that's being done is to really research the materials we put these things in. We actually form these things into another material and that material is actually very very durable with respect to water. The main problem is that if you put this stuff down deep into the ground, the question is whether this material will come into contact with water. That's the only way that the radioactive isotopes will leak out if it comes into contact with water. So that can be controlled by the geology of where you put, or it can be controlled by the material itself. You obviously need a combination of those two, but the better you can make the material in the first place, the more certainty you have in the disposal process.
Chris - What's the situation in America, because they've invested quite a lot of money in deep burial.
Ian - That's right. They have a repository site in Nevada that's about ninety miles west of Las Vegas. All states in the US except one, which is Nevada, have agreed that nuclear waste should be sent there. At the moment I think there's one legal challenge that is preventing the go-ahead of that project. They will have lots of nuclear waste from their nuclear weapons programmes and from their commercial nuclear generation programme, which will be transported to Yucca Mountain and be set in the type of repository that I described earlier.
Kat - I was writing a blog last year for the Institute of Physics that looked into nuclear energy and those kinds of issues. And it did seem to be that there's a lot of discussion about the right way to build nuclear power stations and how environmentally friendly it is, but no-one seems to have solved what to do with the waste.
Ian - If you ask most scientists who work in the area, we have a gut feeling that it'll probably be ok, but that's not good enough.
- Using Radiation in Medicine
Using Radiation in Medicine
with Dr Anant Krishnan, Addenbrookes Hospital, Cambridge
Chris - Now we're going to talk about the science of radiology. From Addenbrookes Hospital in Cambridge here's Anant Krishnan. Now you're a radiologist and that means you use radiation for medical purposes. It must make a big difference to doctor's lives.
Anant - Absolutely. It helps with both the diagnosis and treatment of disease and it's revolutionised the way things are going. Things are only going to get better now.
Chris - They're a bit dangerous though aren't they, x-rays?
Anant - You would think so, but it's about using it responsibly. If I can just put it in perspective, if you have a chest x-ray, the lifetime risk of developing a fatal cancer is less than being killed by a bolt of lightning.
Chris - But can you put some figures on it in terms of how much excess radiation I'm getting through having a chest x-ray because people say it's the equivalent of going out in the sun for three days or something.
Anant - It's getting about ten day's worth of background radiation.
Chris - But that's a simple chest x-ray. What about when you have more complicated procedures like abdominal x-rays or a CT scan?
Anant - CT scans do give more radiation, but you have to balance the benefits versus the risks. If I use the same analogies as before, having an abdominal CT would have the same lifetime risk of developing a fatal cancer as dying from an accident at work.
Chris - How does an x-ray actually work? When we've got someone and image their internal organs, how does that actually work?
Anant - Well first of all we create the x-rays by accelerating electrons at a metal target and that interaction gives off the x-rays, and we can then target that at the part of the body we want to image.
Chris - Because x-rays are a form of light aren't they, just with a short wavelength.
Anant - It's part of the electromagnetic spectrum, so it's a different part of the spectrum. What we do is target it at the body and it can do one of two things: it can either go through or interact with the soft tissue or the bone. It's the x-rays that go through and we can detect that on the x-ray plate, so we develop a shadow of what's going on in the body.
Chris - So some parts of the body mop up the x-rays more than others, and this is what gives you an image?
Anant - Heavier atoms tend to absorb more of the x-rays, so bone obviously.
Chris - Calcium.
Anant - Yes.
Chris - So what about when you want to do more complicated things, because obviously an x-ray is just literally zapping someone straight through. What about if you want to build a three-dimensional picture with say CT? How does that work?
Anant - Well that's using the same sort of thing, except that you're firing x-rays from different angles. That's then being picked up by a computer so that you get a 3D reconstruction. But everyone talks about x-ray and CT, when radiology also uses non-ionising radiation as well, so ultrasound and MRI. So these are much safer forms of radiation as well.
Kat - There are some people that suggest you should have a full-body CT scan every year, and some people in America do. Is that a good idea?
Anant - I don't actually think so because again you're looking at giving someone a radiation dose and it's not without its own risks, as has been made quite clear today. So we have to look at whether the benefits of doing the test outweigh the risks of getting something as an adverse effect.
- Could a woman be colour-blind in one eye?
Could a woman be colour-blind in one eye?
The answer is that your daughter is mosaic, as all women are. I don't mean that all women are little bits of ceramic pottery, but because we have two X-chromosomes as women, one of them gets switched off in every cell. In healthy people, this is a completely random process. Colour blindness is caused when there is a faulty gene on one of the X-chromosomes, and if you're a man then you don't have a counter balance to that (ie: another 'non-faulty' X-chromosome.) If you're a woman and one of your X-chromosomes is dodgy, you may have it switched on in some cells and off in others. The fact it's a mixture means that the healthy cells are going to compensate for that, so you're not going to be colour blind in just one eye. Some of the cells will have the colour blindness problem but there will be enough healthy ones to compensate.
- Why do you twitch as you go to sleep?
Why do you twitch as you go to sleep?
This is called a hypnic jerk, and the reason we think it happens is that when you go to sleep, your body is completely paralysed. The reason for that, we think, is that you don't want to be acting out your dreams because otherwise it could get nasty! You must have had that dream when someone's chasing you and you have that horrible sensation of running through treacle. That's because you're literally paralysed in your sleep. However the process of that paralysis kicking in occasionally causes these funny jerks. People have done experiments on cats where they temporarily turn off the bit of the brain that causes you to be paralysed during sleep. The result is that you get cats prancing around and acting out these dreams.
- Why do windscreens get frosty?
Why do windscreens get frosty?
We've had a few answers sent in for this question. Thanks to everyone for their input!
Dan in New Jersey - I think it's because over time when you're driving around you get pitting in your front windscreen from dust, water and stones. This could act as a nucleation site for ice, which encourages ice to form. Bill in Canada - I think it's probably due to moisture at the front of the car and greater air circulation at the back of the car, making for a greater differential of temperature and moisture at the front. This might make it more likely to freeze up. Thomas Coop in Germany - Ice is more likely to form on the front windscreen because it cools more quickly and to a lower temperature than the side windows. Frost normally forms during nights that are clear and calm and under such conditions, the trees and ground and many other objects cool mainly by a process called radiative cooling. That is, that they emit energy in the form of infrared radiation. The same happens to the front and side windows of your car, but the side windows cool more slowly because they are almost vertical. This allows them to pick up some of the radiation given off by trees and houses, which makes them cool more slowly. In contrast, the front windscreen points up into the clear cold sky and therefore receives very little radiation from other objects and cools more quickly. Since they cool more quickly, they are colder and frost is more likely to form on them.
- What is the smallest thing you can see in an MRI?
What is the smallest thing you can see in an MRI?
The resolution of MR is in millimetres. Obviously if you wanted to go further with CT, you could, but it would require a greater radiation dose.
- How does radiotherapy treat cancer?
How does radiotherapy treat cancer?
There are three ways of using radiotherapy: one is something called x-ray beam radiotherapy where x-rays are fired at a target. Another way is brachytherapy where a radioactive source is put in a tumour, and the third way is injecting a radioactive substance like radioactive iodine, which treats thyroid cancer. The reason it destroys the cancer is due to the way the radioactivity interacts with cells and causes DNA damage. It's specifically the ionising radiation that we use because the interaction with the cell causes electrons to be given off and leaving cells that are ionised. Usually when x-rays or gamma rays interact with the body, they actually interact with water and that water can form free radicals. The free radicals can cause damage to the cells by damaging the DNA.