Going Nuclear

Scientists have found a way to tame hostile bacteria and turn them into docile vaccines, by replacing key genes with those from the bugs Arctic counterparts!

Writing in PNAS, University of Victoria, Canada, researcher Barry Duplantis and his colleagues reasoned that some of the essential genes carried by bacteria that have evolved over billions of years to live in very cold climes will most likely be optimised to those temperatures. So exchanging some of these genes for their equivalents carried by warmth-favouring pathogenic bacteria could produce a temperature-intolerant, disabled bug that could function as an ideal vaccine.

To find out, the team tested out nine genes known to be critical to survival in all known bacterium; the gene sequences were first "cloned" from bacteria that flourish in the Arctic and then inserted into the chromosomes ofSalmonellaandFrancisellabacteria and also aMycobacterialspecies related to TB, replacing the native gene.

The modified bugs grew unhindered at low temperatures, but grown at higher temperatures the bacteria suffered stunted growth. Injected into a cool spot on the bodies of experimental rodents, the modified bugs, which are usually fatal, instead provoked a robust immune response allowing the animals to fend off a lethal dose of unmodified bacteria which were administered a few weeks later.

This suggests that the technique could be used to produce a host of safe, temperature-sensitive live vaccines capable of protecting people against significant pathogens includingSalmonellaand TB.

High-heel tottering fashion slaves often complain that stepping down to normal footwear is extremely uncomfortable following the elevating effects of a six-inch height boost. Now scientists know why.

In a paper in the Journal of Experimental Biology, Manchester Metropolitan University scientist Marco Narici explains how he used newspaper ads to recruit over 80 women with at least a 2 year, 5 cm high-heel history, 11 of whom reported discomfort when walking without their heels.

Ultrasound measurements of the calf muscle lengths amongst these women showed significant shortening - by 13% - of the muscle fibres compared with non-heel wearing controls.

At the same time, MRI scans showed that the Achilles tendons of the two groups were the same lengths, indicating that the tendons of the heel wearers had not lengthened to compensate for the shorter muscle length, although the heel wearers tendons were nonetheless thicker and stiffer than those of the controls.

Consequently, walking on flat-feet becomes uncomfortable for these people because the tendon cannot stretch sufficiently to compensate for the altered posture.

Chris - Radioactive waste produced by the nuclear industry is a very big problem. About 12,000 tonnes of it get produced around the world every single year and at the moment, it needs to be stored somewhere. But what if there was a way to take this waste and actually use it as a fuel instead? That might sound too good to be true, but scientists think that it might be possible by building a nuclear fusion reactor that's nestling inside a fission reactor. This hybrid reactor will then be able to produce large numbers of extra neutrons that can be used to burn off the waste inside the reactor, and therefore make much more efficient use of the nuclear fuel. Bill Stacey, is from the Georgia Institute of Technology. He's with us to explain how this could work. Hello Bill...

Bill - Hi.

Chris - What's the general idea about this? How does it work? What's the concept?

Bill - The basic idea is the actinides that Ian was just mentioning are all fissionable in certain types of reactors: instead of burying them, just put them back in reactors and burn them, which means to fission them. That's much easier said than done because it turns into competition for neutrons because as the fission products build up and the fission products are also competing for neutrons, it's hard to keep the reactor running. So, there's a need for a few extra neutrons. The idea of the fusion/fission hybrid is to have a fusion neutron source that provides these extra neutrons for the fission reactor that's burning up the actinides and spent nuclear fuel.

Chris - Basically, what you've got is in the core of the reactor and at the moment with a fission reactor, where those fuel rods are with the pellets of uranium in them, the waste products that build up as the reaction goes on prevent the reaction from happening very efficiently. In the end, you end up having to take the rods out even though only a tiny fraction of the fuel has been burned. So if we could find a way of getting more bang for the buck by burning off the waste products with extra neutrons, then we'd save a whole lot of money and save a whole lot of waste as well.

Bill - That's right. The waste products that we're talking about burning off are primarily the actinides that are left in the fuel so they are unburned fuel for all practical purposes. The waste products that are the fission products also are competing for the neutrons. The problem is to get a few more neutrons and that's where the fusion idea comes in because the fusion reactor, that would be in the centre, would be producing extra neutrons, and you can dial up a number of extra neutrons that you need. In this way, you can keep the fission reactor running a lot longer and enable it to burn off the actinides. Basically, the efficiency of doing this is that you can probably reduce by at least a factor of 10 the amount of material that would have to be stored in long term geological repositories. That means you would reduce by a factor of 10 the number of repositories that you had to build and that's substantial.

Chris - Talking practically though Bill, we can't even get a fusion reactor to work at the moment sustainably, how practical is it to try and get one that we could then have in the core of a nuclear power station that's a fission reactor. You're going to put one kind of reactor inside another reactor. It's huge, isn't it?

比尔-是的。这是一个想法的佛r a long time because of the arguments that I just made, but the thing that's different now is that it is feasible to talk about building a fusion reactor. The ITER project which is being built in Cadarache, in the South of France right now will have a fusion tokamak reactor that if we just took that technology and that physics, that would be sufficient for the neutron source for a fusion/fission hybrid. That device is being built now. It will start operating in about 10 years and 10 to 20 years from now we'll demonstrate the physics and the technology that's needed for the neutron source. So I think we would say that to be able to deploy something like this, starting in about 2030 or 2040 is a feasible thing.

Chris - What about the safety aspect? Because you'd have a very, very hot and very, very powerful fusion reaction going on in a core of a super critical fission reactor. Is there not quite a big element of danger there?

Bill - Well, not really because if anything happens to the fusion reactor - the [core of the] fusion reactor is a gas like the sun, and basically, the problem is to keep it from going out. If anything happened to it, you would just end up with a spoonful of liquid hydrogen in the bottom of the vessel. There are of course interaction problems that have to be taken into account in the technology to do this, but it's not as if you've got an uncontrolled sun in the middle of a fission reactor.

Chris - Just to look at the numbers to finish this off, apart from the waste issue, and you mentioned the 10-fold reduction in that at least, how much better would this be than what we can achieve at the moment with standard fission?

Bill - Well, that's the question that really needs to be evaluated. The benefit of going with fission/fusion, as opposed to going with just a standard fission reactor to do this job, is that you can leave the fuel and burn it for longer. That means there would be fewer re-processing steps and so fewer re-processing facilities. That means more efficiency in burning up the fuel, so fewer repositories. The other thing is that that since each of these fission/fusion hybrids can use reactors that are completely fuelled with spent fuel you wouldn't need so many of them as you would if you had just conventional reactors which could only be partially fuelled with spent fuel. In fact, we've done some calculations and we estimate that a nuclear fleet that were sort of 75% light water reactors (LWRs) and 25% fusion/fission hybrid reactors would do this job very well. Whereas if we were talking about a nuclear fleet made up LWRs and just plain fission burner reactors, it might be more like 75% the burner reactor and 25% LWRs. So it's a matter of efficiency.

Sarah - Now, on the 16th of July 1945, the project code name Trinity was put into action. Trinity was the first test of an atomic bomb, the first nuclear weapon. The bomb, nicknamed the Gadget, was detonated in a remote area of New Mexico and the test heralded the birth of the atomic age with the "fat man" atomic bomb being detonated over Nagasaki in Japan, less than a month later. Sixty five years on, the test site is hard to access and rarely visited, but journalist and author David Wolman risked the radiation to find out more about this historic site. Hi, David.

David - Hi there, Sarah.

Sarah - Welcome to the Naked Scientists.

David - Thank you.

Sarah - Why don't you start off by setting the scene for us a bit. Where exactly is the Trinity site and what's it like?

David - Sure. Well in the Southern part of the already rather desolate state of New Mexico, there is this giant swatch of land that the military owns. Today, it's called White Sands Missile Range and one spot within that area is a of sort desert basin and blaring sunshine, and creosote and sage brush, and mesquite. You have this black obelisk now standing to mark the spot at ground zero where the first atomic bomb was detonated. And at that time, almost everyone in America didn't know what was happening down there and it was chosen not surprisingly because it is so incredibly remote. There were some people around there who needed to be evacuated and no-one lives there now, but it is safe to visit, and for the past 30 or 40 years or so, twice a year, I think it's the first Saturday in October and in April, the public is allowed to visit the Trinity site.

Sarah - What's it like when people go to visit there? I mean, what sort of thing do people expect to see when they come?

David - Well, another journalist and I joined a caravan of cars leaving from the nearby town of Alamogordo. Because it's in a currently active missile range or military installation, you're not really allowed to colour outside the lines when you visit Trinity and so, you meet up with this caravan, have a brief security check, sort of like going to the airport and then we drove about an hour into the dessert. And when you finally get there, there's sort of a large gravel parking lot with a lot of people, a lot of SUVs it seems from Texas, and there are a couple of stands selling hotdogs and people selling books about atomic history, and then you walk down a corridor that's marked off by a chain link fence with some barbed wire on the top. And there are signs on it that say, 'Caution, radioactive active materials' beyond the fence, but the radar activity there is not a health hazard, I should say that right off the bat because I probably wouldn't have gone if it is!

Anyway, you walk down this long corridor through the dessert. It's very dusty and sunny, so sunny. And then you finally get to a large enclosed area, still with the fencing, and that's where the obelisk sits and people are wandering around, sort of kicking their shoes in the dirt and in the dust because of course, there's a sign that says, please don't handle the Trinitite which is this glassy residue that is this light greenish colour rock that exists in the area that was created by the blast. And of course, there's a sign that says, "Trinitite is government property. Please don't pick it up and handle it." And so, that immediately makes everybody want to look for the stuff. And in fact, it's all over the place. I took a picture with some in my hand, but I figured as a journalist, I better not take any out of there, at least not right about it because that would be trouble.

Sarah - Well, it's this first thing people do, isn't it? You tell them not to do something and they go and do it.

David - Exactly.

Sarah - When you visit - when you look at it, would you know that it was the site of the test at that or is it actually, you know, surprisingly biodiverse or is it very obvious that some huge explosion happened there?

大卫-很不明显。我认为在60s, they bulldozed a lot of the residue and the glass that was created. And so now, you have a lot of this kind of sage brush desert landscape. It's a little more mountainous in the distance than I had imagined. Being from New England myself, I had always pictured it as flat as a pancake, as far as you can see, and in fact, it's sort of this basin area tucked between two mountain ranges. But you really wouldn't know from a distance and of course, there's this 8 or 10 foot tall stone obelisk there and a little monument, but you know, I was a little surprised not to see anything, for example, commemorating the war dead. This is certainly a science pilgrimage. It's not a war memorial. You know, the people there are wearing t-shirts with a periodic table on them, but still, it's a little strange that the tenor of the thing with the hotdog stands and nothing about dead people which is maybe an editorial for someone else to write, but a lot of people there are just snapping pictures, and are really excited to be in the centre of where this great scientific achievement happened regardless of your politics. And so that part is really interesting to me, but from a distance, you would never, ever know and in fact, you know, what brought me to Trinity and also to some other spots around the west this spring was this project I was working on called Accidental Wilderness because this area around Trinity, the White Sands Missile Range is still off limits to the public.

For the past 60 years, you have this flourishing ecosystem there because there are no people. There's no roads, there's no houses, there's very little public disturbance. And so, that is really an interesting irony and the same story can be told for a dozen places across the American west where the military has set out this great boundary and says nobody really can come inside here except maybe some wildlife biologists now and then. And the result is some of the most vibrant ecosystems and biodiversity rich areas left really on the continent.

Sarah - Well that's very exciting. So out of something quite violent can come a good story for biodiversity. Thanks so much, David. That was David Wolman and you can find more of his articles on his website at david-wolman.com.

We put this question to Professor Swadesh Mahajan from the Institute for Fusion Studies at the University of Texas in Austin....

Swadesh: - Yes. The Yucca mountain site which was designed by the US folks - of course not with a tremendous amount of enthusiasm - was expected to cost about $90 billion to $100 billion and it would've stored waste of about 40 years of operation of 50 to 100 nuclear reactors. So if you really try to just divide it to all over, I think it adds just a few cents to the cost of electricity.

Chris: - And, of course, you've got to factor in the environmental impact which is that we're not releasing CO2 as Ian Farnan said. We're sparing, for every ton of uranium, the equivalent in CO2 terms, of a million tons of coal.

Swadesh: - Right. The very important thing of course is that it's very difficult for us to be able to engineer too many such repositories with 10,000 to 200,000 years of lifetime. So I think we should have a minimum number of them and if nuclear energy is going to have a renaissance, we really must destroy this before we store it. Destroy as much as we can, if we reduce it to 10% or to 1%, the better it gets. We are not going to be able to get a hundred Yucca mountains if the nuclear energy were to take off for instance, which is what will be needed if we try to store untreated waste. That's a political as well as a physical impossibility. So we must destroy this.

Chris - They use what are called control rods - these are dense materials which, when dropped down into the reactor, soak up some of the neutrons that are produced by the nuclear chain reaction. The consequence of that is that there are fewer neutrons left to bust open other uranium or fissionable nuclei, and as a result, the chain reaction is slowed down. By putting the fuel rods in, or drawing them out, you can speed up or slow down the chain reaction, and therefore, you can affect how much energy actually comes out of the reactor.