Nuclear 101: How Nuclear Bombs Work" Part 2/2

welcome everyone, thanks for tuning in again today we are going to talk about how the

nuclear

material that is needed to make a

nuclear

bomb is made. In the last talk I talked about how plutonium or highly enriched uranium is needed, these are the materials that are used. in nuclear weapons that exist today, although there are some other isotopes that could possibly be used to make nuclear weapons, so there are two paths to the bomb, the plutonium route and the uranium route, in the plutonium route It needs a reactor in which uranium fuel is placed. that nuclear reactor in that reactor the reaction takes place by releasing neutrons its uranium fuel absorbs neutrons some of it becomes plutonium well, then you have to take that spent fuel as it is called out of the reactor and you have to chemically separate the plutonium that you want from everything uranium and fission products that are very radioactive and you don't want them in the material that you're handling for your nuclear bomb, so you need a reactor and you need a reprocessing plant that produces that chemical.

Medium speed separation in the root of highly enriched uranium. You need an enrichment plant that is something that takes these almost identical I atoms of uranium-235 and uranium-238 and separates them. Well, let me talk for a moment about what uranium 235 and 238 are. and a little bit of physics here, so an element is a type of material characterized by how many protons it has in its atomic nucleus, so hydrogen has one helium has two, uranium has 92, plutonium has 94, okay, different types of elements can have different numbers of neutrons, so last time when we talked about thermonuclear fusion weapons, I talked about deuterium, which is hydrogen with a neutron along with the proton in its nucleus, so it has a dual nucleus of one unit of proton and 1 unit of neutron or and I talked about tritium, so three things in the nucleus, the proton, because always a proton defines that it is hydrogen plus two neutrons make three for tritium.

Okay, so uranium-235 is an isotope of uranium that has 92 protons and the rest, totaling 235, are neutrons. Neutrons plus protons give you the number of isotopes like uranium-235. Okay, uranium 238 has three more neutrons. Okay, there are three extra neutrons that make uranium 238 very difficult to split and unable to sustain a nuclear chain reaction, whether it's a reactor chain reaction or an explosive chain reaction. reaction in a bomb, so you need uranium 235 for that chain reaction to occur, so the uranium that is extracted from the ground includes less than 1% uranium-235, it includes 0.7% uranium-235, all the rest, almost all of the rest is uranium 238, okay, so how do I separate the small amount of uranium-235 from that huge amount of uranium 238?

Well, there are several techniques and I will talk about them today. There are gaseous diffusion centrifuges, lasers, now, as I mentioned last time, none of them. These materials are found in nature, they are all very difficult to produce and one thing to remember last year some students used the terms reprocessing and enrichment interchangeably as if they were the same thing, they are not reprocessing is in the plutonium pathway. it is a chemical process enrichment is done in the uranium route it is generally not a chemical process it is generally a physical process based on the mass of these different isotopes being slightly different okay so what we are processing is not the same to enrichment, so this is just another version of these two paths to the bomb, they both start with natural uranium, you have to extract it from the ground, millet and prepare it.

Okay, one way down the uranium path, you send it to an enrichment plant and you might be done. up and with your product if you are making bomb material with something like 90% uranium-235 instead of the 0.7% you started with and 10% still uranium-238, while your waste, which is known as stories of enrichment, they could be, for example 0.2 percent u-235 instead of the 0.7 percent you started with. It requires a lot of energy to get all the u-235 out, so the tails usually have a fair amount it could be 0.2% it could be 0.3% it could be 0.4% somewhere in that range and the rest uranium 238, that's fine in the plutonium path, you have the reactor in the reactor, the uranium absorbs neutrons, it becomes plutonium, you have the spent fuel that It's about one percent plutonium and then the other 99 percent is uranium. and efficient products, okay, the amount of fission products depends on how long the spent fuel has been in the reactor, how much energy has been generated, how efficiently it has taken place, then the reprocessing is done and that separates the spent fuel in three piles per day.

A lot of plutonium, a lot of uranium and a lot of high-level waste, which are efficient products, are doing well. Both routes begin with uranium mining and end with converting the products, either uranium or plutonium, into metal and then making bomb components from that metal. These are just some images to help you with that same mindset, so you start mining and see a picture of a rock that contains uranium. Now when you dig it out of the ground, it's literally a rock and the rock contains some uranium, but I know it's mostly rock, so you need to do what's called milling to get purified uranium from those rocks and you usually end up with an oxide of

part

icular uranium which is 308, which is known as yellowcake, so you can see the image below of the grinding. a bright yellow powder, which is why it is known as yellowcake.

So if you're going down the enrichment route, you need to find a way to take that uranium, which is a solid when it's on the bottom of the yellowcake, and turn it into a gas because almost every enrichment technique that's been done thought involve a gas going through a process. It now turns out, more or less by accident, that the only uranium chemical compound that is a gas at reasonable temperatures and pressures is uranium hexafluoride, which is uf6, so one uranium atom, six fluorine atoms, any of Those of you who know a lot about chemistry can probably guess that anything containing 6 fluorines is going to be a nasty toxic substance and that's certainly true for uranium hexafluoride, so grab your Rhenium Hexafluoride.

I have a photo of one of the huge barrels that are stored here and are going to an enrichment plant. We'll talk more about enrichment later, but that separates the slightly lighter uranium-235 atoms from the slightly heavier uranium-238 atoms. and then you go to the conversion to metal and to the manufacturing, you can see there a ring of I think it is metallic plutonium in that image, now in the lower path, which is the plutonium path, you take that yellow cake that you got by grinding the uranium that you care about and you send it, you turn it into something different, you can turn it into metal or you can turn it into oxide depending on what type of fuel you're using in your reactor, then you turn it into fuel and you put that fuel in. in the reactor, it stays in the reactor for a while, generates some fish, you end up with plutonium in the spent fuel, you take the spent fuel and after storing it in a pool for a while to let it cool a little, you send it to the reprocessing plant where the plutonium is chemically separated and then you send it to the metal conversion and fabrication stage, so this is just a picture of the civil fuel cycle that gives you an idea of ​​the scale, so you start with one hundred seventy. tons of uranium as uranium oxide on the left side of the image that comes from their grinding plant after its extraction and ends up with only 24 tons of fuel going to the reactor and then as I which is on the right side and then as I mentioned that after it's been in the reactor for a while, you literally put it in a pool of water and of course you don't swim much in that

part

icular pool and you let it cool for a while and then you can OR reprocess it, you can also do for civil purposes to obtain plutonium that would then be used as fuel for civil reactors instead of material for

bombs

, or reprocessing can also be done with

bombs

, until this is one of the basic problems of the nuclear age.

The enrichment that is needed to produce highly enriched uranium is also needed to produce low enriched uranium for civil energy and it is more or less similar technologies that can produce bombs or fuel for civil power plants and similarly the reprocessing that some countries use to treat the spent fuel can then provide plutonium for civilian fuel or plutonium for nuclear weapons, then it turns out that all the ways humans have thought of so far to enrich uranium only do a little bit of enrichment at a time, so it concentrates the uranium-235 is a little more concentrated than it used to be, so you have to connect a bunch of them in what's called a cascade to have a lot of separation units, whatever separation unit technology you have and put feeding.

It comes in more or less in the middle of the cascade and then the material that is a little more enriched goes towards the end of the product of the cascade and becomes more and more enriched at each stage and at each stage the material that is a little The cascades Less enriched ones feed back to the previous stage, so you can eliminate more of these things, so these cascades can be quite complicated to model and certainly complicated to build and operate, but the basic notion is that you have a flow of things each ever more enriched. things heading towards the product and a flow of less and less enriched things becoming tails heading towards the end of the cascade, so if you want to produce highly enriched uranium you need many stages where you have a number each less time of separations. units at each of those stages as you move towards increasingly more enriched material, so you would place the feed on the largest of those green bars and then as you move toward the smaller and smaller number of machines at each stage, you'll be getting to the increasingly enriched material and then these things to the left of the highest green bar is where you're removing the tails from U-235 and then that relatively small green bar on the far left is where tails from U-235 would eventually come out. the cascade now, if you weren't going to enrich it so much, if you just wanted to produce low enriched uranium, you wouldn't need to, since there are so many stages in your cascade, okay, so there's a way to do it.

To set up these cascades, a technology that you can use is called gaseous diffusion and what it means is that you put a uranium hexafluoride gas at a fairly high pressure and you have a barrier that has little microscopic holes in it, and these atoms bounce back. in gas and uranium-235 atoms, because they are lighter for the same amount of energy, they bounce a little faster, so to have the same kinetic energy with less mass, you have to go faster, so there are a little bit higher. probability that one of those atoms will find one of the holes in the barrier material and pass to the other side of the barrier.

Well, there's just a slightly different probability. A very slightly different probability, so you need to have another barrier and another gaseous diffusion unit. another barrier and another gas and insulin diffusion unit and so on and in fact you need gigantic facilities. The facility pictured is one of the US enrichment plants that since they were decommissioned were absolutely enormous. I mean, they used bikes to go up and down the enrichment rooms because it was too far to walk to get there in a reasonable time and this process because you're putting this. high pressure stuff, you need these big pumps to get it through, it requires a huge amount of electricity, a giant amount of electricity, it's essentially a process of converting electricity into enrichment electricity, it's overwhelmingly the biggest cost you have when you're operating one of these gaseous diffusion plants in the United States, we still have a gaseous diffusion plant while we are in the process of closing the last gaseous diffusion plant, as does France, but we have been the last country that still operates large gaseous diffusion plants. gaseous diffusion. diffusion plants in the world and they are in the process of replacing them with centrifuges that I will talk about now, which are much more efficient, so in a centrifuge, what happens?

These now dominate global enrichments in part because they are dramatically more efficient, you know. reduction factor of 20 or more in the amount of energy required, then what happens in a centrifuge is that you have a tube that rotates. I'll get to that in a moment, when I have the image, let me talk about what's on this slide. First, centrifuge technology is problematic from the point of view of nuclear weapons proliferation because, because they are much more efficient, they are small and easy to conceal. A plant to produce enough material for one bomb each year. One bomb a year.

It would easily fit on this floor of this building and consumeless energy than a typical supermarket, so there are many buildings in any country that could easily be a centrifugal plant, from what you know when you look at it from, for example, a satellite. photography, so it is a problematic technology in that sense, it is technologically demanding although, as I will mention, there are debates about how technologically demanding it is that a black market net

work

led by Abdul Qadeer Khan of Pakistan was marketing centrifugal technology, which is really the preferred technology. For the determined nuclear cheater, they marketed to countries around the world, they sold them to Libya, they sold them to North Korea, they sold them to Iran, they also provided at least Libya with a bond design and possibly their other clients tried to sell centrifuges . to the Saiyan sodomists Iraq did not have the opportunity to accept the offer before the 1991 war intervened North Korea now has a centrifuge plant that we still do not know if they are manufacturing HEU there or not and if they have another plant, but they have not shown to the outside world or not is right, so let's go back to what a centrifuge is and how it

work

s.

The basic idea is to spin a tube with this uranium hexafluoride. gas into it at very high speeds and then, because the slightly heavier atoms are harder to deflect off course than with the slightly lighter atoms, the slightly heavier atoms end up being thrown against the outer wall of the tube and slightly the area towards the center of the tube ends up being slightly enriched with lighter atoms now because the designers are clever, they managed to discover that one guy called nut zippy agar in particular discovered that if you add a flow that goes up and down to the action of rotation, you can In fact, it makes the whole system much more efficient, so this flow goes up and down in the centrifuge caused by certain baffles, etc., that you put on the rotating element and so you get the product out of the middle and the queues.

From a little further away from the middle, what is so difficult about making a centrifuge? First of all, you need a really strong and lightweight material because this thing spins at an incredible speed and experiences accelerations thousands of times the acceleration of gravity. And if it's not very strong, it will break apart in the early days of the US program. I was told that workers referred to centrifuges as explosive self-disassembly machines because when they became unbalanced they would tear apart and pieces of metal would literally fly across the room. at something like the speed of sound, said this one of the What they have developed since then is to put casings around the rotating tube so that the rotating tube fails, the trunks don't fly across the room, so you need a very strong material and you need a really good support so that this something that is quite heavy can keep spinning for a long time and there are different types of bearings that people have developed over the years.

Many of the technologies that work remain originally classified. They were basically resting on a piece of piano wire, but as you can imagine, that didn't work very well, so there are, for example, ball bearings with little grooves cut in a particular way to allow certain types of oil to get in there. and keep the device lubricated, or there are magnets. bearings where everything just floats in a magnetic field Magnetic bearings are usually used for the top of the centrifuge, but in some advanced centrifuges they are also used at the bottom. This is President Zen Ahmadinejad of Iran visiting the centrifuges at Natanz.

You can see that they are almost like an experimental facility and that they are connected together in a very complicated way to create this cascading flow of uranium hexafluoride. This is kind of a more standard cascade, but to do it, you need a lot of centrifuges together to achieve substantial enrichment, as I mentioned now. One important thing to understand is that enrichment is a very non-linear process, once it gets going a little bit it speeds up and speeds up and speeds up, so when you pick up the 0.7% u-235 gun that is extracted from the ground up to four and a half percent for a civil energy reactor has already done three-quarters of the work to get up to ninety percent, which is why the international community is so concerned about r1 building up these reserves, some of them are at about four and a half percent, some of which are at about 20%, you know they are far from 90 percent in the actual percentage, but in terms of the actual amount. of the enrichment work that has already been done is a huge fraction once you get to the 20 percent enrichment level you have already done about 90 percent of the work to get to 90 percent enrichment, that means that if you have a stock of that kind of thing then it's much easier to have a small number of centrifuges in some secret place and do the final enrichment up to 90 percent with that smaller number of centrifuges, we'll talk about that later in the class, so a Obvious question is: how difficult is it to do enrichment and in particular to make these centrifuges that are relatively small and easy to hide and are there different views on this difficulty and is there different evidence supporting those different views e.g.

Iran, for example, which has, besides Israel, the most advanced indigenous science and technology base in the Middle East probably had complete centrifuge designs back in 1987 and it took them about 20 years to get a functional cascade that would actually enrich uranium. Despite that, building those types of centrifuges requires special materials that are hard to come by, so remember that I told you I needed these very strong and lightweight materials, which is why you will often see references to a particular type of steel called Mirage Eng steel. This It is a type of steel that is actually quite difficult to produce and there are only a few companies that make fused steel that is used.

In some centrifuges, carbon fiber is also used in centrifuges today, but again, carbon fiber of the required quality is often not easy to source or manufacture, they also require an exquisite balance if the centrifuge is even a slightly heavier on one side than the other. is spinning at these very high speeds and it will tear apart, so the AQ Khan Network centrifuges were discovered in Libya, for example, a colleague I was talking to at the International Atomic Energy Agency there was a centrifuge expert who They showed him the rotors of the centrifuges. that they were going to use for these centrifuges and he told me that the first thing I did was I took my bare hand and I grabbed each of the rotors because naturally there's enough of a pit in my hand that it doesn't matter how much you clean the rotors afterwards. that centrifuges will never be able to be used again, so they require exquisite balance of the bottom bearing, as I mentioned, it is often difficult to manufacture for this type of centrifuge and several countries have been working on that type of sensitivity, but on the other hand There are also several countries that have developed relatively simple centrifuges with a relatively small number of people in a relatively small period of time, so there are people who argue that we shouldn't spend so much time trying to essentially restrict the technology just because the countries, If they do it correctly, they can develop them themselves without needing all these specialties.

Now, as I mentioned, centrifugal plants can be pretty easy to hide. They take up relatively little space and little energy. The plant would produce enough hu, as I mentioned, for one bomb each year this building would fit the leak of uranium, yes, a little bit of uranium, but it's pretty modest, in part because the pressure inside a centrifuge is actually less than the outside atmospheric pressure, so if there is a small leak, it is air coming out. Instead of the hexafluoride matrix coming out of the centrifuge, then how to find them is an interesting problem. A few years ago, the U.S. intelligence community had a big meeting to talk about different ways that people and we're thinking about, you know, how you would do it. you detect centrifuges, could you hear the hum of centrifuges spinning from some distance?

Could the turn signal go back to the electrical system? Could you detect it through the cables of certain frequencies, etc., and a colleague of mine? He was assigned the job of being the reporter for this meeting and going to the individual groups that were working on different types of things and it was a very classified meeting, of course, but his summary of the situation was that no one has a good idea, so This is a photo of the North Korean centrifuge plant that no one knew was there until the North Koreans decided to bring the former director of the US nuclear laboratory, Siegfried Hecker, to visit it, so until they decided to tell us it was there no We knew it was there.

There it is in a building that used to be a fuel factory. The only thing unusual about that building is that they put an elegant blue roof on it. Why it's almost like they're trying to tell Americans to look at this building. Something interesting is happening. here and what's happening in this image is it looks like they're in the process of doubling the size of this centrifugal operation. They are basically building something identical in size next to the original building. This is a picture from a few months ago and now there is an identical blue roof over that area next to this building, okay, so let's talk about producing plutonium for a minute.

Okay, so you irradiated uranium in a nuclear reactor, like I said, U-238 absorbs neutrons and becomes plutonium and then you reprocess the spent one. fuel to extract plutonium from other things, so reprocessing involves well the main technique that was originally developed during World War II and has been used ever since: spent fuel is cut into small pieces, the pieces are thrown into the boil . nitric acid to dissolve uranium and plutonium and fission products and then you take that nitric acid and put it in contact with some organic material. Nowadays they use an organic solvent called tributyl phosphate and if you follow certain chemical steps you can extract the plutonium. the organic, the tributyl phosphate in the solvent and you leave the rest in the acid, and then it usually separates at the same time that the uranium is separated from the fission products, so, as I mentioned before, in You actually have three files per plutonium stack.

A lot of uranium and a lot of fission products resulting from reprocessing and this generally shows that reactors and reprocessing plants are typically, but not always, large, observable facilities, so this photograph is a photograph that a member of the Senate staff took during a visit to North Korea. nuclear reactor that has produced the plutonium that North Korea has so far, which was the focus of the first phase of the North Korean nuclear crisis in 1994, this is a schematic of that reactor, it has a fuel handling machine in The top, the reactor itself is basically a big stack of graphite reflector blocks and you have these fuel tubes going down into the reactor core and a concrete shield around the outside of all of this.

This is the North Korean reprocessing plant on the same site in Yum Goong. You can see that it is a fairly observable facility one thing, if you look closely you will see a tall tower with a long shadow which is the chimney to release some of the gases from the reprocessing which is quite characteristic of a reprocessing plant, usually these are fairly detectable facilities, but again, if you think carefully about it, it's possible that reprocessing could be done at smaller sites that would be less detectable, so a key question is how close the connection is between civil nuclear power and the use military nuclear power between power plants and bombs, so again enrichment and reprocessing are really the key technologies that pose serious proliferation risks.

If there is no enrichment, there is no reprocessing, you cannot manufacture the material needed for a nuclear bomb if you have a plant for any of those purposes. in your country, then in a sense you are one decision away from being able to make material for nuclear bombs. You could use those plants any time you wanted to make material for nuclear bombs. Yeah, some people, I think a lot of people assume when they're first learning. on this topic, oh, but surely to make a nuclear bomb I must need a larger, more complex and more sophisticated plant than just to let you know the relatively low quality material I need for a nuclear power plant, unfortunately, is exactly what Otherwise, you need a much larger one. and a better plant to do civil enrichment or civil reprocessing because you need to be able to make money from it so it has to be efficient etc. then you need it for nuclear bomb purposes and a key element of thatIt's just the scale, so remember that when you're making three four or five percent of material for a nuclear power plant, you've already done three quarters of the work to get to 90 percent, you need a lot of material for that nuclear plant. .

In a nuclear power plant, there might be 30 tons of that four or five percent enriched material in the core of a nuclear power plant, whereas remember the Hiroshima bomb, which is a very inefficient bomb that used much material such as nuclear bombs, weighed only 60 kilograms and an implosion-type bomb could weigh only 15 to 20 kilograms, so the official IEA figures for significant quantities are 25 kilograms of u-235 contained in highly enriched uranium u 8 kilograms of plutonium, as far as we know given that the Nagasaki bomb weighed approximately 6 kilograms of plutonium and that, as We talked about implosion devices that have been developed that are more efficient than the original solid core device, that the bombs They can be manufactured with a smaller quantity than the IAEA significant quantity, but the OEE number is designed to refer not only to the quantity that actually goes into the pump. but also the amount you would need counting the waste and you know various waste and so on that you would end up with and to refer to the relatively crude bomb that a country could make for its first, there are many Even so, there is controversy about whether those figures of the AIE should be reduced in any case.

The key technologies to worry about regarding nuclear proliferation and the intersection with civil nuclear energy are enrichment and reprocessing, so if a country builds a nuclear reactor and doesn't build enrichment and reprocessing, then it doesn't help getting too close to the bomb, it does help, certainly the reactor produces plutonium in the spent fuel, but if you don't have a reprocessing plant to extract that plutonium, then you can't use it. To make a bomb, civilian reactors are usually under the control of the International Atomic Energy Agency. They are all under IAEA safeguards unless they are in states that already have nuclear weapons, so removal of that would be detected material to separate plutonium.

Well, the new fuel in the reactor is this low-enriched material that can't be used in nuclear weapons, they can sustain a chain reaction in a reactor, but they can't sustain a chain reaction that grows explosively. Well, spent fuel contains plutonium, as I mentioned, but it would need to be reprocessed to get it out, but at the same time civilian reactors provide a base of trained people who understand nuclear reactions and who can give you the opportunity to network with other countries, for example. example the country that sells it the reactor and helps it build it, which can lead to more sensitive transfers, as for example in the 1990s, when Russia first contracted Iran to build a nuclear reactor in Bashir, in reality to finish one that the West Germans had started before the Iranian Revolution.

The United States tried to convince Russia not to go ahead with that contract and we were concerned about that contract, not because the US government thought that the plutonium for an Iranian nuclear bomb was going to be produced in a thicker form, but rather because hundreds of Iranians were coming to Russia and training at various nuclear institutes in Russia and making personal contacts that could help them obtain other technologies as it progressed. We discovered that they were already getting the technologies we were most concerned about, centrifugal technology, from the AQ Khan Network and not from Russia, so part of my career in the 1990s ended up being wasted trying to stop something that was difficult to happen. through another channel for them to provide a personnel base a set of contacts that provide a justification for carrying out enrichment or reprocessing whose military purpose would otherwise be obvious, so Iran, for example, argues that our program The enrichment process is completely peaceful, we are only producing fuel for our power plant and fuel for our research reactor.

We don't understand why everyone is so concerned about what we are doing. Finally, a nuclear energy program provides a bureaucratic power base that involves, you know, control of billions of dollars, a large organizational infrastructure, etc., for nuclear energy advocates, who in many cases can also end up advocating nuclear weapons. There are also opposite cases in which the nuclear energy industry, in part to maintain its supply from foreign countries, has opposed a nuclear weapons program in certain countries, so these issues are at the center of several current controversies. about nuclear energy. proliferation and nuclear energy, as I mentioned, Iran says its enrichment is purely for peaceful purposes and completely legitimate.

South Korea right now is in a situation where it's right across the border from North Korea, which already has nuclear weapons, something like two-thirds of the population in South Korea believes that South Korea should develop nuclear weapons, and South Korea is asking the United States, in negotiating a new civil nuclear cooperation agreement, to give it prior approval to move forward with the enrichment and reprocessing of American nuclear weapons. origin nuclear material and the United States is reluctant for fear that it could increase the risk of proliferation in South Korea, that it could make it impossible to convince North Korea to stop doing those things or that it could make it more difficult to convince others countries beyond South Korea. not establish its own reprocessing capabilities and similarly, there is significant controversy in the US government over what is sometimes known as the gold standard for civil nuclear cooperation.

A few years ago, the UAE signed the civil nuclear cooperation agreement with the United States that explicitly prohibited the UAE from building enrichment or reprocessing facilities and some people said we should have that requirement and all of our civil nuclear cooperation agreements They should be the standard we insist on, but a variety of other countries say no. I don't want to give up my rights. I have every right if I want at some point in the future to build an enrichment plant or a reprocessing plant to support my civil nuclear program. Japan as enrichment and reprocessing.

Why don't I see why I should? Giving up my right to be able to do this is not that I want to do it right now, but I don't want to trade away my rights for other people to say that we shouldn't insist on an explicit agreement to ban enrichment and reprocessing because if we do it with other nuclear suppliers that don't insist on it, will come and sell their reactors and have even fewer proliferation controls than we would have if the United States entered into civil nuclear cooperation agreements without such an explicit ban. Similarly, there is a group of major countries that export nuclear reactors or nuclear materials, what is called the Nuclear Suppliers group, and they have just agreed to a new set of criteria that basically says that we will not export enrichment and reprocessing technology to a state that does not yet have it. unless the state meets this set of criteria that we have agreed to now and we will have more information on the link between civil nuclear energy and proliferation later in the class, so again, just to recap two paths to the bomb, the plutonium route, uranium route, plutonium. the route involves a reactor, the uranium absorbs neutrons in the reactor, some of it is converted to plutonium, you take it out of the reactor and then it is called spent fuel, you process it chemically, a process called reprocessing, it separates the plutonium into the uranium root, you take the rhenium that you have extracted you convert it into uranium hexafluoride you put it in an enrichment plant that separates uranium-235 from uranium 238 and you end up with the weapons-grade uranium that you want for yourself and the nuclear bomb thank you very much