Going Nuclear - Part 6 - Uranium Enrichment

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hello it's scott manley here with part 6 of going nuclear if you've been following the series so far then welcome back it's been a while but I've been doing my research now you might have some ideas about how we might go about building a nuclear weapon today we're going to cover the biggest roadblock the refining of the fissile material used in the core the main isotopes used in nuclear weapons are uranium-235 and plutonium-239 and the production of usable quantities of these materials represented the largest parts of the Manhattan Project it takes hundreds of tons of uranium and massive industrial operations to produce enough material to make a bomb the primary uranium processing facility was an okra JH Tennessee and the primary plutonium production facilities were in Hanford Washington it's worth checking out this video over a Cordys lab showing the effort required to refine uranium ore down to less than a gram of uranium metal and this isn't a typical of many oral refining processes by the way scaling up a process like this to the industrial levels needed to produce the tons of uranium required to build a reactor needed a whole lot of specialized installations however the chemical refining hardware was small compared to the equipment required for the enrichment of uranium from the 0.7% uranium-235 to the 80% uranium-235 used in the weapons the difference of three neutrons doesn't amount to much and is commonly stated that different isotopes of the same element are chemically identical which isn't strictly true but for uranium the differences are small enough to have not been considered useful for isotope separation during the Manhattan Project one thing that all the enrichment processors used in the Manhattan Project have in common is that they work with gases so that each individual uranium atom is isolated from every other one and they can move freely to be separated being a heavy metal uranium has a rather high boiling point so instead the enrichment processes would work with molecules like uranium hexafluoride the boiling point of uranium hexafluoride is about 50 degrees centigrade which makes it quite manageable from a thermal point of view also fluorine having only one stable isotope meant that the only thing different in the molecular mass was the uranium however squeezing all those fluorine atoms around a single uranium atom does make them much more interested in jumping off and on to other reactive substances and much of the scary fluorine rich compounds mentioned in the book ignition or their existence to the fluorine chemistry experiments in the Manhattan Project another molecule used was uranium tetrachloride which was less corrosive to the hardware but all the production also generated things like phosgene gas as a side product this was the input material to the first enrichment system used during the Manhattan Project the calutron which is essentially a mass spectrometer designed to electromagnetically separate a beam of uranium atoms passing through a magnetic field the different mast isotopes get deflected by a slightly different amount and collectors would be set up to accumulate each isotope the first such device was constructed using the old magnet from the cyclotron at the University of California Berkeley hence the name Cal U Tron an early test run of this calutron in January 1942 produced two micrograms per hour of 25 percent enriched uranium and this would eventually be scaled up to 50 micrograms per hour industrializing this process ultimately entailed the construction of over 1,000 calutron and with the war on there was actually a shortage of copper to make wires for the electromagnets instead somebody came up with a bright idea to substitute silver supplied by the US Treasury thirteen point three thousand tons of silver or 430 million troy ounces because the u.s. treasury only worked in ounces technically this was a loan from one part of the US government to another and it was supposed to be returned after the project there are some great description of the lengths they went to in their efforts to recover silver such as ripping up and burning the floorboards of the workshops and collecting the melted silver that ran off ultimately they would only lose a few kilograms while the calutron wood contributes to the Manhattan Project they generally wouldn't be used to enrich uranium after the war as other methods proved to be much more cost-effective and I should probably take a moment to explain efficiency all of these enrichment processes use energy to take an input mixture and separate it into two outputs with one being more enriched than the other now the calutron czar an example of an enrichment system which takes lots of power but also produces a large increase in the enrichment other processes may take less power but also produce a lower level of enrichment so comparing the enrichment efficiency of these isn't simple but scientists came up with a number called the separative work unit which can be applied equally to all systems now it's not work in the traditional physics sense rather it's a measure of the energy required for a given input and output composition and different processes can be compared by the energy requirements for each unit unit usually this is measured in kilowatt hours now early systems required megawatt hours / SW modern efficient systems are about a hundred kilowatts per unit it takes less than 10 units to manufacture a kilogram of a reactor agreed uranium and it takes about 200 units to make a kilogram of weapons-grade material so calutron sprue to be exceptionally power-hungry jus mainly to the energy required to ionize the material instead most current methods exploit the small difference in average velocities in the uranium isotopes in the gas phase molecules containing the lighter uranium-235 will have slightly higher velocities the nose containing uranium 238 the majority of uranium enrichment during the manhattan project used gaseous diffusion whereby uranium hexafluoride would be allowed to diffuse through a permeable membrane now grams law shows that the rate of diffusion is inversely proportional to the square root of the molecular mass so on the far side of the membrane you will have slightly more lighter uranium-235 only a tiny bit more roughly 0.1% change in the isotopic ratios from input to output to enriched uranium up to weapons-grade ratios requires thousands of stages arranged one after the other the Manhattan Project also used something called thermal diffusion and this worked on the principle where a thermal gradient in the gas will lead to the heavier molecules collecting near the cold end the Manhattan Project used long Cascades 15 meter tall columns with a heated core and cooled outer walls since the warm gases tend to rise the lower mass uranium-235 we tend to migrate upwards after a great deal of development work it was realized that the process would never be competitive with gaseous diffusion and it would be the only thermal diffusion plant ever built however it was used as the first stage of a multi-tier enrichment process used by the Manhattan Project thermal diffusion would enrich natural uranium up to about 2% enrichment that would then be fed into a gaseous diffusion plant which would bring the uranium-235 October 23% finally this would be fed to the calutron which brought the enrichment October 85% all the experimental processes had been combined in a race to produce the fissile material as quickly as possible but after the war the focus shifted to efficiency and gaseous diffusion was the clear winner in this case the thermal diffusion columns were shut down in the calutron stringent transitioned to isolating other isotopes the main process building at Oakridge became the largest building in the world it would be 50% larger than the pentagon containing almost 3000 diffusion stages and it wasn't the only building on site with dozens of other support systems housed in their own massive buildings since World War 2 however the gas centrifuge process has been developed and it has become the dominant process since is about 50 times more energy-efficient than gas diffusion it was originally developed in the Soviet Union by German scientists and the process uses gas dynamics inside the rapidly rotating cylinder the process actually shares a much in common with the thermal diffusion columns with the lighter isotopes migrating upwards to the war at the top but the rapid rotation serves to enhance the effect of the mass difference between the isotopes the faster rotation the better the performance of course the exact numbers are classified but it's believed that a typical cylinder may be about 10 to 20 centimeters wide and rotating somewhere between 1,000 and 2,000 times per second generating centripetal acceleration of about 1 million G this puts the surface velocity at supersonic speeds but of course the whole assembly is contained inside an evacuated casing with magnetic bearings used to eliminate friction the tolerance is required for constructing these are extremely strict any imperfection is amplified by the acceleration involved and there are stories of centrifuge systems being sabotage by deliberate mishandling by touching the equipment in the wrong way there's even some evidence that the Stuxnet malware was created to attack the old Iranian nuclear program by infecting computers controlling the centrifuges used for enrichment uranium enrichment and intentionally running the centrifuges in a manner intended to destroy them beyond all these gas processes I was surprised to discover that a chemical process was investigated and a pilot plant was built it turns out that in mixture with a different ionic oxidation states the lighter isotope prefers to go to the more ionized levels for example the Chemex process used uranium ions in hydrochloric acid and so uranium the the u4 plus ions would tend to more likely be uranium-235 compared to the uranium 3 plus ions and that enabled useful enrichment after multiple passes but the efficiency was about 375 kilowatt hours per separate of work unit which makes a fine improvement over gasps diffusion but ultimately it could not compete with centrifuges laser enrichment is also a possibility multiple processes have been investigated since in 1970s but the winner right now is a process called Silex which uses tuned lasers that can preferentially excite the molecules containing one isotope over another now this looks like it's a be much more efficient than centrifuge systems but there are people that argue that any improvement in efficiency is undesirable because it would make it easier for a state to enrich uranium in secret and I feel that this is an important moment to bring up the fact that most measures to limit the development of nuclear warheads by nations revolve around limiting enrichment capabilities technologies which can be applied to enriched uranium are strictly monitored which can present problems for technologies which have been an applications the old gas diffusion plants would be huge and building these without letting the rest of the world know is really hard as such technologies which improve the efficiency and shrink the scale of these processes don't present a problem for those working to limit nuclear proliferation and that is why Silex a process developed by a private Australian company has been declared a secret by the US government there's been cooperation here but it is almost unique that a foreign industrial process has been converted to a top-secret by the US government now to allow nations access to enriched uranium for peaceful power reactors the IAEA has worked with existing nuclear powers to establish projects like the international uranium enrichment center in arrancars Siberia where enrichment is handled by an existing nuclear producer with the non producers theoretically owning an equity state in the plant thereby giving them access to enriched uranium without actually giving them the technology to enrich it anyway I hope this has all been enriching next time we'll look in detail at how plutonium is manufactured I'm Scott Manley fly safe [Music] [Music] you

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Channel: Scott Manley

Views: 182,315

Rating: 4.9756765 out of 5

Keywords: nuclear, device, enrichment, science, engineering, manhattan project

Id: JNT28WKAxgs

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Length: 13min 34sec (814 seconds)

Published: Sun Jul 01 2018

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