REAL PLUTONIUM

REAL PLUTONIUM


okay so I’m going to talk to you now about plutonium so I once referred to uranium as the booty man of the periodic table but if you rhenium is sebou demand then there is a hannibal lecter of the periodic table and it’s a couple of places to the right and that element is plutonium plutonium has a really quite nasty reputation for example there’s a book here plutonium history of the world’s most dangerous element when the human race evolved evolved with uranium in the environment so we physiologically can actually deal with it to some extent plutonium is a man-made element it wasn’t there in the environment when we evolved and this means we’ve got essentially zero tolerance to it so that makes it quite dangerous for us we’re at Sellafield in the northwest of England we’re the NLL central laboratory we’re interested in and plutonium because we need to be able to recover it from spend reading irradiated nuclear fuel you can’t just use plutonium in a regular laboratory you have to have a laboratory which is specifically designed to handle so it’s handled safely it’s a at the point in the periodic table were it does interesting things there are not many elements which you can say when they were created you can sometimes say it was discovered in 1869 or 19 whatever but plutonium was made for the first time in 1914 the reason that it was made is that it’s a radioactive element and it decays away with a half-life that depends on which particular isotope it is if lutonium was created at some time during the formation of the solar system it has all decayed away long before scientist ever started looking for it on earth I have seen a lump of plutonium once I don’t think I could tell you where I actually saw it but it does just look like a shiny piece of metal what we’ll see today is plutonium and solution now that’s really interesting because plutonium has got some really intense colors and the colors change depending on the oxidation state of the plutonium as well it’s incredibly dense as a metal you could take two with a hacksaw and the hacksaw blade would break before you chipped any plutonium off the sheer density is shown by the fact that a golf-ball sized lump of plutonium would be over a kilogram easily really quite heavy stuff so here the intention is to recover the plutonium from spent nuclear fuel bouton is present in about 1% what we do is use solvent extraction in order to remove the plutonium from the fission products in the aqueous phase and move the plutonium up into a solvent phase and that solvent phase is a mixture of tributyl phosphate and a dill you in cold order order less kerosene here we have some plutonium nitrate and then this plutonium is in oxidation state 4 and that’s the oxidation state that’s extractable into tributyl phosphate I’ve got two separate solutions here the both plutonium nitrate they’re just at different concentrations it is dangerous for several different reasons it is dangerous because it is the basis of atomic bombs the second atomic bomb so-called fat man that was dropped on Nagasaki in 1945 contained plutonium and it was the plutonium that made it explode it was a bigger bomb in terms of the size of explosion than the first bomb that was dropped on Hiroshima but it’s also dangerous plutonium because it is very poisonous many heavy metals are poisonous particularly say thallium but plutonium is poisonous not just because of its chemistry but because of its radioactivity plutonium decays radioactively by emitting alpha particles helium nucleus and when that hits the cells of your body it can cause terrific damage and that can lead to cancer and so on I’m going to take some 30% tbp but this is the solvent phase you can see there it hasn’t been mixed yet this de solvent is less dense than the aqueous phase and resides on top of the of the aqueous but you’ll see in a minute that that brown color will go up into the top phase according to this book there is a club or there was a club in Los Alamos the bomb factory where they developed the chemistry of plutonium and made the plutonium bone of four people which had rather a strange name this says you pee PU which means your urine contains plutonium and these are people who through some sort of accident had plutonium in their body there was one person that was described called margul who was working with the glovebox just like the ones that we saw in the NLL labs and he had for some reason a needle and he stopped the needle through the finger of one of his gloves and he pulled out his hand and saw that there was a tiny black speck in his hand which was a fragment of plutonium and although the doctors trying to dig this out for the next 50 years plutonium could be detected in his urine and it wasn’t very high concentration according to this he had to provide a gallon of urine that’s four liters before they could detect the plutonium but nevertheless he survived okay so I’ve got two samples there with plutonium nitrate at the bottom and tributyl phosphate or – kerosene on the top so what I’m going to do now is put them into this device which is called a vortex mixer so while that’s that’s mixing plutonium’s going up into the solvent phase it will form an emotion and the solvent and then start to disengage from the aqueous phase and the two phases all separate out plutonium is formed in the nuclear fuel of nuclear reactors uranium which has atomic number 92 can be transformed into plutonium which has atomic number 94 by absorption of neutrons so that uranium absorbs neutrons that is the uranium-238 the sort of uranium that does not spontaneously fission and provide the energy for the nuclear reactor the Hanford Washington active material production plant for uranium 238 the most abundant isotope in natural uranium is converted into a completely new fissionable element known as plutonium 239 so it’s the inner circle if you like in active uranium isotope but that can absorb neutrons and be transformed into plutonium okay that should be I should be done now looks like an emulsion at the moment as it separates you’ll see that the top phase has got now got the color in it the plutonium nitrate has now formed a chemical complex with tbp molecules and those TVP molecules have made the plutonium soluble in the organic phase in the reprocessing irradiated nuclear fuel all the fission products would now be in this bottom phase and the plutonium and uranium would be in this top phase here so you’ve separated them out plutonium itself the metal is actually very fascinating material I’ve never seen it but it’s meant to be very hard metal but it has a surprisingly large number of allotropes an allotrope is a different crystal structure plutonium has six or perhaps seven different allotropes which differ in their hardness their mechanical properties even their density this makes the machining of plutonium which is necessary for manufacture of nuclear bombs extremely difficult it also has quite a low melting point it melts at six hundred and thirty nine degrees centigrade which is really very low melting point for a heavy metal for example osmium which is not far away in the periodic table has a melting point well above three thousand degrees centigrade some of the isotopes of plutonium are so radioactive that they’re really quite hot so if you feel the sample some of them can even be glowing red hot but even the less radioactive ones apparently feel quite warm to touch though you have to be quite brave to touch them what happens in a solvent extraction process is that the solvent is separated from the aqueous phase and then new aqueous liquor is added to that solvent to try and recover the plutonium from it what we’re going to do is remove remove the aqueous liquor from this now from the bottom and replace it with some fresh liquor that’s got a chemical within it that will promote recovery of the plutonium from a solvent taking the ACO space out out from the bottom of course on an industrial scale this is done with a variety of devices why are you trying to get the plutonium on its own because it has to be disposed of in a special way or because you want to reuse it it’s separated and into a pure form so they can be reused in things like MOX fuel which stands for mixed oxide fuels so that’s where you combine plutonium with uranium and you can put it back into nuclear reactors and generate new energy there is also an interesting feature that when they decay radioactively they give off these nuclei of helium atoms so as you get an older and older sample of plutonium the helium builds up in this crystal structure so although it looks like a piece of metal in fact it has helium atoms inside it rather like the fruit inside the cake and because of this crystal structure you tend to have crystallites with boundaries so-called grain boundaries between the crystallites and the helium can accumulate on the grain boundaries and weaken the metal quite substantially the helium has two problems obviously in the short term if you are somebody who makes bombs you have to be careful that you don’t build that too much helium in your the core of your bomb because it then may not perform properly here in sequence are the four snapper blasts detonated atop a steel towers on the 7th and 25th of May and the first and per from Joule certain problem is that if you were storing plutonium which has come from reprocessed nuclear fuel and is just being stored at waste until it’s safe to be in the environment you will bury it somewhere in the ground in a very strong container and when you’re designing that container you have to allow from the fact that your metal will start producing a gas as it decays and therefore your container has to be able to withstand the internal pressure so it doesn’t suddenly explode which would be embarrassing if not for you for your grandchildren or their grandchildren when they suddenly discover that these secure containers have blown up did you did you just describe the explosion of a container containing radioactive plutonium waste as embarrassing yes you were right for all the excitement about plutonium it all looks pretty harmless they had a little that muddy brown solution well it’s a highly radio toxic and you won’t want to drink that either well I won’t you know that looks a little bit like coke in order to get that plutonium back into the aqueous phase I’m going to use two different techniques one is a reduction to get plutonium for into a plutonium 3 oxidation state so what I’m going to do to this one is add a chemical called hydroxyl amine nitrate this is a another method we use in a complex until molecular compound and the chemical that we’re using is called acetyl hydroxamic acid when we’ve mixed it all the plutonium will be in the bottom okay so this is the acetyl hydroxamic acid solution and it’s just disengaging now between the aqueous and the organic phase and as you can see the color in the top phase is completely gone now so that’s the solvent solvent is now free of plutonium and it’s come back into the aqueous phase and that aqueous phase can then be sent to downstream plants for final purification and conversion into the final form which is plutonium dioxide so this doesn’t mean quite as effective but you can see there the alien’s color that was in there there’s in the top half as and has been diluted now and most of the plutonium is in the in the bottom half as plutonium 3 so I have another story I’ve told it before but it’s really good and Brady wants to hear it again one of the people who taught me chemistry a professor at Cambridge Alpha Mandic worked on plutonium during the Second World War and one night when he was really quite tired he spilt the entire United Kingdom supply of plutonium which was ten milligrams onto the table the bench that he was working on he was really upset he’d lost the whole country’s supply so he got a saw and cut a hole in the top of the table he burnt the wood and from the ashes of the wood he got back nine and a half milligrams of the ten milligrams he’d lost and he would have hidden the whole thing that he was so tired by then that he didn’t have the energy to repair the table top so when people came in the next morning there was a big hole and so they discovered what’s happened so the one on the left here with the red solution is an plutonium for with hydroxy tor hydroxamic acid on the right here it’s platonic the blue tony i’m at the bottom is plutonium three that’s been reduced by hydroxylamine nitrate

Leave a Reply

Your email address will not be published. Required fields are marked *