okay so I'm going to talk to you now
about plutonium so I once refer to
uranium as the Boogyman of the periodic
table but if uranium is Boogyman then
there is a Hannibal elector 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 most
dangerous element when the human race
evolved it 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
cellfield uh in the northwest of England
um we're the nnl central
laboratory we're uh interested in um
plutonium because we need to be able to
recover it from spent rad radiated
nuclear fuel you can't just use
plutonium in a regular laboratory you
have to have a laboratory which is
specifically designed to handle it so
it's handled safely it's a at the point
in the periodic table where it does uh
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 1940 the reason
that it was made is that it's a
radioactive element and it decays away
with a halflife that depends on which
particular isotope it is if plutonium
was created at some time during the
formation of the solar system
it has all decayed away long before
scientists ever started looking for it
on Earth uh 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 uh see today is
plutonium and solution and that's really
interesting because plutonium's 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 a
metal uh you could take to it with a
hacksaw and the hacksaw blade would
break before you chipped any plutonium
off the Shia 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
plutonium is present in about 1% what we
do is use solvent extraction in order
order to remove the plutonium from the
fision products in the aquous phase and
move the plutonium up into a solvent
phase and that solvent phase is uh a
mixture of tribu phosphate and a diluent
called or orderless kerosene here we
have some plutonium nitrate and this
plutonium is in oxidation state four and
that's the oxidation state that's
extractable into triti phosphate I've
got two two separate Solutions here
they're 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
thalium 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 this is the solvent
phase you can see there it hasn't been
mixed yet the the solvent is less dense
than the acreas phase and resides on top
of the of the
acreas 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 bomb of
four people which had rather a strange
name this says up puu which means your
urine contains plutonium and the these
are people who through some sort of
accident had plutonium in their body
there was one person that was described
called margle who was working with a
glove box just like the ones that we saw
in the nnl labs and he had for some
reason a needle and he stuck 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 I it wasn't very high
concentration according to this he had
to provide a gallon of urine that's 4
lers 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 tribu phosphate ous 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 is going up into the solvent
phase it will form an emotion and the
solvent will then start to disengage
from the aquous phase and the two phases
will separate out
plutonium is formed in the nuclear fuel
of nuclear reactors uranium which has um
atomic number 92 can be transformed into
plutonium which has atomic number 94 by
absorption of neutrons so the uranium
absorbs neutrons that is the uranium 238
the sort of uranium that does not
spontaneously fishing 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
fishable element known as plutonium 239
so it's the in so-called if you like
inactive uranium isotope but that can
absorb neutrons and be transformed into
plutonium
okay that should be uh that should be
done
now looks like an emotion at the moment
as it separates you'll see that the the
top phase has got now got the color in
it the plutonium nitrate has now um
formed a chemical complex with tbp
molecules and those tbp molecules have
made the plutonium soluble in the
organic phase in the AR reprocessing of
radiated nuclear fuel all the fision
products would now be in this bottom
phase the plutonium and uranium would be
in the 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
and 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 manufactur of nuclear
bombs
extremely difficult it also has quite a
low melting point it melts at 639 de
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 3000° Centigrade some of the
um 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 uh separated from the aquous phase
and then new
aquous liquor is added to that solvent
to try and recover the plutonium from it
what we're going to do is remove remove
the acous 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 the
solvent and taking the Acres phase uh
out out from the bottom of course on a
on an industrial scale this is done with
um a variety of uh
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 and into a pure form so
that it can be reused in things like MOX
fuel which stands for mixed oxide fuels
so that's where you combine plutonium
with
uranium uh and you can um put it back
into nuclear reactors and and generate
new energy there is also an interesting
feature that when they Decay
radioactively they give off um 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-Cal 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 the short term if you are somebody
who makes bombs you have to be careful
that you don't build up 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 at top their steel Towers on
the 7th and 25th of May and the 1st and
5th of June the second problem is that
if you are storing
plutonium
which has come from Pro 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
food 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 tell you what Mark for
all the excitement about plutonium it
all looks pretty harmless there that
little that muddy Brown
solution well it's uh highly radi toxic
and you wouldn't want to drink that
either well I won't then even though it
looks a little bit like
Coke in order to get that plutonium back
into the aquous phase I'm going to use
two different techniques one is uh a
reduction to get plutonium 4 into a
plutonium 3 oxidation state so what I'm
going to do to this one is ADD uh a
chemical called hydroxyamine
nitrate this is uh another method we're
using a
complexant which
means that it forms a
chemical uh
molecular compound and the chemical that
we're using is called aceto hydroxamic
acid when we've mixed it all the
plutonium will be in the
bottom okay so this is the aceto
hydroxamic acid solution and it's just
disengaging now between the aquous 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 aquous phase and that
aquous phase can then be sent to
Downstream plants for final purification
and uh conversion into the final form
which is plutonium
dioxide
so oh yeah this hasn't been quite as
effective but you can see the the orange
color that was in there was in the top
half is um 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 Alfie
madic worked on plutonium during 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 10 mg 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 9 and2 mg of the 10 mg he'
lost and he would have hidden the whole
thing but he was so tired by then that
he didn't have the energy to repair the
tabletop 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
um plutonium 4 with Hydro hydroxamic
acid on the right here it's plutonium
the blue plutonium at the bottom is
plutonium 3 that's been reduced by
hydroxyamine
nitrate