We have had lots and lots of requests to make videos about thorium. People get
really excited about Thorium. We delayed making the video until we had a sample
of thorium and a friend, Max Whitby, who makes nice samples of elements, has told
us, on many occasions, that thorium is the hardest element to get hold of.
One of the problems with thorium is simply obtaining it and there are now very, very
few places in the world where you can buy any.
Even laboratory suppliers don't sell it.
Finally just before Christmas he, gave us a sample.
Brady - What's that, you got it?
And here is the sample. This is a sample of two bits of thorium wire.
Now you can see the first problem with thorium is that it's radioactive,
so you can't post it. I have no idea how this sample got to London. It was brought
to me in London in Max's bag, and I brought it to Nottingham in my pocket.
Now there's no danger bringing it in my pocket because it's got a very thick
piece of plastic and thorium gives out relatively weak radioactivity,
so there is no radioactivity outside this. Thorium as an element is not very
widely used. It used to be used for the elements in gas fires. To get a good fire
you have some sort of ceramic element which gets hot and radiates the heat
because flames don't radiate heat very much, and thorium oxide is very stable so
people use ceramics based on thorium oxide.
But the reason that people get excited about thorium is because of nuclear
reactors. Nuclear reactors that are most widely used in the world are based on
uranium. You remember that different radioactive elements
can have so-called isotopes. These are chemically identical atoms but which
have different numbers of neutrons, and the uranium isotope which is used in
nuclear reactors is uranium 235, which when it is hit by neutrons can split
giving out more neutrons and you get to chain reaction. In a nuclear reactor you
want the reaction to go nice and slowly to keep the thing hot so you can turn
water into steam and generate electricity.
(V.O.) Thus we obtain a constantly increasing number of fissions called a chain reaction.
Prof. Poliakoff - If you're building an atom bomb -- a nuclear weapon --
you want all your uranium to go bang at the same moment.
The problem with current nuclear technology is first of all that
potentially there's a shortage of uranium.
It's a very rare element. Equally important
you can use the uranium in the reactor. The uranium 238, which is the isotope
that doesn't take part in the reaction, can be used to absorb neutrons and make
plutonium, which can then be used in nuclear weapons.
So if you build a reactor somewhere, there is a danger that the waste
products from that reactor (or some of the waste products) could be used for making nuclear bombs.
The atoms of the metals uranium and plutonium can be most readily fissioned to cause nuclear explosion.
And everybody in the world generally agrees that we have to try and reduce the number of bombs rather than
making it easier for people to make more bombs. Thorium can be used for a
completely different approach to nuclear reactors, but which still involves uranium.
The most abundant isotope of thorium is thorium 232.
If this isotope absorbs a neutron it becomes thorium 233; it's mass goes up by one.
Then sequentially, two of the neutrons split into a proton and an electron and
so it goes... jumps from thorium to protactinium to uranium,
so you generate uranium-233. Uranium-233 is a very rare isotope of uranium but
you can breed it from the thorium which you've got a lot of, and the uranium-233
can then do your nuclear reaction, break apart,
give you energy, just like the other uranium isotopes.
But the difference is that it can't produce plutonium and therefore it
cannot be used to make bombs
Of course you can say, well, if it splits in the nuclear reactor,
why can't you make a bomb out of uranium-233? And the answer is, in
principle you could, but as a by-product of all the nuclear processes
you also get uranium 232 and uranium 232 is a showstopper. It absorbs neutrons and
stops uranium exploding like a bomb,
so it's safe in that way. The other advantage of thorium is that it's more
abundant in the earth, and because thorium-232 is the principal isotope
compared to uranium 235, which is in only a small amount
there is an awful lot more thorium that could be used in reactors in the world than there is uranium.
(V.O.) - ...except you use a nuclear reactor to produce phenomenal quantities of heat.
Prof. Poliakoff - The disadvantage is that you need to have some neutrons to get the thing started.
You have to have a nuclear reaction to produce neutrons so that your thorium
will turn into uranium. But that also can be quite an advantage, because for
example you can put waste plutonium mixed with the thorium and you burn up
the plutonium and you get more fuel,
so "breeding reactor". The stability of thorium oxide, the one that was exploited
years ago in gas fires, is both an advantage and disadvantage.
It's an advantage because your fuel is very stable.
The downside of thorium dioxide being so stable is that you have to heat it to a
very high temperature to process it, and that's not easy. Relatively little work
has been done on thorium reactors, compared to the now 70 years or more,
nearly 80 years, of research that have been done on uranium/plutonium reactors.
And therefore, the engineering, the safety and so on
is not developed to the same level and the costs of building full-size thorium
reactors would be very considerable.
Brady - It sounds like if all things being equal
and we could start again, you would advocate going down the thorium route
and we are only doing the uranium/plutonium route because we've been doing it for so long.
Well you have to remember that uranium/plutonium route started because of the
Manhattan Project. The atomic bomb project.
I suspect that if nuclear power had been just started for civilian use, that the
cost would have been prohibitive and people might never have used nuclear
power, so it is built on the legacy of the weapons programs in many of the
major countries in the world.
We now have the situation where we understand how to handle radioactive
compounds. We don't understand entirely how to deal with the waste in practical
terms that we do in principle, so it would be much more feasible now to go on
the thorium cycle than it would have been in the 1940s.
Brady - If you'd like to see a bit more footage from this interview check out the links
on the screen or the video description. I'll also include links to more videos about
uranium, radioactive elements, and our trip to the nuclear facility at Sellafield.
Chris Maher - Yeah, they're centered uranium dioxide pellets
suitable for radiation and nuclear reactors.
Brady - And if you'd like to support periodic videos -- maybe sponsor an element or just help us out --
you can check out our Patreon page. That's patreon.com/periodicvideos
(V.O.) - The sure hand of science brings power unlimited from the magic of the atom