Almost all the nuclear power we use on Earth today uses water as the basic coolant.
At normal pressures water will boil at 100 degrees Celsius.
This isn't nearly hot enough to generate electricity effectively.
So water cooled reactors have to run at much higher pressures than atmospheric pressure.
And this means you have to run a water cooled reactor as a pressure vessel.
If that sounds heavy that's because it is.
We were looking at a nuclear reactor and they tend to be heavy and you need to have a large
amount of shielding.
My dad worked on the snap reactor for NASA.
Did he really?
What my dad did was that he shook the shit out of it.
They would see what broke.
Then they would fix it, shake it again.
See what broke, fix it again.
Nice.
Then they ran it for 1,000 hours.
Up power, down power.
They were going to put it in a Saturn V rocket.
Send it to the Moon.
Never did that.
Send it to the space base that they never built.
Put it onto Mars but they never did that program.
I know.
It's a shame.
We presented this at the Nuclear and Emerging Technologies for Space conference, to accommodate
space travel or off-world living.
That brings in a whole set of more robust variables that need to be attended to.
Nuclear reactors in space, like you just said, they are under such extreme conditions.
You know, the shuddering of the rocket as its going up into space.
The g-forces, the vibrational problems.
But mass is everything in space, and so if you can have a much lighter reactor let's
do it.
Well your choices are limited.
You're not going to make a light water reactor that you need this really thick pressure vessel.
Let me diss on water a few more times.
It's a covalently bonded substance.
The oxygen has a covalent bond with two hydrogens.
Neither one of those bonds is strong enough to survive getting smacked around by a gamma
or a neutron.
And sure enough, they knock the hydrogens clean off.
Now, in a water cooled reactor, you have a system called a recombiner that will take
the hydrogen gas and the oxygen gas that is always being created from the nuclear reaction
and put them back together.
It's a great system as long as it's operating and the system is pumping.
Well, at Fukushima Daiichi, the problem was that the pumping power stopped.
At high temperature H2O can also react with the cladding to release hydrogen.
Or damage the cladding, releasing radioactive isotopes.
These 2 accidents illustrate the need for a coolant which is more chemically stable
than H2O.
In a community on the Moon we would live very close to your power source.
This isn't something that's going to be far away.
If the power source were to fail, you're going to die really quickly.
So I thought, if I were living on the Moon and I was totally dependent on a power source
I'd want one that I'd just about feel comfortable living right on top of.
Three Mile Island, Chernobyl and Fukushima were all radically different incidents.
But what all 3 had in common was how poorly water performed as a coolant when things started
to go wrong.
Steam takes up about 1,000 times more volume than liquid water.
If you have liquid water at 300 degrees Celsius and suddenly you depressurize it, it doesn't
stay liquid for very long it flashes into steam.
That's scuba tank, hot scuba tank, full of nuclear material.
At Three Mile Island, water couldn't be pumped into the core because some of the coolant
water had vaporized into steam.
The increased pressure forced coolant water back out, contributing to a partial meltdown.
At Chernobyl, the insertion of poorly designed control rods caused core temperature to skyrocket.
The boiling point of the pressurized water coolant was passed, and it flashed to steam.
It was a steam explosion that tore the 2,000 ton lid off the reactor casing, and shot it
up through the roof of the building.
At Fukushima, loss of pump power allowed the coolant water to get hotter and hotter until
it boiled away.
These 3 accidents illustrate the need for a coolant with a higher boiling point than
water.
When you put water under extreme pressure like anything else it wants to get out of
that extreme pressure.
Almost all of the aspects of our nuclear reactors today that we find the most challenging can
be traced back to the need to have pressurized water.
Water cooled reactors have another challenge.
They need to be near large bodies of water so the steam they generate can be cooled and
condensed.
Otherwise they can't generate electrical power.
Now there's no lakes or rivers on the moon so if all this makes it sound like water-cooled
reactors aren't such a good fit for a lunar community I would tend to agree with you.
You see i had the good fortune to learn about a different form of nuclear power that doesn't
have all these problems for a very simple reason: it's not based on water cooling and
it doesn't use solid fuel.
Surprisingly it's based on salt.
Science allows you to look at everyday objects for what they really are.
Chemically and physically.
And it really makes you look twice at the world around you.
Your table salt is frozen.
That's a really strange thing to think about your table salt on your kitchen table.
It's frozen.
But once they melt they have a 1,000 degrees [Celsius] of liquid range.
And they have excellent heat transfer properties.
They can carry a large amount of heat per unit volume, just like water.
Water is actually really good from a heat transfer perspective.
Its really good at carrying heat per unit volume.
Salts are just as good carrying heat per unit volume.
But salts don't have to be pressurized.
And that- If you remember nothing else of what I say tonight, remember that one fact.
A nuclear reactor is a rough place for normal matter.
The nice thing about a salt is that it is formed from a positive ion and a negative
ion.
Like sodium is positively charged, and Chlorine is negatively charged.
And they go, we're not really going to bond we're just going to associate one with another.
That's what's called an ionic bond.
Yeah, you're kinda friends.
You know, you're-
Facebook friends!
There you go, facebook friends.
Alright, well it turns out this is a really good thing for a reactor because a reactor
is going to take those guys and just smack them all over the place with gammas and neutrons
and everything.
The good news is they don't really care who they particularly are next to.
As long as there are an equal number of positive ions and negative ions, the big picture is
happy.
A salt is composed of the stuff that's in this column the halogens, and the stuff that's
in these columns the alkali and alkaline.
Fluorine is so reactive with everything.
But once it's made a salt, a fluoride, then it's incredibly chemically stable and non-reactive.
Sodium chloride, table salt, or potassium iodide, they have really high melting points.
We like the lower melting points of fluoride salts.
Sometimes people go, oh you're working on liquid fluorine reactors, No, no!
I am not working on liquid fluorine reactors.
I'm talking about fluoride reactors and there's a big difference between those two.
One is going to explode, the other is like, super-duper stable.
I see moving to molten salt fueled reactor technology as a way to get rid of all the
stored energy term problems we look at in today's reactors.
Whether it is pressure, whether it is chemical reactivity.
Even the potential of fission products in the fuel itself to be released.
Those fission products are bound up very tightly in salts.
Strontium and caesium are both bound up in very, very stable fluoride salts.
Caesium fluoride is a very stable salt.
Strontium bifluoride another very stable salt.
In a light water reactor caesium is volatile, in the chemical state of the oxide fuel in
a light water reactor.
That's been one of the concerns about caesium release.
Caesium would not release from a fluoride reactor at all.
I actually met Kirk in a conference in Manchester in the UK as part of an event put on by The
Guardian newspaper.
Hi, I'm Kirk Sorensen.
They'd invited people to come and present their ideas and Kirk was 1 of the 10 people
that presented.
And I can remember sitting on the panel and just being kind of blown away by the fact
that there was an alternative version of nuclear.
I'm an environmentalist, my passion is climate change and energy.
I worked at Friend of the Earth, a green campaign group in the UK.
And I was an anti-nuclear campaigner.
But I've become a politician.
I will be faithful and bear true allegance to Her Majesty, Queen Elizabeth.
That's changed my life quite a lot.
I'm still getting used to it really, people call me �My Lady� and �The Barronnesse.�
Sellafield Limited is actively working with the 600 people who are going to be losing
their jobs at this time.
And everybody in the area is doing their very best to see if these people can find jobs
very quickly.
Sellafield is a unique site in the UK, and I believe it could become home of world leading
research into next generation nuclear reactors.
Such reactors- as well as being more efficient in their fuel use- generating no long lasting
waste, can be be designed to burn up existing stockpiles of Plutonium held at the Sellafield
site.
Despite greater acceptance of nuclear power there remain concerns about nuclear waste.
So, in light of this, is there more the government can do to support R&D into new nuclear designs
that will help to ensure we develop the safest and the most efficient reactors?
An engineer looks at the world as hundreds of things that are inefficient and should
be more properly designed.
When you tell an engineer that something is 20% more efficient he's like, yeah!
You tell him it's 50% more efficient, oh my gosh!
You tell him it's hundreds of times more efficient it becomes absolutely irresistible.
Making solid nuclear fuel is a complicated complicated and expensive process and we extract
less than 1% of the energy from the nuclear fuel before it can no longer remain in the
reactor.
The solid fuel will begin to swell and crack and the gasses, and you begin to get this
central void.
This is actually a gap in the fuel.
When the fuel swells to a certain point the clad can't hold it any more.
And when the clad can't hold it any more it's time to remove the fuel from the reactor.
At this point only a small amount of the energy has been consumed.
Wigner didn't like solid fuel.
He was a chemical engineer by training and he thought-
What process do we run chemically based on solids?
We don't.
Everything we do, we use as liquids or gasses because we can mix them completely.
You can take a liquid, you can fully mix it.
You can take a gas, you can fully mix it.
You can't take a solid and fully mix it unless you turn it into a liquid or a gas.
I believe part of this came from Wigner's educational background.
He was the only person or almost the only person who combined great skill as a nuclear
physicist with great skill as an engineer.
Wigner was a chemical engineer by training.
He was the only one who commanded both of those attributes.
And so he was able to see both the engineering and physics aspects.
He was a chemical engineer by training and he knew that in chemical processes the reactant
streams are almost always liquids and gases- they're fluids.
And in fluids a completion of the various chemical reactions are possible.
He looked at the nuclear problem and wondered if the same principle might not apply.
And they began investigating some very radical nuclear reactors, totally different from the
stuff we have now.
Wigner was not terribly successful in making converts in the nuclear community.
But he did make one convert, this guy, Alvin Weinberg.
He was his student during the Manhattan Project.
And Weinberg got it, he got the big picture.
We need liquid fuel.
I see it.
I see what we gotta do.
They were into small modular reactors before small modular reactors were cool.
Small, liquid-core, and then you have high-efficiency.
So there were a couple things that jumped right out at us.
The shielding weight became reasonable.
All these great benefits, how do we know this can work?
Quite simply because- because we did it.
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