LESLIE DEWAN: So I'm here because I
think I can save the world with nuclear power.
The slide is a little bit tongue in cheek, but not really.
So right now, the world's energy economy
is dominated by fossil fuels.
But that's untenable.
Just look at the air pollution in China.
You'd think that nuclear power would be an obvious solution
to the problem because it's a well developed technology
that produces large, scalable amounts of electricity.
But nuclear leaves us with its own very nasty problem,
which is nuclear waste, which is radioactive for hundreds
of thousands of years.
So imagine a technology that solves
both of these problems, the clean energy
production and the waste.
And this actually exists.
I have this nuclear reactor that can run entirely
on nuclear waste.
It consumes the waste reducing its radioactive lifetime
while simultaneously generating enormous amounts
of electricity.
Right now, just to put some scope on the problem,
there's 270,000 metric tons of high level nuclear waste that
exists worldwide, and no one knows what to do with it yet.
Most of this waste is just sitting
above ground in spent fuel casks like this waiting for someone
to come up with a solution.
And that's where my technology comes in.
We can take this spent nuclear fuel and extract almost all
of its remaining energy, which translates into a very, very
large amount of electricity.
To put some numbers on it, you can
take all 270,000 metric tons of spent nuclear fuel that
exists worldwide and turn it into enough electricity
to power the entire world for 72 years-- so powering
the entire world for 72 years, even
taking into account increasing demand, while simultaneously
getting rid of almost all of its nuclear waste.
So there's enormous potential here.
The reactor units are small enough
to be co-located with existing nuclear power plants.
So you can consume the waste without it ever
having to leave the site.
And this plant can also run on very low enriched fresh uranium
fuel, which let's it unlock 75 times more electricity
from a given amount of uranium than is
possible with conventional reactors.
The basis of our approach is a liquid
fueled nuclear reactor that's powered by uranium dissolved
in a molten fluoride salt.
The design is actually based on earlier work conducted
in the '50s and '60s at the Oak Ridge National Lab
in Tennessee.
That's where these images are from.
They were able to successfully build and operate
a similar plant called a molten salt reactor that
ran on fresh uranium fuel.
And they showed that it had many safety benefits.
But the project was canceled pretty quickly thereafter
because it was bulky, had a low power density,
and it couldn't be justified on its great safety grounds
because the world hadn't yet experienced Chernobyl,
Three Mile Island, or Fukushima.
So how does it work then?
It works, actually, because what we
call nuclear waste isn't actually waste at all,
because it has a tremendous amount of energy left in it.
Conventional reactors, which are shown in the figure here,
are fueled by pellets of solid uranium oxide that's
held in place by a thin metal cladding.
The metal has to be thin so that it doesn't absorb
too many neutrons, but having a thin metal cladding
means that it's readily damaged by the radiation that's
within the reactor core.
And the accumulating damage limits the amount of time
that the fuel can spend in the core
to about three or four years.
But the problem with this is that it
means you can only extract around
4% of the energy you could conceivably
get out of the nuclear fuel.
So that's, in a way, why the nuclear waste is so dangerous,
because there's so much energy that's left in it.
What we do instead in this design
is take out the spent fuel assemblies
from the conventional reactor, remove the metal cladding,
and dissolve the fuel pellets into a molten fluoride salt.
We don't have any cladding, any metal framework,
in our reactor, nothing to get damaged,
so we can leave the fuel in our reactor
for, essentially, as long as it takes
to extract all of its remaining energy.
And the cool thing is that this also
reduces our radioactive lifetime by a very large amount.
So conventional reactor waste is radioactive for hundreds
of thousands of years, but the majority
of the waste coming out of our plant
is only radioactive for a few hundred
years, which is still a long time.
But humans can build things-- structures and repositories--
that last for a few hundred years.
So that makes it solvable.
This is a very rough schematic of what the reactor looks like.
So up on the far left, you have the primary loop
that has the molten fuel salt flowing through it.
On the very far left, you have the reactor core
where the fuel salt is in a critical configuration, which
means you have a large, stable number of nuclear fission
reactions that are generating a great deal of heat.
This heat is carried from the primary loop,
through an intermediate loop, and into a power production
loop where it powers a turbine that drives a generator that
produces electricity.
So the right side of the plant is all very standard.
Now, just to recap here, the main difference
between conventional nuclear reactors and molten salt
reactors is that molten salt reactors
use a liquid fuel rather than a solid fuel.
But then-- this is what the next two slides
will describe-- what makes my company's design
different from the other earlier molten
salt reactors, the ones that were
abandoned in the '60s and '70s?
The main two changes we make are to modify the materials used
in the moderator and the fuel cell.
A moderator is used to slow down neutrons to the right energy
level so that they're more likely to induce fission.
The early molten salt reactors used graphite
as a moderator, which worked.
It was able to go critical.
But it made the cores very large and bulky, low power
density, expensive.
We came up with the idea of, instead,
using zirconium hydride as a moderator, which
is much more effective at slowing down neutrons
and lets our core be a lot more compact, power dense,
and cheaper.
The other thing we changed was the salt.
So the early molten salt reactors
used what's called Flibe salt, which
is a mixture of lithium fluoride and beryllium fluoride.
But using this salt meant that you
had to enrich the uranium 235 up to 33% to 93% uranium 235
is what your uranium enrichment had to be,
which is not commercially available because it's
very close to weapons grade.
And they also couldn't run on the spent nuclear fuel.
So what we did instead was switch it
to a different type of salt, lithium fluoride and uranium
fluoride, that lets us run on the very
low enriched fresh fuel or the spent nuclear fuel.
And you can see as well that we get a really big increase
in our power density at the same time.
Now, this one is by far the most technical slide here,
but it's worth it.
It's good.
So with our two new materials, the moderator and the fuel
salt, it's pretty simple substitutions,
but it enables a world of difference in the design.
So this is what's called the neutron energy
spectrum within the core.
Transatomic is the big blue line on this graph.
Because we're able to slow down neutrons
much more quickly from the fast region to the thermal region,
they're able to transition more quickly,
so we avoid this epithermal region in the middle.
Our line is much lower down there.
And that's good, because in the epithermal region,
you have a lot of neutrons lost where they're absorbed
by the wrong isotopes, they exit the system,
they're captured by things you don't
want them to be captured by.
So you want to avoid the epithermal region.
Which is good.
We do that.
We also, therefore, have more neutrons on the fast end
of the spectrum for breaking down the long lived
components of the waste and more on the thermal end
of the spectrum for power production.
So this is exactly the sort of dumbbell shaped spectrum
that you want here.
I talked before about the safety benefits of this type of plant,
and this is enabled by the liquid fuel.
This is one of the really crucial things about it
that they proved out at the Oak Ridge National
Lab 50 years ago.
In a conventional nuclear reactor,
you need a constant supply of electric power
to pump water over the core to keep it
from heating up catastrophically.
That's what happened at Fukushima.
But in a liquid fueled reactor, you don't need that at all.
What we have instead is what's called a freeze valve that's
at the bottom of the primary loop of the plant.
And the freeze valve contains a plug
of salt electrically cooled so that it's frozen solid.
If you lose electricity, through an accident say,
you lose cooling to the freeze valve, it melts.
And all the salt from the primary loop
drains into an auxiliary containment.
When it's in the auxiliary containment,
it's not near any moderator.
And also just based on its geometry,
it's no longer critical.
So it's not generating nearly as much heat.
And the small amount of heat that it does produce
can be sunk by natural convection loops that
don't require electricity.
And then over the course of a few hours--
this is the crucial bit-- it freezes solid.
So when it fails, it fails into a frozen mode
not like a liquid mode.
And this is that our reactor is what's called walk away safe.
So if you lose electric power, and even
if there aren't any operators on site, it'll coast to a stop
and stay that way indefinitely.
Here's another rendering of the design.
So the technology is great, but to get
these built, it also has to be cheap, of course.
And luckily, we have that going for us too.
If we use current construction techniques,
it's about 2/3 the cost of conventional nuclear power
right now.
And even more importantly, we can be cheaper than coal.
And these numbers will improve as we
move towards a more modular design and other more advanced
construction techniques that are being developed
in parallel in other parts of the industry.
We've raised significant funding so far,
in addition to money from the US Department of Energy,
filed patents on our design, and gotten a thumbs
up on the technology from our great advisory board that
includes the former chief technology
officer of Westinghouse and the head of MIT's
nuclear engineering department.
So just to wrap it up super quickly, because I'm
pretty close to out of time, what the world needs right now
is a cheap, carbon free alternative to fossil fuels
to feed its growing energy demand.
And this technology makes that possible.
So with this design, we've solved nuclear safety and waste
problems, we've beaten coal, and we've
made this safe, clean, and affordable answer
to what humanity needs for energy.
Thank you all so much.