So we'll heat the whole loop up.
Will pressurize this container and pump the salt into here.
And within here is the pump.
Will be a motor mounted up top.
A long shaft.
Then the bottom here is the impeller of the pump.
And there is a little picture of it here.
It is currently out being assembled.
The salt will be pumped through a test section.
Silicon Carbide pipe almost.
Currently it's upside down.
So if you imagine it flipped around upside down then inserted in this spot here.
We're going to fill it full of these little graphite spheres about three centimeters.
We'll fill it up about this much.
This kind of illustrating how many of these 600 spheres will be inside of it.
And the idea is we're testing a reactor concept where the fuel would be inside these pebbles.
Fuel pebbles in here and that's where the fission and the heat created.
And you've got flowing FLiBe over it.
We're using an inductive power supply which would be located on the outside here so it
comes in kind of through the wall here around the test section and it inductively heats
the pebbles without using fission it's kind of the only way to really get heat into the
system.
Can I ask them what the theory was between up around using a sort of a solid-fuel pebble
into the FLiBe rather than absolving the actinide into the salt?
Currently in this country we're not really looking at the molten salt fueled system.
So the driver from a programmatic research was solid fuel or the pebble.
But there must be some advantages to doing the solid fuel?
Or it's just it's just an extension from previous research study really?
The applicability of molten salt fueled system can be tested also in this system.
This is the base for an awful lot more of our testing for example we'll be doing natural
circulation safety testing.
We're doing a lot of corrosion specimens in here and a pump loop.
Silicon carbide even though we're using that as part of the design that's part of the test.
We're going to find out how that performs in a salt environment now.
There are a number of technologies that have never been done before in salt in here.
That rotating flange up there to allow things to shift between there.
The fact that we've got ceramic and metal pieces all in a single loop.
The joints, which are the nickel carbon-based joints, we can actually gasketed seals.
This one does flow so as the salt flows through it, send sound waves through.
Kinda like the car going by and make different sounds.
Doppler effect.
Doppler effect, there you go, that measures the Doppler shift.
Nice.
Kevin, mention the fluidic diodes.
What you can do with that.
Simply put it's a way to control a liquid flow without using a valve.
Part of the safety system that's used in the Molten Salt Reactor, we've had them in also
liquid metal reactors, where during normal operation the flow goes one direction through
it.
So it would flow, in normal operation it goes this way comes in the side and outside that
side.
And that creates a lot of resistance.
It spins around and comes out.
During an accident the flow reverses and goes this way and there's not
a lot of resistance going from here just flowing out there because it doesn't spin
around.
So that's after the particle bed test, that's the next set of tests, is to test this idea
for the safety system.
Most of the technologies that for a Molten Salt Reactor in the- As far as a thermal hydraulics-
well they're identical.
If you want to use the salt as a coolant it is just much, much, much easier to do something
that's non-radioactive.
So that's why we have the walk before you fly.
The direction that we've gone with the FHR technology is to look at the use of the same
kind of coated particle fuels that have been developed and tested for helium cooled reactors,
to get functional commercial reactors operating sooner than we can with liquid-fueled.
There are advantages specific to thorium-fuel over uranium-fuel when it's dissolved in molten
salt.
But first, let's start with some of the advantages common to all molten salt reactors- even those
which use solid fuel instead of liquid fuel.
Much of their research can be applied to liquid fuel molten salt reactors as well.
It's all laying out that fundamental research so that someday a thorium reactor you can
look up these papers and these publications that we've written here and be like oh this
is how we can do this, you know?
We're studying the fundamental science behind it, thorium fuelled or otherwise.
Hi my name is Grant Buster.
I'm a graduate student here at the thermohydraulics laboratory at UC Berkeley.
I work to develop a fundamental understanding of how pebble fuel moves through a reactor
core.
This is kind of the central column and this would be rotated around it's kind of an annulus-
a doughnut-shaped core.
Some will exit the reactor core quite quickly, while others will be held up for you know
maybe months at a time.
Every time we defuel a pebble we can assay these pebbles using gamma ray spectroscopy,
to discern what the burn up is of this pebble.
And whether it should be placed back into the core or whether it should be put in storage.
When you change your fuel type in a light water reactor it's a huge deal.
You have to you get the new vendor to design and you have to figure out the compatibility
of the new fuel assemblies with the old fuel assemblies and how you're going to shuffle
them and then the fuel will stay for three refueling cycles before it's fully spent-
It's very complicated.
In fact, if you think about how it is that you buy gasoline, compared to how is you buy
nuclear fuel these days- Buy nuclear fuel, you're locked into your vendor.
Yeah.
You know with gasoline, if you want new gasoline you just go to a different gas station, right?
And you fill up your tank with the new gasoline.
You don't worry about it being exactly identical.
Pebbles are very interesting because you can just put in a few pebbles to test.
Once you verify that the new pebble design that you have is working, you can start to
just substitute- because this is a homogeneous bed- new stuff.
Really, pebble fuel is fairly well understood it's been used since like the 70s now.
In Germany ther was a helium cooled reactor.
It was a dry bed so all the pebbles are weighted downwards.
Additionally they drove in control rods from the top.
If you can imagine- They crushed a lot of pebbles.
They didn't like round or make like a nose cone?
They did, but it's still a confined bed- There's not a whole lot of movement.
All the pedals are weighted under gravity and it was just not a very smart system.
But, with our system, everything's buoyant.
Almost neutrally so.
The pebbles are very light so to speak.
With molten salt coolant, graphite is less dense than salt, and floats, and therefore
fuel elements want to float.
We realized that it might be an advantage that pebble fuel floats if you have pebbles.
Because in a salt cooled reactor you want to have the coolant in a vessel that has no
openings around the bottom- That is a pool type of configuration, which means you don't
want to take the fuel out from the bottom of the reactor, right?
You want to take it from the top.
Gravity-driven control blades against the buoyancy, with degrees freedom on the bottom.
The forces on these pebbles are much much smaller.
So all we had to do was to find a 40% scale pebble material that would have the right
density ratio.
I went home that evening and went to the kitchen and started taking out my wife's plastic stuff
and cutting it up to see what would float and after destroying a lot of perfectly good,
you know, plasticware- I finally got around to cutting up a milk jug.
This is science at work.
Science at work.
And the stuff floated.
And then I looked on the bottom and I looked up the recycled number.
We sourced polypropylene tiny little pebbles and have a 13 thousands of an inch tungsten
wire through the center.
You can see the tungsten wires.
This is the control blade insertion experiment.
The blade is kind of a phantom because, plastic, you can't really see it so well.
You can see it moving all the pebbles.
Can see the shadow of it like Predator.
Yeah, yeah.
And you can actually image these large beds.
We've had to develop our own tomography software.
Tell where all the pins are.
Reconstruct how the actual three-dimensional pebble bed is, physically.
The stress chains that are actually created in these granular beds are quite complex.
The white lines where the blade was.
The concentrations of displacements right around the tip, those are the pebbles undergoing
the largest amount of imparted force.
You gotta see that they are propagated up quite far.
But once again- The the forces that we measured were one order of magnitude less than the
recommended force limits, so, we have very high confidence that this is a viable shutdown
method.
Will the molten salt provide lubrication?
Also lubrication, yeah, the lubrication can only help us really.
And I don't know if you guys have heard a lot about this but essentially SINAP, the
Shanghai Institute of Applied Science, has a very aggressive program with Molten Salt
Reactors.
They're doing a two-pronged approach where they build solid fuel test reactors with pebble
fuel, and also Molten Salt dissolved thorium test reactors as well.
Thorium?
Huh?
Thorium?
Yeah.
Yeah, dissolved thorium fuel in the molten-salt.
Similar to the Molten Salt Reactor Experiment in America.
Why aren't we working on liquid fuel?
Well our lab is is specifically designed the PB-FHR, the pebble fuel variant.
I mean the United States in general.
Oh- Licensing.
Licensing a liquid fuel reactor commercially, especially in the U.S. right now, is scary.
The U.S. is electing to go after salt cooled reactor at first.
It's not to say that the U.S. doesn't recognize that Molten Salt Reactors have some very interesting
advantageous capabilities, but, they are more technically challenging thing to do to.
So what is a fluoride salt cooled high temperature reactor?
Essentially it uses coated particle ceramic fuel.
Fluoride salt is a primary coolant.
Dr. David Holcomb is about to describe the safety features of ORNL's reactor design.
Just like the Berkeley pebble bed, all the safety features you'll hear also apply to
reactors where the fuel is dissolved into molten salt.
Our definition for strong passive safety on this is there's no requirement for an active
response to avoid either core damage or larger off-site release following even severe accidents.
And, that's ever.
This isn't three days this is this is ever.
If it just goes black you don't have to do anything.
Large margin to fuel failure.
Good natural circulation coolant.
And very good negative temperature reactivity- Shuts itself off rather than going out of
control.
High radionuclide solubility in the salt.
If you actually did have major fuel failure well you've converted your reactor into a
Molten Salt Reactor, if you go ahead and you fail all the fuel.
It's a low pressure system- There's no driving force to cause things to go outward are this
and which also helps you to make containment barriers because I don't need containment
barriers to be very strong, turns out we're designing a thing with four layers of containment
barrier because they're relatively easy to do.
You put a stainless steel dome around things and you've got a containment barrier.
We can use things like fusible links.
You can set melt point alloys that are 10 or 15 or 20 degrees above your normal operating
point and all your control rods are linked by a melt point and just let them passively
drop-in.
You can have a poison salt injection system which is just held shut by a melt point system
because we do have a lot more margin, and that something which is distinctive to us,
because we're not anywhere near temperature limits for short terms, for anything.
We just let things heat up until you get to a melt point and you stick in a lot of negative
reactivity.
You have hundreds of hours before you even get one in a million type failures, at 1,600
C, if you've operated at low enough temperatures, on this.
There is a large volumetric change in the salt with temperature which says that are
passive natural circulation cooling has got a very strong driving force, which means that
we can rely upon natural circulation, which gives us the ability of making very large
reactors because the natural circulation is not something which is limited, that I have
to wick stuff out to the side.
I can go ahead and just continue to use normal types of cooling and just reject it to the
the atmosphere, which says that my upper limit on my reactor size is actually my grid not
my reactor safety.
By focusing on the areas that give us the most leverage in terms of the benefits to
the salt and trying to, in other areas, stay with what's been done historically- It will
reduce the sort of number of fences we have to jump over.
I'm Raluca Scarlat.
I'm a PhD student at UC Berkeley.
I do research on fluoride salt cooled advanced reactors.
They're cooled by fluoride salts but the fuel is not dissolved in the salt, so it is in
solid form.
Its zoned meaning that you have the blanket of thorium serves a similar purpose as online
chemical reprocessing does in the LFTR reactor.
So this project was built maybe 4 or 5 years ago, and we were considering a very complex
core design.
So this isn't like multiple fuel regions really in the middle it's going to be just one type
of fuel?
Dark green were pure graphite pebbles for shielding.
The green was a thorium blanket.
There's a lot of potential but the designs right now are much more simple with just one
fuel lair and one outer shielding lair.
You couldn't actually do it then with thorium?
The PB-FHR we're designing is a 19-point something enriched U-235.
So just uranium, yeah.
Solid fuel is the fundamental barrier which impedes thorium being used as a much more
efficient source of energy.
We've studied and we tried to identify ways to design solid fuel reactors to utilize thorium
effectively, and it's very challenging.
Their capabilities look, in terms of fuel utilization conversion ratio, look remarkably
similar to Light Water Reactors.