I'm going to discuss salt-cooled fission and fusion reactors-
synergism for the rapid development of FLiBe (LiF-BeF2) salt technology.
I should mention I could not have given this talk three years ago,
because of new technologies in fusion, nothing to do with fission per se.
Technology advances resulted in salt-cooled fission & fusion machines using the same coolant-
FLiBe salt. That implies massive technological overlap,
and it creates very large economic, technical, and schedule incentives
for joint fission-fusion technology development programs and common supply chains.
So the discussion is coupling fission and fusion salt technology. A potential game-changer.
ARC, the affordable, robust, compact fusion and the fluoride salt-cooled high temperature reactor use the same coolant:
FLiBe salt, lithium-beryllium-fluoride salt.
And this is what creates a new synergism.
This particular fusion concept is being developed by Commonwealth Fusion.
They are up to about a hundred employees. Their initial funding trough was about a hundred-some million dollars. So they're
accelerating very, very, very rapidly.
The fluoride-salt-cooled reactor is being developed by Kairos Power, roughly the same size organization.
Needless to say this goes beyond just pure FLiBe salt;
it also applies to molten salt reactors, where you have fuel in the coolant.
That's a much broader broader perspective than the more narrow perspective I've given here.
The salt we're talking about is on the first line, FLiBe salt, melting point about 460℃.
Physical properties a little bit better than water.
Operating range: 550℃ to about 700℃ for most proposed concepts.
We start with ARC Fusion and the liquid FLiBe salt blanket.
Terms of fusion physics, this is a magnetic fusion device, Tokamak.
Nothing new in the physics. What is different?
It has a FLiBe salt blanket. That'll get you and the FLiBe salt itself.
Now, why a new fusion concept?
The development of rare-earth barium copper oxide superconducting magnets
is changing fusion futures. Most important observation-
In the last five years, methods have been developed to manufacture REBCO
superconducting tape. Now this particular
superconductor has been around for decades
if you want to buy five grams of it [laughter].
What happened is a manufacturer learned how to put it on a thin layer of tape, of steel tape.
And, of course, what's important about this is it's a manufacturing method;
it has to be on steel because of the magnetic forces in a large magnet.
But what it developed is a way to make a superconducting magnet using this particular material.
Their goal initially was for magnetic resonance machines used by hospitals,
Siemens, GE.
Fusion community then noticed, gee, that's a really interesting
material. Now,
what this particular new material allows is
doubling of the magnetic field
before bad things happen. And
it turns out the size of a magnetic fusion system for any given power output
varies as one over the fourth power of
the magnetic field,
one over the fourth power.
In other words, higher magnetic fields can shrink fusion system size
by an order of magnitude, more than a factor of 10.
Now this is all because somebody learned how to make something on a manufacturing scale. It wasn't a
breakthrough in science, it was a breakthrough in technology.
Increasing the power density by a factor of 10 has one other little implication;
the power density in the fusion blanket
increases by an order of magnitude.
And
if they had problems cooling a solid blanket,
you run up the power density by a factor of 10, and you're having a really bad day.
So the story here is manufacture of superconductor, run up the power density,
solid blanket looks like it might become a liquid blanket, whether that's your design goal or not.
But it starts out with a manufacturing revolution. It's not a science revolution.
Now the liquid FLiBe salt blanket meets the four fusion blanket requirements:
it converts 14-MeV neutrons into heat. You breed tritium
fusion fuel from lithium. You shield the external components,
that means the magnets, and you cool the plasma first wall.
And it's a big tank of FLiBe.
There's about a meter of space which is required to get the radiation fields down
so the magnets don't get fried in the most literal sense.
REBCO fusion favors FLiBe blankets. There have been many fusion blanket systems have been proposed, some of them partly developed.
The higher power densities in the blanket make it difficult to cool solid blankets.
The higher magnetic fields create large incentives to have a coolant with a low electrical conductivity
to avoid coolant-magnet field interactions.
The main competitor here is lithium-lead metal,
and of course, that's highly conductive and helping that across a magnetic field starts consuming a lot of energy
if you just moved up the magnetic field by a order of magnitude. And it's that combination of events
that there is now an interest in liquid FLiBe blankets. It all follows from a fellow who learned how to make
superconducting tape with really great properties.
Why FLiBe salt? The most fundamental level,
maximize tritium production.
These salts will have probably about a 90% lithium-6 to produce sufficient tritium for a self-sustaining fusion reaction.
This is a big issue in the fusion community, how to make enough tritium. Have to be self-sufficient, and
that's a real challenge. Now, the reason for FLiBe is it has beryllium in it,
and it turns out there's an (n,2n) reaction that generates more neutrons.
So high-energy neutrons hits a beryllium atom, you get two neutrons.
Second, of course, lithium-6 plus a neutron yields tritium. So this is a particular case where the choice of FLiBe is
based on reactor physics. We need the tritium.
Turns out it's also an excellent heat transfer agent compared to other salts, but the initial driver is fusion reactor physics.
Now FLiBe salt fusion blankets are applicable to all
fusion technologies. ARC is the first design using the new superconducting magnets.
It is likely that other fusion systems will follow because of the same rationale.
So we're talking about new material, a
couple of years later, a first concept for fusion based on the new material and going forward.
But we would expect that many other fusion programs are going to take a very hard
look at this magnetic material for the same exact reasons.
A case study of a change in technology, a second observation,
of course, is that the FHR which uses FLiBe salt and pebble-bed, I think many of you know about it.
This is a pebble-bed, salt-cooled reactor, same fuel is used in HTGR except the FLiBe salt,
of course, you need the coolant because it has high performance
capabilities. You can roughly increase the power density over an HTGR
by a factor of 10 by going to a liquid coolant.
And, of course, the fuel is the HTGR coated particle fuel noted for its high temperature capabilities.
Now the basis of choosing FLiBe salt for an FHR coolant:
first and most important one is that fluoride salts are compatible with graphite matrix-coated particle fuels. It's a chemical issue.
Second, fluoride salts enable low pressure operation; FLiBe boils at about 1400℃. And
third, among fluoride salts FLiBe has the best coolant properties in terms of heat transfer,
neutronics with low parasitic neutron absorption and the capability to dissolve fission products if failed fuel. They do require
high purity lithium-7 to minimize tritium production.
So, you know on the fission side everything is done to minimize
tritium production; on the fusion side
absolutely everything is done to maximize
tritium production or the system will not work. It's really elementary.
Now I want to briefly mention the market basis for all salt systems--
higher-temperature delivered heat to the power cycle.
I show water, sodium, helium, salt, the inlet temperatures, the outlet temperatures, and in the last column
the average temperature of delivered heat, which for water systems is about 280℃ or sodium, about 500℃, for helium about
550℃. Helium has a high peak temperature, but the helium going into the cores at a relatively low temperature.
Salt systems have an average temperature of delivered heat of 650℃, and that has a
very large implication in terms of economics on
a salt system versus any other system. And you know, this is strictly a characteristic of salt.
It's not a characteristic of fission or fusion or molten salt or whether it's a molten salt chloride system.
It's independent of all of those characteristics.
And of course, there's specific reasons for the FHR with FLiBe salt. You have a high-temperature fuel failure temperature;
you have a low-pressure salt and of course if you have failure in a
FHR, what you've converted it into is a molten salt reactor where you dissolve the fission products in the fuel.
So it's a great backup safety mechanism and, last of course, limited chemical reactions with air or
water. Now, what does this mean going forward?
What it implies is very, very large synergisms between FLiBe salt cooled fission and fusion reactors.
Obviously, the same concern, same issues for the terms of the basic
sciences of the salts, such as thermodynamics.
Exactly the same questions,
same design tools in many respects, thermal hydraulics,
instrumentation, CAD systems, a lot of commonality.
Technology, same materials issues, a little higher neutron flux, a lot of high energy neutrons,
but a lot of the same issues, particularly in heat exchangers,
tritium control. Now, this is important to remember, that the fusion system has a thousand times as much tritium.
So it has a little bit greater tritium control problem than the fission people have.
Three orders of magnitude is important. (chuckle)
Salt purification,
this is an issue.
When you have 14-MeV neutrons wandering around in FLiBe salt, you know, it's going to splatter them into all sorts of
interesting things that you did not want to see in your salt.
So you have to have chemistry control, you have to remove certain impurities that build up in the salt. If you have corrosion products
from your heat exchanger going through that 14 MeV
neutron blast, you're going to see some interesting chemical species.
So you do have a salt cleanup system that you have to address with many of the same issues. There's some specialty
concerns but many of the same identical issues and of course power cycles because it's you know, it's a salt.
Last, I think perhaps,
most important, in the long-term is a supply chain in terms of equipment.
You know,
it's one thing if you're developing a pump, and you could go to the pump manufacturer and say, "Oh, I'd like to buy
a pump.
Take me a lot of time, I've charged a lot of money. That doesn't look like a great market."
On the other hand, if the pump supplier recognizes there might be two or three or four or five
customers, suddenly his
enthusiasm for helping you develop a pump for one of these salts is going to be substantially greater.
Well, the supply chain is a big thing. Of course, FLiBe salt,
the same FLiBe salt, the same identical supply chain, and of course lithium isotopic separation.
Same problem except the fission guys want the lithium-7 and the fusion guys want the lithium-6.
But what you see here is this commonality of problems, commonality of challenges,
commonality of
opportunities.
And I think that's the really important message here that
we're going to begin to see, I think, from the fusion community over the next decade
pouring increased resources in this specific area,
where there's a lot of chances for cooperation between the two communities.
Major salt players today, of course, Kairos, the Department of Energy, NE, fusion,
EERE, I didn't go into the discussion of this. It turns out that our solar-concentrated solar power people
want to build the next generation of solar power towers using a chloride salt that operates at about
700℃ and sodium-potassium-magnesium salt. And it turns out the chemistry and other factors results in a lot of overlap
between the CSP people and the fusion guys and the fission guys.
Now their catch is that they want to build it in the next five years.
And that means they're gonna have to have a pump that oh, let's see, what's the height of that tower?
Well, it's about 300 feet. There's going to be a high lift pump. So there's some other people out there
who have a sudden interest in high-pressure drop pumps
for salts that are chemically reducing conditions. Many universities, MIT
of course, are doing salt irradiations as I'm sure you're well aware of, Wisconsin with FLiBe loops,
corrosion loops, and lots of other universities in various areas.
And, of course, there's a growing effort overseas, SINAP in China.
There's ongoing work in the United Kingdom and in the European
community. So what we're beginning to see is a rapidly expanding community both on the fission side and on the solar side and
on the fusion side with lots and lots of overlap of technology.
Synergisms can accelerate the development of all salt systems, and
so the next step is the strategy to maximize benefits of cooperation.
I'm just going to stop there and open it to any questions you might have. Thank you very much.
Q: Rol Johnson from Muons, Incorporated. There's one advantage of the
YBCO, or rare earth, the
superconductor that I think is actually put on Hastelloy at times." A: "Yes, and it's very strong."
Q (cont): "One thing that you can also add to your list of advantages is this its very radiation resistant
and we've actually done an SBIR program studying that for that purpose."
A: "But most importantly, it allows doubling the magnetic field for the fusion guys. That's the
thing that really sets it apart from the other
superconductors." Q: "I also wanted to comment about the use of
the lithium and fission reactor, yes, we actually are looking at using a natural
isotope ratio lithium in the molten salt that we'd like to use to make tritium for the NNSA.
So there's another
possibility."
A: "I won't go to the defense applications of which there are obviously many. That's a separate community,
but I'm sure they're keeping notes.
There will be some papers out on this; if you have any interest, send me an email, and I'll be happy to send you
the four-pager we have on this. There will be some more detailed papers out in addition.
You can go to the Commonwealth Fusion website and they they'll provide you lots more information on what's happening in the fusion side
But as I say, my guess is within about three or four years you may have a session on fusion salt systems,
maybe three years.
Thank you very much.