I'm Kirk Sorensen, founder of Flibe Energy, a Huntsville-based startup dedicated to building clean, safe, small liquid fluoride thorium reactors (LFTRs), which can provide nuclear power in a way considered safer and cleaner than conventional nuclear reactors.

Motherboard and Vice recently released a documentary about thorium, and CNN.com syndicated it.

Ask me anything!

Comments: 853 • Responses: 62  • Date: 

Sid_Harmless189 karma

First up, I'd just like to say that I have an immense amount of respect for the work you're doing, and I don't believe it's an exaggeration to say that the technology may be seen by future generations as the defining one of the century.

My question is this: Do you believe that China's recent announcements that they intend to pursue the technology force the hand of Western states, much like the launch of Sputnik created a space-race?

kirksorensen110 karma

Hello Sid_Harmless,

Thank you for the kind words. I do believe China's recent announcement will have as much if not more significance (ultimately) than the events that surrounded the launch of Sputnik.

JayKay_0087 karma

Why is the United States so far behind the curve on Thorium reactors? From what I understand, they are much cleaner and safer than the current reactors in use in the US.

kirksorensen96 karma

Hello JayKay_00,

There has been very little interest in the US in molten-salt reactors since the early 1970s. When you understand MSR technology you begin to see how thorium can be used with extraordinary efficiency. If your paradigm is solid-oxide ceramic fuel, thorium's advantages do not appear particularly compelling. Therefore, until MSR technology was disseminated to a greater audience (via the Internet) it was hard to get too excited about thorium. Just my opinion.

b_ohare81 karma

Your presentation at Google is what got me interested in thorium. Pure awesomeness.

kirksorensen35 karma

Thank you b_ohare!

coveritwithgas74 karma

According to Wikipedia, you're five years from a prototype, which your own estimates peg at several hundred million dollars. A lot of your personal efforts are PR-focused. Your company may or may not consist of the four people on your webpage. What do you say to people who suspect you have a slim chance of delivering?

kirksorensen40 karma

Hello coveritwithgas,

I say "watch and see" if you think we're too risky to get involved. I say "come and talk to us" if you think we're worth talking to.

lastchance59 karma

What can an average folk (like me) do to help see this developed and deployed outside of China? No engineering background. Not rich.

kirksorensen62 karma

Hello lastchance,

Talk to people about it. You'd be amazed what a difference that makes. I've been blown away by the informal channels through which real resources ($, people, capability) have made their way to us.

giggsy66442 karma

ELI5: Why your reactor is safer?

Also, how would this fare cost-wise to a conventional reactor?

kirksorensen84 karma

Hello giggsy664,

The liquid fluoride fuel operates at high temperatures and at low pressures. The chemical form of the fuel and fission products is stable. Gaseous fission products are continuously removed. There is no fluid in the core like water that could undergo a phase change in the event of pressure loss. The core can be configured to drain passively in the event of a loss of coolant into a subcritical configuration.

darngooddogs36 karma

Bless you sir. I have been advocating this for about a year now (since I discovered it) and talking about it on reddit. People who are educated about it have trashed the idea because of "lack of infrastructure". What now doubters?

kirksorensen41 karma

Hello darngooddogs,

I love to study the history of technology development. The common thread is that most people don't believe it til they see it. But the ones who reap great rewards are the ones who see what it can be before it's there.

[deleted]36 karma

What would happen to a LFTR in a Fukushima style station blackout situation?

kirksorensen74 karma

Hello mrwadia,

If there had been a LFTR where F-D was, the detection of the earthquake would have caused the reactor to shut down, just as it did at F-D. In a minute or two, the freeze plug would have melted and the fuel would have drained into the drain tank, where it would reject decay heat to the air. If the system had been flooded, the rate of heat loss would have improved and soon the fuel salt would solidify. Cesium would have been trapped chemically (as CsF) in the fuel and would not have been in a volatile state with the potential to be released to the environment.

Optimash_Prime27 karma

Are they still doing construction on Memorial Parkway?

Also, what is your five-year goal with your company?

kirksorensen33 karma

Hello Optimash_Prime,

We would like to provide the electrical power for a military facility within five years. I would very much like that facility to be Redstone Arsenal here in Huntsville. We endured a week without power after the terrible tornadoes this spring (April 27th) and the community is still smarting from the after-effects.

kaythetall22 karma

What's your reaction to the initiation of Thorium reactors in India?

One one hand, any development of the technology is a good thing, but India has such an appalling safety record if anyone could screw this up it would be them. A poorly made Thorium plant would discourage any further investment, would it not?

kirksorensen23 karma

Hello kaythetall,

India's on the right idea with thorium but on the wrong track with solid-fueled reactors. They need to get on liquid-fluoride reactor technology.

SirPompitous15 karma

What are your thoughts on Helium-3 and its ability to produce safe and efficient fusion reactions?

kirksorensen22 karma

Hello SirPompitous,

I used to study helium-3 fusion reactors in great detail as a graduate student at Georgia Tech. The more I studied the less optimistic I became. I have kept tabs on technological developments over the years but haven't found anything to stoke renewed optimism in the field.

munkeegutz10 karma

No way! I'm graduating from Georgia Tech this semester! I hear that the Nuclear Engineering program is simply brutal (I'm in ECE).

Respect points +100

kirksorensen16 karma

I was in AE at Georgia Tech. I walked past the old nuke-E building on the way to the Graduate Living Center on 10th street and it always bothered me how they pulled off the word "nuclear" from the building leaving the unweathered white stucco behind. Which clearly read "nuclear".

SirPompitous6 karma

Thanks for the reply. I find it fascinating because of the space exploration implications. F.H. Cocks wrote a really interesting paper about how it is would make economic sense to send ships to the moon, where helium-3 is much more plentiful due to there not being an atmosphere. I believe some asian nations are still looking into this possibility. I think that the pursuit of fusion is about the only way you can make space exploration economically viable.

kirksorensen11 karma

"Plentiful supply" here is measured in parts-per-billion. It's pretty hard to get excited about helium-3 the more you look at the technology.

bryanobrian12 karma

Ironically, I just was interviewed for a position in Thorium Reactor research at UCI.

  1. What did you get your degree in?
  2. Have you worked at a reactor before that has achieved breeding?
  3. Also, my adviser also talked about the ability to reuse 'waste', except for the compromise Jimmy Carter made back at the tail end of the Cold War. What proposals would you make for the reuse of this 'waste'?

Thanks so much, sorry for loading up the questions.

kirksorensen20 karma

BS in mechanical engineering, MS in aerospace engineering, one class away from another MS in nuclear engineering.

Never worked at a reactor before. No reactors in the US currently operating have "achieved breeding", which I would define as "making more fissile material from fertile material than they consume."

I had a cousin who works at a nuclear plant who suggested I become an operator, but it would be a four-year detour from building LFTR and would just teach me a great deal about a type of reactor that is totally different from the kind I'm trying to build.

Multi_Pass12 karma

How close are we to having in home thorium generators? and how plausible would that tech be for private use? Could we use this tech in cars and other areas of life?

kirksorensen20 karma

Hello Multi_Pass,

I don't think we will be able to make thorium reactors small enough for home use. There could be a pretty good case for making one small enough to power a small town though (1-10 MWe). The reactors could make synthetic hydrocarbons from CO2 extracted from air and hydrogen separated from water in order to fuel cars.

TiltedPlacitan11 karma

I'm a software engineer. Hire me.

kirksorensen14 karma

Hello TiltedPlacitan, at some point, that may be a very good idea for both of us, but it's too soon to know now.

zenon10 karma

How hot does an LFTR run? I was wondering what kind of industrial processes that can run directly on the heat from the reactor rather than on electricity from the plant's generators.

Anything with "fluoride" in the name makes me nervous... How toxic is the FLiBe molten salt mixture? And how do you pronounce Flibe?

Can the reactor burn other isotopes than 233 U?

edit: Are you interested in funding from small (very small) investors :-)

kirksorensen21 karma

Hello zenon,

The core outlet temperature is around 1000K.

Fluorides have exceptional chemical stability. Perhaps you're confusing them with fluorine? The primary toxicity of flibe comes from the beryllium component rather than the fluorides. We pronouce flibe with a long I and a silent E, but I've heard French researchers pronounce it in a way that sounds like "flea-bee". The nice thing is that the name is made from "letters" from a universal alphabet (the periodic table).

Yes, other fissile isotopes than 233U can be consumed, but in each case whatever fissile we start the reactor on we are working towards an equilibrium consumption of thorium/233U.

shipmate10 karma

Hey kirk, I have a question for you.

I watched the video, and didn't seem to be presented with any evidence save for the fact that "Thorium energy is awesome and will save the world!" I googled a few things, and lo and behold, most of what I can find seems to be more along the lines of testimonials rather than evidence. I did find one site that had some fairly impressive statistics regarding the size of the reactor and its energy production capabilities. This is where I draw my question.

As a former Navy nuke, a reactor like this would do immense favors for the navy. As it stands now, reactor spaces on an aircraft carrier account for about 1/3 of the ships total volume. Most of these spaces are actually either support systems or propulsion systems that utilize the reactor's power, but nonetheless, a very large portion of the ship is utilized for the very big reactor, and it's necessary auxiliary systems. Why, then, has the Navy not pursued this type of energy? Every nuke has in them the same spirit of ingenuity that Admiral Rickover had, regardless of how much they hate the Navy (yes we all hate it!). A reactor like this would save so much space, reduce a bunch of cost, basically make our current warships so many times better. So why, Kirk, has the Navy, who should be more concerned about proper reactor operation and the safety of this country, not pursued such a dream?

kirksorensen11 karma

There are interested parties in the Navy. I helped a bit on a student design project at the Naval Postgraduate School five years ago:


Ninjatertl9 karma

how frustrating is it for you to watch the government fund all of the inefficient means of power, while thorium is essentially getting the cold shoulder? Also, how long do you think it will be until the U.S. will be 100% thorium?

kirksorensen16 karma

Hello Ninjatertl,

Very frustrating. My co-founder and I very much want the US and the world to be overwhelmingly powered by thorium by the end of the century and I think it's an achievable goal.

adelaarvaren9 karma

How would you compare your project to Terrapower, or other Traveling Wave Reactors?

kirksorensen10 karma

No where nearly as well-funded.

[deleted]9 karma


kirksorensen18 karma

Hello KalahariHoneyBadger, thorium exists in the crust of the earth at an average concentration of 12 parts-per-million. With the energy return that could be expected from a LFTR, even average continental crust would be "worth" mining for its thorium content. The concentrations in granite tend to be much higher--hundreds of parts per million if i'm not mistaken.

taccosnoger9 karma

Would you consider moving your work to another country if it offered better funding and more promise of being implemented? Why?

kirksorensen12 karma

Hello taccosnoger,

No, I'm not interested in moving this work to another country. I think we can get this working in the US.

Hagiology8 karma

What's your stock symbol?

And are you planning on building AND consulting thorium power plants, or just building them?

kirksorensen6 karma

Hello Hagiology,

We do not have a stock symbol nor are we publicly traded. It is our intention to build and operate LFTRs for power generation on important sites. Things may change but that's how they stand today.

forcefielddog7 karma

How do you expect to compete with the TVA? It'll be pretty hard to beat hydroelectric power as a source of energy.

kirksorensen14 karma

Hello forcefielddog,

TVA is very interested in carbon-free generation sources coming on line in their service area so that they can buy from them. All of our (limited) interactions with the TVA have been completely positive and supportive.

ddwgclan7 karma

I have three questions.

  1. Do you work the Scandinavian interests developing Thorium nuclear technology, are you in competition with them, or is your reactor based on different technology?

  2. Are you encountering considerable resistance from the established Uranium players in the nuclear market, or is that just a myth?

  3. Considering this might well be the magic bullet for energy production, are you getting any assistance at all from the energy dept?

kirksorensen14 karma

Hello ddwgclan,

  1. No, they're working solid-oxide thorium, we're working liquid-fluoride thorium.

  2. No, the conventional nuclear industry has paid no attention at all to us, either positive or negative.

  3. No.

duckandcover3 karma

Do you ever interact with the DOE or other gov't agencies on this? What do they say etc?

kirksorensen9 karma

DOE's a very large agency and yes, we talk to many of the people who work there. Some are very interested and want to help us, some are mildly interested and want to watch us, some think we're completely bonkers and want to stop us. It's a big place.

theorymeltfool7 karma

  • I saw a video that featured you on Youtube. Did you really just happen to notice that book on Thorium in your colleagues study?

  • Can I invest in your company yet?

kirksorensen8 karma

Hello theorymeltfool,

Yes, to the best of my recollection I just noticed the book on the shelf.

If you're a qualified investor with an appetite for high risk, high payoff proposals, then yes, there is the potential to invest.

haltingpoint7 karma

How did you get your start in this field and what is the story of how you founded the company? Basically I'm wondering if you're like, an engineer and did this in your garage with some small investors, or if you're a big business guy who got lots of VC funding and went to town.

kirksorensen27 karma

Hello haltingpoint,

I'm an engineer, not a business guy. I got into this because no one else was doing it, and I was sick of waiting.

zenfish7 karma

Do you see nuclear/energy sustaining the economy in Huntsville with all the cuts to NASA and Redstone coming down the pipe?

kirksorensen10 karma

Hello zenfish,

I very much hope so. I have a lot of friends who have left NASA in the last few years or anticipate doing so in the near future.

Tabdelineated6 karma

I think that there is a huge amount of potential for small self contained reactors.
How does your reactor differ from the hyperion reactor? (Another small self contained thorium reactor also under development.)
Edit: I thought they were thorium based, but it looks like it's uranium based

kirksorensen5 karma

Flibe Energy's LFTR and the Hyperion Power Module are extremely different, in just about every way. LFTR uses liquid fluoride fuel, HPM uses solid nitride fuel. HPM is cooled with lead-bismuth eutectic, LFTR uses fluoride salts in the fuel salt and coolant salt. HPM uses a steam turbine, LFTR uses a closed-cycle gas turbine. HPM has an ill-defined strategy for fuel recycling and waste disposal, LFTR's approach is simple and well-defined. HPM uses a fast neutron spectrum, LFTR uses a thermal-neutron spectrum. HPM uses uranium as the basic fuel, LFTR uses thorium as the basic fuel. Hyperion was run by a guy named Grizz, Flibe is run by two guys named Kirk.

cliftonixs6 karma

Hi Kirk. I wanna say, keep up the good work. We need guys like you and your company to make the world a better place. A very awesome Thank You!

kirksorensen8 karma

Thank you cliftonixs!

87linux5 karma

You're being very professional about all this. You do realize where you are, right?

kirksorensen19 karma

It's beginning to dawn on me.

quigley0075 karma

How does thorium fit in with wind and solar technologies. What advantages over these does it have?

Why would we choose thorium over wind and solar?

kirksorensen9 karma

Hello quigley007,

Wind and solar are intermittent and location-dependent. Thorium is energy dense and can be stored and transported to where it is needed, and its energy can be released as desired.

Gforce15 karma

I thought that I had herd you say that Plutonium-238 is a byproduct of LFTR reactors. Assuming that is the case and also that NASA is running out of their Plutonium-238 stockpiles used in space exploration. Would it make sense to push for funding into LFTR technology from the government based on that?

kirksorensen9 karma

Hello Gforce1,

Pu-238 can be made in thorium-fueled LFTRs, depending on how we decide to operate the reactor. It is neutronically costly to make, because every neutron consumed to form Pu-238 from Np-237 is a neutron that we didn't "spend" on fissioning U-233 and making electrical power. But there may be circumstances where it would be a good idea to accept this loss and make material for NASA.

700express5 karma


kirksorensen3 karma

Thank you, 700express...

snasu4 karma

I'm a recent graduate with a BS in chemistry. How far under qualified am I for this work, and what would it take for me to get a job working with something like this?

kirksorensen5 karma

The more you knew about fluoride chemistry or radiochemistry, the more qualified you would be for the work. I'm a good mechanical engineer but no chemist.

winterbeard4 karma

After reading every word of your website, and every word of every comment here...I'm blown away. Sid_Harmless hit it right on the head with his comment earlier.

You've got something really incredible, Kirk. I wish you the utmost success.

kirksorensen5 karma

Thank you very much!

striped_zebra4 karma

Hey Kirk, I've watched one of your lengthy presentations on LFTR and was really sold on the idea. I wish the Dept of Energy and NRC would focus on R and D and put more money in future reactor designs. I am actually about to start a 2 month program to become qualified in refueling reactors for US naval ships. I am very excited to learn the ins and outs.

As far as the LFTR, I am not completely sure about the fuel in the vessel. From what I understand, the thorium is the fuel source, which reacts with neutrons, fission and creates heat just like LWRs. What I am confused about is how this heat is transfered. It seems like the thorium fuel is in a liquid form with a floride salt moderator. I guess I dont understand the moderator and fuel being in a liquid form together. How does that work? In PWRs the fuel is encompassed in fuel cells and water flows over that to collect and transfer the heat.

Thanks for all your help and I would love to see LFTRs in my lifetime!!

kirksorensen4 karma

Graphite is used as the moderator. The thorium absorbs neutrons and decays to uranium-233 which is fissile. The fission of the U-233 gives off enough neutrons to sustain the fission reaction and to convert more thorium to U-233. The fuel salt is pumped throughout a loop that includes a core (moderated region) and a heat exchanger, where it gives up heat (enthalpy) to another salt, which is turn gives up enthalpy to the gaseous working fluid of a closed-cycle gas turbine, generating work.

hi_zen_berg3 karma

Are there university programs that specialize in LFTR reactor and process engineering?

kirksorensen5 karma

Hello hi-zen-berg,

Per Peterson's program at UC Berkeley is probably the best one in the world to get involved with if you're interested in MSR technology.

Radioactdave3 karma

Hi Mr. Sorensen! First, I think the way you're pursuing your thing is awesome and inspiring and I hope that you'll be successful with your work.

A few questions:

How easy is it to mine the ore containing thorium and are there any special geological constellations necessary?

As far as I understood one feature (from my point of view) of thorium reactors is the lack of waste that can be weaponized. In your opinion, is that why the technology was abandoned in the 70s, and do you think that it'll be a problem/obstacle in the future?

What's your favorite alcoholic and non-alcoholic beverage?

kirksorensen4 karma

Don't drink alcohol.

Diet coke.

colindean3 karma

From reading some of the responses, I can't tell if you're more business or more engineer. Where do you align yourself? You can go 2D on this, or add in another variable if you desire.

kirksorensen3 karma

More engineer, definitely.

asfdlkjasfd3 karma

What is the biggest engineering problem facing LFTRs?

Also in what way could an LFTR fail?

kirksorensen9 karma

Restoring the knowledge base possessed by about 100 scientists and engineers at Oak Ridge in 1972.

maverickaz3 karma

Kirk, I have great respect for technology pioneers such as yourself! Do you seen any future use for this technology in the field of space travel? If so can you go into detail? Thanks!

kirksorensen6 karma

I certainly hope so. When I first learned about the technology I worked to promote its use for space exploration within NASA.

HandsomestNerd3 karma

What is your post secondary education background?

Khoeth_Mora3 karma

I am a chemist with a great deal of interest in your work. My biggest question is, do you have any research positions open?

More to the point, how long do you think it will be until your company produces an efficient product at a profit?

kirksorensen5 karma

We will. Please keep us in mind. Chemistry is central to our success.

dancing_bananas3 karma

As a math major with an interest in physics I would really like to know what background does your employees have, are they mostly nuclear engineers and physicist? (I'm unsure if you have that in the US but we have it here)

What's the greatest technical challenge that you face and what are you doing to overcome it?

I'm glad you did this and I hope you get to my question.

Apple9873 karma

I'm a freshman in college, majoring in electrical engineering. Do you have any positions open (preferably four years in the future) I'd love to work for you guys. I firmly believe nuclear is the way to go and want to get involved to get us off fossil fuels!

kirksorensen3 karma

Four years in the future is a much more likely time for us to be hiring widely--study hard and keep us in mind!

[deleted]3 karma

What alloy do you plan on using for the reactor vessel and core structure, since Hastelloy-N is no longer in production and is extremely expensive? Also, what is the highest Li-7 enrichment your company can achieve, in order to offset the the high absorption cross-section of Li-6?

kirksorensen3 karma

Hastelloy-N is in production. I just talked with the representative of the manufacturer last year at Oak Ridge.

TehObviousAnswer3 karma

Hiring graduating Chemical Engineers?

kirksorensen3 karma

We will be. Keep us in mind.

warrickneff3 karma

Have you had any 'real' conversations with the U.S. NRC?

What unique licensing difficulties does your technology present - and do you expect the NRC to be understanding of such things?

Do you foresee another alternate technology being adapted before your own? What sort of drawbacks and benefits does your technology have over Travelling Wave reactors?

kirksorensen3 karma

We have not had any conversations with the NRC because our initial goal is to develop reactors to power military facilities, and they are licensed through military authority.

[deleted]3 karma

What's your education like? How does one get into a job like this?

PaleInTexas3 karma

Can a thorium reactor really use weapon grade plutonium and waste from older nuclear power plants as fuel?

kirksorensen4 karma

Potentially yes. There are disadvantages for using these materials to start the reactor but they may be outweighed by other advantages. It all depends on how important plutonium disposition is to the government. For our first reactor we're not planning to use any plutonium in the startup. http://energyfromthorium.com/pdf/NAT_MSBRfuelcycle.pdf

[deleted]3 karma


kirksorensen9 karma

I created the job.

FockerCRNA3 karma

I've read that Xenon has the potential to be used as a next generation anesthetic gas, less soluble than desflurane without being pungent. One problem is apparently the limited availability and expense of producing Xenon. You mention in one of your answers that Xenon is a byproduct of your process. Is the amount of Xenon produced in your LFTRs significant enough that it could be a source for the medical community in the future?

kirksorensen4 karma

Possibly. Xenon is the single most common fission product and it's very easy to extract from a fluid-fueled reactor like LFTR. It's longest-lived radioisotope will be completely decayed in about a month after removal, so xenon aged a month will be non-radioactive.

EternalStudent3 karma

What's your opinion of Radkowsky reactors?

kirksorensen7 karma

An extremely inefficient use of thorium.

aliaspete3 karma

is your company open to public investment?

kirksorensen3 karma


eigervector3 karma

Itinerant Nuclear Engineer here. Good to see someone pushing this technology, and I really hope it works.

You may see my resume someday; I want to get in to a part of this industry that is not stuck in the 60s.

How do you stand as far as licensing is concerned? Any buyers to make the NRC push the issue?

kirksorensen5 karma

I agree with you--I don't want to be in the part of the industry that's stuck on 50s-60s technology.

[deleted]3 karma


ElectricRebel3 karma

Given your history with NASA, can you talk briefly about LFTR and space applications in the long term? Obviously, the Mars Science Lab and other important projects are using RTGs, but these have limited output. Is LFTR better suited than other reactor designs for space applications? Would LFTR make sense for a nuclear-thermal or nuclear-electric rocket (I have read your blog posts in the past speaking negatively of nuclear thermal, but would LFTR help fix some of the problems such as thrust/weight ratio)? Or what about just as a very energy dense power supply for electricity for a space station/colony or other applications?

Feel free to answer this with as much or as little detail as you want. I'm just interested in hearing a brain dump since you have a background in both nuclear technology and space exploration.

kirksorensen5 karma

No time for a brain-dump. If you've read my postings on Selenian Boondocks you know my opinions on nuclear-thermal, and my calculations.

OzJuggler3 karma

Environmental groups campaign to have "renewable energy" (ie ambient energy) power plants installed on the basis that it is practical today and that generation IV nuclear power plants require huge taxpayer subsidies and are unproven. At the same time they typically demand capital investments and subsidies from governments to install CSP, PV, and wind farms on the basis that governments should be investing in the development of "renewable energy". Do you see any hypocrisy in that view?

What do you say to long term nuclear power detractors such as Helen Caldicott?

kirksorensen3 karma

Helen Caldicott believes in the "linear, no-threshold" response to radiation. Even by that (erroneous) assumption her proposed strategies are utterly in error:


Gnomie862 karma

What are the main advantages to this appeoach compared to the Rubia reactor?

And, while the Earth's thorium reserves are indeed vast, is it not also true that much of this is scattered so thinly that mining the stuff in an economicallu viable manner would be a tremendous challenge?

kirksorensen4 karma

Hello Gnomie86,

The Rubbia reactor needs an accelerator that is very big, expensive, and shuts down too much. LFTR doesn't need that, it controls itself.