Kirk Sorensen, founder of Flibe Energy, discusses Thorium at TEDxYYC 2011. Below is the full transcript.
Listen to the MP3 Audio here: Kirk Sorensen on Thorium at TEDxYYC
Nearly everyone in the world is part of some community whether large or small and all of these communities have similar needs. They need light, they need heat, they need air conditioning. People can’t function very well when it’s too hot or too cold. They need food to be grown or provided distributed and stored safely. They need waste products to be collected, removed and processed.
People in the community need to be able to get from one place to another as quickly as possible and a supply of energy is the basis for all of these activities. Energy in the form of electricity provides light and air conditioning. Energy in the form of heat keeps us warm and energy in chemical form provides fertilizer, drives farm machinery and transportation energy.
Now I spent 10 years at NASA and in the beginning of my time there in 2000 I was very interested in communities but this is the kind of community I was thinking of — a lunar community. It had all of the same needs as a community on earth would have but it had some very unique constraints and we had to think about how we would provide energy for this very unique community. There’s no coal on the moon. There’s no petroleum. There’s no natural gas. There’s no atmosphere. There’s no wind either.
And solar power has a real problem: the moon orbits the earth once a month. For two weeks the sun goes down and your solar panels don’t make any energy. If you want to try to store enough energy in batteries for two weeks it just simply isn’t practical. So nuclear energy was really the only choice.
Now back in 2000 I really didn’t know too much about nuclear power, so I started trying to learn. Almost all of the nuclear power we use on earth today uses water as the basic coolant. This had some advantages but it has a lot of disadvantages. If you want to generate electricity you have to get the water a lot hotter than you normally can. At normal pressure 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.
Some water-cooled reactors run at over 70 atmospheres of pressure and others have to run at as much as 150 atmospheres of pressure. There’s no getting around this. It is simply what you have to do if you want to generate electricity using a water-cooled reactor. And this means that you have to build a water-cooled reactor as a pressure vessel with steel walls over 20 centimeters thick. If that sounds heavy that’s because it is.
Things get a lot worse if you have an accident where you lose pressure inside the reactor. 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. So water-cooled reactors are built inside of big thick, thick concrete buildings called containment buildings, which are meant to hold all of the steam that would come out of the reactor if you had an accident where you lost pressure.
Steam takes up about 1000 times more volume than liquid water, so the containment building ends up being very large relative to the size of the reactor.
Another bad thing happens if you lose pressure and your water flashes to steam. If you don’t get emergency coolant to the fuel in the reactor it can overheat and melt. Now the reactors we have today use uranium oxide as a fuel. It’s a ceramic material similar in performance to the ceramics that we use to make coffee cups or cookware or the bricks we use to line fireplaces. They are chemically stable but they’re not very good at transferring heat. If you lose pressure you lose your water and soon your fuel will melt down and release the radioactive fission products within it.
Making solid nuclear fuel is a 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.
Water cooled reactors have another additional challenge. They need to be near large bodies of water where the steam they generate can be cooled and condensed. Otherwise they can’t generate electrical power.
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.
One day I was at a friend’s office at work and I noticed this book on his shelf Fluid Fuel Reactors and I was interested and asked him if I could borrow it. Inside that book I learned about research in the United States back in the 1950s into a kind of nuclear reactor that wasn’t based on solid fuel or on water cooling. It didn’t have the problems of the water-cooled reactor. And the reason why it was pretty neat. It used a mixture of fluoride salts as a nuclear fuel, specifically the fluorides of lithium, beryllium, uranium and thorium.
Fluoride sales are remarkably chemically stable. They do not react with air and water. You have to heat them up to about 400 degrees Celsius to get them to melt but that’s actually perfect for trying to generate power in a nuclear reactor.
Here’s the real magic: they don’t have to operate at high pressure and that makes the biggest difference of all. This means that they don’t have to be in heavy thick steel pressure vessels. They don’t have to use water for coolant and there’s nothing in the reactor that’s going to make a big change in density like water. So the containment building around the reactor can be much smaller and close fitting. Unlike the solid fuels that can melt down if you stop cooling them, these liquid fluoride fuels are already melted at a much, much lower temperature.
In normal operation you have a little plug here at the bottom of the reactor vessel. This plug is made out of a piece of frozen salt that you’ve kept frozen by blowing cooled gas over the outside of the pipe. If there’s an emergency and you lose all the power to your nuclear power plant the little blower stops blowing, the frozen plug of salt melts and the liquid fluoride fuel inside the reactor drains out of the vessel through the line into another tank called a drain tank. Inside the drain tank it’s all configured to maximize the transfer of heat so as to keep the salt passively cooled as its heat load drops over time.