What is a LFTR? Molten-fueled, salt-cooled nuclear power | Molten Salt Reactors (incl Liquid Fluoride Thorium Reactor)

by George Lerner | Aug 25, 2012 |

Nuclear power produces a million times as much energy as fossil fuels, per pound of fuel, without releasing pollution or affecting climate. People think nuclear power releases lots of radiation, but actually fossil fuels release more radioactive material.

We don’t have to use a Light Water Reactor to generate nuclear power. Though we’ve been using LWR almost exclusively, it is not the best type of nuclear reactor, it is the design that coal/oil companies, who owned and still own USA Congress, picked in the 1960s.

As safe as our current Light Water Reactors (LWR) are, there are much safer nuclear reactor designs possible, that also produce dramatically less long-term nuclear waste. Some even use LWR “nuclear waste” as fuel. Some have been built and tested. Yet we’re not using them, for political reasons and from inertia. In most industries, major advances are welcomed — nobody wants to use 1950s computers or cars, yet we’re using 1950s-design nuclear reactors! Even the designers of LWR were pushing better designs by 1960.

Molten Salt Reactors use no water. Most designs of MSR use over 99% of the fuel (LWR uses about 2%).

Since they are not cooled by water, but by salts far below their boiling temperature, MSRs run at atmospheric pressure, eliminating the main risks of LWR (water-based pressure explosions and loss of water coolant).

Since the fuel is molten, dissolved in the salt coolant, and thermal expansion of the fuel salt strongly regulates the fission rate, the fuel temperature can never get high enough to melt the reactor vessel or components.

Less radiation has been released into the environment from all nuclear reactors combined, over the ~60 years we’ve used them, in normal operations and minor accidents and major accidents, than from a single year of using a single average coal plant. (Coal companies got coal ash classified as “naturally occurring radioactive material”, NORM, so they don’t have to clean it up. Coal plants even want cleanup of ash spills, containing radioactive and poisonous chemicals, to be paid for by their customers or the government — highly irresponsible.) There is radioactive radon in all natural gas.

Carbon dioxide from fossil fuels is increasing average global temperatures, enough to raise ocean levels to flood large areas of our cities (which are almost all next to oceans, major rivers, or large lakes). But this isn’t the worst effect of using fossil fuels. CO2 enters the oceans, and becomes carbonic acid; this acid dissolves sea shells including of the microscopic shells of plankton and coral; there are already areas in the North Atlantic where there is no more plankton — we are killing the base of the food chain, which will cause mass extinctions in the oceans. Even if you don’t care about animals, care about how many people around the world are dependent on seafood as their primary protein.

People died in the Fukushima area from the earthquake and tsunami due to fires from coal, oil, gasoline, and natural gas. Nobody died (or is likely to die) from the nuclear reactor failures. The only person found dead at the reactors, was from drowning. The reactors and cooling system survived the earthquake and tsunami — the tsunami destroyed the diesel generator supposed to power the cooling system when the reactors were shut down; the cooling system was run as long as possible on car batteries from the parking lot; nobody brought in a replacement diesel generator. TEPCO management left the diesel generator in the flood zone and didn’t build a sea wall, unlike every other nuclear power plant operator in the region. (Want “nuclear safety”? Check for companies, not just in the nuclear power industry, that ignore consequences of their decisions; companies that have no morals, positive or negative, so if something costs money they can ignore it.)

LWR uses solid fuel in carefully prepared fuel rods, and is cooled with water. High temperature water must be kept under very high pressure, or it boils. Solid fuel traps fission byproducts, which stop fission with <2% of the fuel used; then the fuel rod has to be replaced. All the uranium and plutonium in the fuel rod, with all the fission byproducts, have to be stored for 100,000+ years.

Molten Salt Reactors (MSR), including Liquid Fluoride Thorium Reactors (LFTR), have molten fuel that circulates through the reactor, so over 99% of the fuel is fissioned, and continuously refueled. The patent holder for LWR ran Oak Ridge National Laboratories for the Molten Salt Reactor Experiment, which successfully demonstrated the design and operation procedures.

Unlike water-cooled LWRs, MSRs are cooled by molten salt, very good at transferring heat. The salt coolant is several hundred degrees below its boiling point, so the reactor runs at atmospheric pressure. The fuel is strongly chemically bound to the salt, so MSRs have no chance of “loss of coolant accidents”. Since the salt doesn’t boil, MSRs have no risk of high-pressure explosions.

Since the coolant can’t boil away, and the fuel/salt expands/contracts with heat, and that thermal expansion strongly regulates the fission rate, all Molten Salt Reactors are very stable. The fuel can’t get hot enough to melt the reactor vessel, in any normal or emergency condition — even though the normal reactor temperature is much hotter than LWR (about 600°C to 950°C vs 350°C).

In an emergency, or for scheduled maintenance, turn off cooling on a “freeze plug” and the fuel quickly drains to passive cooling tanks, where fission is not possible. Power is required to prevent the reactor shutting down. This could be controlled by operators, remote seismic sensors, temperature sensors.

In a LFTR, (a type of Molten Salt Reactor with a “thorium blanket” to make U-233 from plentiful thorium for fuel) none of the waste is radioactive long-term. Fission byproducts are easily removed from the molten salt and safely stored. Almost all fission products have short half lives: 83% are safe in 10 years or less; 17% (135kg or 300lbs per 1 giga-watt-year electricity) are safe in 350 years. Elements with long half-lives stay in the reactor, where neutron bombardment causes them to fission or to decay into elements with short half-lives. (LWR leaves 250,000kg waste to store for 100,000+ years, per 1GW-year. Wow! See LFTRs No Long-Term Waste Storage.)

There are three possible fuels for nuclear reactors: uranium-235 (0.7% of all U), uranium-233, plutonium-239. MSRs can use all three. LFTRs can convert plentiful thorium (Th-232) to U-233. Other types of MSRs could convert U-238 (over 99.2% of all U) to Pu-239. This is done inside the reactor, no fuel fabrication needed. MSRs could eliminate (fission) long-term nuclear waste from LWRs, with all the safety of MSRs. (Note: Power generating reactors can’t produce weapons-grade U-235 or Pu-239; that requires specialty reactors, and very strict timing of procedures. A weapon made with reactor-grade U or Pu would explode “God only knows when”, probably in the terrorists’ lab.)

Thorium is 4 times as abundant as uranium, and virtually 100% of naturally occurring thorium is Th-232. Thorium is found in high concentration for mining with rare earth elements, in coal (far more thorium energy in coal ash piles than energy from burning coal), and in some types of sand. There are a few grams of thorium per cubic meter in almost all the surface of the earth.

LWR temperature is limited by steel’s ability to contain the water pressure; MSR has atmospheric pressure and is limited by the melting point of the reactor materials. MSR can operate with greater safety than LWR, at much higher temperatures.

In a MSR, the reactor is cooled by a molten salt (no water used). The heat from fission, much higher in MSR than in LWR, turns a turbine to make electricity (like in a LWR or coal plant, or with more efficient high-temperature turbines), and/or is used for high-temperature industrial processes (for example, desalinating seawater or making gasoline or a direct diesel-replacement, from CO2 and water).

With no high pressures, no water, and materials designed for high-temperature operation, MSRs will be much less complex (and therefore less expensive) to build than LWRs. They can be factory assembled, with modern quality control, modern sensors and monitoring, and shipped wherever needed. One design for a 220 MW LFTR would fit in a standard shipping container (think “18-wheeler” truck/rail/boat containers), a few more containers for the fuel cooling tanks, waste processing, electric generator, water desalinating equipment, and gasoline-maker.

If you include all the start-to-finish costs of generating power (but not even counting the carbon tax, pollution cleanup, or health care costs of using fossil fuels), electricity from LFTRs would be less expensive than from coal or oil or natural gas, per gigawatt-year electricity. MSRs also require very little land, and no water cooling, so can be located where electricity is needed, or even deployed for disaster relief.

Oak Ridge National Laboratories (ORNL) designed and built a Molten Salt Reactor from 1960-1965, and operated it for over 15,000 hours, see Molten Salt Reactor Experiment. They demonstrated the design, materials, equipment, procedures, operations, safety, use of different fuels. It was found to be an extremely stable reactor (rate of fission automatically regulated by the natural heat expansion/contraction of the molten fuel). They turned off the fan keeping the freeze-plug frozen on some Friday nights, left for the weekend, reheated the fuel on Monday and pumped it back into the reactor.

With modern materials, computer-aided simulations and design tools, modern manufacturing techniques, modern instrumentation and testing, and all the ORNL experimental results, we could build LFTRs, or other MSR designs, and then have factories mass-producing them, in 5 years. ORNL designed and built a MSR (most of a LFTR, just without the “thorium blanket” to breed fuel) in 5 years, with slide rules and good engineers.

(The Nuclear Regulatory Commission says will take at least 20 years; but they don’t want MSRs to work, they want to keep LWRs going, keep doing what they know, and keep their high-power high-pay jobs; the NRC takes over 5 years to license a new reactor that is virtually identical to the last one that was built. Maybe when China builds them and tries selling us MSRs, the NRC will wake up?)

Wind and solar are intermittent; they need either a source of “base load” power, or energy storage systems capable of powering a city through a month of bad weather. LFTRs make an excellent base load power to combine with solar or wind power, and easily follow the electric demand (when wind/solar are producing electricity, LFTRs automatically generate less), to replace our using coal and oil as fast as possible.

To prevent ocean acidification (CO2 entering oceans making carbonic acid) destroying the microscopic sea shells of plankton and other small organisms, killing the base of the food chain, leading quickly to mass extinctions throughout the oceans, we have to generate approximately the current total global energy use for over 10 years. We obviously can’t burn enough fossil fuels to undo the damage of using fossil fuels; we can’t build wind and solar fast enough to even meet the increase in coal use; nuclear energy mass produced is the only way to power removing CO2 from the air and oceans fast enough.

Source: Liquid Fluoride Thorium Reactor


 


 

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