What if we could design and build a nuclear reactor :
- That uses no water and so can’t have high pressure steam or hydrogen explosions,
- With fuel that can’t have a nuclear melt down, or melt through the reactor walls,
- That fissions over 99% of its fuel, so there’s no waste needing storage for hundreds of thousands of years,
- and some designs can consume spent nuclear fuel from other reactors?
Well, we’ve already built one, and we ran it for 5 years! (But you probably never heard about it…)
What Is A Liquid Fluoride Thorium Reactor?
A Molten Salt Reactor, such as Liquid Fluoride Thorium Reactor (LFTR, pronounced “lifter”) produces energy using a liquid (molten) nuclear fuel, not a solid fuel. MSRs also use a coolant that remains liquid at atmospheric pressure.
LFTRs are designed to convert Thorium (Th-232), an inexpensive and abundant material, into Uranium-233 which can then undergo nuclear fission. Other types of MSR can use spent uranium, depleted uranium, or plutonium, eliminating nuclear waste from solid-fueled reactors.
With liquid fuel and atmospheric pressures, MSRs solve the safety and waste disposal problems our current (1970’s design) Light Water Reactors (LWR) have.
With all the attention lately on nuclear waste, nuclear accidents like Fukushima, and producing energy without CO2 that increases climate change, we need to look at nuclear energy that is not from our current type of reactors.
Most safety concerns of LWRs are from using water coolant; MSR is a molten salt reactor (uses a special salt as coolant). The salt remains liquid at extremely high temperatures, there is reactor temperature can get high enough to boil the coolant. The fuel and coolant remain strongly chemically bound, don’t dissolve in water, can’t be carried by air, can’t enter the water supply or food supply.
All the nuclear waste problems of LWRs are from using solid fuel (less than 2% of the fuel gets used); MSR uses molten fuel, so can consume well over 99% of the fuel leaving only short-term waste.
With a reactor design that is inherently safer, the expensive “engineered in depth” safety equipment of LWRs is not needed, making MSR smaller and dramatically less expensive than LWRs. Molten Salt Reactors can be assembled in factories, much like large ships are built in ship yards, with modern quality control and sensors. There is minimal on-site construction beyond the building the reactor and operators would be in.
We abandoned MSRs in the 1970s (we decided to go with the liquid-metal-cooled fast breeder reactor (LMFBR) which produced reactor fuel faster). We later dropped the LMFBR due to proliferation concerns and reactor control issues.
We never came back to MSR, mainly from political inertia. We got the type of nuclear reactor the fossil fuel “energy experts” convinced the USA Congress to go with, the type that wouldn’t destroy the fossil fuel industries. Now, reducing CO2 production is so important we’re looking at nuclear power with renewed interest.
A demonstration Molten Salt Reactor (MSR) was developed at Tennessee’s Oak Ridge National Laboratory in the early 1960s and ran for a total of 22,000 hours between 1965 and 1969.
Alvin Weinberg, who ran Oak Ridge National Laboratory (ORNL) while the Molten Salt Reactor Experiment was conducted, was also the original inventor of the Pressurized-Water Reactor PWR used today (got the patent in 1947).
Of the Generation-IV reactors being developed, only the MSR has been built and operated. Some Generation-IV reactors are being built, see https://en.wikipedia.org/wiki/Generation_IV_reactor .
FLiBe Energy in the USA is working on the engineering to bring a full LFTR into production (an MSR with a Thorium “blanket” to convert Thorium to Uranium fuel).
Others in several countries are building Molten Salt Reactors. Thorcon is designing MSR building-and-shipping factories, with experience building shipyards.
The Chinese Academy of Sciences has MSR plans — in 2010 they visited Oak Ridge National Laboratory; and Chinese New Year in 2011 they announced they would be starting a Thorium Molten Salt Reactor program (and patenting every advance they make).
MSR modeling and design work is also being done in other countries, incl. Canada, France, Czech Republic.
Liquid: The fuel is molten Uranium in a molten salt, circulating continuously through the reactor, for over 99% fuel burnup, and easy processing of fission byproducts.
Fluoride or Chloride: The salt used in many MSR is made of Fluoride, Lithium and Beryllium, (or similar salts), or Chloride salts. These salts are very chemically stable, have a very high boiling point (for example FLiBe is liquid from ~400° to ~1400° C), and essentially impervious to radiation damage. The high heat capacity of fluoride salts lets a MSR operate safely at temperatures much higher than water-cooled reactors (1000° vs. 350° C) for more efficient electric generation and industrial use. Most fission byproducts chemically bond with the salt.
Thorium: If a MSR uses thorium, it is a plentiful metal, probably a couple of grams in your yard. Among the least radioactive elements, commonly discarded as waste from Rare Earth mines. The reactor converts Thorium to Uranium for fuel.
Reactor: MSRs fission uranium to produce heat. All MSRs are extremely resistant to nuclear proliferation (from mining to disposal) and produce only a very small amount of short-lived, low toxicity waste which is radioactivity-wise completely benign within 350 years.
MSRs run at approximately atmospheric pressure, or “garden hose” pressure, so they will have less expensive construction than LWR, and be much less expensive to operate. Passive safety features handle emergencies, even if no water or power is available, without needing operator intervention.
Molten Salt Reactors operate at much higher temperatures than LWR can, yet the fuel temperature never can exceed the temperature the materials can withstand. (In LWR, the temperatures inside the fuel pellets is always higher than the materials can withstand, if cooling fails.)