B. Molten Salt Reactors

We thank Hargraves, R.: Aim High. Thorium Energy, Cheaper than from Coal, Solves more than just Global Warming. thoriumenergyalliance.com for many of the figures used in this article.

If one were to fantasize about an ideal solution to replacing fossil fuels with renewable energy some of the requirements would be:

• zero carbon footprint
• able to burn up waste from Light water nuclear reactors (LWRs)
• cheaper than coal
• inexhaustible energy supply
• minimal waste
• capable of producing both electricity and fuel
• relatively inexpensive
• no environmental impact – (no threat to birds as with wind turbines or the desert as with solar)
• modular (thus avoiding the gigantic gigawatt reactors)
• does not require long power lines as with wind and solar
• very safe
• resistant to earthquakes (i.e. Fukushima)
• resistant to meltdowns (i.e. Chernobyl, Three Mile Island)
• resistant to terrorism
• affordable to developing nations

This sounds like an impossible mix of dream requirements. There is however, one energy source that meets all these criteria — the Thorium Based Nuclear Power or Liquid Fluoride Thorium Reactors (LFTRs) and its cousin Denatured Molten Salt Reactors (DMSRs) that burn thorium or spent fuel from LWRs. A more generic term is simply Molten Salt Reactors (MSR).

What is a LFTR?

Liquid Fluoride Thorium Reactor. Fertile compounds are those that do not undergo fission themselves, but upon capturing neutrons are transformed to fissile compounds. Thorium is such a fertile compound. When exposed to a source of neutrons, thorium Th-232 decays to fissionable uranium U-233. It is the fission of U-233 that provides the heat of a LFTR.

A blanket of fertile Th-232 as liquid ThF4 and two fluoride salts, lithium fluoride (LiF) and beryllium fluoride (BeF2) surrounds a liquid core of ThF4, LiF and BeF2 and some starter fissile U-233. The fission of U-233 produces the heat and neutrons for the further conversion of Th-232 to more U-233.

The great safety feature of the LFTR and MSRs in general is a freeze plug in a pipe from the main liquid container to safety collection vessels. A portion of the pipe is kept frozen by an electric freezing apparatus. If electricity fails, even in the total absence of human intervention, the plug unfreezes and the liquid thorium fluoride passively drains to the safety vessel where it solidifies, stopping the heating process.

Working models built at Oak Ridge National Laboratory (ORNL) in the 1950's and 1960's were turned off over the weekend by simply opening the freeze plug. To restart the reactor on Monday they turned on the heater and re-liquefied the LiF and BeF2. Thus, it is as much a matter of resurrecting old technology as inventing new.

Advantages of LFTR over Current Nuclear Power

• Inexhaustible fuel. Unlike uranium, which is in relatively scarce supply, thorium is common. In one area of Idaho there is enough thorium to supply the energy needs of the United States for one thousand years. Thorium is also present in many other states and many other countries, making it easily available worldwide.
• Much more efficient than uranium based nuclear power. Standard nuclear power plants use enriched U235 as the source of their fissionable material. After the reaction is complete only 3% of the fuel has been converted to fissionable products. By contrast, LFTRs are close to 100% efficient. It only requires 0.9 tons of ThO2 to produce 1000 MWyr while 293 tons of U3O8 are required to produce the same amount of electricity.
• Minimal nuclear waste. After 300 years LFTRs produce 10,000 times less radioactive waste than today's nuclear plants. LFTRs reduce the needed storage time of by-products from millions of years for LWRs to hundreds of years for LFTRs. The waste from standard reactors can be used to fuel LFTRs, providing a use for this waste and potentially removing it from the environment.
• No periodic replacement of parts. Solid fuel rods in standard nuclear power plants have to be replaced every few years because cracks in the covering can release radioactive fission products. This is not a problem with the liquid fuel of LFTRs.
• Safe. LFTRs can never have a meltdown because they are already in a constant meltdown or liquid state. In the case of an emergency, even if the electricity was permanently knocked out and the plant was unmanned, the liquid would automatically and passively drain to a collection vault and solidify into an inert mass shutting off the reactor.
• Less water use. A high temperature LFTR cuts the heat loss in half and can be air cooled, thus requiring no water. This is a great advantage in arid sites with little water supply.
• Less of a threat from terrorists. LFTRs produce only as much fissionable U-233 as they consume. U-233 is considered an unsuitable choice for nuclear weapons material. LFTR technology is a proliferation-resistant source of electrical energy.
• Less expensive. Because there is no risk of explosion and no high pressures, LFTRs require no containment domes. Because of the design and safety features of LFTRs they also require fewer operating personnel leading to further reductions in the cost of running the plants.
• Cheaper than coal. If modular LFTR units are built on an industrial scale, like airplanes, the cost per kWhr would be less than coal.
• Can produce transportation fuel. The high temperatures of LFTRs allow them to easily decompose water into hydrogen gas H2. LFTRs can also produce fuel from H2. Such fuels would add no carbon to the atmosphere since they are derived from non-fossil sources.
• Can replace coal plants dramatically reducing CO2 emissions. Mass production of 100 MW LFTRs can result in each plant costing about $200 million dollars, less than a large commercial jet. The relatively low cost of such 100 MW LFTRs could allow even developing countries with more limited finances to utilize this energy source.

Denatured Molten Salt Reactor

The only reactor specifically designed to be proliferation resistant. The Denatured Molten Salt Reactor (DMSR) is a single fluid reactor using fertile Th-232 and fissile uranium U-235. The U-235 is denatured by adding 80% U-238, thus making it unsuitable for weapons. The DMSR has the further advantage that it operates within a sealed containment from which no fissile material is added during the life of the plant.

Past MSR Efforts in the United States

A Molten Salt Reactor (MSR) program was initiated in 1957. By 1960 enough favorable experimental results were obtained to support authorization for design and construction of a 10-MW Molten Salt Reactor Experiment (MSRE). The reactor went critical in June 1965, and the MSRE initiated power operation in early 1966.

The MSRE experience was of major importance to the molten salt concept. Starting in late 1966, an uninterrupted one-month run was made, then a three-month run, and finally a six-month run. When shut down, the MSRE had circulated fuel salt at around 650°C for a total of 2.5 years. Perhaps the most important result from the MSRE was the conclusion that it was quite a practical reactor.

In January 1973, ORNL was directed to terminate MSR development work. The program was reinstated a year later, and in 1974 ORNL submitted a more elaborate proposal calling for about $720 million to be spent over an 11-year period. This last proposal was also rejected, and in 1976 ORNL was again ordered to shut down the MSR program for budgetary and political reasons.

New US Laws Support MSRs

On September 28, the Nuclear Energy Innovation Capabilities Act (NEICA) and the DOE Research and Innovation Act were signed into law. These acts support the near-term development and commercialization of advanced nuclear technologies such as Terrestrial Energy's Integral Molten Salt Reactor. They set into motion a set of key initiatives that include the development of a national reactor innovation center and an advanced reactor licensing grant program.

Current MSR Efforts in the United States and Canada

Other MSR Companies

• Alpha Tech — Salt Lake City, UT — http://alphatechresearchcorp.com
• Elysium Industries — Schenectady, NY — http://www.elysiumindustries.com
• Kairos Power — Oakland, CA — https://kairospower.com
• Oak Ridge National Laboratory (ORNL) — Oak Ridge, TN — https://www.ornl.gov/msr
• ThorCon Power — Stevenson, WA — http://thorconpower.com
• Thorium Power Canada — Toronto, ON — http://www.thoriumpowercanada.com

What can the Comings Foundation do?

The Comings Foundation will help to financially support the most promising of the above entities in an effort to accelerate the development of MSRs in the U.S. and Canada and eventually the rest of the world.

© 2018 David E Comings, M.D.