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INTRODUCTION *

  "The potential utility of a fluid-fueled reactor that can operate at a high temperature but with a low-pressure system has been recognized for a long time. Some years ago, R. C. Briant of the Oak Ridge National Laboratory suggested the use of the molten mixture of UF4 and ThF4, together with the fluorides of the alkali metals and beryllium or zirconium, as the fluid fuel. Laboratory work with such mixtures led to the operation, in 1954, of an experimental reactor, which was designated the Aircraft Reactor Experiment (ARE).

  Fluoride-salt mixtures suitable for use in power reactors have melting points in the temperature range 850 to 950°F and are sufficiently compatible with certain nickel-base alloys to assure long life for reactor components at temperatures up to 1300°F. Thus the natural, optimum operating temperature for a molten-salt-fueled reactor is such that the molten salt is a suitable heat source for a modern steam power plant. The principal comparison with one or more of the other fluid-fuel systems are (1) low pressure operation, (2) stability of the liquid under radiation, (3) high solubility of uranium and thorium (as fluorides) in molten-salt mixtures, and (4) resistance to corrosion of the structural materials that does not depend on oxide or other film formation.

  The molten-salt system has the usual benefits attributed to fluid-fuel systems. The principal advantages over solid-fuel-element systems are (1) a high negative temperature coefficient of reactivity, (2) a lack of radiation damage that can limit fuel burnup, (3) the possibility of continuous fission-product removal, (4) the avoidance of the expense of fabricating new fuel elements, and (5) the possibility of adding makeup fuel as needed, which precludes the need for providing excess reactivity. The high negative temperature coefficient and the lack of excess reactivity make possible a reactor, without control rods, which automatically adjusts its power in response to changes of the electrical load. The lack of excess reactivity also leads to a reactor that is not endangered by nuclear power excursions.

  One of the attractive features of the molten-salt system is the variety of reactor types that can be considered to cover a range of applications. The present state of the technology suggests that homogeneous reactors which use a molten salt composed of BeF2 and either Li7F or NaF, with UF4 for fuel and ThF4 for a fertile material, are most suitable for early construction.

  These reactors can be either one or two region and, depending on the size of the reactor core and the thorium fluoride concentration, can cover a wide range of fuel inventories, breeding ratios, and fuel reprocessing schedules. The chief virtues of this class of molten-salt reactor are that the design is based on a well-developed technology and that the use of a simple fuel cycle contributes to reduced costs.

  With further development, the same base salt, that is, the mixture of BeF2 and Li7P, can be combined with a graphite moderator in a heterogeneous arrangement to provide a self-contained Th-U233 system with a breeding ratio of one. The chief advantage of the molten-salt system over other liquid systems in pursuing this objective is that it is the only system in which a soluble thorium compound can be used, and thus the problem of slurry handling is avoided. The possibility of placing thorium in the core obviates the necessity of using graphite as a core-shell material.

  Plutonium is being investigated as an alternate fuel for the molten-salt reactor. Although it is too early to describe a plutonium-fueled reactor in detail, it is highly probable that a suitable PuF3-fueled reactor can be constructed and operated.

  The high melting temperature of the fluoride salts is the principal difficulty in their use. Steps must be taken to preheat equipment and to keep the equipment above the melting point of the salt at all times. In addition, there is more parasitic neutron capture in the salts of the molten-salt reactor than there is in the heavy water of the heavy-water-moderated reactors, and thus the breeding ratios are lower. The poorer moderating ability of the salts requires larger critical masses for molten-salt reactors than for the aqueous systems. Finally, the molten-salt reactor shares with all fluid-fuel reactors the problems of certain containment of the fuel, the reliability of components, and the necessity for techniques of making repairs remotely. The low pressure of the molten-salt fuel system should be beneficial with regard to these engineering problems, but to evaluate them properly will require operating experience with experimental reactors." - -   *By H. G. MacPherson.
http://www.energyfromthorium.com/pdf/FFR_part2.pdf 

 

Genesis of the Naturally Safe, Thorium-fueled, Molten Salt Reactor
 Molten Salt Reactor:  The reactor technology path not taken.
 A very light and very powerful molten salt reactor was developed to power nuclear bomber airplanes a few years before Intercontinental Missiles were developed.
The NB-36 made nearly 50 flights in the 1950s carrying an operating nuclear reactor.  The crew worked from a lead-shielded cockpit.

Thorium:  The nuclear energy path not taken.
 By the time the Manhattan Project was completed 3 viable nuclear energy paths were identified: Uranium, Plutonium, and Thorium.
Thorium had very poor weapons potential and was subsequently abandoned and forgotten.

 

(Left) The NB-36's "Fireball" reactor using dissolved uranium liquid fuel  and the 4 nuclear jet engines it powered.  It has little in common with today's solid core reactors.
 

(Right) The USS Nautilus got the first operational solid fuel nuclear reactor.
 

A major objection to nuclear airplanes was the possibility of a crash in a large city.

Today's low temperature (550°F) solid fuel core power plant reactors are massively scaled up versions of the first desk-size submarine solid-fuel core reactors.  They are not hot enough to duplicate the efficient superheated steam coal makes in a coal-burning power plant.  The very hot (1,300°F) liquid fuel core in airplane nuclear reactors can easily duplicate, and thus replace, any any steam found in any coal or natural gas power plant.  (Right) The Molten Salt Reactor Experiment salt-to-air heat exchanger ran so hot it glowed like the burners on your kitchen range. (Click on chart to prove to yourself how hot it was. The chart is in Kelvin, an absolute temperature measurement. 1,300°F = 978 K )     Also:  Color temperature

n

Liquid Reactors:  May, 1946, marked the beginning of the ultra-secret nuclear powered bomber program that eventually progressed as far as the NB-36H bomber.  By 1955, this program produced the successful X-39 jet engine - two modified General Electric J47 jet engines with reactor-heated heat exchangers replacing the standard jet engine's jet fuel combustors - and would probably have gone on to power the X-6 successor to the NB-36H had that program been pursued.  Nuclear powered airplane programs were eventually abandoned in favor of far faster, more difficult to intercept, intercontinental ballistic missiles.

The airplane engine's nuclear reactor was extremely light, simple, fast responding, powerful, and hot enough to replace jet fuel.  The uranium nuclear fuel, dissolved in molten salt, flowed through the reactor and its heat exchangers much like energy-transporting blood flows through the organs of animals.  Unlike water, 1,300°F molten salt produces no vapor pressure and, as a consequence, the reactor cannot explode like conventional high pressure steam nuclear reactors. 

Later, a slightly larger version of the same type of reactor was built in the same aircraft reactor development building at Oak Ridge National Laboratories.  Completed in 1965, it was called the "Molten Salt Reactor Experiment" (MSRE) and, over the next 5 years, ran at full power for the equivalent of one and a half years.

Thorium:  The nuclear energy path not taken.  By the time the Manhattan Project was completed, 3 viable nuclear energy paths were identified: Uranium, Plutonium, and Thorium.  Thorium had very poor weapons potential and was subsequently abandoned as being suitable for weapons.  Later, along with uranium and plutonium, thorium was explored as a potential reactor fuel in both solid fuel reactors (Shippingport, near Pittsburgh, PA) and liquid fuel reactors (Oak Ridge Molten Salt Reactor Experiment - MSRE).

Unlike polyisotopic uranium ( http://en.wikipedia.org/wiki/Isotope ), thorium is monoisotopic and therefore does not need costly enrichment to be used as nuclear fuel.  Several combinations of liquid reactors and thorium fuels appear to be ideal for making cheap, extremely hot heat for millions of years.  Unlike solid fuel reactors which cannot consume more than several percent of their uranium fuel before becoming too weak to run, liquid fuel reactors are capable of almost completely consuming their nuclear fuel, and, as a consequence, produce about 250 times the heat and 1% the nuclear waste of a solid fuel reactor.  Further, most of this small amount of nuclear waste decays to a safe level in less than a decade, the remainder in several hundred years.

This combination of running coal-hot and load-following while making about 250 times as much heat and producing 1% the waste - in a far less expensive to build reactor - attracted great interest from the electrical utilities.  Conceptual designs for large, utility size molten salt reactors were on the drawing boards as early as 1960.

Today, heat from thorium could be 8,000 times cheaper than heat from coal.  We have arrived at energy's final frontier where all of civilization's heat must come from nuclear.  Burning our last remaining deposits of oil, natural gas, and coal will only make Global Warming worse.  The hydrocarbons in oil, natural gas, and coal are far more valuable for bringing us good lives by using them as feedstock for plastics and fertilizers rather than wasting them as mere sources of heat.

This book is about re-starting America's thorium-fuelled molten salt reactor program using a modern version of the 1972 EBASCO 1,000 megaWatt electricity generating plant reactor. The Single Fluid (Converter) Thorium-Powered Liquid Reactor
 

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Reactor Safety

Reactor Safety

MSR - Reactor Safety .pdf   

How are they "Naturally Safe"?

If, for any reason, the reactor gets too hot, a freeze plug in the reactor tank’s bottom melts, causing the reactor's fuel-carrying molten salt to drain away from the graphite rods down into passively air cooled dump tanks (blue) located beneath the reactor.  There, away from the graphite rods, the chain reaction ceases and the molten salt will cool and solidify.  Solidification prevents the radioactive materials from entering the environment.  Heaters re-melt the salt to restart the reactor.

Radiation Leakage

Radiation leakage.  In this type of reactor there are 2 or more loops of circulating melted salt.   1) The inner loop carries the dissolved radioactive fuel (called "Fuel Salt") first to the reactor's core, where the fuel in the salt heats the salt, then to a heat exchanger where the salt's heat is transferred to the outside world via 2) a second loop of melted salt (called "Clear Salt").  The fuel salt loop is completely contained within the confinement cell. 

In the unlikely event some fuel salt escaped the confinement cell, it will turn solid when it cools below 680°F.  So there would be a solid lump you could easily locate.  Today's conventional reactors leak radioactive water which quickly sinks into the ground, dispersing unstoppable radioactivity far and wide into the environment. 

Unlike table salt, the fuel salt lump would take a long time to dissolve in rain.  At 2.7grams/liter of water, FLiBe, the salt used to carry radioactive fuel in this reactor, has 133 times less solubility in water than common table salt at 359 grams/liter of water. 

Unlike water, FLiBe cannot become radioactive through exposure to radioactivity, so if the secondary loop leaks, its just a chemical spill.  You won't be able to find these lumps with a Geiger counter.  Unlike table salt, FLiBe is not safe to eat.

 

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The Thorium Reactor Libraries

How mature is the single-fluid "converter" molten salt reactor?
How mature is thorium as a nuclear fuel?

The Thorium-Fueled Molten Salt Reactor Libraries

Oak Ridge National Laboratories is a reputable organization and they have hundreds of documents about several experimental molten salt reactors, HTRE-1, HTRE-2, HTRE-3, and MSRE, which ran for about 5 years, some of the time on liquid thorium.  Also, the Shippingport reactor ran for several years on solid thorium. 

The author knows of no reason to doubt the accuracy of these documents. 

These documents may be found, examined, and downloaded without restriction at:

http://moltensalt.org/references/static/downloads/pdf/index.html  Bruce Hoglund's web site ORNL collection.
http://www.energyfromthorium.com/pdf/  Kirk Sorensen's web site ORNL collection.

MSR - The Molten Salt Adventure .pdf  NUCLEAR SCIENCE AND ENGINEERING: 90, 374-380 (1985) "The Molten Salt Reactor Adventure" H. G. MacPherson, Consultant, Oak Ridge, Tennessee 37831, Accepted March 15, 1985

MSR - Safety and Licensing Aspects of the Molten Salt Reactor - 120507.pdf 

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About Naturally Safe Liquid Thorium Reactors

ABOUT NATURALLY SAFE LIQUID THORIUM REACTORS
   Liquid Thorium Reactors Have Little In Common With Today's Reactors
WHAT THEY ARE,  HOW THEY WORK,  how their NATURAL SAFETY FEATURES WORK 

Good article by Dr Ralph Moir and Dr. Edward Teller, (inventor of the hydrogen bomb) explaining a single fluid reactor:  Thorium-Fueled Underground Power Plant
 Good article by Dr. Ralph Moir and Dr. Robert Hargraves explaining dual fluid reactors:  www.energyfromthorium.com/forum/download/file.php?id=791
Note: Like gasoline engines, there are several different kinds of single fluid reactors.  This is the one that has been built and tested twice.

The Single Fluid (Converter) Thorium-Powered Liquid Reactor

 

"A pot, a pump, and a pipe."
 - Oak Ridge National Laboratories quip.

 

 

 

 

Advantages

Walk-away safe.      Extremely simple.      Fire hot.      Almost limitless amounts of extremely cheap thorium for fuel.      Produce 1% the nuclear waste of a conventional reactor.      Naturally safe slow neutron nuclear device (atomic bombs are fast neutron nuclear devices).      Small and very cheap for the amount of heat they produce.      Cannot be kept from ending fission upon loss of electricity.      No steam pressure, so can't explode.  Run 30 years at full power between maintenances.      Air cooled, can be used in deserts.      Can be installed in underground silos for maximum isolation.      Can be installed in concrete barges so they can be hauled away forever when no longer needed, leaving no residual radioactive materials at user's site.      The heat transfer cooling salt contracts when it freezes solid so it doesn't burst the pipes.      If any of the heat transfer cooling salt leaks, it turns solid so the radioactivity can't sink into the ground and make drinking water radioactive like the cooling water from conventional reactors.  You just scoop it up with a very long handle shovel.      Largely naturally self-heat-regulating and thus load-following: Fuel density changes in the heat transfer salt tend to make it become warm when it is cool, cool when it is warm.

Disadvantages

Fire hot - runs red-hot.      The heat transfer cooling salt is expensive.      The heat transfer salt that has the radioactive fuel dissolved in it has to be immune to radioactivity forever.  That stuff is very expensive.        The heat transfer cooling salt turns solid if allowed to get too cool.      The heat transfer cooling salt is corrosive so the reactor tank and circulating pumps have to be made out of expensive Hastelloy-N.      Molten salt reactors are radioactive like all other nuclear reactors.      Special equipment will be needed for the 30 year maintenance.      Unlike table salt, FLiBe heat transfer salt is toxic like the chlorines.  Its fumes cannot be breathed, it cannot be eaten, it cannot be handled with bare hands.      

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The Single Fluid (Converter) Thorium-Powered Liquid Reactor
 

The Single Fluid (Converter) Thorium-Powered Liquid Reactor
 

Introduction:

We are talking about a combination of TWO entities:
1. Thorium instead of Uranium as a nuclear fuel. 
2. Unpressurized (incapable of exploding) molten salt cooled liquid fuel reactors instead of high pressure (capable of exploding) water cooled solid fuel rod reactors.

 

A QUICK INTRODUCTION TO THE BASIC "CONVERTER" MOLTEN SALT REACTOR

1. Solid salt, if heated hot enough, will melt into a clear water-like liquid (color-coded yellow in sketch at right).  At the temperatures discussed here, the salt is far below its boiling point and, since the salt has little vapor pressure, Molten Salt reactors are unpressurized and thus incapable of making a steam-like explosion.  (Click on image for larger view.)

2. Uranium and Thorium can be dissolved in molten salt.  A tub of molten salt with some radioactive uranium dissolved in it (think blood - which carries nutrients) will become a nuclear reactor if rods of synthetic non-flammable "nuclear" graphite (vertical black bars in reactor sketch) are inserted into the liquid salt pool to promote nuclear fission (think muscle - which turns nutrients into energy). 

Once running, adding more uranium will keep it running.  If non-radioactive thorium-232 is added instead, the radioactivity will convert thorium-232 into radioactive uranium-233 (this takes about a month) and the reactor will continue to run.  Radioactive plutonium-239 can also be used to start and run the reactor.

3. "Cruise Control"  As the pool becomes hotter, the liquid salt expands, reducing the concentration of radioactivity near the graphite rods, thereby reducing the intensity of the nuclear chain reaction.  As the pool becomes cooler, contraction of the liquid salt intensifies the chain reaction, making the fuel salt hotter.  A Molten Salt reactor will “load follow” (think “cruise control”) over a surprisingly large portion of its power range.  Control rods will bring the reactor down to "idle" or allow full power.

4. The first heat exchanger heats a second loop of clear non-radioactive molten salt called "coolant salt." This salt is used to safely carry the reactor's heat to the outside world.  Coolant salt then heats the second heat exchanger to make steam to drive an electricity generator.

5. Fresh make-up thorium is added as needed for up to thirty years - at which time the fuel salt becomes saturated and has to have its dissolved waste products removed by precipitation.

How are they "Naturally Safe"?

6. If, for any reason, the reactor gets too hot, a freeze plug in the reactor tank’s bottom melts, causing the reactor's fuel-carrying molten salt to drain away from the graphite rods down into passively air cooled dump tanks (blue) located beneath the reactor.  There, away from the graphite rods, the chain reaction ceases and the molten salt will cool and solidify.  Solidification prevents the radioactive materials from entering the environment.  Heaters re-melt the salt to restart the reactor.

Thorium's Proliferation Risk

"Thorium fueled [breeder] reactors may pose a slightly higher proliferation risk than uranium based reactors because, while Pu-239 will fairly often fail to undergo fission after neutron capture and produce Pu-240, the corresponding process in the thorium cycle is relatively rare. Thorium-232 converts to U-233, which will almost always undergo fission successfully, meaning that there will be very little U-234 produced in the reactor's thorium/U-233 breeder blanket, and the resulting pure U-233 will be comparatively easy to extract and use for weapons. However, the opposite process (neutron knock-off) happens as a matter of course, producing U-232, which has the strong gamma emitter Tl-208 in its decay chain. These gamma rays complicate the safe handling of a weapon and the design of its electronics; this explains why U-233 has never been pursued for weapons beyond proof-of-concept demonstrations." - - - http://en.wikipedia.org/wiki/Breeder_reactor 

This is why the author is suggesting that only the "Single Fluid Converter" molten salt reactor be built and run as a DMSR.

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The Thorium Cycle

The Thorium Cycle
 (We are talking about the basic THORIUM CONVERTER reactor that makes its own radioactive fuel and then consumes it.)

From here on, things just get better.  Once started with a small amount of radioactive uranium or plutonium, Molten Salt reactors will continue to run on non-radioactive thorium by first converting the dissolved thorium into radioactive uranium-233 and then fissioning (breaking) that atom.  These two reactions will happen naturally and simultaneously when you get things right. 

Thorium is found everywhere, is 4 times as common as all forms of uranium combined, and, used this way in liquid form, produces 250 times as much heat energy in a single reactor pass as a solid uranium fuel rod.   This means thorium heat could cost less than 1/8,000th as much as coal heat.  This also means, since so little is needed, we will never consume all the thorium available on Planet Earth.  Today, thorium is simply a waste tailing of rare earth mining.

In Detail: How non-radioactive thorium can power a reactor.

HERE IS HOW NON-RADIOACTIVE 232-THORIUM IS FIRST CONVERTED INTO RADIOACTIVE 233-URANIUM (Breeding Reaction) AND THEN IS LATER FISSIONED (Chain Reaction).    BOTH REACTIONS MAKE HEAT.

(The author took the liberty of editing the diagram appearing in the Moir-Teller article to make it more understandable to non-nuclear folks like himself.)
 (The original Moir-Teller diagram.)

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There appears to be no practical obstacle to vastly different sizes of Molten Salt reactors.

A more detailed introduction by a professional writer in a hurry.   MSR - The Thorium Paradigm .pdf

A conservative introduction.  http://energyfromthorium.com/joomla/index.php?option=com_content&view=article&id=64&Itemid=63 

An on-line Wikipedia article:  http://en.wikipedia.org/wiki/Molten_salt_reactor   http://en.wikipedia.org/wiki/Thorium_fuel_cycle 

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Quick History of Thorium-fueled and Molten Salt Reactors

Quick History of Thorium-fueled and Molten Salt Reactors

Born in Cold-War secrecy, this reactor type was first developed as a nuclear aircraft engine in the 1950s by Pratt and Whitney, test-stand run successfully, given multiple rides in a B-36 bomber to get crew shielding right.  Nuclear intercontinental bombers were abandoned as reliable, extremely accurate, and virtually impossible to intercept intercontinental missiles were being perfected.  Interestingly, the Soviet version of the nuclear powered bomber weighed within 5,000 pounds of our 75-ton NB-36.  The idea of nuclear civilian airplanes with their potential of crashing into a city caused the successful X-39 dual J47 nuclear jet engine to be forgotten.

Thorium as a weapons material was abandoned by the U.S. military when it proved to have poor military weapons value in every respect.  After a discouraging test firing of the only atomic bomb ever made from thorium, MET, 1955, development work on thorium as a weapons material was ended.  http://en.wikipedia.org/wiki/Operation_Teapot 

A ten megaWatt Molten Salt Reactor was later built at Oak Ridge National Laboratories.  It ran well for about 5 years on both pure and various blends of thorium, uranium, and plutonium.

Solid thorium fuel rods were used experimentally in the 1957 conventional 60 MWe "Shippingport" reactor near Pittsburgh, PA, between 1977 and 1982.  http://en.wikipedia.org/wiki/Shippingport_Reactor  (Right, Shippingport reactor vessel.)

A 1,000 megaWatt (e) Molten Salt electricity generating unit was designed by EBASCO (a consortium of 15 Midwest power companies) for Oak Ridge National Laboratories in 1965, and then shelved in favor of established conventional solid fuel reactors.  

The MSR program had very poor weapons material breeding potential and was cancelled about 1974 when the government decided in favor of funding liquid metal fast breeder reactors which could make far more, and better, weapons material far faster. 

The liquid metal fast breeder reactor program, in turn, was killed for nuclear proliferation reasons in 1994 by an administration with strong anti-nuclear ties.

Czech Republic, France, China (molten salt reactor development, large thorium deposits, small uranium deposits), India (solid thorium fuel rod reactors, large thorium deposits), are currently active in thorium energy research with Norway (large thorium deposits), Japan, and Russia looking on. 

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About Using Molten Salt as a Coolant.
 

About Using Molten Salt as a Coolant.

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Nuclear Aircraft Engines  1946-1962
 

Nuclear Aircraft Engines  1946-1962

"Aircraft Nuclear Propulsion (ANP) Program",  Mid-1950s

Molten Salt Reactors (MSRs) - a type of Nuclear Reactor

The most interesting application of molten salt technology was the development of the Molten Salt (Nuclear) Reactor (MSR). Originally developed to power a deep penetration bomber for targets in the Soviet Union during the early Cold War (1946 - 1962), it is a remarkable, yet virtually unknown reactor. Part of the problem was the limited geographical experience of the MSR as both operating MSRs were built only at Oak Ridge National Laboratory (ORNL), near Knoxville, Tennessee, USA.

The first MSR was the 1954, 100-hour operation of the Aircraft Reactor Experiment (ARE) at ORNL.  Its sole purpose was to demonstrate the then unheard of notion of operating a reactor at red heat (~750°C; ~1,550° F) with a molten fuel and coolant consisting of melted fluoride salts (sodium fluoride, NaF; zirconium fluoride, ZrF 4; and UF4 [enriched in 235U]).

The second MSR was a civilian power plant prototype, the Molten Salt Reactor Experiment (MSRE)7. Hugely successful, it was ignored by the US Atomic Energy Commission (US AEC), which had decided to favor the Liquid Metal Fast Breeder Reactor (LMFBR).

The Director of ORNL, Dr. Alvin Weinberg, pushed for the MSR, but was fired for his efforts.

The notable features of this reactor are:

●  Meltdown proof
●  Does not produce weapons grade plutonium
●  Has inherent non-proliferation features
●  Thousands of years of energy
●  Simplified fuel cycle (no fuel elements nor reprocessing required)
●  Its wastes are simpler and less toxic than current nuclear wastes
●  Only hundreds of years of storage versus thousands for the current wastes
●  Can completely destroy military plutonium
●  Can burn the existing wastes (spent fuel)!
●  Higher thermal efficiencies (operates at a "Red Heat"; ~700° C [1,260° F])

The above was written and created by Bruce Hoglund <bhoglund@earthlink.net.DoNotSpamMe>, © 1997
Please send me any HELPFUL comments. Responsible use is allowed as long as the author is cited.
Above from:   MSR - What is Molten Salt & Its Technology_ .pdf  

(Right)  In fact, there were TWO nuclear aircraft engines under development at the time.  Heat Transfer Reactor Experiment - 3 (HTRE-3) is the large one above and on the left in the small picture.  It came from Pratt & Whitney.  The other one, HTRE-1 (later rebuilt as HTRE-2) was an air-direct-core-cooled General Electric design.

(Small image above from Wikipedia (click on it for large image), large image (above) taken by author Sept, 2010 from Idaho National Labs parking lot.)

"The US Aircraft Reactor Experiment (ARE) was a 2.5 MW thermal nuclear reactor experiment designed to attain a high power density for use as an engine in a nuclear powered bomber. It used the molten fluoride salt NaF-ZrF4-UF4 (53-41-6 mol%) as fuel, was moderated by beryllium oxide (BeO), used liquid sodium as a secondary coolant and had a peak temperature of 860 °C. It operated for a 1000-hour cycle in 1954. It was the first molten salt reactor. Work on this project in the US stopped after ICBMs made it obsolete. The designs for its engines can currently be viewed at the EBR-I memorial building at the Idaho National Laboratory." - -  http://en.wikipedia.org/wiki/Aircraft_Nuclear_Propulsion 

For more information about the airplane photos, see ASME web article: 
http://www.asme.org/kb/news---articles/articles/nuclear/molten-salt-reactors 

 

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After Nuclear Aircraft Engines
 

After Nuclear Aircraft Engines

Molten-Salt Reactor Experiment 1965 to 1969.  (Oak Ridge National Labs Photo from Kirk Sorensen's 2011 TEA talk slides.)
Notice the water-cooled pump motor.  The 1,200°F reactor was so hot you could take a photograph of it at night without a flash.  Both the heat and corrosiveness of the salt makes this a place to stay away from.  EBASCO did some unrecognized brilliant engineering and came up with a far better reactor confinement cell design.

 

  (Left)  SHOW ME THE FIRE-HOT HEAT.

 

Molten salt-to-air heat exchanger running full-blast.  1,200°F+ is the normal discharge temperature of this reactor.  It can replace most coal, natural gas, and oil fires.  Molten salt reactor experiment, Oak Ridge National Laboratories.   Temperature Colors - 540.jpg

 

 

(Right) Assembling the graphite core of the experimental 10 megaWatt Molten Salt Reactor (MSRE).   

"The MSRE's piping, core vat and structural components were made from Hastelloy-N and its moderator was a pyrolytic graphite core. The fuel for the MSRE was LiF-BeF2-ZrF4-UF4 (65-30-5-0.1), the graphite core moderated it, and its secondary coolant was FLiBe (2LiF-BeF2), it operated as hot as 650 °C (1,200°F) and operated for the equivalent of about 1.5 years of full power operation."

From: http://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment

 

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Costs

Molten salt is salt heated hot enough to melt and flow like water.  So a liquid reactor fueled by thorium is called "Liquid Thorium" (at least on this web site). 

One unpleasantness is the is the reactor's salt, FLiBeF (Flibe).  While a great reactor salt that will last forever carrying radioactive fuel dissolved in it, is toxic (as are most salts) and also expensive.  Fortunately, not a large amount is needed to fill the reactor and the primary heat exchangers.  FLiNaFKF (Flinak) could be a secondary coolant loop salt.  Some think a much cheaper commercial heat transfer salt such as HITEC (used in solar heat collectors) might suffice in some secondary loop designs and would certainly work in any tertiary loops.  Corrosion is addressed by using alloys such as Hastelloy-N, with 2% titanium added to avoid long-term embrittlement due to radiation.  The operating design life would be 90 years with 30-year major maintenance intervals.

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NEWS ITEMS

Richard Houghton, March 26th, 2011 at 10:46

I wish that Mr. Gates had first seen the research already done and already tested for 5 years at Oakridge, namely liquid fluorine thorium reactors. This nuclear reactor uses liquid salts with dissolved thorium which is converted to a fissile material (u233) and burned. No cooling system required, no bomb material is possible, can be shut down and restarted in same day, uses nuclear waste material as fuel, needs no massive containment structure, operates at atmospheric pressure, needs no water to cool or create steam. And it has been proven by our own nuclear program and run for 5 years. They would run it during the week and turn it off for the weekend and restart it on Monday. Will cost half of what a conventional nuke plant costs. Is scalable for large plants and for industrial business use.
Check out thoriumalliance.org for more information.

Bill Gate's Traveling Wave Reactor: How do you turn it on and off for maintenance?  How do you turn it up and down for load following?  How hot is it?  Is there some web site where these questions are answered?

I wonder about the neutron spectrum, and whether the reactivity control is accomplished by a combination of Doppler and density (as a function of temperature). This seems to be an interesting exercise on paper, but I'm highly skeptical with respect to practicality.

I'm curious about the transport of fission gases (Xe, Kr) and volatiles to the plenum volume, and the conduction of heat to the liquid metal coolant. - Astronuc

 

Thorium  Another sign it is the coming nuclear fuel .pdf