A Better Source of Nuclear Power?

Two disturbing scientific reports have surfaced recently from Europe. The first is that a plume of radioactive particles has been detected drifting across northern Europe with a suspected source from within Russia. The second report is a post-mortem concerning the Chernobyl Nuclear Facility meltdown, in that report, it was concluded that the very first explosion at the nuclear facility was the result of a supercritical, rapid, and uncontrolled nuclear fission chain reaction, or as the popular press calls it, a nuclear explosion. These reports derive their conclusions from the detection of an isotope of Xenon gas which can only be produced by nuclear fission.  

There are currently over 400 Uranium-based nuclear reactors operating all over the industrialized world. Since the introduction of nuclear power plants, four have had serious malfunctions. The first of these was in 1959 in Simi Valley, California when a liquid sodium cooled reactor suffered a partial meltdown. The next accident occurred in 1979 at Three Mile Island in Pennsylvania when another partial meltdown occurred. Following that accident was the Chernobyl disaster, which was then followed by the Fukushima nuclear power plant in Japan which suffered a meltdown.

Uranium-based reactors have numerous safety features built into their designs, yet catastrophic failures have occurred.

Considering the alternative is fraught with difficulties. The long shadows of Three Mile Island, Chernobyl, and Fukushima have made the debate over nuclear power a minefield for politicians and policymakers alike. All the incidents from 1959 to present have a common thread and that is that they were all designed on the principle of using solid fuel Uranium rods. The lesson to be learned from these incidents is that it does not matter how many safety precautions are in place; eventually Murphy’s Law will prevail, and an unanticipated scenario will occur and cause a problem. This is because conventional solid fuel reactors cannot be designed to failsafe, no matter how hard we try.

But there is a solution to this problem: Generation IV reactors based upon Thorium instead of Uranium.

In 1942, the first-generation nuclear reactor design was successfully operated at the University of Chicago. The fuel was made of Uranium, with graphite bricks moderating the nuclear reaction to ensure against a runaway chain reaction. It was understood very quickly that using graphite presented a serious fire risk (case in point: the Chernobyl reactor used graphite as the moderator) so the designers began looking for other nonflammable ways to moderate the nuclear reaction.

As an alternative to the graphite-moderated reactor design, work began on a second-generation heavy water reactor. The first of these was put into operation in 1944 at the Argonne National Laboratory. The problem with the heavy water reactor is that it had to be operated under extremely high pressure, giving rise to the possibility of piping failure or a radioactive steam explosion risk. This is the design that was employed at Three Mile Island and Fukushima.

The third generation reactor design was the result of the Cold War arms race between East and West. These political tensions created a significant demand for Plutonium as a weapons material, Fast Breeder Reactors designs satisfied this demand. The Fast Breeder Reactor relies on liquid sodium as a coolant. The first liquid-sodium cooled reactor was built in 1957 in Simi Valley, California. The risk with this design is that sodium is explosive when it comes into contact with water. This design is inherently unsafe since the liquid-sodium piping is used to create steam for power by passing the piping through a boiler filled with water. The wall of the piping is all that stands between the liquid sodium and the water; a leak in that piping would be disastrous.

Continuing this trend was an insanely bad idea that fathered a fourth generation of nuclear reactor design. Someone in the U.S. Air Force hierarchy decided that if the Navy has nuclear-powered vessels, then the Air Force should have nuclear-powered bombers. Even though the scientists involved thought that this was a bad idea, they did see an opportunity to design a new type of reactor which did not use Uranium fuel rods. To head the project, Oak Ridge National Laboratory (ORNL) selected Dr. Alvin Weinberg, the same scientist that taught Admiral Rickover how to operate the Navy’s nuclear fleet.

This crazy idea began to get traction, and therefore funding from Washington. Dr. Weinberg knew that a flying nuclear reactor had to be exceptionally safe, lightweight, and small to operate for aviation applications. His solution was to go into an entirely new direction than the standard Uranium reactor. Dr. Weinberg decided to use liquid fluoride-thorium salt as the fuel. The advantages of this design over Uranium reactors are numerous; but most important was inherent safety. Thorium is a metal which, when combined with Fluoride, forms an insoluble salt; and when it is heated, it turns into a stable liquid. While it may seem as though molten salts are dangerous, in fact, such salts are currently used as the heat exchange medium for solar power generation in California. Additionally, there is an experimental molten salt solar concentrator at Sandia National Laboratory, so the idea of using molten salt to provide energy is not as farfetched as it might seem.

Unlike conventional nuclear reactors, the molten salt reactor can be designed to failsafe. An experimental Liquid Fluoride Thorium Reactor (LFTR) was designed and built at Oak Ridge National Laboratory in 1964 under the project title of Molten Salt Reactor Experiment (MSRE). Developed by Dr. Weinberg, the reactor was so inherently safe that operation of the reactor almost boring.

Even the waste products from a LFTR design are safer. They do not need long-term storage (e.g. 10,000 years for Uranium waste products). Safe storage is only needed for 300 years before becoming inert.

MSRE was operated successfully from 1965 to 1969. However, as with many successful projects that the government embarks upon, the MSRE project was ended and the reports were shelved.

Within the pages of those dusty reports, it is revealed that there are numerous advantages of LFTR designs over solid fuel Uranium reactors. For Instance, the melting point of the Fluoride-Thorium salt is in excess of 2000o F. If a reactor containment vessel breach were to occur and the molten salt were to spill out of containment, it would quickly solidify and plug the leak.

During operation, a failsafe salt plug at the bottom of the reactor vessel is actively cooled so that it will remain in a solid state. This cooled plug keeps the molten salt from draining into a fail-safe tank which would stop the reaction. In the event of a power failure, like the one in that occurred in Japan at the Fukushima facility, the lack of power would result in this salt plug melting, and the molten salt would drain into a fail-safe tank where it would cool and solidify without an incident.

The LFTR design has proven to be self-correcting. In one instance, there were indications that the reactor began to overclock and approach dangerously high temperatures. Before the operators could react and correct the problem, the molten salt began to thermally expand and decrease the density of the nuclear material. The nuclear reaction slowed down, dropping temperatures. The problem self-corrected before the operator could intervene. 

Now that the Twenty-First Century has dawned, this may be the time to renew interest in molten salt reactors for three very good reasons. The first is that the United States will be retiring many of the 99 nuclear power plants currently in operation at a more accelerated rate in the coming decade, and these power plants are not being replaced.

Secondly, Thorium is three times more abundant than Uranium.

Perhaps the most surprising reason for renewed interest is that the Nuclear Regulatory Commission is not telling the industry what direction to take, a significant departure from the past.

As demands upon the electrical power grid continue to grow, the LFTR design is poised to provide a safer solution for future power needs not just in the U.S. but worldwide.

Mac McDowell is a freelance writer and retired government scientist.

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