Nuclear Energy Doesn’t Have To Be Scary

nuclear-power-plant-837823_960_720

 

Quick – can someone tell me what potential source of energy could single-handedly provide all of the energy requirements of the US for the next 1000 years? And at the same time, foster independence in rare earth materials that are mainly sourced from China? And would not generate carbon dioxide as it is consumed?

No, it’s not coal. Coal can provide a significant portion of energy needs, and coal ash is a prospective source of rare earth metals that may be harvested, but it creates a huge amount of CO2 and has other detrimental effects, like the mountain top removal that is a blight in my home state of West Virginia. (Point of personal perspective – over 40 years ago, I had a part-time job as a chemist for a concrete company. There was a new coal fired power plant coming on line in Nebraska, and the concrete company was considering using coal ash as an extender for cement in making concrete. I performed wet chemical analysis of fly ash, going through most of the metals by reacting with reagents, then precipitating out various compounds and evaporating them to dryness in platinum crucibles. The reaction stream went all the way to sodium, which had to be precipitated with some uranium salt. I had fun doing that work, but the one thing I remember is that if you hit a fly with a stream of acetone used to dry dishware, you would cause the fly to drop out of the air instantly, and a dehydrated fly husk would be all that was left behind.)

Give up on the original question? It’s thorium, the radioactive material that has a 14 billion year half life. Thorium, along with uranium, was looked at by the US government when nuclear power and nuclear weaponry were uppermost in the minds of the government. But one factor weighing against thorium, turns out to be now a very beneficial factor. See, it is nigh unto impossible to obtain any nuclear weapon grade material out of the thorium fission reaction process. Uranium reactors will create plutonium as one of the natural byproducts of fission. If U238 (the most common uranium isotope in reactor fuel) absorbs a neutron, it becomes an extremely unstable isotope U239, which eventually transmutes into a plutonium isotope. Since U238 is the primary isotope in a pressurized water reactor, the spent fuel rods from a reactor will always contain plutonium. That is one reason why fuel rod security is required, since plutonium can be chemically separated from the toxic mix of radioactive stew found in a fuel rod.

Thorium, though, does not create plutonium. It does create the uranium isotope U233  which is the active fuel for a thorium reactor.  It also creates small quantities of another uranium isotope U232 which acts as a poison against creating a fission bomb out of U233 . So the issues of nuclear weapon proliferation by segregating out fissile material from thorium fuel are not of concern.

(Paragraph of translation. If you understand the concepts of isotopes, please skip over this paragraph.  Now, the last paragraph used a bit of physics jargon that is necessary to understand this post. I mentioned Uranium 232 (U232)  and Uranium 233 (U233).   Both of those refer to the element uranium, which has 92 protons. Where they differ is in the number of neutrons. Uranium 233 has one more neutron than does uranium 233. An element may have many different numbers of neutrons, and that is especially true in the heaviest (by atomic number) elements. These different isotopes have remarkably different characteristics, especially when dealing with nuclear reactions. This is important in the discussion below.

In order to appreciate the difference between a thorium reactor, and the current pressurized water reactors (PWR) using uranium, it is necessary to discuss PWR’s. The current nuclear power industry takes fuel rods and inserts them into the core of the reactor. A reactor contains control rods of neutron-absorbing materials. These control rods are raised and lowered in order to moderate the nuclear fission occurring in the fuel rods. If the control rods were raised totally out of the core, the fuel rods would not be able to hold the runaway nuclear reaction that would ensue. The zirconium cladding of the fuel rods would melt, and the contents of the fuel rods would pool at the bottom of the reactor. This event would not be good, putting it mildly.

When a PWR works properly, it heats water which is kept pressurized in the primary coolant loop. The water is circulated into a steam generator, where the steam is created which runs the electrical generators. Fuel rods in a PWR have a limited lifespan, and once they are no longer useful to generate electricity, these rods must be pulled out and stored in water to handle the immediate heat generated from nuclear reactions still continuing in the fuel rods. In some cases, the rods are held in water pools for 10-20 years. Then the rods must be kept secure and eventually stored somewhere where they will be able to stay segregated from the environment for geologically significant periods of time (hundreds of thousands of years). It is only after that much time has gone by before the spent fuel rods no longer pose a threat to health.

So, with uranium as the source fuel, you can generate enormous amounts of energy without CO2 generation, but with huge potential issues. You have extremely complex systems operating at incredible pressures and temperatures that must keep operating in order to prevent a runaway reaction. Then, if all works right, you have to take the fuel rods out after only a few percent of the potential energy is released, since the fission byproducts work to poison the reaction long before all of the uranium has fissioned.  And then you must isolate the fuel rods for hundreds of thousands of years, or else there is a risk of radioactive contamination of the environment. No wonder nuclear power is viewed with disfavor.

Thorium would be significantly different, though. Thorium reactors can use a molten salt as the liquid that would carry the thorium, the U233, and all fission products coming from the nuclear reactions. This means that the operating pressures of the system are far lower than in a PWR, reducing the potential for leakage or cracking of the containment system. And if the liquid salt does leak out, what would happen? It would freeze in place. Indeed, the possibility of a reactor core meltdown disappears with a thorium-fueled reactor.

It is essential to separate out the fission products and radioactive isotopes generated in this type of reactor. This can be done by taking a small side stream of the circulating salt solution, and using standard chemical separation techniques to return the unburned U233 to the salt solution. Other radioactive isotopes can be removed using this method. Because the fuel can be recycled indefinitely until it is burned, the remaining daughter fission products (the lighter elements remaining from a uranium nucleus that has fissioned) have a much shorter half life. Instead of hundreds of thousands of years for spent fuel rods to become harmless, it will only take a couple of hundred years for the fission byproducts from thorium to decay to a harmless state.

One thing that thorium has going for it is 4 times more plentiful in the earth’s crust than uranium. And it’s primary ore is one that includes rare earth metals and phosphate. So a commercial mining operation aimed at recovering thorium will also produce rare earth metals, and phosphate for fertilizer. All of these materials are essential for our modern economy.

Granted, any process involving radioactive materials has risks, and even though a thorium-fueled liquid salt reactor is simpler than a PWR, there are many challenges concerning the commercialization of this technology. But if we as a society are concerned with trying to develop energy sources that do not produce CO2 , and can serve as baseload power generators, certainly thorium reactors are a technology that should actively be researched. To think, we may have had the answer to our energy dilemmas in hand over 60 years ago, only to throw it away since thorium doesn’t lend itself to making good bombs (an oxymoron of the first degree).  Let’s try to rectify humanity’s mistake and work to investigate and commercialize this amazing resource we have been given from our earth.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s