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By A.J. Roan
For Metal Tech News 

The nuclear option for carbon-free energy

Power of atom presents possible answer to energy concerns Metal Tech News Weekly Edition – March 18, 2020

 

Last updated 6/27/2020 at 5:33am

Uranium thorium nuclear reactor low carbon energy fuels

Adobe Stock

Roughly 10% of the world's electricity is currently generated from uranium in nuclear reactors.

As the cultural and economic shift towards renewable energy continues to develop, the pursuit for new renewable technologies is emerging as well. Some believe these pursuits should include revisiting a bygone, yet controversial, energy source to combat the encroaching climate issue.

Nuclear energy, a hot button issue due to our sordid history with the technology, but a discussion regarding the viability of nuclear energy may soon be approaching.

For almost a hundred years the secrets of the atom have been known, yet the potential of such incredible energy has barely scratched the surface.

To explore a future with nuclear energy, one must understand the process, the mistakes, the difficulties and the potential that the fundamental building block of our universe provides.

Splitting the atom

Today, nuclear energy depends on uranium. Though this element was discovered in 1789, it would be another 100 years until its radioactivity is discovered and longer still until the potential energy it could create is learned.

In the following decades, further discoveries would lead to a more complete picture of the atom and ultimately the incredible discovery that would change the world forever, nuclear fission.

The earthshattering power of this atom-splitting technology was demonstrated with the bombing of Nagasaki and Hiroshima in 1945.

So how does an element found naturally on earth cause such devastation?

The reaction that causes nuclear explosions is due to a sudden release of energy produced by splitting the nuclei of the fissile elements making up the bombs' core.

The two most readily useable materials were uranium and plutonium because they easily undergo fission.

This means that when a neutron strikes the nucleus of the isotope, this splits the nucleus into fragments and releases a tremendous amount of energy, fission occurs.

The fission process becomes self-sustaining as neutrons produced by the splitting of the atom strike nearby nuclei and produce more fission. This is known as a chain reaction and is what causes an atomic explosion.

This is the splitting of the atom, a power that has been harnessed for destruction in war and the creation of electricity.

The uranium standard

Uranium, the traditional source of this energy, is found naturally as an ore. It is one of the more common elements, being 40 times more common than silver and 500 times more common than gold.

The major challenge for commercial uranium extraction is to find areas where concentrations are adequate to form an economically viable deposit.

Currently, the primary use for uranium obtained from mining is in fuel for nuclear reactors.

Globally, the distribution of uranium ore deposits is widespread on all continents, with the largest deposits found in Australia, Kazakhstan, and Canada.

After mining, the ore is crushed and treated with an acid to produce a uranium oxide concentrate, a kind of yellowy powder that is sealed in drums to be sold raw.

Before it can be used in a reactor for electricity generation, however, this "yellowcake" must undergo a series of processes to produce a useable fuel for power generation.

Most of the world's current reactors apply further steps by converting the uranium oxide to a gas, uranium hexafluoride, which enables it to be enriched.

This increases the amount of uranium, this is a much more efficient and safer method, especially in larger reactors and allows the use of ordinary water as a coolant.

Even further still, the gas is then converted again to uranium dioxide, the finished form, which is made into fuel pellets.

These fuel pellets are placed inside thin metal tubes, known as fuel rods, which are assembled in bundles to become the fuel elements or assemblies for the core of the reactor.

In a typical large power reactor, there might be 51,000 fuel rods with over 18 million pellets.

Uranium, however, has two issues – inherent instability of the isotope due to its fissile nature and plutonium another ingredient in nuclear weapons that is even more explosive than uranium.

The meltdown

Presently, there are six different commercial types of nuclear reactors.

The original design that led to the development of the atom bomb is known as a pressurized water reactor (PWR) – essentially a giant radioactive-powered steam engine that uses heat given off by the fission reaction of uranium to generate electricity.

The fuel rods are inserted into slots built around the reactor core, essentially a trigger to excite the subatomic particles in a controlled pressurized water tank.

Excite, meaning millions, if not billions of these particles undergoing fission in a monitored game of whack-a-mole.

Due to the nature of the design, in the event of the reactor or fuel rods overheating this can cause a meltdown.

In recent times, the meltdown of the Fukushima Daiichi reactors in Japan is an example of the problems that can arise when reactor temperatures cannot be maintained. Similar loss-of-coolant accidents (LOCA) led to three of the six reactors going meltdown with three hydrogen explosions.

Historically, the most infamous of nuclear meltdowns is perhaps Chernobyl, not just a popular historical drama television series, the fallout from the Chernobyl incident will affect the world for generations.

Both plants used several different types of reactors, with Fukushima using a boiling-water reactor and Chernobyl utilizing two separate types – a high-power channel-type reactor and a pressurized light-water reactor.

With these different designs, ultimately, they functioned the same way. Keeping the superheated atoms cool and producing vast amounts of energy.

A typical 1,000-megawatt electrical (MWe) reactor provides enough electricity for a modern city of one million people.

About 10% of the world's electricity is currently generated from uranium in nuclear reactors.

This amounts to over 2,500 terawatt-hours (TWh) each year, equal to as much as all sources of electricity worldwide in 1960.

This energy comes from over 440 nuclear reactors in 30 countries.

About 50 more reactors are under construction and over 100 are planned.

Belgium, Bulgaria, Czech Republic, Finland, France, Hungary, Slovakia, Slovenia, Sweden, Switzerland and Ukraine all get 30% or more of their electricity from nuclear reactors.

The United States has just under 100 reactors operating, supplying 20% of its electricity. While France gets over 70% of its electricity from uranium.

It is clear that nuclear energy is being used, but is it at its full potential?

The push towards solar, wind and hydro power, the advancements in battery technology for storage of that energy, are worthy endeavors. Yet as civilization continues to expand, and the population continues to grow the consumption will too and the attempts at decarbonizing the planet may not be the only issue of an energy hungry planet.

So, is there an option that can produce nuclear energy with possibly less risks?

The thorium alternative

There is a potential element that has had little to no development since its discovery in 1828.

Thorium shares a radioactive place on the periodic table with uranium yet is more abundant, found at concentrations of over three times its counterpart.

According to proponents, a thorium fuel cycle offers several potential advantages over a uranium fuel cycle – greater abundance of thorium, superior physical and nuclear fuel properties and reduced nuclear waste production.

Thorium, naturally, is not fissile and so is not directly usable in a thermal neutron reactor, it is a "fertile" element meaning it will not excite when bombarded by separating atoms.

However, upon absorbing a neutron it can transmute to a specific uranium isotope-233, which is an excellent fissile fuel material.

So, for any thorium fuel concept to be viable it therefore requires that it first become irradiated in a reactor to provide the necessary neutron dosing to produce its artificial uranium isotope, uranium-233.

Uranium-233 can then be recycled into new fuel, or it may be usable 'in-situ' in the same fuel form, particularly in molten salt reactors (MSRs), which have several safety and economic advantages over its solid fuel counterparts but has its own set of issues.

It is important to know that nuclear waste is recyclable. Once reactor fuel – uranium or thorium – is used, it can be treated and put into another reactor as fuel.

In fact, typical reactors only extract a few percent of the energy in their fuel. It is estimated that you could power the entire U.S. electricity grid off the energy in nuclear waste for almost 100 years.

Also, if the waste is recycled, the final waste that is left over decays to harmlessness within a few hundred years, rather than a million years as with standard (unrecycled) nuclear waste.

Due to its purported superior properties it is claimed a single metric ton of thorium burned in an MSR –– otherwise known as a liquid fluoride thorium reactor (which uses liquid thorium rather than the uranium pellets –– has the capability of producing 1 gigawatt of electricity.

While a traditional PWR uranium reactor would need to burn 250 metric tons of uranium to produce the same amount of energy.

Hence the assertion of reduced waste is of added benefit for thorium reactors.

Possibly the single largest concern next to a meltdown is the weaponization of uranium and plutonium. A thorium reactor could lessen the convenience of these isotopes for militarization.

Radioactive thorium nuclear fuel near uranium on periodic table

Theodore Gray; Periodictable.com

The only fissile material produced in a thorium reactor would be the fuel itself and while the immediate cessation of uranium reactors is highly unlikely, the concern for weaponization of uranium or plutonium could be somewhat alleviated.

The future of nuclear energy and the technology to utilize it more efficiently, safely and on a larger scale may be a long way off. Nevertheless, it has been discovered and is here to stay, and possibly a future entrepreneurial pioneer will labor to take it to the stars.

The unexplored potential of such an incredible technology, either with uranium or thorium, remains on the table and with the growth of the planet, so too will the growth of energy be needed.

 

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