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"Why Not Thorium"


By: Jason Hagerman



When Canadian scientists set out to design nuclear reactors in the early 1950s, they did so with an eye to the future, the far future, when uranium supplies ran out. The Canada Deuterium Uranium (CANDU) reactor, the product of this foresight, can burn thorium as well as uranium. At the time of the initial design, burning thorium, a cleaner burning nuclear fuel, seemed fantastic—the market wanted uranium reactors, and besides, thorium burns so hot that scientists had no technology at the time to actually burn thorium.

Now we do. Robotics can now support the thorium cycle in a commercial environment, giving way to the possibility of a commercial-scale CANDU reactor burning thorium.

Now it seems that thorium’s time—a time Canadian scientists envisioned at the dawn of the nuclear age—has finally come, as China’s growing economy adopts thorium reactors, as countries around the world look more closely at their growing energy needs, at the dangers associated with nuclear power, and the inadequacy of so many renewable energy sources.








The Canadian perspective
In the 1950s, Canadian scientists designed nuclear reactors to use natural uranium, instead of enriched uranium, in an effort to combat nuclear proliferation. “[Canadian labs] designed a technology that worked with natural uranium,” says Dr. Dave Novog, Associate Professor in the Department of Engineering Physics at McMaster University. “This meant we didn’t need enrichment facilities that could be construed as being weapons. In fact, we’re quite far from any technology that would be needed for weapons.”
 
 
Canada poured hundreds of thousands of dollars into thorium research in the 1950s and 60s, planning to eventually migrate to a domestic thorium cycle and sell the country’s substantial uranium stores as other countries run dry. Knowing the necessities of a thorium cycle, scientists designed the reactor to one day flourish in a thorium economy.
“The developers always had this thorium cycle in mind,” says Dr. Dan Meneley, former Chief Engineer of Atomic Energy of Canada Limited. “I’d say a fair amount of good management and a whole lot of luck went into those reactors.”
 














 
 
So why use uranium at all?
“Things that happen early on tend to determine which way a country goes with a given technology,” Meneley says. “You can’t run a nuclear reactor without a fissile material and thorium doesn’t come with a fissile material. Without the technology to support thorium in the beginning, our only choice was to use natural uranium in our nuclear reactors, so that’s what we used.”
 
 
Thorium becomes uranium 233 in a thorium reactor. Advanced reprocessing at substantial cost is necessary in the thorium-to-uranium conversion.
 
 
“Reprocessing has always been expensive,” Novog says. “The material is very radioactive when it comes out of the core and it has to be done robotically, and this is a stage we avoid when burning natural uranium like we do today. So really from the outset this complexity in reprocessing within the thorium cycle is something we avoided because we didn’t have the technology and it was prohibitively expensive to develop.”
 
 
While they used natural uranium as a fuel source, Canadian scientists developed early CANDU reactors with a thorium agenda. And for good reason. Canada holds about 100,000 tons of thorium according to the World Nuclear Association, outstripped only by India (360,000), Australia (300,000), Norway (170,000), the U.S. (160,000) and possibly China.
 
The dollar economy
Canada possesses large stores of thorium and the technology to use it, but, like most other nuclear countries, continues to burn uranium for fuel.


“It’s much cheaper to do things the way we do right now,” says Dr. Adriaan Buijs, President of the Canadian Nuclear Society. “We do have large quantities of thorium, but we also have one of the largest reserves of uranium on the planet. At the moment, thorium simply isn’t a priority for us and that’s why we’re not focused on it. In China, it’s a different story.”
 
 
According to Buijs, thorium is burning in CANDU reactors in China today. “The reactors we designed are the only type of reactor that can use thorium essentially as they are,” he explains. Canada holds enough uranium to power its nuclear reactors for decades while still exporting to countries like India with rising demand.
 
 
For any country to migrate to a thorium cycle, the associated costs must drop. Currently, thorium costs about $5,000 per kilogram compared to uranium 235 at $40. However, the World Nuclear Association projects thorium could drop as low as $10 per kilogram when mined en masse.
A one gigawatt uranium plant costs about $1.1 billion to build and $30 million to fuel annually. The World Nuclear Association says a thorium plant of equal size could cost as little as $250 million and fuelling it might cost $1 million annually.
 
 
 













Experts believe this is the future of energy mass production and it will
come when necessity dictates. “For somewhere like Germany or Italy, life is going to be very painful when oil is up to $300 per barrel,” says Meneley. “We can’t count on natural gas and we can’t count on oil. Without nuclear, and thorium as a significant part of that, it will be a low energy future.”
 
 
The neutron economy
Natural uranium requires a heavy water moderator, and in the case of CANDU reactors, the water-like substance deuterium. Deuterium is hydrogen with an extra neutron. Without a heavy water moderator, natural uranium requires enrichment to react favourably in the burning process. A deuterium heavy water moderator absorbs fewer neutrons during the burning process, freeing more neutrons for other activities, activities like converting thorium into uranium by making the thorium absorb some extra neutrons. The heavy water moderator helps Canadian reactors achieve high neutron economy for converting thorium to uranium and using less mined uranium than most reactors.
 
 
Today, scientists are examining the commercial viability of the reactor’s neutron economy. Canadian reactors in China are testing a once-through-thorium-cycle, Novog says.  Thorium absorbs neutrons from the heavy water moderator, becoming uranium 233. In this process thorium is used once and then stored, as processing for reuse is expensive and technically challenging.  But as China’s uranium stockpile dwindles, Chinese and Canadian scientists seek even greater neutron economy to support the possibility of a closed thorium fuel cycle.
 
 
Most scientists agree a closed, self-perpetuating thorium cycle is possible, but to demonstrate it on a commercial scale requires major capital investment. Countries like China and India, facing a future with little uranium and skyrocketing demand for energy, may invest significant resources into closed-cycle research.

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