Sept. 11, 2011, Forbes / Energy

For the past several months, a friend of mine has been telling me about the potentially game-changing implications of an obscure (at least to me) metal named Thorium after the Norse god of thunder, Thor.

It seems like he is not the only person who believes thorium, a naturally-occurring, slightly radioactive metal discovered in 1828 by the Swedish chemist Jons Jakob Berzelius, could provide the world with an ultra-safe, ultra-cheap source of nuclear power.

Last week, scores of thorium boosters gathered in the United Kingdom to launch a new advocacy organization, the Weinberg Foundation, which plans to push the promise of thorium nuclear energy into the mainstream political discussion of clean energy and climate change. The message they’re sending is that thorium is the anti-dote to the world’s most pressing energy and environmental challenges.

So what is the big deal about thorium? In 2006, writing in the magazine Cosmos, Tim Dean summarized perhaps the most optimistic scenario for what a Thorium-powered nuclear world would be like:

What if we could build a nuclear reactor that offered no possibility of a meltdown, generated its power inexpensively, created no weapons-grade by-products, and burnt up existing high-level waste as well as old nuclear weapon stockpiles? And what if the waste produced by such a reactor was radioactive for a mere few hundred years rather than tens of thousands? It may sound too good to be true, but such a reactor is indeed possible, and a number of teams around the world are now working to make it a reality. What makes this incredible reactor so different is its fuel source: thorium.

A clutch of companies and countries are aggressively pursuing Dean’s dream of a thorium-powered world.

Lightbridge Corporation, a pioneering nuclear-energy start-up company based in McLean, VA, is developing the Radkowsky Thorium Reactor in collaboration with Russian researchers. In 2009, Areva, the French nuclear engineering conglomerate, recruited Lightbridge for a project assessing the use of thorium fuel in Areva’s next-generation EPR reactor, advanced class of 1,600+ MW nuclear reactors being built in Olkiluoto, Finland and Flamanville, France.

In China, the Atomic Energy of Canada Limited and a clutch of Chinese outfits began an effort in mid-2009 to use thorium as fuel in nuclear reactors in Qinshan, China.

Thorium is more abundant than uranium in the Earth’s crust. The world has an estimated 4.4 million tons of total known and estimated Thorium resources, according to the International Atomic Energy Association’s 2007 Red Book.

The most common source of thorium is the rare earth phosphate mineral, monazite. World monazite resources are estimated to be about 12 million tons, two-thirds of which are in India.  Idaho also boasts a large vein deposit of thorium and rare earth metals.

Thorium can be used as a nuclear fuel through breeding to fissile uranium-233.  For those technically-inclined readers, here is a geek-friendly explanation of what that means:

Although not fissile itself, Th-232 will absorb slow neutrons to produce uranium-233 (U-233)a, which is fissile (and long-lived). The irradiated fuel can then be unloaded from the reactor, the U-233 separated from the thorium, and fed back into another reactor as part of a closed fuel cycle. Alternatively, U-233 can be bred from thorium in a blanket, the U-233 separated, and then fed into the core.

In one significant respect U-233 is better than uranium-235 and plutonium-239, because of its higher neutron yield per neutron absorbed. Given a start with some other fissile material (U-233, U-235 or Pu-239) as a driver, a breeding cycle similar to but more efficient than that with U-238 and plutonium (in normal, slow neutron reactors) can be set up. (The driver fuels provide all the neutrons initially, but are progressively supplemented by U-233 as it forms from the thorium.) However, there are also features of the neutron economy which counter this advantage. In particular the intermediate product protactinium-233 (Pa-233) is a neutron absorber which diminishes U-233 yield.

I have no idea whether thorium is the panacea many people claims it is likely to be, but I believe we’ll be hearing more about it in the years to come.

UPDATE: If you want to know more about Thorium, the person to ask is my fellow Forbes contributor – and resident nuclear energy expert – Kirk Sorensen.  Check out Sorensen’s work here:  http://blogs.forbes.com/kirksorensen/

William Pentland

Contributor