A week ago, Ambrose Evans-Pritchard of the UK newspaper the Telegraph demonstrated that he is a staunch advocate of Free Lunches in his Obama could kill fossil fuels overnight with a nuclear dash for thorium—

If Barack Obama were to marshal America’s vast scientific and strategic resources behind a new Manhattan Project, he might reasonably hope to reinvent the global energy landscape and sketch an end to our dependence on fossil fuels within three to five years.

Human beings love the Free Lunch, so there were comments & chatter galore on the internets
about Evan-Pritchard's article. He quoted nuclear physicist Carlo Rubbia to make his point, with one easily forgettable caveat—

There is no certain bet in nuclear physics but work by Nobel laureate Carlo Rubbia at CERN (European Organization for Nuclear Research) on the use of thorium as a cheap, clean and safe alternative to uranium in reactors may be the magic bullet we have all been hoping for, though we have barely begun to crack the potential of solar power.

Dr Rubbia says a tonne of the silvery metal – named after the Norse god of thunder, who also gave us Thor’s day or Thursday - produces as much energy as 200 tonnes of uranium, or 3,500,000 tonnes of coal. A mere fistful would light London for a week.

Thorium eats its own hazardous waste. It can even scavenge the plutonium left by uranium reactors, acting as an eco-cleaner. "It’s the Big One," said Kirk Sorensen, a former NASA rocket engineer and now chief nuclear technologist at Teledyne Brown Engineering.

"Once you start looking more closely, it blows your mind away. You can run civilization on thorium for hundreds of thousands of years, and it’s essentially free. You don’t have to deal with uranium cartels," he said.

Not only does small amounts of thorium produce prodigious amounts of energy, but it seems you can't leave your house in the morning without tripping over it—this would be the only sense in which it is hazardous, apparently.

Thorium is so common that miners treat it as a nuisance, a radioactive by-product if they try to dig up rare earth metals. The US and Australia are full of the stuff. So are the granite rocks of Cornwall. You do not need much: all is potentially usable as fuel, compared to just 0.7pc for uranium.

If something sounds too good to be true, it's a good bet it is. There is a joke among economists pertaining to the Efficient Market Hypothesis that goes like this—

Two economists spot a $10 bill on the ground. One stoops to pick it up, and the other advises, “Don’t. If it were really $10, it wouldn’t be there anymore.”

If thorium reactors are that $10 bill, it would be fair to say that no, they're not just lying on the ground waiting for somebody to pick them up. However, there really is an opportunity in these reactors which various groups are pursuing. Carlo Rubbio, being a nuclear scientist, no doubt just waves his hands in the air when confronted with the engineering problems of creating a commercial thorium reactor.

Needless to say, no such reactor exists, and that's not entirely due to the fact that uranium was chosen over thorium decades ago because you can make atomic bombs with it—this story is popular among the usual conspiracy theorists, who probably also believe that the political power of the oil & coal companies is the sole reason we don't the run the whole economy on renewable energy today. Nevertheless, a promising path for nuclear energy was largely abandoned in the past, and is now being picked up again.

Without much effort, I found several credible sources of information about the state of thorium reactor development. I will quote from IEEE Spectrum's Is Thorium the Nuclear Fuel of the Future? 

...several countries are investigating the possibility of thorium-based energy generation: India's working on an Advanced Heavy Water Reactor, Japan has the miniFuji, Russia is working on the VVER-1000 and even the United States has long term plans to experiment with commercial energy generation by thorium. Most of these plans are nebulous, but for some it’s a serious option. The country with the most specific plan is India, which has drawn up a three-stage process to rely almost entirely on thorium by 2030.

[My note: Did you spot an important keyword in that paragraph? — "and even the United States has long term plans..."]

India has been very aggressive about meeting its energy needs with thorium. They are embarked on a multi-stage development which may pay off a few decades from now—

The fast breeder reactor is only the second stage of a long-term project. “There are no defined time lines as lot of technology development, research and demonstration activities need to be completed before commercial deployment of thorium reactors for power,” Thakur told me in an email. “I think it is decades away.” First, he explains, “we need to have a significant capacity of the fast breeder reactors where thorium could be used as a blanket.” (For a good overview on what this means, read this article on thorium reactor physics at the World Nuclear Association.)

The IEEE Spectrum article talks about other designs (e.g. LFTR, liquid fluoride) and provides links to additional information. Here's the bottom line—

... I must note here that there are counter-arguments to these arguments and counter-counter-arguments to boot. If I listed them all it would just be turtles all the way down.

Ultimately, we can argue all we want, but the proof will come in the most basic possible form—someone submitting a credible design to the US Nuclear Regulatory Commission or some analogous body. So far, that hasn’t happened. NRC spokesperson Scott Burnell told Spectrum that there “isn't anything on our radar for a thorium-based reactor at this point.”

As the old saying goes, the proof is in the pudding. Religious disputes about energy from thorium go on and on, just as they always do when one is arguing about something—a commercial thorium reactor providing real power to real people—that does not exist. 

The Free Lunch is not free, and is dangerous besides, because of the cost of opportunities foregone as we engage in single-minded pursuit of it—

The true cost of something is what you give up to get it. This includes not only the money spent in buying (or doing) the something, but also the economic benefits that you did without because you bought (or did) that particular something and thus can no longer buy (or do) something else...

If we did as Evans-Pritchard suggests—marshal America’s vast scientific and strategic resources behind a new Manhattan Project to develop thorium reactors—we would forego the opportunity to develop other sources of energy, to learn how to live with less energy, etc. Since he writes about economic issues for the Telegraph, one would think he knows this already. And if he knows about Free Lunches & opportunity costs, then only shamelessness, combined with willful ignorance, can explain why he wrote such a  misleading sales pitch for thorium reactors. 

Wake me up when there's a commercial thorium reactor up & running somewhere on Earth. Then, and only then, will we know the true costs & benefits of energy from thorium.