A new lease for nuclear?

Graphite core of the ORNL molten salt reactorI’ve focused on nuclear energy for the past three posts, and my appraisal is bleak. It looks cheaper than other options, but only if you ignore costs such as construction overruns, accidents, waste storage, and the inherent risk in long-term energy demand forecasting.  Chernobyl and Fukushima prove that the technology was and continues to be far from foolproof. And between the need for public financing and inevitable swings in public opinion, cost overruns are inescapable. Is that the end of the story? Is there any hope that nuclear energy can overcome these problems and recapture the public imagination the way it did back in the glory days of the 1950s?

There is hope. But we must change the fuel and change how it is burned.

Uranium is rare. Mining uranium ore is difficult and costly, as the mineral deposits are often deep underground. Separating the uranium from the rest of the ore leaves tailings ponds which are a huge environmental liability. The uranium must be enriched to separate out the usable isotope; the rest is wasted. The enriched uranium is then used as fuel, and all of it eventually ends up as waste. Some of that waste can be used to produce nuclear weapons. The waste will remain highly radioactive and deadly for tens of thousands of years.

It takes about 100,000 tonnes of low-grade ore to produce 250 tonnes of natural uranium, which then yields only 35 tonnes of enriched uranium. That’s enough fuel to produce 1GW of power, and 100% of the spent fuel ends up as waste. The nuclear industry produces 10,000m3 of high-level, long-lived waste each year.

However, uranium isn’t the only game in town. Thorium has the necessary properties to be a nuclear fuel. It is three times more abundant than uranium. It is already being produced and discarded as waste in the process of extracting rare earth metals. In any case it is often found in monazite sand deposits on the surface, so mining is much easier than it is with uranium. Thorium is usable as-is, so it does not require enrichment the way that uranium does. Thorium can be used as nuclear fuel in liquid form, so there is no need to form the fuel into rods or pellets as is required with uranium. A given amount of power can be produced with 3% of the amount of thorium compared to uranium. The waste cannot easily yield material for nuclear weapons, only 17% of it needs to be stored for the long term, and that for the comparatively brief period of 300 years.

It takes less than 20 tonnes of monazite to yield one tonne of thorium. That’s enough to produce 1GW of power. Of the resulting one tonne of spent fuel, only 17% requires long-term storage. The technical and anthropological challenge of storing waste for 300 years is anything but trivial, but it is not nearly as daunting as planning a dump that has to last longer than the span of recorded human history.

That’s the fuel. Now let’s look at the engine.

In a typical uranium-fuelled reactor, fuel rods in the reactor core undergo fission reactions to produce heat. Control rods, which stifle the fission reaction by absorbing neutrons, are used to modulate the amount of heat being produced. Circulating water carries the heat away to turn a turbine, thereby generating electricity.

The big problem with these types of plants is that the coolant is water. If the water gets too hot it becomes steam, expanding in volume a thousand fold. Because the coolant water is in direct contact with the core, it is radioactive, and must be contained in the event of a leak. That means that the containment vessel around the reactor must be a thousand times larger than the reactor itself. That is why commercial nuclear power plants are so massive.

One of the most promising thorium-based reactor designs is the Liquid Fluoride Thorium Reactor, or LFTR. In the LFTR, the fuel is dissolved in the working fluid itself, and that working fluid is a molten salt rather than water. The system operates at atmospheric pressure, and never approaches the boiling point of the fluid. As a result, the containment structure only needs to be slightly larger than the reactor itself, allowing for very small plants. One experimental reactor produced 2.5MW of power and was designed to be small enough to power an aircraft.

A particularly compelling design feature of the LFTR is its safety. At the bottom of the reactor is a plug made of a material which melts at ambient temperature. The plug must be constantly cooled; if the power goes out, the cooling stops, the plug melts, and the working fluid – which includes all of the fuel – drains out of the reactor and into a reservoir where the fission chain reactions stop.

In summary, a thorium-fuelled molten salt reactor such as the LFTR offers some very promising advantages over traditional uranium-fuelled, water-cooled reactors. The fuel comes from a raw material that is cheap, abundant, and high-yielding. A given amount of fuel generates much more energy, and produces much less waste. That waste is less susceptible to covert diversion toward nuclear weapons programs, and does not need to be stored for an unimaginable time frame.

The reactors can be made much smaller and therefore much faster and cheaper, rendering public sector financing unnecessary. Build-out plans can also be adjusted over time if electricity demand turns out to be different from what was predicted.

There are just two problems. Uranium is an elephant, and thorium is a flea on its backside. And LFTRs are pie-in-the-sky.

According to the European Nuclear Society, there were 435 nuclear reactors in operation worldwide as of February 2012 with a total output of 368GW. Of these, eight were thorium-fuelled, with a cumulative power of less than one GW. All eight are in India, where abundant thorium deposits have made the fuel very attractive. For all intents and purposes, all of the worldwide industry expertise and experience is in uranium and not thorium. Changing the industry over to the thorium fuel cycle would be a mammoth undertaking.

For all its apparent advantages, the LFTR is theoretical. The only one ever built, at the Oak Ridge National Laboratory, was shut down 43 years ago. Those involved have long since retired and their knowledge has been lost. Any new LFTR initiative will start from scratch. Some state-funded initiatives are doing just that, as is at least one private company (Flibe Energy), but they will need a great deal of time and money before they will have anything to show for it.

Proponents of LFTRs have their work cut out for them. Thorium may well be all that they claim. However, they face an uphill battle. Uranium-based fission did not live up to its potential. Neither did thermonuclear fusion, nor cold fusion. The history of nuclear energy is littered with broken promises. I won’t be a bit surprised if thorium, for all its possibilities, never gets the chance to prove its case in the court of public opinion.

Many thanks to my readers Steve Dyck and Dr. Alexander Cannara for inspiring this week’s post.