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Sustainable Energy

Can Better Power Plant Designs Stimulate Nuclear Energy?

In the wake of Fukushima disaster, safer nuclear options are only slowly making progress.

Even though nuclear power plants don’t emit carbon dioxide, their appeal is still limited in certain countries. For one thing, getting power from nuclear tends to cost more than deriving electricity from burning coal or natural gas. And of course fears linger about its safety and the dangers of nuclear waste. After the partial meltdown at Japan’s Fukushima Daiichi plant in 2011, many countries rethought nuclear power. Germany, as one example, decided to decommission all its nuclear plants by 2022.

A Westinghouse power plant under construction in Haiyang, China.

But some countries still are moving ahead with nuclear. China, for example, is complementing its 23 plants in operation with 26 under construction and even more planned (see “Nuclear Options”). Meanwhile, some “meltdown-proof” alternative designs could raise the bar for safety and lower nuclear’s cost. Here are some promising ideas.

Molten Salt Reactors

Many companies and research groups have been researching potential next-generation reactors since well before the Fukushima disaster. Known as Generation IV reactors, these designs exist only on paper and won’t come online until 2030 or later.

One type of reactor in that category is known as the molten salt reactor. First demonstrated at Tennessee’s Oak Ridge National Laboratory back in the 1960s, this type of reactor has gained attention recently from startups hoping to revamp it.

Today’s reactors generate electricity by heating water to make steam that turns turbines. That water is then cooled and circulated back through the system. Fueling the core’s activity is uranium encased in pellets and housed in metal rods. Water flows through the reactor to cool down the rods so that they don’t overheat and damage the core’s structure.

Molten salt reactors are different in a few ways. The main one is that a radioactive material such as uranium is dissolved into a fluoride or chlorine salt that acts as a cooling agent, eliminating the need for water and the assemblies protecting the fuel pellets in conventional plants. Those assemblies need to be replaced every few years. In addition, the technology is supposed to be meltdown-proof because the molten salts will expand if the fuel heats up too much, slowing and eventually halting the fission reactions inside. Some of these reactors may be able to use thorium, which is more abundant than uranium, as fuel.

MIT spinoff Transatomic Power says it has found a way to improve the Oak Ridge design by using fuel with low uranium levels, making it possible for it to run on leftover fuel from today’s nuclear plants.

Canada’s Terrestrial Energy is pursuing a molten-salt reactor that is closer in design to Oak Ridge’s than Transatomic’s. It aims to have engineering blueprints ready by 2016 and plans to eventually build a demonstration plant in Canada.

Liquid Metal Cooling

Next-generation reactors that cool down the reactor core with liquid metals are also a huge area of interest for researchers.

GE Hitachi, a joint venture formed by General Electric and Hitachi in 2007, is working on an advanced nuclear reactor based on an experimental reactor developed at Argonne National Laboratory in the 1960s. It is designed to run off of the radioactive plutonium in spent waste fuel. The reactor uses fuel rods that sit in a bath of a liquid sodium coolant. It’s similar to a molten salt reactor in that it slows fission in an emergency situation because the fuel expands at higher temperatures.

Colorado-based Gen4 Energy is also researching a metal coolant. It’s looking into using lead bismuth to cool the reactor. The design wouldn’t rely on electricity to power pumps that remove heat from the core.

There are also a few research projects in Europe focused on using metals to cool the reactors. One design being developed by the Belgian Nuclear Research Center uses a lead-bismuth liquid to cool the core.

Gas Cooling

Other reactor designs cool the reactor core with gas. A design called the XE-100 from Maryland-based X-Energy uses helium to do the job. Known as a “pebble bed” reactor, the design encases the radioactive fuel in pebble-shaped balls. X-Energy claims that the small reactor could consume 95 percent of its fuel, which is several times more than nuclear reactors today. This model is also supposed to be meltdown-proof. China is working on building a pebble bed reactor today. A pebble-bed reactor was planned in South Africa, but the government cut funding for the project in 2010 before a demonstrator could be constructed due to its failure to attract other investors.

Improving Standard Designs

Alternative reactor designs will take years to test, refine, and commission. A quicker route is to simply upgrade existing designs with new safety features designed to shut down reactors without human assistance or pumps that require electricity.

U.S. authorities in September approved the design for GE Hitachi’s new boiling water reactor, which the joint venture touts as the “world’s safest reactor.” This is designed to cool down the reactor cores for seven days after an accident without human intervention. The design of the new reactor is more modular than that of other boiling water reactors. This allows water to circulate with fewer pumps, valves, and motors. Thirty-five older boiling water reactors are operating in the U.S. today, the World Nuclear Association’s website shows. These were built between 1967 and 1990.

The other 65 nuclear power plants in the U.S. are based on a design called a pressurized water reactor. This is the design for the five new power plants under construction today, all designed by Toshiba subsidiary Westinghouse. Four of these new plants in Georgia and South Carolina are based on the company’s most advanced design, the AP1000. China is also building at least four of these plants. The reactor is smaller and more modular than older power plants, making it easier to build. It’s designed to shut down safely without needing humans or a connection to the power grid.

Shrinking Plants

Many of the above-mentioned reactors are smaller than today’s power plants and could be assembled in a factory rather than as big, one-off projects. Smaller reactor designs could make nuclear attractive for power providers that can’t afford the $6 billion to $7 billion needed to finance large reactors, the Nuclear Energy Institute’s Daniel Lipman said during a congressional hearing last December.

 In 2013, the U.S. government offered to help two companies fund their designs for small modular nuclear reactors.

Oregon-based NuScale Power is working on a small reactor that can shut off and cool without a human operator or power source. It plans to submit a design for approval in the second half of 2016. Commercial operations would start in 2023 or 2024.

DOE also chose a separate model called the B&W mPower reactor, backed by a company called Babcock & Wilcox, which provides parts and services for power plants. The company aimed to begin commercial operations in 2022, but it announced last April that it had failed to find enough investors and was slowing development of its small reactors.

The Takeaway:

Advanced reactor designs are still only on paper and will need substantial investment to get through a rigorous certification process that’s geared toward older reactor designs. Even if the public can be convinced that new reactor designs are safer, economics will likely remain a stumbling block. Factors like the low cost of natural gas will play a big role in dictating whether these new concepts have a chance at moving beyond the blueprint.

Thanks to Insider Harry Babad for suggesting this week’s topic. Do you have a big question? Send suggestions to questionoftheweek@technologyreview.com

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