Next Up in Nuclear: Small Modular Reactors

The Obama administration's next move in boosting energy techonlogy will be nearly $500 million in support of small modular reactors. Individually, these nuclear reactors would produce less energy than traditional reactors, but could be used more flexibly and operate more efficiently. Here's what to know about the next thing in nuclear.

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Today, one-fifth of America's electricity comes from nuclear power. The federal government wants to gradually expand that fraction in order to phase out greenhouse-gas-emitting coal-fired plants, which generate most of our energy. But nuclear power plants take a long time and a lot of money to build. That's why the Department of Energy is pushing a new technology called the small modular reactor (SMR). Last week, the department announced that it would invest $452 million toward developing and licensing a smaller and sleeker nuclear reactor.

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SMRs will be small enough to be pre-assembled in a factory and shipped to location. These easy-to-install reactors could potentially shave years and millions of dollars off the construction of nuclear power plants, and could make it economical to bring nuclear power to rural areas or developing countries that lack infrastructure. That's why SMRs are being hailed as the next generation in nuclear technology.

How It Works

First, don't let the name fool you. "These are not going to fit in your backyard," says Paul Genoa, a policy director with the Nuclear Energy Institute. "They'll still be industrial facilities, but the footprint will probably be like that of a small shopping mall, but with more land around it." SMR plants could fit inside the footprint of the old coal-fired plants they're expected to replace, Genoa says.


There are three main varieties of SMR in development.

Light-Water SMRs







Gas-Cooled SMRs

The idea behind gas-cooled reactors, Genoa says, is to rule out even the possibility of a meltdown. "It is physically impossible for the reactor to get hot enough to damage the fuel," he says. That's because rather than using water as a coolant, gas-cooled SMRs would use helium.


But unlike water, helium doesn't boil or react. This allows the gas-cooled reactor to operate safely at temperatures up to 1000 degrees C, which increases the reactor's efficiency. While a light-water reactor typically extracts roughly 34 percent of its core's potential energy, a gas-cooled reactor would operate at more than 40 percent efficiency. A gas-cooled reactor developed by the Japanese Atomic Energy Research Institute has achieved 45 percent efficiency, and General Atomics' Modular Helium Reactor achieves up to 47 percent.


Fast Reactors

Typical nuclear reactors use what are called moderators to slow down neutrons and control the chain reactions that happen during fission. That's because the "fast neutrons" created when uranium splits are less likely to cause fission in the neighborhood—and keep the chain reaction going—than slightly slower neutrons are.

Fast reactors, though, are optimized for fast neutrons, which allows them to extract 60 times more energy from uranium than a typical light-water reactor can. That also means that fast reactors can digest the nuclear waste of other reactors, reducing the waste's radiotoxicity while extracting energy in the process.

Fast reactors already in development include Argonne National Lab's 175Mw reactor, Advanced Reactor Concept's sodium-cooled ARC-100, and the 25Mw Hyperion Power Module. But because uranium is still in abundant supply, and because some fast reactors can be used to breed weapons-grade plutonium, using these SMRs to recycle uranium is not economical at this point.

Potential Snags

Before any SMR can be used in a power plant, the Nuclear Regulatory Commission must create regulations for it. Any new reactor design raises a slew of new questions. Since SMRs are smaller and have lots of passive safety features, are fewer operators needed per reactor? Should the 10-mile evacuation radius mandated for traditional reactors be smaller for a smaller reactor? What are the proper safety protocols for an SMR? Once the NRC figures out how to adapt current regulations, it could go certify SMR designs and issue licenses to operate new power plants.

SMRs may be the reactors of the future, but Genoa says traditional reactors aren't going away anytime soon. "Small reactors are not a substitute for big reactors, but we can't build a big reactor everywhere," he says. "Just like when you go to the auto store and you can choose a sedan, a minivan or a truck, the nuclear market needs more options."

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