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Energy

Small Nuclear

Self-contained power plants could supply growing energy demand in poor countries.

Now more than ever, the world needs nuclear energy, says this year’s Nobel Peace Prize laureate, Mohamed ElBaradei. In a talk at MIT last week he cited a new report from the International Energy Agency that said world energy demand will increase by 50 percent in the next 25 years. Meanwhile, carbon dioxide emissions, which are a leading cause of global warming, will increase by the same percentage. Nuclear power could provide a significant amount of that power, without producing the carbon dioxide, says ElBaradei.

It’s an argument that’s attracting more and more proponents these days. But traditional nuclear power plants are very expensive to build, which can be a serious obstacle to their construction in poor countries. One solution being proposed, according to ElBaradei, is to build hundreds of small nuclear power plants, each designed to serve a single town. Such plants could be built for a fraction of the cost of the current large-scale regional ones. And they could be installed without the need to also build an extensive and expensive power grid. As a country’s energy needs grow, more plants can be added to keep up. Such plants might also be a good solution for remote communities.

A countryside dotted with hundreds of small reactors might seem like a safety and nuclear proliferation nightmare. But, according to ElBaradei, director general of the International Atomic Energy Agency, they can be built with safeguards against meltdowns and theft of materials by would-be terrorists.

Researchers at Argonne National Laboratory in Argonne, IL, described a concept for such a small-scale reactor this summer. One of the safeguards is a passive cooling system, which continues to work even if power goes down. The reactors could also operate for 30 years without refueling, which would mean fewer deliveries that could be hijacked. And stealing the fuel while it was in the reactor would require bringing to the site extensive heavy equipment, which would be easily visible by satellite, according to David Wade, senior technical advisor at Argonne and one of the developers of the concept.

“It’s good to have a reactor that requires a minimum of maintenance and refueling” for remote locations in some situations, says Mujid Kazimi, a nuclear engineer at MIT. He says that similar small reactors are under development in Argentina and Brazil, and Toshiba has recently offered to build one for an Alaskan town.

The Argonne concept uses a reactor cooled by liquid lead that allows for high operating temperatures and efficient use of the fuel, which is programmed to produce energy slowly over the 30-year cycle. The lead coolant also circulates without the need for the expensive back-up diesel generators required by today’s plants. “If it is built correctly, it will be able to be cooled by natural convection alone,” says Kazimi, who was not part of the concept development team.

The power plant would be mostly buried underground for protection, and surrounded by a back-up passive air cooling system – hot air rises out of the exhaust stack and cool air is pulled in through low vents. This system would run continuously, essentially wasting about one percent of the heat generated, yet ensuring that the reactor would cool off in the case of a problem.

The reactor is partially self-regulating. If the temperature rises, the structures containing the fuel expand, causing the fuel to spread out, and slowing down the frequency of the neutron collisions that create the nuclear reaction. This, in turn, causes the temperature to fall. These features, says Wade, should simplify the control of the plant and prevent meltdowns.

The lead will also serve as a safety measure. The fuel will be delivered inside the lead in a solid form, to be melted on site. When this module is removed and replaced after thirty years, the lead will cool off – now encasing the used fuel. This can be returned to a central facility for reprocessing, after which almost all of the spent fuel can be reused, says Wade.

On the downside, building small reactors means losing out on the economy of scale that has driven a trend toward bigger and bigger reactors, says Wade. He hopes to make up for this by creating ways to mass-produce the reactors in modules that can be quickly assembled on site.

For Wade, small reactors are part of a vision for large-scale changes. “What we’re trying to do is not only change the technology, but also exploit it, by changing the infrastructures. You can ship thirty years of energy with a single core loading, to provide energy security for a country without the need to install the infrastructure [for processing the fuel] right on its own territory.” ElBaradei says designs such as the one developed at Argonne could actually “reduce access to sensitive nuclear material” if countries agreed to share fuel facilities. “We cannot afford to have every country sitting on an enrichment factory or reprocessing facility,” he says. If a country with such a facility begins to feel threatened, it “would be able to develop nuclear weapons within a matter of months.”

“We who live in the nuclear age are approaching a crossroads, a moment of truth,” ElBaradei told the audience at MIT. “Will this technology continue to be harnessed as a servant of development? Or will we become the victim of its destructive power?” For now, he says, “the benefits of nuclear energy are needed more than ever.”

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