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Sustainable Energy

A Preassembled Nuclear Reactor

A new modular design could make building nuclear reactors faster and cheaper.

A new type of nuclear reactor that is designed to be manufactured in a factory rather than built at a power plant could cut construction times for nuclear power plants almost in half and make them cheaper to build. That, in turn, could make it possible for more utilities to build nuclear power plants, especially those in poor countries. The design comes from Babcock and Wilcox, a company based in Lynchburg, VA, that has made nuclear reactors for the United States Navy ships for about 50 years.

Going nuclear: This illustration shows a 4.5-meter-wide, 23-meter-long nuclear reactor designed to fit on a railcar for shipping to the site of a power plant.

Typically, the nuclear reactors found in commercial power plants are large, each generating more than 1,000 megawatts of electricity. That’s because overall, it’s cheaper to build a single, large power plant than several smaller ones, in part because it’s not necessary to duplicate components such as containment walls and control rooms. But this approach also requires taking a big financial risk, which is one of the reasons that it’s been decades since the last nuclear power plant was built. Each plant can cost $9 billion or more–too much for all but the largest utilities to afford–and it can take more than five years from the time that construction starts to the time that the plant starts generating electricity and providing revenue to cover construction costs, says Andrew Kadak, a professor of nuclear engineering at MIT.

The new Babcock and Wilcox reactor design could make nuclear power plants less of a financial risk, Kadak says. The reactors are much smaller, designed to generate 150 megawatts each, but could also be strung together to generate as much as a conventional nuclear power plant. They also integrate two separate components of a conventional power plant in a single package: the reactor itself and the equipment used to generate steam from the heat that the reactor produces. As a result, the entire system is small enough to be shipped on a railcar. And because the system can be shipped, it can be manufactured at a central facility and then delivered to the site of a future power plant.

Building a reactor in a factory should save construction time, says Kadak. He estimates that what takes eight hours to do in the field could be done in just one hour in a factory. Once the reactor is manufactured, it would then be shipped to the site of a power plant along with the necessary containment walls, turbines for generating electricity, control systems, and so on. Christofer Mowry, CEO of Babcock and Wilcox, estimates that total construction time will be three years–at least two years less than conventional construction would take.

The reduced construction time could save on both construction and financing costs, since less time would be spent waiting for the plant to start producing power. The design also avoids a bottleneck in conventional nuclear power plant construction, which is that the large reactor vessel–a pressurized chamber containing the reactor core and necessary coolant–can only be manufactured in a few plants in the world, and none of these is in the United States, Mowry says.

Two other features of the design could also cut down on operating costs. First, each reactor will be housed in a containment structure big enough to store all of the waste generated by the plant during its 60 year life span, eliminating the need for a separate storage facility. That could be especially important, as nuclear plant operators may have to store their own waste while they wait for the government to provide a permanent storage facility, which it is obliged to do by law. Second, the reactors are also designed so that fuel has to be replaced only once every five years, instead of the usual two years. That will increase the amount of time that the plant can operate.

Kadak says that small reactors make the most sense for poor countries that can’t afford to finance $10 billion plants and do not have the necessary electricity grid infrastructure to distribute power from 1,000-megawatt facilities. However, at this point, it’s not yet clear that the cost savings from manufacturing the reactors will be enough to convince large utilities in the United States–which can finance conventional plants–to adopt the design. “In the United States, it’s a harder sell,” Kadak says.

Although the new reactors are smaller than conventional ones, they use the same underlying technology–they’re light water reactors–so Mowry says that it will be possible to get them certified under existing regulations. At least two other companies in the United States are developing small, modular light water reactors. One design, from Westinghouse, provided the template for combining the steam generator and the reactor, although it isn’t designed to be built in a factory. A startup called NuScale also has a design for a small modular system that can be built in factories and shipped to power plants. Those reactors would generate only about 40 megawatts each. Other companies and researchers, including Kadak, are developing designs for future modular reactors using more advanced technology that will require a new regulatory process.

Mowry says that Babcock and Wilcox plans to file the official certification application in 2011. The company is already working with the Tennessee Valley Authority to start the process of evaluating a site for a plant that would use the reactor technology. Mowry says that the first plants using the technology could be up and running by 2018. But Mujid Kazimi, another professor of nuclear engineering at MIT, says that goal sounds “very ambitious” given what’s known about the regulatory process.

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