One of the biggest obstacles to constructing nuclear power plants is that they tend to be extremely large and expensive. Now one utility is taking steps toward constructing a plant that uses small modular reactors that can be built faster and more cheaply than conventional ones. This week the Tennessee Valley Authority signed a letter of intent with nuclear-reactor maker Babcock & Wilcox to work together to build up to six small reactors near Clinch River, Tennessee. If the plan goes ahead, these could be the first small modular commercial nuclear power plants.
The plan comes at a time when many nuclear projects are stalled because of safety concerns and also for reasons of cost. Babcock & Wilcox’s modular reactors require less capital than conventional ones, and they have some safety advantages as well. The letter of intent does not guarantee that the plants will be built, according to TVA, but it will start work on the engineering needed to undertake the extensive nuclear-plant permit process and environmental reviews of the site. Last year, TVA initiated discussions with the Nuclear Regulatory Commission on how to proceed with licensing the novel small nuclear-reactor design.
In the past, utilities have preferred very large nuclear reactors—over 1,000 megawatts—to take advantage of economies of scale. But large reactors have a long lag time between when funding is raised and when the plant starts generating revenue, and this creates a problem, says Andrew Kadak, a former professor of nuclear engineering at MIT and a consultant at Exponent Failure Analysis. When the cost of interest is figured in, smaller reactors look more attractive. Lenders are typically willing to charge less interest on smaller loans, and the plants can be expected to start generating revenue faster. TVA’s are projected to take three years to build, as opposed to five or more for conventional plants. Smaller reactors also avoid the need for expensive transmission upgrades to link them to the grid.
Some features of smaller reactors can further offset the economies-of-scale advantage of large ones. They can be assembled in factories rather than custom-assembled on-site. .
Babcock & Wilcox has supplied small reactors for ships, but reactors at this scale haven’t been used commercially to generate electricity on land. A few companies have recently designed small land-based reactors that would generate just 10 percent of the power of a conventional one but could be linked together to generate power comparable to the output of a conventional plant. Some of these use advanced nuclear reactor designs that haven’t been tested extensively. B&W’s reactor, however, is very similar to conventional pressurized water reactors, the predominant type used in Western countries, so it is likely to be comparatively simple to get permitted and built. One difference is that conventional reactors can have multiple expensive pressure vessels linked by 75-centimeter-diameter pipes, but the new design requires only one pressure vessel, eliminating the need for such large pipes. The large pipes are a source of vulnerability in a conventional reactor—if they break, the reactor can lose coolant very quickly, so expensive backup cooling systems are required.
Only after the plants are operating will it become clear what the electricity they generate actually costs. Many costs are fixed no matter the size of the reactor—a small plant will still require the same number of guards, for example, says Michael Golay, a professor of nuclear engineering at MIT. It’s also not clear how much simpler, if at all, the containment structure and other safety systems can be, he says. “If it were my money, I wouldn’t invest in them,” he says.