The [U.S. Department of Energy] said it would help bring to market a small, modular nuclear-power reactor from Babcock & Wilcox Co., under a program in which the Obama administration wants to spend up to $452 million over five years on the technology.[...]The small reactor could provide about 180 megawatts of power, about one-fifth the size of a typical nuclear reactor but still enough for tens of thousands of homes. It has an underground radiation-containment structure, meant to be safer and less expensive than those at larger plants.The small reactors are modular, meaning manufacturers hope to build them at a central location before shipping them and installing them, potentially reducing the costs of constructing a nuclear plant. The reactor is about 83 feet tall and 13 feet in diameter, allowing it to be shipped by rail as opposed to being assembled on site. The cost of building a conventional nuclear-power plant today tends to make it