For more than 30 years, no one has begun construction on a new nuclear reactor in the U.S. But amid growing concern about energy supplies, the U.S. Nuclear Regulatory Commission (NRC) has registered applications for licenses to build 25 new reactors since July 2007.

Two of the reactor designs specified in the applications feature passive safety systems, which are activated by natural forces and are intended to remove the risk of operator error or malfunctioning electronics. Of these, only one has been approved by the NRC: the Westinghouse Advanced Passive 1000, or AP1000 (below). The first AP1000 is likely to be built in China, where construction is scheduled to start in March 2009.