In January of this year, the US Department of Energy announced that it would invest $452 million toward developing and licensing a new technology called the small modular reactor (SMR). These nuclear reactors are smaller than and produce less energy than traditional reactors, but their small size allow them to be manufactured, transported, and operated more efficiently. 
An SMR generates one-tenth to one-third the energy as a traditional reactor, and the International Atomic Energy Agency defines “small” as under 300 MWe. However, their small size “makes them very attractive to poorer, energy-starved countries; small, growing communities that don’t require a full-scale plant; and remote locations such as mines or desalination plants.”  Furthermore, because SMRs are modular, they are scalable, and additional SMRs can be installed as electricity demand increases in a location. 
Another advantage of SMRs is its greater simplicity of design, which consequently allows it to be mass produced at a lower cost, shipped easily by rail, ship, or truck, and assembled on-site. And most use technologies and cooling techniques that have inherent passive safety features to prevent meltdown in the case of malfunction. “A 2010 report by a special committee convened by the American Nuclear Society showed that many safety provisions necessary, or at least prudent, in large reactors are not necessary in the small designs forthcoming.” 
There are three primary types of SMRs currently in development: Light water SMRs work like traditional light-water reactors, where heat from a uranium core turns water into steam and spins turbines to generate electricity. One difference with light-water SMRs is that the generator is located inside the reactor rather than outside, which decreases the amount of piping (and potential leaks) required. High-temperature gas-cooled SMRs use helium rather than water as coolant to eliminate the possibility of a meltdown. Because helium does not boil or react, it can safely operate at temperatures up to 1000 degrees C with higher efficiency and without fear of reaction with the zirconium alloys as is present with water at high temperature. Fast neutron SMRs are those optimized for “fast neutrons” created during fission, which allows them to extract 60 times more energy from uranium than a traditional light-water reactor can. “That also means that fast reactors can digest the nuclear waste of other reactors, reducing the waste’s radiotoxicity while extracting energy in the process.” 
In April of this year, Ameren Corp., a St. Louis-based electric company, and Westinghouse Electric Co. announced plans to pursue the aforementioned $452 million federal subsidy to “advance development of small modular reactors that could be built alongside the utility’s much larger Callaway nuclear plant near Fulton, Mo.”  This is the first major step in the investigation of this new technology for use in the United States, but SMRs still face many difficult challenges. “Indeed, it is in government regulations that the modular reactors face their greatest challenges. Whatever the facts about nuclear accidents from Windscale to Fukushima, a large fraction of the public, especially in the West, is very nervous about nuclear energy in any form.”  Furthermore, SMRs are not expected to completely replace traditional reactors – it merely provides a sizing and output option for use in areas where building a large conventional reactor is not feasible.