The word "small" is relative, especially in the context of nuclear power. Traditional reactors generate on the order of a gigawatt of power with a plant cost of several billions of dollars. When describing a small reactor, the spectrum can range from units with the capacity to power a small town down to reactors for personal vehicles. Practical and safety concerns have relegated nuclear powered small vehicles to the realm of science fiction, but there has been recent interest in utilizing nuclear power on the scale of towns and even single buildings. Since traditional reactors have been operating with relative success, the logical question is: what is/are the benefit(s) of going small? While small scale nuclear power may seem like a field that is driven by technology needs (e.g. a need to fit a reactor in a small space), the recent boom in small reactors can primarily be attributed to the same driving force behind any other method of power production: cost. Although economies of scale would suggest that large reactors produce cheaper power than smaller ones, many of the current small reactor designs promise a dollar per megawatt rate equal to or less than currently operating nuclear plants.  As a result, the overall cost of energy to the consumer can be less due to the ability to tailor (and possibly modify) the capacity of a plant according to demand. In addition, small scale nuclear power can be a cheaper option for small/rural locations that are dependent on a single, expensive source of power (e.g. diesel generators) but without the grid capacity for a traditional nuclear plant. [2,3]
From a technology standpoint, small nuclear reactors are not new. Warships around the world, including over 80 U.S. Navy vessels, are powered by small reactors.  However, only recently have companies come to market with reactors designed for civilian use in urban environments. The reactors described here must undergo the same Nuclear Regulatory Commission (NRC) approval process as large plants, taking approximately 3-5 years.  As a result, the adoption of small reactors is estimated to take place around 2015 to 2020. [1-3,6]
For the purposes of this article, a "small reactor" will be defined as one that can be pre-built and transported to site (e.g. modular). Many of the current small reactors are based on a traditional light water design which has been proven in warship applications.  Since these reactors utilize the same features as current Gen III reactors, the assumption is that the NRC approval process will be accelerated.  One of the largest of such designs is the mPower reactor made by Babcock & Wilcox, manufacturer of U.S. Navy reactors. The mPower reactor is designed to produce 125 megawatts at under $5000 per megawatt.  In early 2010, three major U.S. utilities agreed to partner with Babcock & Wilcox to get the reactor approved for commercial use.  A newer and smaller light water design by NuScale Power is also gaining traction in the U.S. Capable of producing 45 megawatts, the NuScale reactor is considerably smaller than traditional reactors with a containment vessel size of 4-5 meters.  Toshiba has introduced a 10 megawatt Gen IV reactor using liquid sodium as the heat transfer medium. Current plans are for the Toshiba reactor to be used in the small and rural town of Galena, Alaska. [2,3]
Lower initial cost: Since the initial cost of a small reactor is much less than that of a large one, the likelihood of adoption is higher. The typical cost of a traditionally sized nuclear reactor is several billion dollars (a recent plant in France cost over $5 billion).  In late 2010, Constellation Energy in Maryland cancelled plans to construct a large nuclear plant citing the high initial cost, even with $7.5 billion of guaranteed government loans.  With the initial cost of small reactors 10 to 100 times less, the probability of adoption is much higher.
Modular/Scalable: Small reactors have been designed to be modular, and thus scalable. This allows utilities to cater the plant capacity to the demand of the area being served. This feature is also complimentary to the lower initial cost cited above since a plant can expand capacity as required, avoiding a high initial outlay.
Size/Containment: Since small reactors are designed to be constructed by the manufacturer and shipped to site, the reactor core is designed to be fully contained in a transportable package. This allows the use of much smaller power facilities (the small reactor cores are designed to be buried underground) without the need for enormous cooling stacks or containment buildings. In addition, the self-contained core package can be shipped back to the manufacturer for refueling or disposal.
U.S. Job Economy A related advantage of being able to produce the entire reactor locally is the resulting increase in domestic factory jobs. Current large reactors require imports from Japan and South Korea [2,4] while small reactors can be built entirely in the U.S.
Safety Features: The small scale of the reactors allow some passive safety features that may not be feasible on a large reactor. For example, the NuScale reactor does not require any pumps for water circulation, instead relying on convection for heat transfer. 
Localized Danger: Since one of the major advantages of small nuclear reactors is the ability to use them closer to urban centers (requiring smaller grids and plant facilities), it is possible to imagine an increased accidental exposure to radioactive material by the general population (whether through leaks or catastrophic failure). While current large reactors are isolated in relatively remote areas, the widespread adoption of small reactors may bring potential nuclear hazards closer to population centers.
Terrorism: Although proponents of small reactors argue that stealing fissile material from the reactors is near impossible (via features such as a sealed core and the ability to bury the core underground), the risk is still higher than that of a large reactor. In addition, the smaller facilities required (e.g. containment structures) mean that attacks intending to destroy plants and spread nuclear waste may be more of a danger.
The revitalization of the nuclear power industry has been attributed to the growth of small nuclear reactors.  Considerable interest in small and modular reactors has formed due to their lower initial cost and potential scalability. As a result, they are an attractive solution to changing the balance of the U.S. power portfolio away from oil. However, public acceptance and a lengthy regulatory process may hamper the adoption of small reactors, especially as renewable energy sources (wind and solor) improve in technology and decline in cost.
© Chris Yu. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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