Small Modular Reactors

Darren Handoko
March 21, 2014

Submitted as coursework for PH241, Stanford University, Winter 2014


Fig. 1: SMRs can be constructed in factories and transported to the site location. [5] (Courtesy of the U.S. Department of Energy)

The development of clean, safe, and reliable nuclear power is key to fueling America's energy demands. While renewables are playing a crucial part in displacing electricity generation powered by fossil fuels, there will always be a need for steady, base load generation in the grid. In the U.S., no nuclear power plant has been built since the Three Mile Island accident in 1979. The decommissioning in June 2013 of the San Onofre Nuclear Generating Station in California signaled another blow to the continued viability of nuclear energy in the U.S. The development of small modular reactors (SMRs), however, may be instrumental to revitalizing the stalled nuclear energy industry.

The Need for Small Modular Reactors

In the last decade, the world population has increased by more than 12% and is expected to reach a population of 9 billion people by 2050. Along with population growth, primary energy consumption has increased by 20% and electricity consumption has increased by 31.5%. World electricity demand is projected to grow at a rate of 2.5% until 2030. Many countries have been developing diverse energy mixes in order to match this demand. SMRs could be a potent non-fossil solution for many countries. [1]

The International Atomic Energy Agency (IAEA) defines a small reactor as having electrical output of less than 300 MWe, but the general consensus of SMRs is anything with an output of less than 700 MWe. [2] The smaller, compact design can be mass-produced, factory-fabricated reactors that can be transported by truck or rail to a nuclear power site. The US-DOE led Global Nuclear Energy Partnership (GNEP) initiative in 2007 identified the development of Grid-Appropriate Reactors as crucial for the growth of peaceful, safe nuclear power in the world.

According to the IAEA, 139 of the 442 commercial power plants in operation worldwide are SMRs. However, these reactors are merely scaled down versions of large reactors, and are not what are considered deliberately small reactors. SMRs are reactors that utilize their small scale to achieve certain performance characteristics. Small modular reactors offer many benefits over the traditional, large-scale reactors of over 1000 MWe. They can reach areas difficult to access or without infrastructure for transportation of fuel. The modularity of the design reduces the amount of work on-site, which makes it cheaper, simpler, and faster to construct. SMRs have a long life cycle and reduced need for refueling. Overall, they leave a smaller footprint, have lower initial costs and operation and maintenance costs, and are resistant to proliferation. [3]

Scalability and Flexibility

SMRs are frequently labeled as not economical because they supposedly lack economies of scale. However, cost savings do occur from mass production economies because for a certain installed power, many more small plants than large plants are required. This allows small plants to achieve mass production economies of scale and a more standardized procurement process. The inherent modularity of SMRs leads to shorter construction times and greater flexibility as well. Plant capacity can be readily adjusted to changing market conditions so investors can closely and quickly adapt to early signals of changing market conditions. Large, traditional reactors must cope with upward and downward swings in price and demand. Large amounts of invested capital may go to waste as investors debate the decision to invest or not to invest. [4]

Plant-Grid Matching

An important technical requirement for nuclear reactors is its connection to the power grid and its stability. Some developed countries and areas, like the western European Union, have well interconnected grids that can sustain large power stations. Other areas are less developed and cannot accept the connection of a large, concentrated power station providing 1000MWe or more. The development of SMRs could provide energy solutions to a huge market segment with smaller electrical grids, while avoiding grid instability concerns, the use of fossil fuels, and emissions of greenhouse gases. [3]


SMRs can provide other products besides electricity. The heat generated from the nuclear reactor can be used for urban heating or desalination processes. Using the heat to be rejected to the environment, as required by the Rankine thermal cycle in the heat-to-electricity conversion process, maximizes resource and revenue. The technical requirement for heat or desalination plants is that they be placed near the end-user areas, which is what limits the cogeneration benefit of large nuclear reactors. However, the smaller size, increased safety, and reduced radiation, of SMRs allow them to be strategically placed at a moderate distance from urban areas. The thermal energy generated can be used for the heating needs of urban spaces. [4]

© Darren Handoko. 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.


[1] J. Vujic et al., Small Modular Reactors: Simpler, Safer, Cheaper?" Energy 45, 288 (2012).

[2] D. T. Ingersoll, "Deliberately Small Reactors and the Second Nuclear Era," Prog. Nucl. Energy 51, 289 (2009).

[3] G. Locatelli and M. Mancini, "Small - Medium Sized Nuclear Coal and Gas Powerplant: A Probabilistic Analysis of Their Financial Performances and Influence of CO2 Cost," Energy Policy 38, 5072 (2010).

[4] M. D. Carelli et al., "Economic Features of Integral, Modular, Small-to-Medium Size Reactors," Prog. Nucl. Energy 52, 403 (2010).

[5] S. R. Greene et al, "Pre-Conceptual Design ofa Fluoride-Salt-Cooled Small Modular Advanced High-Temperature Reactor (SmAHTR)," Oak Ridge National Laboratory, ORNL/TM-2010/199, December 2010.