The Future of Nuclear Energy: Small Modular Reactors

Kalvin Wang
March 1, 2018

Submitted as coursework for PH241, Stanford University, Winter 2018


Fig. 1: Diagram of NuScale Small Modular Reactor (Source: Wikimedia Commons)

As delays, costs and risk of devastating accidents mount on new large nuclear projects around the world, attention is shifting towards smaller alternatives which industry experts hope will push nuclear energy to the next generation of electricity. These small modular reactors (SMRs) are defined as nuclear power plants with a capacity of less than 300 megawatts. [1] They are designed and produced in factories and are capable of being moved by train, truck or barge to its designated location. SMRs are not a new technological innovation or concept, in fact, small reactors are already used on nuclear submarines and in developing countries like India and Pakistan. [2] However, with increasing interest in low cost, low risk energy sources and an influx of governmental support, SMR technology is now moving closer to wide adoption in a multitude of countries.

Since the invention of nuclear power, bigger has generally been seen to be better. Once a company had gone through the time and expense of securing a site along with planning approval and grid connections, most wanted to build as much capacity on that site as possible. [3] However, SMRs promise the benefits of full-scale nuclear plants low costs and renewable energy without the significant cost and construction issues that conventional nuclear projects face. [4]

NuScale Reactors

NuScale Power is a company that aims to leverage the growing interest in small modular reactors by building the first SMR in America. [5] In early 2017, the company submitted the first design certification of any SMR in the United States to the Nuclear Regulatory Commission. NuScale's SMRs designs utilize the light water approach to cooling and power generation. Within the 2.7m diameter by 20m height reactor vessels, water is heated by the nuclear core at the base of the reactor vessel - as shown in Fig. 1. The heated water is then driven upwards instead the riser and down over the steam generator turning an electrical generating turbine. Once the heat is transferred into steam, the water condenses and sinks back to the bottom of the device, where the cycle repeats. The vessels are intended to be kept in an underground pool - absorbing the shock of any potential earthquakes, with a concrete lid over the pool. Additionally, In the event that AC power is lost for normal cooling systems, the pool water begins to absorb heat and boil. [5]

Each NuScale reactor vessel are pre-fabricated, delivered by rail, barge or trucks and assembled at the designated site. [5] The united are designed to produce approximated 50 MW of electricity each and require refueling with standard 4.95 percent enriched U-235 every two years. The vessels 50 MW reactor capacity is small compared to conventional reactors. Compared to traditional large scale nuclear reactors of approximately 1000 MW, NuScale's reactors would generate a twentieth (50MW/ 1000MW = 1/20) or 5% of the electricity. However, because its small it would contain much less fuel and energy therefore could be operated with less risk and costs. Additionally, the modular system design enables power plants to activate one reactor and generate revenue as they install the next. [6]

© Kalvin Wang. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. 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] "Status of Small Reactor Designs Without On-Site Refuelling," International Atomic Energy Agency, IAEA-TECDOC-1536, January 2007.

[2] K. Stacey, "Small Modular Reactors Are Nuclear Energy's Future," Financial Times, 25 Jul 16.

[3] S. Harber, "Small Modular Reactors Are Nuclear Energy's Future," Physics 241, Stanford University, Winter 2017.

[4] G. Locatelli et al., "Cogeneration: An Option to Facilitate Load Following in Small Modular Reactors," Prog. Nucl. Energy 97, 153 (2017).

[5] J. Conca, "NuScale's Small Modular Nuclear Reactor Keeps Moving Forward," Forbes, 16 May 17.

[6] K. Schneider, "The Future of Nuclear Power? Think Small," Los Angeles Times, 1 Feb 18.