Key Issues

Small nuclear reactors are attracting the attention of government officials, regulators and energy leaders as a potential addition to the nation’s energy mix. Because of their small size—300 megawatts or less, compared to a typical nuclear power plant of 1,000 megawatts—they have many useful applications, including generating emission-free electricity in remote locations where there is little to no access to the main power grid or providing process heat to industrial applications. They are “modular” in design, which means they can be manufactured completely in a factory and delivered and installed at the site in modules, giving them the name “small modular reactors,” or SMRs.

Still in the early stages of development, small reactors will benefit from the industry’s 50-year history of incremental safety improvements through design. They will include many of the same safety and security features that are in use today at the nation’s 104 nuclear plants. In addition, some small reactors will have long operating cycles between refuelings, and others can be air-cooled, making them suitable for arid regions.



Most of the nation’s operating nuclear power plants use light water reactor technology, so this will likely be the first type of small reactor to receive design certification from the U.S. Nuclear Regulatory Commission. 

The Energy Department’s 2012 budget includes research and development funding for small reactors.  Legislation recently introduced in the U.S. Senate, S. 512, the Nuclear Power 2021 Act, and S. 1067, the Nuclear Energy Research Initiative Improvement Act, would help move two reactor designs through the safety certification process and study ways to reduce manufacturing and construction costs. The first small light water reactor could be licensed and in operation around 2020. The other types—high-temperature gas-cooled reactors and liquid-metal cooled and fast reactors—will follow.

Light Water Reactors

Small light water reactors are designed to capitalize on the benefits of North American modular construction, ease of transportation and reduced financing, making them a good option for areas where large nuclear reactors are not needed. These designs typically are smaller than 300 megawatts electric and could replace older fossil-fired power stations of similar size. Designs under development include:

Babcock & Wilcox Co. mPower Reactor
The mPower reactor design is a 125-megawatt electric advanced light water reactor design that uses natural phenomena such as gravity, convection and conduction to cool the reactor in an emergency with a belowground containment.

Holtec Inherently Safe Modular Underground Reactor (HI-SMUR) 140
The HI-SMUR 140 is a 140-megawatt reactor with an underground core. That feature, Holtec says, means there is no need for a reactor coolant pump or off-site power to cool the reactor core.

NuScale Power Inc. NuScale Reactor
The NuScale is a 45-megawatt electric advanced light water reactor. NuScale’s passive cooling systems uses natural circulation to maximize safe operation.

The Westinghouse SMR
The Westinghouse SMR is a 200-megawatt integral pressurized water reactor with all primary components located inside the reactor vessel. It is based on the AP1000 reactor design, which is being built in many new nuclear plants around the world.

High-Temperature Gas-Cooled Reactors

High-temperature gas-cooled reactors could be used for electricity generation, but they would be especially well-suited to providing process heat for industrial purposes, including hydrogen production. These reactors also could be used in the development of tar sands, oil shale and coal-to-liquids applications. The small nuclear reactors would reduce the life-cycle carbon footprint of all these activities. Designs under development include:

AREVA Antares
AREVA based the design for the Antares on the concept of a gas-cooled (helium) reactor. The company is developing the design in the context of the Generation IV International Forum.

General Atomics Gas Turbine Modular Helium Reactor (GT-MHR)
The GT-MHR is a high-temperature reactor with advanced gas turbine technology.

Pebble Bed Modular Reactor Ltd. (PBMR)
The PBMR is a high-temperature reactor that uses a gas or steam turbine for power conversion. Substantial design, component testing and fuel development have been undertaken in South Africa.

Liquid Metal and Gas-Cooled Fast Reactors

Liquid metal or gas-cooled fast reactor technologies hold the promise of distributed nuclear applications for electricity, water purification and district heating in remote communities. Fast reactors also could provide sustainable nuclear fuel cycle services, such as breeding new fuel and consuming recycled nuclear waste as fuel, and could support nonproliferation efforts by consuming material from former nuclear weapons, thus eliminating them as a threat. Designs under development include:

GE Hitachi Nuclear Energy Power Reactor Innovative Small Module (PRISM)
The PRISM is an advanced reactor cooled by liquid sodium. As with some other small reactor designs, the plant will be built underground on seismic isolators to dampen the effects of earthquake motion.

General Atomics Energy Multiplier Module (EM2)
The EM2 is a modified version of General Atomics’ high-temperature, helium-cooled reactor. The 240-megawatt reactor is capable of converting used nuclear fuel into electricity and industrial process heat without conventional reprocessing.

Gen4 Energy: The Gen4 Module (G4M)
The reactor, known as the Gen4 Module (G4M), is designed to fill a previously unmet need for a transportable power source that is safe, clean, sustainable and cost-efficient. The reactor has been designed to deliver 70 MW of heat (25 MW of electricity) for a 10-year lifetime, without refueling.

Toshiba 4S (Super-Safe, Small and Simple)
The 4S is a 10-megawatt reactor cooled by liquid sodium for use in remote locations.