NPR logo Graphic: Rethinking Nuclear Power, On The Small Scale

Graphic: Rethinking Nuclear Power, On The Small Scale

Conventional nuclear power plants are expansive and expensive building projects. Entrepreneurs and engineers are hoping to build miniature reactors that can be assembled smaller, more cheaply and on demand.

Below, a comparison between a full-size boiling water nuclear reactor and a miniature reactor.

Diagram showing the differences between a boiling water nuclear reactor and a mini-reactor
Boiling water reactors, or BWR, were developed in the 1950s by Idaho National Energy Laboratory and General Electric. They use heat created by nuclear fission to generate steam that powers a turbine. Today, there are more than 90 BWRs operating in the world, and 35 of these are in the U.S. The diagram above is based on the design of the stricken BWRs at Japan’s Fukushima Nuclear Plant. Like BWRs, mini-reactors boil water with nuclear-generated heat to create electricity. However, these minireactors are simpler, smaller, and contain less nuclear material. Several companies plan to submit designs to the Nuclear Regulatory Commission for approval, but no minireactors are currently operating in the U.S. The diagram above is based on the designs of NuScale Power of Corvallis, Ore.
Traditional nuclear reactors are so large, they must be assembled on-site. The steel vessel that will hold the fuel is typically larger than 25 feet in diameter, and the only company with the equipment to build such a vessel in one piece is based in Japan. Minireactor designs range in size from 60 feet tall and 14 feet wide to just 8 feet tall and 5 feet wide – advertised as "hot-tub sized." This means they can be completely manufactured in the U.S. Some companies intend to have fuel sealed inside and ready to go, so each reactor can be shipped as a modular unit to a plant.
Cost Vs. Power
Electrical Output: ~ 400 - 1,500 MWe
Average Cost: ~ $5 billion – $15 billion
Electrical Output: ~ 20 - 45 MWe
Average Cost: ~ $25 million – $200 million per unit, differs with company and design owing to size differences
Cooling System
Active cooling — Pumps and valves that require external power circulate water through the reactor core and help keep it cool. If pumps fail to keep the water moving, a Fukushima-style meltdown is possible. Passive cooling — Some minireactor designs use natural convection of water to cool nuclear fuel — requiring no outside power source. The NuScale reactor sits in a 4 million-gallon tank of water that provides long term cooling if other systems fail.
BWRs require outside power for their cooling systems to function in an emergency. Reactors that are aboveground are potentially more vulnerable to natural disasters and attacks. In addition to a cooling system that can operate without outside power, many minireactors are placed underground to protect against disasters and attack and have multiple additional barriers to prevent the escape of nuclear material.

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