UPower's Truck-Size Nuclear Power Plant

Photo: Martin LaMonica

UPower CEO Jacob DeWitte.

There are a number of efforts to build small modular nuclear reactors aimed at lowering the cost of nuclear power. But one company is designing a reactor that’s so small it would fit in a shipping container.

Boston-based UPower Technologies, founded by three nuclear engineers from MIT, is betting that its very small nuclear “battery” can be cost-competitive with power from diesel generators used in remote locations. It’s one of a handful of companies creating new reactor designs with the hopes of improving nuclear power’s safety and cost.

By building a very small reactor, the company thinks it can test full-scale prototypes cheaply and meet a market need for energy in remote places, such as mining operations, island nations, or military microgrids. It expects that its reactor would generate between one and two megawatts of electric power. By contrast, a full-size nuclear power plant typically produces about 1000 megawatts.  

In addition to being small, its reactor technology breaks with the dominant light water design. In today’s power plants, fuel rods held in metal assemblies are submerged in water. The heat from the core is converted into steam to turn a turbine and generate electricity. To avoid overheating in the core, water needs to be constantly circulated through it.

With UPower’s design, the nuclear reactor would be placed in a tall cylinder buried underground. Rather than remove heat from the core with water, company engineers have developed a system that’s similar in concept to steam radiators.

The reactor is equipped with a number of vertical stainless steel pipes filled with a mixture of liquid and gas. Those pipes are slotted into channels, or holes, in a metal block at the base of the reactor, explains CEO Jacob DeWitte. 

As the core produces heat, it causes the liquids at the bottom of the pipes to evaporate and rise to the top. That heat would then be converted into electricity using conventional generators. Removing the heat from these steel loops causes the gas to condense and drop to the bottom to begin the evaporation cycle again. "You don’t need pumps and it’s able to move the heat,” DeWitte says. “It’s a completely passive, self-contained phase change.”

In a light water reactor, water acts to both moderate the nuclear reaction and to transport heat from the core. With the UPower design, the steel pipes are enclosed and would only carry away heat. The nuclear fuel would also fit into channels in the metal block at the base of the reactor, DeWitte adds. He envisions using the same low-enriched uranium in conventional reactors but it could use other nuclear fuels.

The company went with this scaled-down approach for business reasons. The cost of testing a prototype of a new type of nuclear reactor costs millions of dollars, whereas DeWitte expects UPower could test its thermal management system at full size for thousands of dollars.

The reactor also seeks to improve on the safety of current plants. In the Fukushima disaster three years ago in Japan, a loss of back-up power to run water pumps caused the cores to overheat and melt down. With the UPower design, the heat would dissipate through a separate set of horizontal cooling loops that would transfer heat to the ground through natural convection, DeWitte says.

A number of countries, including China, Russia, and South Korea, are building new nuclear power plants. But in the United States, nuclear power is more expensive than building a new natural gas plant. UPower’s strategy is to target locations that pay high costs for energy because they need to import diesel fuel. Its reactors could supply both heat and electricity at lower costs, DeWitte says.

The company is one of a handful of nuclear startups that are hoping to bring advanced reactors to market. Among them are Bill Gates-backed TerraPower, Transatomic Power, and a few companies pursuing nuclear fusion, including General Fusion, Helion Energy, and TriAlpha Energy. There are also a number of efforts to build small modular reactors, which are light water reactors designed to be simpler to build and install than full-size plants.

By working through a startup, rather than a national lab, entrepreneurs hope to move quickly and commercialize new nuclear technology But the process of obtaining a license to operate advanced reactors will likely take many years, says Jessica Lovering, a nuclear policy analyst at think tank the Breakthrough Institute. “All the regulations and applications are very focused on the light water designs,” she says. “The whole fuel cycle is optimized for it.”

DeWitte is hopeful that the company can test its basic design by the end of next year and start the licensing process. There’s a demand for alternatives to diesel generators in remote locations and strong commercial interest could help speed up the approval process, he says. 

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