Office of Nuclear Energy

What Should I Do if a Small Modular Reactor Loses Off-Site Power?

April 10, 2019

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Absolutely nothing!

Small modular reactors, or SMRs, are setting a new standard for safety in the industry.

NuScale Power is moving through the U.S. Nuclear Regulatory Commission's (NRC) review process and is on pace to deliver America’s first SMR in 2026.

Its unique design allows the reactor to passively cool itself without any need for additional water, power or even operator action.

So why are these small advanced reactors so different?

In NuScale's case, it all comes down to simpler design choices, natural water flow and passive safety features.

Photo of small modular power module with a diagram of natural water flow circulation
Illustration of natural water flow circulation during normal operating conditions for NuScale's power module.
NuScale Power, LLC.

Enhanced Safety

NuScale’s design uses natural water circulation to passively cool its reactor.

The core is housed in a pressurized steel reactor vessel that is located within a steel containment vessel (kind of like a thermos bottle). Each module is submerged in water to help divert heat away from the reactor during off-normal conditions.

If emergency cooling is needed, specialized valves open automatically—allowing steam to discharge from the reactor vessel into the containment vessel. The steam then condenses and water flows back into the core through a second set of valves at the bottom of the reactor vessel. This helps cool the reactor down.

As the water boils, the steam that is created recirculates, setting up a passive safety cooling process that continues until the heat and pressure eventually stabilize.

Take a look:

Emergency Core Cooling System

Simple is Safe

NuScale’s specialized valves are part of an emergency core cooling (ECC) system that is fundamentally less complex than traditional reactor designs.

With fewer parts needed to accomplish the same safety function, the company’s simplified design allows the valves to open automatically without the need for additional pumps, power or operator action.

This leads to greater reliability of the safety system and lower capital costs when building the reactor.

An illustration of an emergency core cooling vavle.
Illustration of an emergency core cooling valve prototype.
NuScale Power, LLC.

Built in the USA

NuScale recently selected an American supply chain to build a prototype of these valves for its ECC system.

Illinois-based Scot Forge Company will manufacture the forgings for many of the critical valve components. The forgings will then be machined, assembled, and tested in New York by Curtiss-Wright, Target Rock Division, the company which designed the valve for NuScale.

The theme here is American.

NuScale is looking domestically to identify U.S. suppliers to build its first SMR.

The Oregon-based company expects to have more than 90% of its supply chain made up of American materials and companies.

They recently brought BWX Technologies in Virginia on board to start the engineering work to manufacture the SMR. BWXT will also be responsible for integrating all of the different parts, including the ECC valves, into the manufacturing process.

A worker forges metal at a manufacturing facility.
A worker from Scot Forge Company forges material for a valve prototype for NuScale Power, LLC.
Scot Forge Company

What’s Next?

NuScale is on pace to receive NRC design approval by 2020. The first SMR is expected to be sited at Idaho National Laboratory in 2026.

In addition to supporting siting of the nation’s first SMR plant, DOE is considering purchasing two modules from NuScale’s first utility customer, UAMPS, to meet its research and power needs at the lab.

DOE has invested more than $400 million dollars to help develop advanced SMRs since 2012.

Learn more about our work in this area.