The latest milestone in a Southern Company-TerraPower partnership that began in 2015, the test system supports the molten chloride reactor experiment at Idaho National Labs.
The system, officially designated as the “Integrated Effects Test” (IET), is designed to simulate how molten salt works when scaled to the large sizes and volumes needed in a commercial system. This propels it from existence as essentially a lab experiment and into the next level of the serious design and testing phase. The reactor core is simulated and heated from an external source, with the molten fuel passing through a heat exchanger. This test system does not use actual nuclear fuel.
Major Differences Compared to Existing Reactors
Most commercial nuclear reactors use normal or “light” water (as opposed to “heavy water” that contains deuterium) as their coolant and neutron moderator with a solid fuel source in the core.
But the molten salt reactors are significantly different, using molten salt as both the coolant and the fuel. The Department of Energy states the design is more efficient and produces less waste. Perhaps just as importantly, the reactor design contains inherent and desirable passive safety characteristics:
“The MCFR has what the industry calls a ‘walk-away-safe’ design that would shut down the reactor without any need for electric pumps to prevent fuel damage. If there is a loss of coolant flow, the fuel salt would expand through the reactor core to passively halt the process and naturally circulate to remove decay heat.”
This walk-away-safe quality is important, as it was the unplanned loss of emergency power that led to the events at the Fukushima reactors in the wake of the destructive tsunami of 2011. Those reactors, like many in commercial operation, rely on “active” safety systems that require a constant source of electricity to remove the decay heat produced by the fuel even after a plant has shut down.
This is why new reactors, like those based the AP1000 design at Vogtle Units 3 and 4, incorporate “passive” safety systems to create much safer designs. “The AP1000 plant’s passive safety systems,” states Westinghouse, “require no operator actions to mitigate design-basis accidents. These systems use only natural forces such as gravity, natural circulation and compressed gas to achieve their safety function. No pumps, fans, diesels, chillers or other active machinery are used, except for a few simple valves that automatically align and actuate the passive safety systems.”
Verification and Validation
The intent of the integrated test system is to gather data that will be used to validate the computer models that have been developed to ensure they accurately predict the behavior of the system in operation. Accurate codes and programs that model the system behavior will be necessary to substantiate the final reactor’s safety, much like existing nuclear plant designs.
As explained by the NRC, computer codes (programs) are used “to model and evaluate fuel behavior, reactor kinetics, thermal-hydraulic conditions, severe accident progression, time-dependent dose for design-basis accidents, emergency preparedness and response, health effects, radionuclide transport, and materials performance during various operating and postulated accident conditions. Results from applying the codes support decision-making for risk-informed activities, review of licensees’ codes and performance of audit calculations, and resolution of other technical issues.”
You can watch a short video explaining the test system that was published by the Department of Energy below:
Additional details are provided by Southern Company:
“Located at TerraPower’s laboratory in Everett, Washington, the Integrated Effects Test is a nonnuclear, externally heated, up to 1-megawatt multiloop system to support future deployment of a fast-spectrum salt test reactor.
The project continues work initiated in 2015 by Southern Company Services and TerraPower under the U.S. Department of Energy (DOE) Advanced Reactor Concepts (ARC-15) award, a multiyear effort to promote the design, construction and operation of Generation-IV nuclear reactors.
This is a long-term project based on the collaboration of many organizations: CORE POWER, EPRI, Idaho National Laboratory, Oak Ridge National Laboratory and Vanderbilt University.
Click here to learn more about TerraPower’s Molten Chloride Fast Reactor Technology.
Advanced Reactor Demonstration Program
Federal funding of molten chloride reactor research goes back to at least 2016, when the Obama administration announced that it would provide $40 million over five years to Southern Company and X-energy to develop alternative advanced reactor designs.
Congress authorized additional funding for advanced reactor research in the 2020 Energy Act. The appropriations are being used to fund the Advanced Reactor Demonstration Program being implemented by the U.S. Department of Energy. An infographic published by the DoE outlining the program is reproduced below: