Energy photo
molten salt reactor
Going nuclear Sinelab

Radioactive elements produce heat as they decay. Nuclear plants draw power from this process, and typically ­stabilize the temperature with water. But during a power outage, H2O—which needs pumps to flow—can’t always prevent meltdowns. Molten salt reactors, which instead control heat with melted lithium and potassium fluorides, have a fail-safe: If the electricity dies, a plug will melt, causing the salts to seep down a safety drain and solidify around the uranium, preventing overheating. After a decades-long lull in development, countries from China to Denmark are building new molten salt reactors. Here’s how they work.

1. Reactor vessel

Uranium floats in a stabilizing bath of melted fluoride salts inside this container. As the radioactive atoms split apart, their fission steadily heats the vessel to 1,300 degrees Fahrenheit, the approximate temperature of magma.

2. Primary heat exchangers

Tubes on either side of the reactor vessel transfer the heat to intermediate pipes, which are filled with clean molten salts. The uncontaminated substance can carry energy without producing any additional radioactive waste.

3. Coolant salt pumps

These pumps move the clean salts in the heat exchangers away from the radioactive reactor vessel and toward a steam generator housed in a separate building. This limits the hazardous material to a single, isolated location.

4. Steam generator

The searing salts heat water into steam, which spins a turbine to produce electricity. In one hour, a molten salt reactor may be able to crank out 500,000 kilowatts, enough to power 45 U.S. households for an entire year.

5. Drain tank

Contaminated reactor salts and radioactive gases filter into a waste-disposal system. These materials remain hazardous for only hundreds of years—compared with hundreds of thousands for traditional reactors’ byproducts.

This article was originally published in the January/February 2018 Power issue of Popular Science.