...AND CHEAPER...:

In the 1950s, U.S. researchers started exploring the concept of molten salt reactors, which use molten salt -- salt that's solid at room temperature, but liquid at high temperatures -- in place of water as the material transferring the heat and keeping the fuel at a stable temperature.

The type of salt proposed for these reactors remains liquid at temperatures as high as 2,500° F -- without any pressurization. That higher temperature would increase the reactor's efficiency and generate more electricity, while the lack of pressurization would reduce the risk of a leak.

The nuclear fuel can't melt if it's already liquid.

Instead of solid fuel rods, separate from the water that transports the heat, some molten salt reactor designs call for the fuel to be dissolved in the molten salt itself.

This eliminates the risk of a meltdown -- the fuel can't melt if it's already liquid -- and if there was a leak, any salt and fuel that escaped would rapidly solidify into rock as it cooled. This would be easier to clean up than the radioactive water or steam released if a pressurized water reactor leaks.

Molten salt reactor designs also include a safety feature called a "freeze valve" or "freeze plug." This plug separates the molten salt mixture above from a holding tank below it. If the mixture ever gets too hot, the valve melts, and the molten salt falls into the tank under the pull of gravity -- stopping a disaster even if all the backup systems failed.

molten salt reactor

An example of solid (left) and molten (right) salt. (Credit: Oak Ridge National Laboratory)

While we don't know for sure what it would cost to build a molten salt reactor, analysts expect that construction would be cheaper than standard water reactors since the design includes fewer parts.

The reactors may also be more reliable -- today's reactors typically have to go offline every 18-24 months for refueling, but the spent fuel dissolved in molten salt could potentially be processed out and new fuel added while the reactor was operational.

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