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This Molten Salt Reactor Is the Next Big Thing in Nuclear

Photo credit: Maksim Tkachenko - Getty Images
Photo credit: Maksim Tkachenko - Getty Images

From Popular Mechanics


A new molten salt reactor design can scale from just 50 Megawatts electric (MWe) to 1,200 MWe, its creators say, while burning up nuclear waste in the process.

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Energy Daily founder Llewellyn King suggests the large reactor represents a move of public sentiment after public obstacles have continued to push the timeline on popular tiny reactor startup NuScale.

King explains the way light-water reactors—the majority of nuclear plants in the world and all the nuclear plants in the U.S. today—grew to dominate nuclear energy development the way internal combustion engines eclipsed and then crushed the original electric cars over 100 years ago.

That means that while scientists first developed molten salt reactors decades ago, they’ve never had the opportunity, King says, to gain public favor. The combination of factors is redolent of politics and human whims, seen over and over when major technology is introduced.

Startup Elysium Technologies is behind the new molten salt design, and it scales from tiny to huge, partly because the Nuclear Regulatory Commission (NRC) will require a very small reactor plant as an exemplar and pilot project. Elysium is far from the only molten salt reactor in the game—a 2019 NRC presentation lists Elysium and seven others in the molten salt column of an advanced reactor table.

Where the vogue crop of tiny reactors tout their safety as a major selling point, molten salt reactor concepts also require less safety infrastructure. They’re mostly at ambient pressure instead of the high pressure that has escalated containment structures at traditional light-water nuclear plants.


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Elysium’s reactor is also a fast reactor. “[B]ecause it will be a fast reactor with a molten fuel, it will be able to use nuclear waste as a fuel and burn it up over time. A fast reactor has an unslowed neutron flux and needs no moderator, like the water in light water reactors,” King explains. This is key to the technology, but has also caused problems in other molten salt designs—the bombardment of fast neutrons must be robustly shielded against.

Photo credit: Elysium Technologies USA
Photo credit: Elysium Technologies USA

Elysium’s design also uses up its fuel in the reactor process, and the fuel itself can be recycled from other reactors or even weapons. The reactor uses up 95 percent of the fuel, Elysium says, and what’s left is toxic for a much shorter period.

“These fission products generally decay to background levels in about 300 years, as opposed to over 10,000 years for conventional solid-fuel reactors waste,” Elysium explains on its website.

Elysium also touts “natural” safety designs, like one extremely low-tech and effective emergency valve. The company explains:

“A freeze plug is a section of pipe that is actively cooled to produce and maintain a plug of frozen salt. If temperature limits are exceeded or electrical power is lost, the plug melts and the contents of the reactor drain to passively cooled tanks that are configured for safe shutdown in sub-critical geometries with passive cooling.”

This is emblematic of how today’s advanced reactor concepts are designed, taking the best of the best from a dozen scientific and engineering fields and proposing ideas that blend them all. If Elysium’s pilot plant is approved, it will be just 10 MWe—enough to power a very small town, and to show that Elysium means safe and efficient business.

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