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Published 12/12/2014

[font size=5]Leslie and Mark's Old/New Idea[/font]

[font size=3] The Nuclear Science and Engineering Library at MIT is not a place where most people would go to unwind. It’s filled with journals that have articles with titles like “Longitudinal double-spin asymmetry of electrons from heavy flavor decays in polarized p + p collisions at √s = 200 GeV.” But nuclear engineering Ph.D. candidates relax in ways all their own. In the winter of 2009, two of those candidates, Leslie Dewan and Mark Massie, were studying for their qualifying exams—a brutal rite of passage—and had a serious need to decompress.

To clear their heads after long days and nights of reviewing neutron transport, the mathematics behind thermohydraulics, and other such subjects, they browsed through the crinkled pages of journals from the first days of their industry—the glory days. Reading articles by scientists working in the 1950s and ‘60s, they found themselves marveling at the sense of infinite possibility those pioneers had brought to their work, in awe of the huge outpouring of creative energy. They were also curious about the dozens of different reactor technologies that had once been explored, only to be abandoned when the funding dried up.

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Though nuclear engineers were mostly men in those days, Leslie imagined herself working alongside them, wearing a white lab coat, thinking big thoughts. “It was all so fresh, so exciting, so limitless back then,” she told me. “They were designing all sorts of things: nuclear-powered cars and airplanes, reactors cooled by lead. Today, it’s much less interesting. Most of us are just working on ways to tweak basically the same light water reactor we’ve been building for 50 years.”

But because of something that she and Mark stumbled across in the library during one of their forays into the old journals, Leslie herself is not doing that kind of tweaking—she’s trying to do something much more radical. One night, Mark showed Leslie a 50-year-old paper from Oak Ridge about a reactor powered not by rods of metal-clad uranium pellets in water, like the light water reactors of today, but by a liquid fuel of uranium mixed into molten salt to keep it at a constant temperature. The two were intrigued, because it was clear from the paper that the molten salt design could potentially be constructed at a lower cost and shut down more easily in an emergency than today’s light water reactors. And the molten salt design wasn’t just theoretical—Oak Ridge had built a real reactor, which ran from 1965-1969, racking up 20,000 operating hours.

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