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JUNE 13, 2013

A New Way to Do NuclearBY GARETH COOK

In February of 2010, Leslie Dewan and Mark

Massie, two M.I.T. students, were sitting on a bench

in a soaring marble lobby under the universitys

iconic dome. They had just passed their Ph.D.

qualifying exams in nuclear engineering, and were

talking about what to do next. This being

Cambridge, they began to muse about a start-up. By

the end of their conversation, theyd decided to

design their own nuclear reactor. Even as start-up

concepts go, it was pretty weak. Constructing anuclear power plant is not like tossing together a

ninety-nine-cent app, and the industry is not an obvious one to try to disrupt. Nuclear

engineering is a complex and potentially dangerous field that drives international

conflicts. Dewan and Massie would need money and an abundant amount of patience.

Another flaw in their scheme: they didnt actually have an idea for a new and better

nuclear power plant.

Three years later, Dewan and Massie have a company, called Transatomic

(http://transatomicpower.com/), with a million dollars in funding, an impressive board ofadvisers, and a vote of confidence from the Department of Energy, which recently

awarded the pair first prize in their Future Energy innovation contest (http://www.arpae-

summit.com/2013-Agenda/Future-Energy-Pitching-Session). Russ Wilcox, a co-

founder of E Ink, has joined as C.E.O. and resident grownup. In the months after their

first conversation, Dewan and Massie drew up a design for a nuclear reactor that is small,

relatively cheap, and walk-away safe: even if it loses all power, it cools on its own,

avoiding a Fukushima-style meltdown. Theoretically, the reactor can put out as much

electric power (five hundred megawatts) as a standard coal plant without belching carbon

into the atmosphere. It can also run on nuclear waste, generating power even as it relieves

another environmental burden. We had this sense that there are so many unexplored

aspects of nuclear technology, Dewan said. We knew that there would be something

out there that would work, and would be better.

Dewan is twenty-eight and the kind of person who fits right in at M.I.T.: she is dubious

of received wisdom, fond of building, and unabashedly geeky. Growing up outside

Boston, she always knew that she wanted to attend school there; as an undergraduate, she

learned of an archeological debate regarding the seaworthiness of Ecuadorian balsa rafts,

http://www.arpae-summit.com/2013-Agenda/Future-Energy-Pitching-Sessionhttp://www.arpae-summit.com/2013-Agenda/Future-Energy-Pitching-Sessionhttp://transatomicpower.com/http://transatomicpower.com/http://www.arpae-summit.com/2013-Agenda/Future-Energy-Pitching-Sessionhttp://transatomicpower.com/http://www.newyorker.com/contributors/gareth-cook

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so she built one and sailed it down the Charles River with a crew of six. To help recruit

students to her dorm, she constructed a My Little Pony Trojan horse that rolled on

casters and comfortably seated eight. (It sadly passed away in its prime: papier-mch,

rain.) Her father, David, an M.I.T. grad himself, gave her a credit card when she left for

college, and for the first two years, he said, the largest expense category by far was Home

Depot.

When I met Dewan on campus recently, she was stylishly dressed in a black herringbone

blouse, jeans, and silver flats. Her long brown hair was pulled back in a loose braid. She

laughed easily and encouraged me to stop her if, in her enthusiasm, she veered into

argon.

A nuclear power reactor is just a fancy way of boiling water, she began. Nuclear fuel

typically contains uranium-235, a massive and slightly unstable atom famously capable of

sustaining chain reactions. Under the right conditions, its nucleus can absorb an extra

neutron, growing for an instant and then separating into two smaller elements, releasing

heat and three neutrons. If, on average, at least one of these neutrons splits anotheruranium atom, the chain continues, and the fuel is said to be in a critical state. (Criticality

has to do with the concentration of uranium, and whether the neutrons are bounced back

toward the fuel. A Ph.D. in nuclear engineering is helpful for understanding the concept,

as is this video (http://bit.ly/16X8crd) of ping-pong balls mounted on mouse traps.)

Water is pumped past the heat source and becomes steam, which then turns turbines,

generating electricity.

Traditional nuclear power plants, however, come with two inherent problems. The first is

the threat of a meltdown. Even after a reactor is shut off, the fuel continues to generatesome heat and must be cooled. Dewan compares it to a pot on a burner that just wont

turn off; eventually, the water boils over, and the pot gets scorched. If a plant loses all

electric power, it cant pump water past the fuel, which gets hotter and hotter, leading to

disaster.

The second problem facing traditional plants is that the fuel must be manufactured in

long rods, each encased in a thin metal layer, called cladding, that deteriorates after a few

years. The rods then have to be replaced, even though the fuel inside is still radioactive,

and will remain so for hundreds of thousands of years. Unsurprisingly, nobody wants thistrash in their backyard.

Dewan and Massies design seems to solve both problems at once. Its based on a method

that worked successfully at the Oak Ridge National Laboratory, in Tennessee, in the

nineteen-sixties. Called a molten salt reactor, it eschews rods and, instead, dissolves the

nuclear fuel in a salt mixture, which is pumped in a loop with a reactor vessel at one end

and a heat exchanger at the other. In the vessel, the fuel enters a critical state, heating up

the salt, which then moves on to the heat exchanger, where it cools; it then travels back to

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the vessel, where it heats up again. Heat from the exchanger is used to make steam, and,

from this, electricity. At the bottom of the reactor vessel is a drain pipe plugged with

solid salt, maintained using a powerful electric cooler. If the cooler is turned off, or if it

loses power, the plug melts and all of the molten salt containing the fuel drains to a

storage area, where it cools on its own. Theres no threat of a meltdown.

To explain the second trickmodifying the reactor to run on nuclear wasteDewan

explained a key subtlety of nuclear physics: a neutron can only split an atom if it is

moving at the right velocity, neither too slow nor too fast. Imagine cracking eggs: if you

bring the egg down too softly on the lip of a mixing bowl, it will not break. In the bizarre

world of atomic physics, the egg will also fail to break if struck too hard. To keep a

uranium chain reaction going, engineers employ materials that slow neutrons to exactly

the speed required to split uranium-235. The Transatomic reactor uses a different set of

materials, slowing neutrons to the velocity needed to cleave uranium as well as other

long-lived radioactive elements in nuclear waste, breaking them down and releasing their

energy. Transatomic can crack plutonium, americium, and curium. Any egg will do.

The environmental advantages are huge. There are no rods to fall apart, so the reactor can

keep working on the uranium. (This was proven at Oak Ridge.) And the Transatomic

reactor can also work off the radioactive byproducts, gleaning more energy and

substantially reducing both the amount and radioactivity of the waste. Todays nuclear

power plants extract about three per cent of the fuels available energy, while Transatomic

wrings out more like ninety-six per cent, according to computer simulations carried out

on industry-standard software.

Transatomic faces a challenging climb. The company hasnt built anything yet; there isalways the danger of a inhibitive engineering problem emerging. If, for example, the

corrosive salt fuel severely limits the life of the heat exchanger, the reactor could prove

too expensive to compete commercially. The most daunting obstacle, though, is the

United States government: it is exceedingly difficult to get permission to build a

demonstration reactor, no matter how good the idea. In many industries, companies

trying to do something hard face what investors call the valley of death: that long,

financially barren stretch between proving a concept with a bit of seed money and taking

the first commercial steps. Ray Rothrock, a prominent venture capitalist who is an

investor in Transatomic and a partner at Venrock, told me that, in the case of nuclearenergy, the valley of death might be a Grand Canyon.

The accidents at Three Mile Island, Chernobyl, and Fukushima are partly to blame, but

so is a flaw in the way we approach risk. When nuclear power plants fail, they do so

dramatically. Coal and natural gas, through air pollution, kill many more people every

year, but the effects are diffuse. One recent paper

http://pubs.giss.nasa.gov/abs/kh05000e.html

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(http://pubs.giss.nasa.gov/abs/kh05000e.html) estimated that nuclear power has

prevented 1.84 million air-pollution-related deaths globally. Nobody died at Three Mile

Island.

Attitudes are shifting, though. Chernobyl melted down when Dewan was one year old,

and the Three Mile Island accident unfolded before she was born. For her generation, the

defining environmental horror is not Fukushima but the inherited, ongoing catastrophe

of climate change. Put aside emotions, and certain facts are not in dispute. The planet is

going to need a lot more power. Engineers have not yet found a way to substantially scale

up wind and solar power. Oil and gas contribute to climate change and air pollution.

Within the nucleus of each atom, there are huge amounts of energy, and humans have

only begun to explore the ways in which it can be tapped.

There are signs that we are moving toward a pro-nuclear moment. A new Robert Stone

documentary, Pandoras Promise, about the green case for nuclear power, is in theatres

now. (Michael Specter wrote about the film for todays Daily Comment

(http://www.newyorker.com/online/blogs/comment/2013/06/time-to-go-nuclear.html).)More students are entering nuclear degree programs. Transatomic is just one of several

nuclear power start-ups, including a Bill Gates venture called TerraPower

(http://www.terrapower.com/). My time on the M.I.T. campus made it evident that more

are undoubtedly on the way.

After our interview, Dewan and I stepped out for a walk. It was one of the first hot days

of the year. The students were out, in backpacks and shorts. She slipped on a pair of

sunglasses, and we strolled by a Alexander Calder sculpture. Ive always thought of

nuclear as something thats good for the environment, she said. I worry about my polarbears.

Illustration by Maximilian Bode

GARETH COOK

http://www.terrapower.com/http://www.newyorker.com/online/blogs/comment/2013/06/time-to-go-nuclear.htmlhttp://pubs.giss.nasa.gov/abs/kh05000e.html