12 years. It’s also extremely rare and expensive, but it would be
bred in fusion reactors.
When deuterium and tritium nuclei fuse, energy gets released
as an alpha particle (a helium nucleus, which is two protons and
two neutrons) and a very energetic neutron. Those neutrons are
neutral, unconfined by the magnetic field holding the plasma. They
crash into whatever material is facing them, which in tokamaks,
for example, is called the first wall. The crash transfers heat and
also knocks the atoms in the wall’s material out of place, damaging
it and making it radioactive.
Daniel Jassby, a retired researcher from the Princeton Plasma
Physics Lab, says the incessant barrage of neutrons from burning
D-T will create a lot of radioactive waste. Replacing weakened
first-wall structures will drive up costs, he says, because of the
expense of installing the new components as well as the downtime
in which the system won’t be selling power. What’s more, the size
of the machines means fusion reactors may produce as much as
10 times more waste than conventional fission reactors, he says.
And while the levels of radiation may not be as intense as those of
spent uranium fuel rods, that just means the byproducts of fusion
systems are dangerous for a century instead of millennia.
The true operating costs for fusion reactors may not be lowenough to cover their costs, let alone compete with existing power
plants, according to Jassby. “Why would anybody want this?”
Nevertheless, a certain strain of utopian idealism has always
run through the fusion endeavor. It may be what prompted the
1985 agreement between U.S. President Ronald Reagan and the
Soviet Union’s Mikhail Gorbachev to cooperate on building a fusion
energy project. Now known as ITER, the giant, long-delayed,
35-nation cooperative project is under construction—and about
60% complete—in the south of France.
When ITER achieves its first plasma, which is slated for 2025,
it’s expected to hit a fusion milestone: It will produce more energy
than it consumes. “There’s nobody knowledgeable in the space who
doesn’t believe when they turn ITER on that it’s going to produce
net energy out,” says General Fusion’s Mowry. ITER is expected
to produce 500 megawatts while consuming 50. In the parlance of
the field, it will have a Q>1. Specifically, since it’s expected to produce
10 times the energy put in, it would have a Q=10.
In the plasma physics community, there’s no question that
fusion is viable. Now these startups are aiming to build a working—
and profitable—fusion power plant, Mowry says. “Private fusion
ventures are not going to work on fundamental plasma physics and
fusion science,” he says. “They sit on top of that half a century of1969
In an example of
cooperation, the U.K.
brings laser equipment
to the Soviet Union
to measure the
temperature of the T-3
tokamak, confirming
10 million C plasma.1997
The Joint European
Torus, or JET,
sets a record with
a fusion output of
16.1 megawatts,
equivalent to about
67% of the input
energy, a Q of 0.67.2019
Construction of ITER,
an international fusion
demonstration project,
in the south of France
is 60% complete.
When turned on, ITER is
expected to produce
10 times the energy
it consumes, a Q of 10.1985
The Soviet Union
proposes international
collaboration on
fusion at the Geneva
summit of Mikhail
Gorbachev and Ronald
Reagan, which leads
to the start of ITER.1989
Chemists Martin
Fleischmann
and Stanley Pons’s
cold fusion experiment
can’t be replicated.1982
Tokamak Fusion Test
Reactor, or TFTR, starts
at the Princeton Plasma
Physics Laboratory.
It sets a record plasma
temperature of
510 million C.FROM LEFT: HULTON/GETTY IMAGES. BETTMANN/GETTY IMAGES. INTERFOTO/ALAMY. CTBTO. DAILY SKETCH. COURTESY G.E. COURTESY CULHAM CENT
ER FOR FUSION ENERGY.
DIRK HALESTEAD/LIFE COLLECTION/GETTY IMAGES. RAVEN CALL/AP PHOTO. COURTESY PRINCETON PLASMA PHYSICS LAB. COURTESY EURO VISION.COURTESY ITER“Private fusion ventures are not going to
work on fundamental plasma physics and fusion science. They sit
on top of that half a century of hard-won knowledge, and
they’re all about commercialization”VOLUME 28 / ISSUE 5 73