HomeMy WebLinkAboutMaking hydrogen fusion feasible challenges 1980Makin
g ragen ftision feasible
h Y d
challenges scientists, engineers
Second of two articles
By DAVID F. SALISBURY
Christian Science Monitor
LIKE PROMETHEUS, the legendary fire-
bringer, a group of researchers is trying
to harness the celestial fire - hydrogen fu-
sion - that powers the sun and other stars.
But while they are optimistic that control
of this process is within their grasp, they are
not certain they can transform successful
laboratory experiments into an economically
attractive source of electric power.
These researchers are beginning to ap-
preciate the tremendous engineering chal-
lenges that will be involved.
For the past year, the International Atom-
ic Energy Agency has been conducting an
assessment of these engineering require-
ments. According to one of the participants,
Weston M. Stacey Jr. of the Georgia Institute
of Technology, the conclusion is that "there
is an awful lot of development and engineer-
ing to be done, but it is do-able."
THE IAEA REVIEW concentrated on the
mainstream of experimental fusion
technology, which is embodied in a class of
devices called the tokamak. This is a ma-
chine in which magnetic forces confine the
hot hydrogen gas in what amounts to a
doughnut-shaped magentic bottle. When heat-
ed to 10,000 times the temperature of the sur-
face of the sun, the hydrogen atoms fuse to-
gether to form helium, releasing tremendous
amounts of energy.
-,ate this ?r.-:..nsun;ing more energy than is produced by the
fusion reaction itself, a special type of mag-
net is required. This is a "superconducting"
magnet, which carries electrical current with
virtually no resistance when cooled to within
a few tens of degrees of absolute zero (minus
273 degrees•Celsius).
For fusion power plants, superconducting
magnets must be developed that can gener-
ate magnetic fields twice the intensity of
those achievable with present technology.
WHILE THE OUTLOOK for supercon-
ducting coils that generate a constant
magnetic field seems good, the same can't be
said for the coils that would generate the pul-
sating magnetic fields needed to control
instabilities by which the hot fusion medium
tends to escape its confinement.
Radiation damage to the walls of the reac-
tor vessel also is an important engineering
consideration. High-energy radiation from
the fusion reaction weakens metals and
causes them to become radioactive. To be
economical, the reactor lining must be de-
signed to last four to five years and then be
rerr l i ? ,,'<<ti%ely easiiy by re-
mote control.
Today, about the only available material
that is suitable would be stainless steel, ac-
cording to Stacey. Yet it suffers more from
radiation damage than other, more exotic,
materials.
Niobium and vanadium, for instance, with-
stand radiation better and also become less
radioactive than stainless steel. Unfortunate-
ly, materials such as these also are rare and
Fem.
touch?s on a tokamak
- Monitor photo
expensive. Set the material used for the
reactor verse has a major bearing on envi-
ronmental art social questions.
One of thenain advantages of fusion over
fission poweris that it involves less radioac-
tivity. Yet th; is a potential advantage rath-
er than an artomatic benefit, said John P.
Holdren of he University of California at
Berkeley, wh has analyzed the environmen-
tal implicatins of present design concepts
for the fusion:)ower plant.
CURREN'IPLANS for tokamak plants use
lithium,either as a coolant or to gener-
ate tritium, t,e radioactive form of hydrogen
that would beused as fuel. This liquid lithium
would be thelargest source of stored energy
in such a reator, Holdren said, and a lithium
fire well mayrepresent the "maximum hypo-
thetical acci(--nt." The fusion specialist has
made a preliainary study of possible "worst
case" accide.ts that would release radioac-
tive materialrom tokamaks of several possi-
ble designs.
In a fusionreactor, the amount of radioac-
tive matter hat would exist in a volatile
form is only <small fraction of that typically
found in a fiston reactor. A lithium fire, how-
ever, can be tot enough to melt the metal in
the reactor s,ucture. This could release any
radioactive laterial trapped there. Conse-
quently, the "worst case" of a release of
radioactive raterial from a stainless-steel fu-
sion reactor is estimated to be a sizable frac-
tion (about three-fourths) of that estimated
for a fission reactor, in terms of radioactivity
released per megawatt of capacity of the
reactor.
On the other hand, second- or third-genera-
tion fusion plants, using "advanced" materi-
als and with reduced tritium inventories,
could have "worst case" releases one-tenth
to one-hundredth that of first-generation
plants, Holdren believes.
IN THE CASE of radioactive waste, fusion
plants begin with a considerable advan-
tage over the breeder reactor, the fission
reactor that "breeds" more nuclear fuel than
it consumes, the scientist has calculated. Per
unit of electricity generated, the first-genera-
tion fusion plant would produce only one-fifti-
eth of the waste produced by the breeder.
And advanced fusion plants could be even
more waste-free, generating one ten-thou-
sandth the amount of radioactive byproducts
as the breeder did.
Achieving fusion's full environmental
advantages depends on realizing the benefits
of these advanced designs. This may prove to
be considerably more difficult than the
present problem of making fusion work in the
laboratory.
For, perversely, the approaches to control-
ling fusion that now seem closest to technical
success are among the least attractive possi-
bilities from the environmental standpoint,
Holdren said. To forego the earliest possible
commercialization of fusion power in favor of
realizing its full potential will be expensive in
time and dollars, he said. But he believes it
to be the proper course.
Another group that sees environmental and
social problems with current fusion technol-
ogies is the utilities. "Public acceptability is
of primary importance," said Clinton P. Ash-
worth of Pacific Gas & Electric Co. He is
deeply disturbed by the direction taken by
the U.S. Department of Energy's fusion pro-
gram. In particular, he and a number of col-
leagues in the utility business are concerned
about the concentration on a few, large-scale
technologies such as that of the tokamak in
the drive to show that controlled fusion is
possible.
< ]E ARE LIKELY to end up with fu-
sion reactors that are well tested
but totally unacceptable," Ashworth warned.
The large scale of current designs is the
utility expert's major objection. Driven by
design and cost factors, federal engineering
studies have envisioned giant fusion plants
with 3,000-megawatt capacity and each cost-
ing almost $5 billion. "These are far too large
to be of use," Ashworth said.
There are alternative fusion concepts that
have been given low priority in the federal ef-
fort that could result in smaller and more ac-
ceptable power plants, he said. Pacific Gas &
Electric, with the Electric Power Research
Institute, has chosen one such concept to sup-
port. And the nuclear industry is attempting
to organize itself to influence the course of
the federal program.
Meanwhile, some fusion researchers and
influential congressmen are convinced! that a
demonstration fusion reactor could come on
line as early as the 1990s.,
Putting finishing