The development of the nuclear chain reaction was not in the direction
of bombs only. Nuclear reactors designed for the controlled production
of useful energy multiplied in number and in efficiency since Fermi’s
first “pile”. Many nations now possess them, and they are used for a
variety of purposes.[2]
[Illustration: _The USS_ Nautilus, _the world’s first nuclear powered
submarine, in New York harbor_.]
In 1954 the first nuclear submarine the USS _Nautilus_ was launched by
the United States. Its power was obtained entirely from a nuclear
reactor, and it was not necessary for it to rise to the surface at short
intervals in order to recharge its batteries. Nuclear submarines have
crossed the Arctic Ocean under the ice cover, and have circumnavigated
the globe without surfacing.
In 1959 both the Soviet Union and the United States launched
nuclear-powered surface vessels. The Soviet ship was the icebreaker,
_Lenin_, and the American ship was a merchant vessel, the NS _Savannah_.
In the 1950s nuclear reactors were also used as the source of power for
the production of electricity for civilian use. The Soviet Union built a
small station of this sort in 1954, which had a capacity of 5,000
kilowatts. The British built one of 92,000 kilowatt capacity, which they
called Calder Hall. The first American nuclear reactor for civilian use
began operation at Shippingport, Pennsylvania, in 1958. It was the first
really full-scale civilian nuclear power plant in the world.
The world appeared to have far greater sources of energy than had been
expected. The “fossil fuels”—coal, oil and natural gas—were being used
at such a rate that many speculated that the gas and oil would be gone
in decades and the coal in centuries. Was it possible that uranium might
now serve as a new source that would last indefinitely?
It was rather disappointing that it was uranium-235 which underwent
fission, because that isotope made up only 0.7% of the uranium that
existed. If uranium-235 were all we had and all we ever could have, the
energy supply of the world would still be rather too limited.
There were other possible “nuclear fuels”, however. There was
plutonium-239, which would also fission under neutron bombardment. It
had an ordinary half-life (for a radioactive change in which it gave off
alpha particles) of 24,300 years, which is long enough to make it easy
to handle.
But how can plutonium-239 be formed in sufficient quantities to be
useful? After all, it doesn’t occur in nature. Surprisingly, that turned
out to be easy. Uranium-238 atoms will absorb many of the neutrons that
are constantly leaking out of the reactor and will become first
neptunium-239 and then plutonium-239. The plutonium, being a different
element from the uranium, can be separated from uranium and obtained in
useful quantities.
Such a device is called a “breeder reactor” because it breeds fuel.
Indeed, it can be so designed to produce more plutonium-239 than the
uranium-235 it uses up, so that you actually end up with more nuclear
fuel than you started with. In this way, all the uranium on earth (and
not just uranium-235) can be considered potential nuclear fuel.
[Illustration: _The Shippingport Atomic Power Station, the first
full-scale, nuclear-electric station built exclusively for civilian
needs, provides electricity for the homes and factories of the greater
Pittsburgh area. The pressurized-water reactor, which now has a
90,000-net-electrical-kilowatt capacity, began commercial operation in
1957. The reactor is in the large building in the center._]
[Illustration: _The lights of downtown Pittsburgh._]
The first breeder reactor was completed at Arco, Idaho, in August 1951,
and on December 20 produced the very first electricity on earth to come
from nuclear power. Nevertheless, breeder reactors for commercial use
are still a matter for the future.[3]
Another isotope capable of fissioning under neutron bombardment is
uranium-233. It does not occur in nature, but was formed in the
laboratory by Seaborg and others in 1942. It has a half-life of 162,000
years. It can be formed from naturally occurring thorium-232.
Thorium-232 will absorb a neutron to become thorium-233. Then 2 beta
particles are given off so that the thorium-233 becomes first
protactinium-233 and then uranium-233.
If a thorium shell surrounds a nuclear reactor, fissionable uranium-233
is formed within it and is easily separated from the thorium. In this
way, thorium is also added to the list of earth’s potential nuclear
fuels.[4]
If all the uranium and thorium in the earth’s crust (including the thin
scattering of those elements through granite, for instance) were
available for use, we might get up to 100 times as much energy from it
as from all the coal and oil on the planet. Unfortunately, it is very
unlikely that we will ever be able to make use of all the uranium and
thorium. It is widely and thinly spread through the crustal rocks and
much of it could not be extracted without using up more energy than
would be supplied by it once isolated.
Another problem rests with the nature of the fission reaction. When the
uranium-235 nucleus (or plutonium-239 or uranium-233) undergoes fission,
it breaks up into any of a large number of middle-sized nuclei that are
radioactive—much more intensely radioactive than the original fuel. (It
was from among these “fission products” that isotopes of element 61 were
first obtained in 1945. Coming from the nuclear fire, it reminded its
discoverers of Prometheus, who stole fire from the sun in the Greek
myths, and so it was called “promethium”.)
The fission products still contain energy and some of them can be used
in lightweight “nuclear batteries”. Such nuclear batteries were first
built in 1954. Some batteries, using plutonium-238 rather than fission
products, have been put to use in powering artificial satellites over
long periods.
Unfortunately, only a small proportion of the fission products can be
put to profitable use. Most must be disposed of. They are dangerous
because the radiations they give off are deadly and cannot be detected
by the ordinary senses. They are very difficult to dispose of safely,
and they must not be allowed to get into the environment, especially
since some of them remain dangerous for decades or even centuries.
[Illustration: _The Experimental Breeder Reactor No. 2 building complex
in Idaho. The reactor is in the dome-shaped structure._]