On a December afternoon in Chicago
during the middle of World War II, scientists cracked open the nucleus
at the center of the uranium atom and turned nuclear mass into energy
over and over again. They did this by creating
for the first time a chain reaction inside a new
engineering marvel: the nuclear reactor. Since then, the ability to mine great
amounts of energy from uranium nuclei has led some to bill nuclear power as a plentiful utopian
source of electricity. A modern nuclear reactor generates enough
electricity from one kilogram of fuel to power an average American household
for nearly 34 years. But rather than dominate the global
electricity market, nuclear power has declined from
an all-time high of 18% in 1996 to 11% today. And it's expected to drop further
in the coming decades. What happened to the great promise
of this technology? It turns out nuclear power
faces many hurdles, including high construction costs and public opposition. And behind these problems lie
a series of unique engineering challenges. Nuclear power relies on the fission
of uranium nuclei and a controlled chain reaction that reproduces this splitting
in many more nuclei. The atomic nucleus is densely packed
with protons and neutrons bound by a powerful nuclear force. Most uranium atoms have a total
of 238 protons and neutrons, but roughly one in every 140
lacks three neutrons, and this lighter isotope is less
tightly bound. Compared to its more abundant cousin, a strike by a neutron easily splits
the U-235 nuclei into lighter, radioactive elements
called fission products, in addition to two to three neutrons, gamma rays, and a few neutrinos. During fission, some nuclear mass
transforms into energy. A fraction of the newfound energy
powers the fast-moving neutrons, and if some of them strike uranium nuclei, fission results in a second
larger generation of neutrons. If this second generation of neutrons
strike more uranium nuclei, more fission results in an even
larger third generation, and so on. But inside a nuclear reactor, this spiraling chain reaction is tamed
using control rods made of elements that capture excess
neutrons and keep their number in check. With a controlled chain reaction, a reactor draws power steadily
and stably for years. The neutron-led chain reaction
is a potent process driving nuclear power, but there's a catch that can result in unique demands
on the production of its fuel. It turns out, most of the neutrons emitted
from fission have too much kinetic energy to be captured by uranium nuclei. The fission rate is too low
and the chain reaction fizzles out. The first nuclear reactor built in Chicago
used graphite as a moderator to scatter and slow down
neutrons just enough to increase their capture by uranium
and raise the rate of fission. Modern reactors commonly use
purified water as a moderator, but the scattered neutrons are still
a little too fast. To compensate
and keep up the chain reaction, the concentration of U-235 is enriched to four to seven times
its natural abundance. Today, enrichment is often done by
passing a gaseous uranium compound through centrifuges to separate lighter U-235
from heavier U-238. But the same process can be continued
to highly enrich U-235 up to 130 times its natural abundance and create an explosive chain reaction
in a bomb. Methods like centrifuge processing
must be carefully regulated to limit the spread of bomb-grade fuel. Remember, only a fraction
of the released fission energy goes into speeding up neutrons. Most of the nuclear power goes into the
kinetic energy of the fission products. Those are captured inside the reactor
as heat by a coolant, usually purified water. This heat is eventually used to drive
an electric turbine generator by steam just outside the reactor. Water flow is critical
not only to create electricity, but also to guard against the most dreaded
type of reactor accident, the meltdown. If water flow stops because a pipe
carrying it breaks, or the pumps that push it fail, the uranium heats up very quickly
and melts. During a nuclear meltdown, radioactive vapors escape
into the reactor, and if the reactor fails to hold them, a steel and concrete containment building
is the last line of defense. But if the radioactive gas pressure
is too high, containment fails and the gasses
escape into the air, spreading as far
and wide as the wind blows. The radioactive fission products
in these vapors eventually decay into stable elements. While some decay in a few seconds, others take hundreds
of thousands of years. The greatest challenge
for a nuclear reactor is to safely contain these products and keep them from harming humans
or the environment. Containment doesn't stop mattering
once the fuel is used up. In fact, it becomes an even greater
storage problem. Every one to two years, some spent fuel is removed from reactors and stored in pools of water
that cool the waste and block its radioactive emissions. The irradiated fuel is a mix of uranium
that failed to fission, fission products, and plutonium, a radioactive material
not found in nature. This mix must be isolated from
the environment until it has all safely decayed. Many countries propose deep time storage
in tunnels drilled far underground, but none have been built, and there's great uncertainty about
their long-term security. How can a nation that has existed
for only a few hundred years plan to guard plutonium
through its radioactive half-life of 24,000 years? Today, many nuclear power plants
sit on their waste, instead, storing them indefinitely on site. Apart from radioactivity, there's an
even greater danger with spent fuel. Plutonium can sustain a chain reaction and can be mined from the waste
to make bombs. Storing spent fuel is thus not only
a safety risk for the environment, but also a security risk for nations. Who should be the watchmen to guard it? Visionary scientists from the early years
of the nuclear age pioneered how to reliably tap
the tremendous amount of energy inside an atom - as an explosive bomb and as a controlled power source
with incredible potential. But their successors have learned
humbling insights about the technology's not-so-utopian
industrial limits. Mining the subatomic realm makes for
complex, expensive, and risky engineering.
Former US Navy nuclear technician here. This is a good video covering the basics for the laymen out there. It also covers the point I've always been downvoted into oblivion for raising in regards to nuclear's viability as a energy solution. Reddit loves their nuclear power, and as someone that worked in the field, of course I see the appeal.
I eventually changed my mind on this issue, however, for essentially one reason. I don't think humans are ready for the long-term responsibility of waste storage. The US government is the most powerful organization humans have ever created, and they're responsible for the regulation and ultimately, the handling of a very large quantity of nuclear waste products for the foreseeable future (and much, MUCH longer)... yet they can't even pass a budget for even a single year. If our most powerful human institutions can't plan even one year ahead, we have no business creating substances that require us to be responsible for their safeguarding for millennia.
I've been called "anti-science" or even a Luddite for pointing this out on Reddit in the past. I can only assure you that this isn't the case. You'll have to take my word for it that the Navy isn't typically in the habit of training Luddites to operate nuclear reactors on board their submarines, and people that "just don't understand science" don't make it through Naval Nuclear Power School. And while I understand the dangers of climate change as well, I don't think trading one long-term problem for another is the solution. I think we just have better options at this point. I'm 100% behind further research into fusion, and even thorium fission reactors, but I think our best bet, for now, is renewables and more research. Maybe one day we'll find the solution to rendering the waste completely inert, but until then, building more nuclear capacity or continuing to operate at current levels makes no more sense than taking up smoking on the assumption that lung cancer will be cured before it kills you.
The video says that we've yet to build a deep storage facility for nuclear waste, but this isn't technically true. We've yet to complete it, but one is currently being built in Finland. Even this ambitious project, the only of its kind (that I'm aware of), which has long been touted as the ultimate "long-term" solution for the waste problem, has its problems.
I'd encourage anyone that's actually interested in this topic to watch the excellent documentary on Onkalo (the storage facility in Finland) and the problems with the long-term storage of nuclear waste products in general: Into Eternity.
Edited for correct country.
Somehow didn't talk about the challenge posed by the steadily decreasing costs of renewable energy and storage.