On a December afternoon in Chicago during the epicenter 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 a chain reaction inside a new engineering marvel the nuclear reactor for the first time. Since then the ability to mind great amounts of energy from uranium nuclei has led some to build nuclear power as a plentiful unrealistic source of electricity.
A modern nuclear reactor generates enough electricity from 1 kilogram of fuel to power an average household for almost 34 years but rather than conquer the international electricity market. Atomic power has declined from an all-time high of 18 % in 1996 to 11 % today and it's envisioned 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.
How does nuclear power work?
Nuclear power depends on the fission of uranium nuclei and a controlled chain reaction that multiplies this splitting into numerous more hearts. The atomic nucleus is densely packed with protons and neutrons found by a strong nuclear force. Most uranium atoms have a total of 238 protons and neutrons but roughly 1in every 140 lakhs three neutrons and this lighter isotope is less tightly bound. Compared to its abundant cousin a strike by a neutron can easily split the u-235 nuclei into lighter radioactive elements called fission products. In addition, 2-3 neutrons gamma rays, and a few neutrinos.
During fission some nuclear mass converts into energy a fraction of the newfound energy powers the fast-moving neutrons and if some of them hit uranium nuclei fission results in a second larger generation of neutrons. If this second generation of neutrons strikes more additional uranium nuclei then more fission results in an even larger third generation and the chain goes 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 is stable for years. The neutron lead 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.
Light water reactor
The main nuclear reactor created in Chicago used graphite as a moderator to disperse and slow down neutrons just enough to grow their capture by uranium and boost 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 4 to 7 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 resumed to highly enriched 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 ultimately utilized 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 the water flow stops because a pipe carrying it breaks or the pumps that push it fails 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 gases 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 hold these products and keep them from damaging humans or the environment.
Storage of Fuel
Containment doesn't stop mattering once the fuel is used up 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 mixture of uranium that failed to fission products and plutonium a radioactive material that is very rare in nature this mix must be separated from the environment until it has all safely decayed, many countrysides propose deep time storage in tunnels mined far underground, but none have been built and there's great uncertainty about their long-term security.
How can a nation that has lived for only a few hundred years plan to protect plutonium through its radioactive half-life of 24,000 years? today many nuclear power plants sit on their waste instead of storing them indefinitely on-site, Apart from radioactivity, there's an even greater danger with spent fuel. Plutonium can uphold a chain reaction and be excavated from the waste to make bombs storing spent fuel is thus not only a safety hazard for the environment but also a protection risk for nations.
Who should be the watchman to safeguard it? imaginative scientists from the earlier years of the nuclear age pioneered how to reliably tap the enormous amount of energy inside an atom as an explosive bomb and a controlled power source with incredible potential. But their successors have learned humbling insights about the technology's not-so-idealistic industrial limits. Mining the subatomic realm makes for complicated, costly, and risky engineering.
