Well, why nuclear? The work of Dr. Robert J. Moon shows that one tiny pellet (1.86 grams) of uranium fuel equals 1,260 gallons of oil, or 6.15 tons of coal, or 23.5 tons of dry wood. This means that nuclear energy is 2.2 million times more energy efficient than oil, and 3 million times more energy efficient than coal (Completing the Nuclear Fuel Cycle).
The reactors are built with separate water loops, one loop for the irradiated water (shown in orange) and one for the heated water (blue loop). This allows for the radioactive isotopes to be contained while still transmitting heat to the water in the second loop to create steam, and therefore power. The steam is then cooled, usually by cooling towers that are extremely large (such as the ones that were in the title page), and the water is pumped back into the reactor for heating.
As far as the fuel itself goes, the reactors take fuel rods that have enriched uranium pellets put inside them. Even though the uranium in these pellets is often referred to as enriched, the mined uranium is changed from .7% U-235 to 5% U -235. The reason this occurs is because U-235 is fissionable - able to start and maintain a nuclear reaction, while U-238 and U-234 are not due to inelastic scattering (Uranium Enrichment). Furthermore, the low amount of fissionable material that is used in these fuel rods essentially contains the risk of a reactor reaching criticality by reducing the amount of particles in the fuel that can actually react. In the words of the World Nuclear Association "Risks are managed through the rigorous control of materials, indeed, fuel fabrication facilities operate with a strict limitation on the enrichment level of uranium that is handled in the plant – this cannot be higher than 5% U-235, essentially eliminating the possibility of inadvertent criticality." (Nuclear Fuel Fabrication)
The Chernobyl Disaster was the first major catastrophic failure of a reactor core. In April of 1986, engineers were preparing for a routing shutdown of the reactor. In accordance with protocol on site, new electronics were to be tested at the time of the shutdown. These electronics were of unknown quality. Despite the risk, the reactor's automatic shutdown protocol was disabled in order to test the extent of the new electronics. This shutdown, along with inherent design flaws such as using graphite (a metal with a relatively low melting point) as a main building material set up the plant for disaster.
As the reactor was shutdown, improperly trained personnel were unable to identify the seriousness of the situation. The team onsite lost significant control over the reactor, and this resulted in a series of two powerful steam explosions, instantly killing two workers. Over the next few months, another 28 personnel would die as a result of acute radiation poisoning. Approximately 5% of the reactor’s total mass was released.
The nearby town of Pripyat was evacuated almost immediately following the explosion, and the town of Chernobyl followed suit a week later, leading to around 70,000 people being displaced in total. The Chernobyl Disaster is the deadliest reactor failure to date. The inadequacy of employees, combined with ignorance of proper safety protocols caused an otherwise completely avoidable accident.
In the recent years, Chernobyl has become home to Ukrainian people again, as well as becoming a tourist site. In 2016, the Ukrainian government slid a large concrete and steel shield over the reactor to further insulate the nuclear material, and allowing people to approach the area near the reactor without any real risk of radiation poisoning. (Chernobyl Accident 1987)
After a major earthquake struck 130 km offshore the city of Sendai in Miyagi, Japan, a 15 meter high tsunami disabled the cooling and power supply of three reactors on March 11, 2011, and caused a nuclear accident at Fukushima. It rated 7 on the INES scale with radioactive releases as high as 940 Petabecquerels (PBq). The three cores mostly melted in the first three days, with large releases of radioactivity in days 4 and 6. After two weeks, the three reactors were stable with water addition and two months later they were being cooled with recycled water from the new treatment plant. The official cold shutdown condition was announced at the end of 2011. 100,000 people were evacuated from their homes as a result of this accident but no deaths or radiation sicknesses were reported. The Fukushima plant incident was mainly caused my an inadequate tsunami break wall, which was only built to protect against 5.7m tsunamis. All of the back-up generators were on the ground, and were washed away by the flood. This is what caused the cooling pump failures. Most modern plants have now addressed many pressing environmental hazards such as this; for example, all Duke Energy plants now have their backup generators 11 ft. off of the ground. (Fukushima Accident).
Pic: Fukushima Disaster