HOW REACTORS WORK:
Nuclear reactors work by fission, or splitting atoms apart. The most common fuel for reactor plants in the United States is Uranium- 235. The Uranium starts out as an ore, Uranium- 238, and has to be enriched to better suit the reaction process. It is easier to cause the Uranium- 235 atoms to split (fission process). The reactors are made up of fuel rods, which are twelve-foot long rods that contain pellets of U-235 and are pumped with helium. This mixture is the cause of the fission process: the helium atoms hit the U-235 atoms and cause them to split. The fuel rods are placed in spacer grids that allow for coolant to flow around the rods to keep them cool enough. The fuel assemblies are always placed underground in a pool of water (Site 4).
There are two types of reactors that are used in the U.S., the boiling water reactor and the pressurized water reactor. They both work the same way, creating steam to turn the turbine and create a current or flow of electrons though wires, creating energy. The boiling water reactor is less pressurized and the heat causes the water to boil and create steam, while the pressurized reactor keeps the water at such a high pressure that even at extremely high temperatures the water wont boil. After the steam is produced and moved through the turbine (the element that turns the electric generator) it condensed back into water and sent back into the reactor to cycle around again (Site 1).
Second, we look at the disaster of Chernobyl and what went wrong:
The Chernobyl accident in 1986 was the largest uncontrolled radioactive release into the environment ever recorded. Due to a flawed reactor design and poorly trained personnel, radioactive substances were released into the air for 10 days, killing and injuring hundreds of people in the area.
The accidental disaster occurred in April of 1986 at the Chernobyl power plant in Ukraine. The reactor used Uranium-235, as most other plants, and was a boiling water reactor made by the Soviet Union (Site 2).
On April 26, the crew at Chernobyl was to test out new energy regulator designs. The automatic shutdown mechanisms had been disabled due to a series of actions by operators, but the routine test began to see if they could use less energy. The reactor went into a very unstable state, and they could not shut it down in time manually. The control rods were also strangely designed and caused a major power surge as they were inserted into the reactor. The reactor destructed as the steam from the very hot fuel rods and the cooling water collided. The fuel channels were ruptured and the control rods were jammed, only halfway inside. The large amount of steam created a very large explosion, shooting fission products (radioactive materials) into the air. A second explosion occurred seconds later, sending large amounts of graphite into the air as well. This problem and explosion only happened to one of the four reactors present at Chernobyl. It caused a major disruption in Belarus, Russia, and Ukraine because the elements in the air traveled to these countries. Hundreds of thousands of people had to be resettled into safer areas, many had to get treatment for radiation poisoning, and many hours and a lot of money was put into cleaning the mess up and getting the remaining three reactors up and running again. It took over two years to fully clean it all up (Site 3).
Japan's nuclear crisis: is it as bad as Chernobyl?
JAPAN'S NUCLEAR CRISIS:
The nuclear crisis in Japan began with an earthquake and tsunami at Japan’s Fukushima Dai-1 nuclear power plant. After the earthquake the emergency shutdown of the reactors went into effect, and worked perfectly. The shutdown was not the problem, as in Chernobyl, but what happened afterwards. The cooling facility to the reactors was hit by the tsunami and halted the cooling process of the rods and reactors, leaving the past fission products to remain harmful. As in Chernobyl, by the time operators got there to manually turn back up generators on, it was too late. The people managing the situation knew the gas build up would lead to an explosion, so they vented a lot of it into a containment facility, where it reacted with another gas and exploded. This was the secondary chamber, which was good, because the primary chamber contained most of the harmful elements. The primary chamber was getting too hot, and the rods were beginning to melt. This is very bad because if the rods melt too much and create a pool in the chamber, the Uranium and other elements will eat through the walls and eject massively radioactive substances into the air. The chamber walls did crack, but then helicopters full of water were sent to dump cold water onto the reactor to try to cool it down and contain the nuclear elements. Some of the radioactive substances were released into the air and caused harm to some of the population around the reactors when the explosion happened, but the primary containment vessel is being kept cool enough to keep most of the nuclear matter contained. Also, some of the substance is said to have been leaked into the water supply and the ocean. The operators’ biggest fear is that more radioactive substances will be leaked into the ocean or water supply that would harm many people either way. They have blocked off an area of the ocean to stop people from fishing near the reactors, in case the fish have been exposed, and are trying to contain the rest of the radioactive substances. We should be a bit worried, but for now it is contained and is not much of a harm. Although it has harmed many and has sent many people away from their homes, it is not as bad as the disaster at Chernobyl(Site 5).
Here is a video to further explain the crisis in Japan in relation to the disaster of Chernobyl! Click on the word "video."
Video- YouTube: http://www.youtube.com/watch?v=IDfAZhhqkCI
SIte 1- http://www.nrc.gov/reading-rm/basic-ref/teachers/01.pdf
Site 2- http://www.tesec-int.org/chernobyl/History.htm
Site 3- http://www.world-nuclear.org/info/chernobyl/inf07.html
Site 4- http://science.howstuffworks.com/japan-nuclear-crisis1.htm
Site 5- http://spectrum.ieee.org/tech-talk/energy/nuclear/explainer-what-went-wrong-in-japans-nuclear-reactors