To maintain a sustained controlled nuclear reaction, for every 2 or 3 neutrons released, only one must be allowed to strike another uranium nucleus. If this ratio is less than one then the reaction will die out; if it is greater than one it will grow uncontrolled (an atomic explosion). A neutron absorbing element must be present to control the amount of free neutrons in the reaction space. Most reactors are controlled by means of control rods that are made of a strongly neutron-absorbent material such as boron or cadmium.Nuclear Fission: The Heart of the Reactor:
In addition to the need to capture neturons, the neutrons often have too much kinetic energy. These fast neutrons are slowed through the use of a moderator such as heavy water and ordinary water. Some reactors use graphite as a moderator, but this design has several problems. Once the fast neutrons have been slowed, they are more likely to produce further nuclear fissions or be absorbed by the control rod. [Source: http://www.atomicarchive.com/Fission/Fission4.shtml]
Despite all the cosmic energy that the word "nuclear" invokes, power plants that depend on atomic energy don't operate that differently from a typical coal-burning power plant. Both heat water into pressurized steam, which drives a turbine generator. The key difference between the two plants is the method of heating the water.Fears of Fission Rise at Stricken Japanese Plant:
While older plants burn fossil fuels, nuclear plants depend on the heat that occurs during nuclear fission, when one atom splits into two and releases energy. Nuclear fission happens naturally every day. Uranium, for example, constantly undergoes spontaneous fission at a very slow rate. This is why the element emits radiation, and why it's a natural choice for the induced fission that nuclear power plants require. [Source: http://science.howstuffworks.com/nuclear-power1.htm]
By HIROKO TABUCHI Published: November 2, 2011
TOKYO — Nuclear workers at the crippled Fukushima power plant raced to inject boric acid into the plant’s No. 2 reactor early Wednesday after telltale radioactive elements were detected there, and the plant’s owner admitted for the first time that fuel deep inside three stricken reactors was probably continuing to experience bursts of fission. [Source: New York Times Full story Fears of fission Rise at Stricken Japanese Plant ]I read this quote by Joieau in the Daily Kos:
"Best to remember that officials - Japanese or American or anybody else's - are always going to diminish the situation until the point where the truth just cannot remain hidden any longer. At least one corium flow is in the groundwater, and hydrogen is building even as fission product releases are increasing and will continue to increase for the next few months at least." ~ JoieauThe entire post is an eye opener and can be found at Fukushima: Stage Two
Another story ran in Bloomberg News: Full Story: Tepco Detects Nuclear Fission Here are some excerpts from that article -
Tokyo Electric Power Co. detected signs of nuclear fission at its crippled Fukushima atomic power plant, raising the risk of increased radiation emissions. No increase in radiation was found at the site and the situation is under control, officials said.
The company, known as Tepco, began spraying boric acid on the No. 2 reactor at 2:48 a.m. Japan time to prevent accidental chain reactions. Tepco said it may have found xenon, which is associated with nuclear fission, while examining gases taken from the reactor, according to an e-mailed statement today.
“Given the signs, it’s certain that fission is occurring,” Junichi Matsumoto, a general manager at Tepco who regularly talks to the media, told reporters in Tokyo today. There’s been no large-scale or sustained criticality and no increase in radiation, he said.
“Melted fuel in the No. 2 reactor may have undergone a sustained process of nuclear fission or re-criticality,” Tetsuo Ito, the head of Kinki University’s Atomic Energy Research Institute, said by phone. “The nuclear fission should be containable by injecting boron into the reactor to absorb neutrons.”
Fissioning involves the splitting of atoms, which, in the case of certain uranium isotopes, can lead to an uncontrolled reaction and emittance of radiation.
Tepco and the government have said they are on track to bring the damaged reactors into a safe state known as cold shutdown by the end of the year.
We are now almost eight months in since the nuclear disaster at Fukushima and things are really no better. The elephant keeps getting moved to a bigger room with the hope that no one will notice it. Here in the United States we move closer to extending more nuclear plant licenses and issuing new ones. Again, we keep producing more and more spent fuel on a daily basis with no safe place to store this waste.
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