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	Glossary
		Chain reaction: A reaction that stimulates its own repetition, in particular where the neutrons originating from nuclear fission cause an ongoing series of fission reactions.
		Control rods: Devices to absorb neutrons so that the chain reaction in a reactor core may be slowed or stopped by inserting them further, or accelerated by withdrawing them.
		Nuclear reactor: A device in which a nuclear fission chain reaction occurs under controlled conditions so that the heat yield can be harnessed or the neutron beams utilised.
	www.world-nuclear.org /info/inf51.html (2742 words)

	AllRefer.com - chain reaction (Physics) - Encyclopedia
		In the case of the fission of a nucleus, the reaction is begun by the absorption of a slow neutron.
		In order to sustain a chain reaction, a sample must be large enough to slow the neutrons so that one can be captured by another nucleus and produce a second fission.
		In a nuclear fission bomb, a chain reaction is started by forcing together two or more samples of fissionable material, each of less than critical mass, to form one sample of supercritical mass.
	reference.allrefer.com /encyclopedia/C/chainrea.html (479 words)

	Nuclear Energy - MSN Encarta
		A nuclear fission reaction releases 10 million times as much energy as is released in a typical chemical reaction.
		The two key characteristics of nuclear fission important for the practical release of nuclear energy are both evident in equation (2).
		In Fermi's “pile,” or nuclear reactor, the graphite moderator served to slow the neutrons.
	encarta.msn.com /encyclopedia_761558960/Nuclear_Energy.html (833 words)

	Nuclear PowerPlant Safety: Operations
		The Nuclear Regulatory Commission (NRC) requires that the containment structure for a nuclear powerplant be capable of withstanding severe outside events such as an earthquake, a tornado, or the impact of a large aircraft.
		Nuclear powerplants develop extensive plans for warning the public and notifying the authorities within a ten-mile radius in case of any unexpected event that could affect public health and safety.
		Nuclear powerplants maintain strict security to help ensure operating safety and prevent the loss of nuclear materials or acts of sabotage that could cause and unplanned release of radioactive material.
	www.nuc.umr.edu /nuclear_facts/design/design.html (2020 words)

	Nuclear Power
		Nuclear fission is a process where an atom, generally an isotope of uranium, is split by a neutron into two lighter atoms and emits both heat and radiation, in addition to ejecting two or three new neutrons, which in turn split other uranium atoms causing a chain reaction.
		Nuclear fusion, on the other hand, is a process where two atoms are forcibly joined, usually isotopes of hydrogen, using large amounts of energy that in turn produces a helium atom plus a neutron plus energy that is absorbed or release (which is considerably larger than the amount used to join the atoms together).
		Nuclear reactors are the machines that control and contain the nuclear fission chain reaction as well as releasing the heat at a controlled rate.
	www.unc.edu /~kjdesai/nuclear.htm (769 words)

	Nuclear Files: Library: Welcome Desk
		The minimum mass of a fissionable material that will just maintain a fission chain reaction under precisely specified conditions, such as the nature of the material and its purity, the nature and thickness of the tamper (or neutron reflector), the density, and the physical shape.
		Nuclear fusion is a process during which light atoms fuse to form heavier ones.
		Nuclear fuel elements that are discharged from a nuclear reactor after they have been used to produce power.
	www.nuclearfiles.org /menu/library/terms-acronyms/index.htm (1766 words)

	NASAexplores 9-12 Lesson: Chain Reaction (Student Sheets)
		Nuclear propulsion is a very attractive option for human exploration and development of space.
		Nuclear Fission is a reaction in which an atom's nucleus splits into smaller parts, releasing a large amount of energy in the process.
		The heat released during this reaction is harvested and used to generate electrical energy.
	www.nasaexplores.com /show_912_student_st.php?id=021220141116 (1115 words)

	Nuclear reactor
		In a fission reaction, besides the two fission products, a few (in the case of U-235 2.47 on the average) neutrons are emitted (flash animation, 70 kB).
		The principle of chain reaction is very easy therefore: a U235 nucleus is hit by a neutron, upon which fission occurs at a high probability.
		If the neutrons generated from a fission reaction induce more than one fission than more and more fission reactions will take place in a unit time and the chain reaction will be diverging (flash animáció, 16 kB).
	www.npp.hu /mukodes/lancreakcio-e.htm (1091 words)

	Introduction to Nuclear Power
		In the vast majority of the world's nuclear power plants, heat energy generated by burning uranium fuel is collected in ordinary water and is carried away from the reactor's core either as steam in boiling water reactors or as superheated water in pressurized-water reactors.
		The amount of energy in the reservoir of nuclear fuel is frequently expressed in terms of "full-power days," which is the number of 24-hour periods (days) a reactor is scheduled for operation at full power output for the generation of heat energy.
		The fraction of the reactor's fuel core replaced during refueling is typically one-fourth for a boiling-water reactor and one-third for a pressurized-water reactor.
	www.eia.doe.gov /cneaf/nuclear/page/intro.html (1989 words)

	#1 Site For Learning Science
		A nuclear reactor produces immense amount of heat energy; we have seen earlier that there is a mass difference between the U-235 and its fission products which leads to release of energy.
		To control the chain reaction, so that only a required amount of fission occurs, the extra, unwanted neutrons have to be removed from the nuclear fuel.
		To sustain a chain reaction, a minimum quantity of fissionable material is needed.
	home.att.net /~cat4a/nuclear_VI.htm (1034 words)

	Natural Nuclear
		Nuclear power is controversial - it produces relatively pollutant-free energy and is independent of oil, but is dangerous and generates extraordinary radioactive waste.
		Modern nuclear power plants — or nuclear reactors - face two huge issues: The first one is the careful management of the dangerous nuclear reactions that produce the plant’s energy.
		It has been known since the beginning of the nuclear age that water encourages nuclear chain reactions by slowing neutrons down so they are more likely to split more uranium atoms.
	www.acfnewsource.org /science/natural_nuclear.html (1005 words)

	The First Nuclear Chain Reaction (Site not responding. Last check: )
		These facts implied the possibility of a chain reaction, similar in certain respects to the reaction which is the source of the sun's energy.
		This quantity of uranium necessary for a chain reaction under given conditions is known as the critical mass, or more commonly, the "critical size" of the particular pile.
		An atomic chain reaction may be compared to the burning of a rubbish pile from spontaneous combustion.
	hep.uchicago.edu /cp1.html (4322 words)

	Nuclear Energy
		Nuclear energy is energy that comes from the nucleus (core) of an atom.
		Nuclear energy is released from an atom through one of two processes: nuclear fusion or nuclear fission.
		Nuclear fission is the only method currently used by nuclear plants to generate electricity.
	lsa.colorado.edu /essence/texts/nuclear.htm (2092 words)

	energy uses: What is a nuclear reactor
		All nuclear reactors are devices designed to maintain a chain reaction producing a steady flow of neutrons generated by the fission of heavy nuclei.
		Nuclear power reactors can be classified according to the type of fuel they use to generate heat.
		Plutonium (Pu) is an artificial element produced in uranium-fuelled reactors as a by-product of the chain reaction.
	www.euronuclear.org /info/energy-uses.htm (1503 words)

	Japan Nuclear Reaction Contained
		Still, these officials said, it is extremely rare for nuclear fuel to reach so-called "criticality," as apparently occurred at the fuel plant in Japan in which three workers were exposed to high levels of radiation and hundreds of people were evacuated.
		While the Japan incident continues to be investigated, it is believed the nuclear chain reaction occurred when workers placed more than six times the amount of uranium allowed into a vat of nitric acid, said an industry source, who spoke on condition of anonymity.
		There have been a number of incidents of unplanned nuclear chain reactions, but most have involved very small amounts of material such as used in research environments.
	www.washingtonpost.com /wp-srv/aponline/19990930/aponline222658_000.htm (693 words)

	Unplanned Nuclear Reaction Rare
		It is extremely rare for nuclear fuel to reach unexpected ``criticality,'' as apparently occurred at a fuel plant Thursday in Japan where three workers were exposed to high levels of radiation and hundreds of people were evacuated before the reaction was controlled.
		The only incident involving a nuclear chain reaction at a fabrication plant was 35 years ago at a plant no longer in operation near Charleston, R.I., said Michael Weber of the Nuclear Regulatory Commission.
		While the Japan incident continues to be investigated, it is believed the nuclear chain reaction occurred when workers placed more than six times the amount of uranium allowed into a vat of nitric acid, said an industry source who spoke on condition of not being further identified.
	www.beachbrowser.com /Archives/Environment/October-99/Unplanned-Nuclear-Reaction-Rare.htm (706 words)

	Nuclear Fission (Site not responding. Last check: )
		nuclear fission - chain reaction - atomic bomb
		In a nuclear reactor or atom bomb, a fissile material such as 235U can capture a neutron.
		If there is above a critical concentration of fissile material, this chain reaction will continue unaided, and if unregulated, can result in a very loud bang.
	www.fas.harvard.edu /~scdiroff/lds/QuantumRelativity/NuclearFission/NuclearFission.html (491 words)

	Science Projects - Nuclear Chain Reaction
		In a nuclear fission reaction in a nuclear power plant, the radioactive element Uranium-235 is used in a chain reaction.
		The chain reaction continues on and on, getting bigger and bigger with each split.
		The things that slow down a chain reaction are the control rods.
	www.energyquest.ca.gov /projects/nuclear.html (228 words)

	Researchers describe how natural nuclear reactor worked
		To operate a nuclear power plant like Three Mile Island, hundreds of highly trained employees must work in concert to generate power from safe fission, all the while containing dangerous nuclear wastes.
		Prior to this calculation, it was known that the natural nuclear reactor operated two billion years ago for 150 million years at an average power of 100 kilowatts.
		Another vital condition for self-sustaining nuclear reaction is the high content of a moderator to slow the neutrons, Meshik said.
	www.eurekalert.org /pub_releases/2004-10/wuis-rdh102804.php (911 words)

	Nuclear Disasters
		Two of the most famous nuclear accidents occurred at the Three Mile Island reactor 2 in the United States and the Chernobyl reactor 4 in the former Soviet Union.
		The problem is that, even if the control rods are completely dropped in and the nuclear chain reaction stops, the reactor is still extremely hot and will not cool down unless coolant is put back in.
		A partial nuclear meltdown is when the uranium fuel rods start to liquefy, but they do not fall through the reactor floor and breach the containment systems.
	library.advanced.org /17940/texts/nuclear_disasters/nuclear_disasters.html (2718 words)

	A Science Odyssey: People and Discoveries: Fermi creates controlled nuclear reaction
		Fermi's task, however, was to create a controlled nuclear reaction; that is, to split the atom without creating a deadly explosion.
		If the chain reaction speeded up, the cadmium rods could be inserted to slow it down and could be removed to accelerate it again.
		Nuclear reactors have been built in many countries to supply energy for military uses such as nuclear submarines and civilian uses such as ordinary electricity.
	www.pbs.org /wgbh/aso/databank/entries/dp42fe.html (482 words)

	Nuclear chain reaction (Site not responding. Last check: )
		The accidental fission reaction, which raised radiation levels to over 10,000 times the norm, began when a worker mixed too much uranium with nitric acid in a storage tank.
		By draining water from the tank, officials were able to stop the reaction early on Oct. 1, and radiation levels quickly returned to near normal levels.
		Nuclear fission reactions take place when uranium atoms are split by neutrons releasing huge amounts of energy.
	whyfiles.org /updates/nuclear (235 words)

	Nuclear Chemistry - First Chain Reaction (1942)
		The first nuclear reactor, called a pile, was a daring and sophisticated experiment that required nearly 50 tons of machined and shaped uranium and uranium oxide pellets along with 385 tons - the equivalent of four railroad coal hoppers - of graphite blocks, machined on site.
		The pile itself was assembled in a squash court under the football field at the University of Chicago from the layered graphite blocks and uranium and uranium oxide lumps (Fermi's term) arranged roughly in a sphere with an anticipated 13 foot radius.
		The achievement of the first sustained nuclear reaction was the beginning of a new age in nuclear physics and the study of the atom.
	www.chemcases.com /nuclear/nc-05.htm (824 words)

	ScienceDaily: New Details On Japan Nuclear Accident
		Science Daily — In September, a nuclear accident in Japan made international headlines, as workers at a fuel processing plant in the village of Tokai (also known as Tokaimura) inadvertently started a nuclear chain reaction when adding enriched uranium to a tank at the plant.
		Reducing The Risk Of Unintended Nuclear Chain Reactions In Fuel Reprocessing (September 18, 2006) -- With the rising cost and dwindling supply of fossil fuels, nuclear power may again be considered a plausible energy option in the U.S. Safety is the public's major concern, and researchers at the...
		Nuclear reaction -- In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide, to produce different products than the initial particles.
	www.sciencedaily.com /releases/1999/12/991206072234.htm (1827 words)

	Health/Environment Issues Linked to the Nuclear Fuel Chain -- Section C
		Accordingly, if nuclear boilers were to last for more than a few decades as an energy source, they saw a need to "breed" a man-made substitute for uranium-235; either plutonium-239 bred from uranium-238, or uranium-233 bred from thorium-232.
		The Chicago nuclear pile was a large geometrically-formed pile of blocks alternating between graphite and uranium, with room for long-handled "control rods" made of neutron poisons needed to regulate the chain reaction.
		Nuclear reactors were called "piles" for many years, because the first reactor was in fact a pile of graphite and uranium blocks.
	www.ccnr.org /ceac_C.html (7759 words)

	Basic Nuclear Fission
		arlier, we explained the concept of a chain reaction, in which neutrons are released and then produce more reactions that release more neutrons.
		Unchecked, as we said earlier, each nuclear reaction generation will produce 2.5 times as many neutrons as went into it.
		However, in order to maintain stability (and to keep the chain reaction from running away from itself), each generation of reactions in a nuclear power plant must produce exactly the same number of neutrons as went into it.
	library.thinkquest.org /17940/texts/fission/fission.html (1168 words)

	The Chain Reaction
		This exhibition was organized to commemorate the fiftieth anniversary of the world's first controlled, self-sustaining nuclear chain reaction, an achievement of Enrico Fermi and his colleagues at the Metallurgical Laboratory at the University of Chicago.
		On December 2, 1942, scientists at the University of Chicago produced the world's first self-sustaining nuclear chain reaction in a nuclear pile constructed in a squash court beneath the West Stands of Stagg Field, the University's athletic stadium.
		Fermi further concluded that it should be possible to sustain a chain reaction in uranium which, under the right conditions, might multiply fast enough to cause a nuclear explosion.
	www.lib.uchicago.edu /e/spcl/chain.html (2432 words)

	The World Today - Nuclear chain reaction feared following North Korea test
		ELEANOR HALL: A nuclear analyst in the United States is warning that the North Korean nuclear test could now set off a chain reaction around the region that could trigger the collapse of the entire nuclear non-proliferation regime, and could see nuclear devices funnelled to terrorist groups.
		JOE CIRICIONE: This could be the event that tips the scales, that sends a nuclear reaction chain careening though the region and around the world.
		It's this nuclear reaction chain that you worry about, that the whole system could tip, a collapse of the non-proliferation regime, and a cascade of proliferation.
	www.abc.net.au /worldtoday/content/2006/s1759987.htm (1304 words)

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