Nuclear Fission

Nuclear fission occurs by the nucleus of an atom (typically a large atom, like Uranium or Plutonium) spliting to form two new smaller atoms. There is a large binding energy, called the Nuclear force (Strong and Weak) within the nucleus. Much like there is a binding energy that hold componds together (the chemical bonds that hold hydrogen to oxygen to form water), only the nuclear bond is much, much more powerful.

So when the atom slpits, it releases some of this energy in the form of light. however this light is of such a high frequency (meaning it has a lot of energy), it can damage cells and body tissue. You can think of it like the Hulk of UV light.

Fission of Uranium-235, splitting of this atom into two smaller atoms of different elements. A neutron must hit the nucleus at just the right speed to cause the Uranium-235 to undergo fission. When the Uranium atom is split into smaller atoms called fission products, free neutrons are released which can split more Uranium atoms. The fission product atoms separate at high speed, transferring lots of energy to its surroundings making them very hot. This heat is used to boil water, making steam which is used to turn turbines. The turbines turn generators which produce electricity.

At the moment it's not because nobody has been able to get it to work for the sort of duration necessary for power production.

There are, however a couple of nice advantages over fusion:

- No radioactive waste products (the product is helium-4)

- No radioactive raw material (need heavy hydrogen)

- Theoretically large energy gain per reaction

On the down side it is technically very challenging, requiring extremely high pressure. Getting the inital reaction to start requires a lot of energy.

The breakup of large nuclei into two nearly equal fragments is called nuclear fission. It sometimes produces neutrons, protons or other nuclei. This is important in nuclear reactor and bombs, where neutrons emitted from one fission event cause other nuclei to fission, releasing more neutrons and so causing chain reaction. If this chain is controlled then you have a nuclear reactor whose heat can be used to boil water and generate electricity. If the chain is uncontrolled it causes a nuclear explosion.

Harry S. Truman is the only president who authorized the use of nuclear weapons, ordering the bombings of Hiroshima and Nagasaki in Japan during World War II in 1945.

The term critical mass does not relate to nuclear fusion. Nuclear fusion is the fusing, the joining, of two or more nucleons or nuclei to create a heavier nucleus. It takes enormous energy to set up the conditions that will make this happen. Fusion occurs naturally in stars, and is the mechanism that powers them up. Stars operate in an equilibrium wherein nuclear fusion tries to force everything apart and gravity holds everything together.

Nuclear fission is the splitting of atoms, the splitting of atomic nuclei, and it can be looked at as the opposite of fusion. In fission, certain materials - and of them, only uranium-235 occurs naturally - will, when a certain minimum amount is brought together, begin to fission. They will spontaneously begin to fission because that certain minimum amount, the critical mass, has been brought together. The natural decay of the radionuclide releases neutrons, and when a critical mass is brought together, the naturally released neutrons now can build a chain reaction. The material goes critical because critical mass has been reached.

Note: We're giving thorium the day off here (which does not fission well itself but is usually converted in a reactor to uranium-233), and plutonium can be found with uranium only in the most minute amounts.

A link is provided to an article on critical mass posted by our friends at Wikipedia, where knowledge is free.

Basically, critical mass is the level of mass that something reaches to make something happen.

As a solid metal sphere inside a sphere of uranium, the critical mass of plutonium is 6.4 kg, the core of the MK-III atomic bomb (Gadget at Trinity & Fatman at Nagasaki) was 6.2 kg and became a supercritical mass when imploded using chemical explosive lenses. To ensure a good yield and not depend on natural spontaneous neutron production (which might cause a fizzle) at the optimal moment of supercriticality, a neutron source fired a pulse of neutrons to start the chain reaction.

There is a sense where stellar fusion has critical mass: a protostar whose mass is too low cannot ignite fusion in the first place and becomes a brown dwarf. However the term critical mass is not normally used to describe this stellar mass threshold. There is also a sense where neutron star and black hole formation processes have critical mass, but that is a topic for a different category on another day.

Uranium-235, plutonium-239, and thorium-232 are examples of reactants used in nuclear fission reactions. These heavy elements can split into smaller nuclei when bombarded with neutrons, releasing a large amount of energy.

it comes from nuclear fission
Nuclear energy is the fission of certain, materials such as uranium or plutonium,within a nuclear reactor. This produces heat, which turns water into steam. This steam rises, driving a turbine which creates electricity for commercial and public use.

The positive aspects of nuclear fission are:

it is an energy source which uses fuels which will last for a long time.

It can produce a large amount of energy from a small energy input.

It produces very little carbon emissions.

It is often considered to be better for the environment than coal power plants.

It produces more energy than coal power plants and most other energy sources.

With nuclear fission, a large atomic nucleus (such as a uranium nucleus) breaks apart into smaller nuclei, and energy is released. With nuclear fusion, small atomic nuclei (such as hydrogen) join to become larger nuclei, and energy is released. Fusion of hydrogen releases much more energy than any other type of either fusion or fission. Note that the dividing line between heavy nuclei and light nuclei is the iron nucleus, which is at the perfect point of nuclear stability, so that neither fusion nor fission of iron nuclei would release any energy.

We need to back up a bit and lay a foundation for what sequential fission is. It begins in the nuclear physics lab (an accelerator facility) where we investigate nuclear events using heavy nuclei. We'll start there, and it'll be easy to understand what's up. Ready? Let's jump. We're big on investigating the mysteries of subatomic physics by smashing stuff. (Plus, it's fun!) One of our ideas was to take a fat atom like, say, lead, and make a bullet out of it. We'd strip off all its electrons (with really high voltage). Then we'd take the big positively charged nucleus and accelerate it in a big electromagnetic pump (an accelerator). With our bullet sufficiently speeded up, we'd slam it into something like, say, a uranium nucleus. In the collision event, a big "something" would form when the "lead was added to the plutonium" in the target area. Things then begin to happen. There are a number of events that could result when we try to glue two big, fat anomic nuclei together. First, they don't like to be stuck to gether. They decay. And fission is common. But what frequently happens is that our "resultant nucleus" fissions, then one or both of the fission fragments fission, and then one or more of those fragments fission. It's a sequence of fissions, and what actually happens will depend on what was combined and at what energies (as well as a good bit of probability as to what was actually created). Make sense? It's not that hard. It might help to build a "family tree" of events. And physicists do. Let's take the analogy. Grandparents don't have grandkids. They have kids who have kids which become the grandkids. It's sequential, and each "step" has a precursor event. Does that lock it in for you? It's just as simple as it seems. Really!

Some nuclei, notably U235 and Pu239, can be made to cause a chain reaction where neutrons are produced in nuclear fission, and propogate more subsequent neutrons so that a steady rate of fissions can be achieved. Each fission releases an amount of energy in the form of heat, which is then used in generating plant similar to that in a fossil fuelled power plant.

The principle con, or problem with nuclear power plants in the US, is that there is no permanent solution to the spent fuel that is the result of operations. Spent fuel assemblies are about 12 feet long and about a foot square, made up of metal tubes which are about 1/2" in diameter. The actual fuel is in pellet form inside the tubes, about 1" long. It is extremely radioactive when it comes out of the core and must be stored under water to keep it cool for about 10 years. It decays rather quickly - relatively speaking - and can be removed from the water for air cooling after 10 years. It decays down to background radiation levels in about 600 years and it's a good idea to keep it locked up for at least a few hundred.

The federal government agreed in the 1970's to build a permanent storage facility and to have it operational by about the year 2000. That was supposed to be Yucca Mountain in Nevada. Harry Reid, the senator from Nevada, has opposed Yucca since he got into office and has done everything he can to block it's opening. As a result, all the nuclear sites in the US (something like 70 sites for 103 power plants) store their fuel inspent fuel pools or in above ground storage until a permanent solution is accepted.

The French have an extensive nuclear power program (80% of their electricity from nuclear power) and have been reprocessing their spent fuel for about 30 years. We were originally going to reprocess ours, but the program was cancelled by Jimmy Carter in the 70's in favor of long term storage.

The principle problem with nuclear power is political, not technical. What few understand is that Coal plants generate over 100 times the radioactive waste but this is not documented and published because it does not fit the image. Partly because of these concerns about radioactivity and the cost of containing it, the American public and electric utilities have preferred coal combustion as a power source. Today 52% of the capacity for generating electricity in the United States is fueled by coal, compared with 14.8% for nuclear energy. Although there are economic justifications for this preference, it is surprising for two reasons. First, coal combustion produces carbon dioxide and other greenhouse gases that are suspected to cause climatic warming, and it is a source of sulfur oxides and nitrogen oxides, which are harmful to human health and may be largely responsible for acid rain. Second, although not as well known, releases from coal combustion contain naturally occurring radioactive materials--mainly, uranium and thorium. that is a paragraph from this web site : http://www.ornl.gov/info/ornlreview/rev26-34/text/colmain.html So the issue with Nuclear is what to with its radioactive waste the issue with coal is how to hide that it has radioactive waste

Nuclear energy is produced by one of two methods, fusion or fission. Fusion is the bonding of atomic nuclei or nuclear particles (nucleons - protons and neutrons). Fission, on the other hand is the splitting of the atom. As the atoms fuse or split they release energy. Lots of it. And most of it is heat energy. In nuclear weapons, the energy is released "all at once" to create a blast. If the energy is released in a "controlled" way, we can release heat at a "useable" rate and apply it to boiling water to make steam. In fusion, protons or neutrons or the nuclei of atoms are forced together and are fused to make a new atomic nucleus. The release of lots and lots of energy accompanies this reaction. That's what powers stars. Currently we can't really do any fusion reactions to make useful power. There are a few agencies working on fusion devices, but the high temperatures required to attain fusion require very special materials and controls. The current "state of the art" fusion facility is the International Thermonuclear Experimental Reactor (and a link is provided). Fusion is unlikely to become a useful source of power for many years. But what about fission? Nuclear fission involves the splitting of large atoms, usually uranium (or sometimes plutonium). When large atoms fission they produce two smaller atoms or fission fragments (and a couple of neutrons and lots of energy). The total mass of the products is less than the mass of the original atom. This mass difference is turned into energy in accordance with the Einstein equation E=mc2. Most of the energy appears in the recoil of the fission fragments, and the heat that is generated is considerable. It is that heat that we capture to turn water into steam to generate electricity.

Links are provided to related articles.

No, moderation of neutrons is not always used to slow nuclear fission. In some types of nuclear reactors, such as fast breeder reactors, fast neutrons are intentionally not moderated to slow down the fission process. These reactors operate using fast neutrons to sustain a chain reaction. However, in most commercial nuclear reactors, moderation of neutrons is employed to slow down the fission process and maintain a controlled chain reaction.

In general, however, a nuclear fission reaction involves the fissioning (or splitting) of heavy atoms (heavy, as in greater than lead, due to the binding energy curve), which results in release of some of the binding energy that was used to sustain the un-fissioned combination.

Also, depending on which nuclide is fissioned, extra neutrons result, and these neutrons can (under the right conditions) go on to fission more atoms, in a process called criticality, or, simply, a nuclear fission chain reaction.

A gas turbine extracts energy from a flow of hot gas produced by combustion of gas or fuel oil in a stream of compressed air. It has an upstream air compressor (radial or axial flow) mechanically coupled to a downstream turbine and a combustion chamber in between. "Gas turbine" may also refer to just the turbine element. Energy is released when compressed air is mixed with fuel and ignited in the combustor. The resulting gases are directed over the turbine's blades, spinning the turbine, and mechanically powering the compressor. Finally, the gases are passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure. Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, electrical generators, and even tanks. A gas turbineextracts energy from a flow of hot gas produced by combustion of gas or fuel oil in a stream of compressed air. It has an upstream air compressor (radial or axial flow) mechanically coupled to a downstream turbine and a combustion chamber in between. "Gas turbine" may also refer to just the turbine element. Energy is released when compressed air is mixed with fuel and ignited in the combustor. The resulting gases are directed over the turbine's blades, spinning the turbine, and mechanically powering the compressor. Finally, the gases are passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure. Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, electrical generators, and even tanks.

The most active and dangerous part is the spent fuel itself, because it contains very active fission products. Less active arisings come from contaminants in the reactor primary system water circuit (crud). The least active category will be clothing and cleaning materials which have been used in slightly contaminated areas of the plant.

Fission is the splitting of an atom, fusion is the joining of 2 atoms into one. In most fission, neutrons are bomabarded at the nucleus of uranium or plutonium and this causes a ripple effect of more neutons being released from the fuel. The process generates large amounts of heat which is either used for destruction or steam engines. Fusion most often occurs with 2 Hydrogens being fused together to form helium. Deuterium (Hydrogen with a neutron and proton instead of just a proton) and tritium (one proton and two neutrons) are high energy atoms that are used in testing nuclear fusion. Our star (the sun) is based, like most stars, on Hydrogen being fused to generate heat and Helium.

yes, Nuclear fission as used in nuclear power plants produces radioactive waste with long half lives. However, this creates no problems. This wastes are either confined in the spent nuclear fuel (that is stored either in wet storage or in dry storage facilities) or stored as vitrified nuclear waste.

The nuclear energy obtained from uranium or plutonium is the most important alternative to fossil fuels. Oil and methane will be exhausted in less than 100 years. Wind, geothermal, solar, organic wastes etc. are useful but not serious alternative for 10 billions inhabitants.

coal

1. fuel
2. moderator
3. cooling system
4. control rods
5. SCRAM system