P. Andrew Karam, an adjunct professor of physics at the Rochester Institute of Technology, explains.
Nuclear reactors generate energy through fission, the process by which an atomic nucleus splits into two or more smaller nuclei. During fission, a small amount of mass is converted into energy, which can be used to power a generator to create electricity. In order to harness this energy, a controlled chain reaction is required for fission to take place. When a uranium nucleus in a reactor splits, it produces two or more neutrons that can then be absorbed by other nuclei, causing them to undergo fission as well. More neutrons are released in turn and continuous fission is achieved.
Neutrons produced by fission have high energies and move extremely quickly. These so-called fast neutrons do not cause fission as efficiently as slower-moving ones so they are slowed down in most reactors by the process of moderation. A liquid or gas moderator, commonly water or helium, cools the neutrons to optimum energies for causing fission. These slower neutrons are also called thermal neutrons because they are brought to the same temperature as the surrounding coolant.
In contrast to most normal nuclear reactors, however, a fast reactor uses a coolant that is not an efficient moderator, such as liquid sodium, so its neutrons remain high-energy. Although these fast neutrons are not as good at causing fission, they are readily captured by an isotope of uranium (U238), which then becomes plutonium (Pu239). This plutonium isotope can be reprocessed and used as more reactor fuel or in the production of nuclear weapons. Reactors can be designed to maximize plutonium production, and in some cases they actually produce more fuel than they consume. These reactors are called breeder reactors.
Breeder reactors are possible because of the proportion of uranium isotopes that exist in nature. Natural uranium consists primarily of U238, which does not fission readily, and U235, which does. Natural uranium is unsuitable for use in a nuclear reactor, however, because it is only 0.72 percent U235, which is not enough to sustain a chain reaction. Commercial nuclear reactors normally use uranium fuel that has had its U235 content enriched to somewhere between 3 and 8 percent by weight. Although the U235 does most of the fissioning, more than 90 percent of the atoms in the fuel are U238--potential neutron capture targets and future plutonium atoms.
Pu239, which is created when U238 captures a neutron, forms U239 and then undergoes two beta decays, happens to be even better at fissioning than U235. Pu239 is formed in every reactor and also fissions as the reactor operates. In fact, a nuclear reactor can derive a significant amount of energy from such plutonium fission. But because this plutonium fissions, it reduces the amount that is left in the fuel. To maximize plutonium production, therefore, a reactor must create as much plutonium as possible while minimizing the amount that splits.
This is why many breeder reactors are also fast reactors. Fast neutrons are ideal for plutonium production because they are easily absorbed by U238 to create Pu239, and they cause less fission than thermal neutrons. Some fast breeder reactors can generate up to 30 percent more fuel than they use.
Creating extra fuel in nuclear reactors, however, is not without its concerns: One is that the plutonium produced can be removed and used in nuclear weapons. Another is that, to extract the plutonium, the fuel must be reprocessed, creating radioactive waste and potentially high radiation exposures. For these reasons, in the U.S., President Carter halted such spent fuel reprocessing, making the use of breeder reactors problematic.
The U.S. constructed two experimental breeder reactors, neither of which produced power commercially. The Enrico Fermi Nuclear Generating Station in Michigan was the first American fast breeder reactor but operated only from 1963 until 1972 before engineering problems led to a failed license renewal and subsequent decommissioning. Construction of the only other commercial fast breeder reactor in the U.S., the Clinch River plant in Tennessee, was halted in 1983 when Congress cut funding. Elsewhere in the world, only India, Russia, Japan and China currently have operational fast breeder reactor programs; the U.K., France and Germany have effectively shut down theirs.
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Add Comment"Reactors can be designed to maximize plutonium production, and in some cases they actually produce more fuel than they consume. These reactors are called breeder reactors"
Reply | Report Abuse | Link to this1st Law of Thermodynamics? I don't understand how it produces more energy than it consumes...
Energy in the atomic nuclei is released, not 'created'. So a breeder reactor sets up a chain reaction to release more energy than a slow-reactor. - Just as no energy is supplied to a slow-reactor for that matter (i.e. the 'closed system'). I would think that concerning the 2nd law of thermal dynamics, the 'energy supplied' is that involved from the original creation of the nuclear elements (supposedly in star cores). Then that energy as 'work' is released in nuclear fission. If you would like a novel perspective on atomic theory, try Walter Russell's work ( www.philosohpy.org), which up-ends some scientific sacred cows. (maybe that could be thought of as scientific cow-tipping :D) - where he posited that atoms are 'compressed' and 'unwind/decompress' with carbon as a 'zero-point' of balanced 'wound up' vs. 'unwinding'. He, by the way, may have been responsible (at least inspiring, as he predicted them first) for the discovery of the trans-uranium elements.
Reply | Report Abuse | Link to thiscorrection - i meant 1st law of thermodynamics.
Reply | Report Abuse | Link to thiscurrent topics should be covered on nuclear energy and about should know about IInd stage erection at kalpakkam
Reply | Report Abuse | Link to thistell me about fast breeder reactors and what topics should cover for an interview related to nuclear power station.
Reply | Report Abuse | Link to thisThe Enrico Fermi event was not quite as innocent as this article makes it sound. The reactor suffered a partial meltdown which left it unusable, and it was subsequently decommissioned and disassembled. Three Mile Island was not the first or worst such commercial record incident - the Fermi incident was just better squelched.
Reply | Report Abuse | Link to thisWhy couldnt breeder reactors be utilized to substantially reduce the half life and dramatically reduce the bulk volume of waste from conventional reactors?
Reply | Report Abuse | Link to thisTerry Wakefield
Why couldn’t breeder reactors be utilized to substantially reduce the half life and dramatically reduce the bulk volume of waste from conventional reactors?
Reply | Report Abuse | Link to thisTerry Wakefield
actually using waste from the conventional nuclear power plant in fast breeder reactors is one of the aim of bulding fast reactors.fast reactors are not vialating 1st law of thermodynamics which says conservation of energy from one form to another.here there is conversion one form of fuel to the other usefull form of fuel.in a very simple language suppose you are using 1 kg fuel1 in fast breeder reactor along with this something which can be converted to usefull fuel and it can be converted in the field of fast region.now suppose the converted fuel2 is 2kg so you got 1kg more than you consumed.i think now it is clear.
Reply | Report Abuse | Link to thisin core all are distributed in a particular fasion so that we get maximum breeding.
Perhaps my interest about breeders would be more clearly defined if I outlined my current assumptions. I am assuming that the following define the current situation:
Reply | Report Abuse | Link to thisWhat about the FFTF facility at Hanford Wa. , wasn't that a breeder design? I know that it didn't generate any electricity as it had dump heat exchangers instead of generators. It was supposed to be a scale model of the reactor to be built in Clinch River.
Reply | Report Abuse | Link to thisAnyone know if that facility is still in operation?
The key in the statement was produce more fuel not more energy. The 1st law of Thermodynamics has not been violated, In breeder reactors less energy is produced per atomic fission because at least one of the neutron is absorbed by the U238 to become PU239. Overall energy and hence heat is lower but that's ok because Non breeder reactors require too much cooling and the full energy is never recovered from the fission process anyway. The problem is extracting the newly made fuel from the core for reprocessing. Even if you used all robots. Eventually the structure of the robot would break down from neutron damage and the robot would be part of the growing radioactive waste pile that we cant store forever and seem to launch into outer space.
Reply | Report Abuse | Link to thisi am not a nuclear experts, but there are different kinds of fuel: the comparison is the food we eat, which serves to keep our body temperature at37°c. the "remains" of our food can be used as combustible after dried.
Reply | Report Abuse | Link to thise.g. in some desert countries people use dry camel faeces for cooking. the meaning of "breeders produce more(???) fuel" is that the whole process depends on the fast neutrons. but, is there really any reactor working with pu239 in the world?
there is a better alternative to the fast breeder... one that was born here in the US in the 1950's and 1960s that has none of the safety, waste or weapons proliferation issues of our current reactors:
Reply | Report Abuse | Link to thisthe Thorium based Molten Salt Reactor - also known as the Liquid Flouride Thorium Reactor or LFTR. as a molten salt fueled design, they have no need of pressurized water as a coolant or energy transfer medium, and run at normal atmospheric pressure. this fact alone makes them completely immune to any kind of material release in the manner of chernobyl, TMI or fukushima. the flouride salts are in a liquid form, so fission products such as xenon are easily separated, which allows for fuel utilization exceeding 99% depending on the exact variant of the design. this also translates to a directly proportional reduction in waste material - even greater when one considers that none of the fission products have half-lives of more than 300 years, and are themselves valuable to industry and medicine.
as a simple example, a single ton of thorium in a reactor can produce energy equivalent to the use of 200 tons of enriched uranium. not because there is that much energy in thorium, but because the liquid fuel allows for the use of *all* of it. even the most modern solid core designs can only use about 0.7% of the enriched uranium they employ.
the intrinsic safety of LFTRs is of great note, unlike solid core designs, the flouride salts can be easily drained out of the reactor into a holding tank where the solution cools to solid form over the course of several hours, without any need for active cooling systems. indeed, LFTRs are endowed with an intrinsic safety system that needs power to NOT function.
we have seen what loss of power does to the active safety systems of solid-core reactors - no power... reactor melts. in a LFTR, loss of power leads to the fuel becoming a stable solid.
finally, concerning weapons proliferation. L the liqud thorium fuel cycle produces very little weapons grade material, thanks to the fact that to reach those transuranics in this cycle requires 7 neutron capture events opposed to the 3 needed in a solid core uranium reactor. in addition, Pu239 can be left in the fuel salt to be used as fuel right alongside the thorium. in this way, LFTRs can in fact consume existing weapons grade material, leaving nothing.
these are only a few of the enormous advantages of LFTRs over solid-core reactors. there are many more.
Breeders actually breed fissile isotopes, which are useful as reactor fuel, from neutrons and fertile isotopes. It is equivalent to a fire producing more volatile flame material. Laws of thermodynamics are not violated.
Reply | Report Abuse | Link to thisAs pertaining to obtaining more energy from a breeder reactor than is put into it, each molecule of matter is information, information as to where and when it has been. Each molecule is individual and varied. It will only require one or two molecules that have previously been at the core of a black hole or similar event to be present in any given reactor for it to produce, reproduce, and continiue at a rate that is considered to be more than was accounted for. Therefore, those that are at the forefront of atom smashing will be the first to see this as a recordable event.
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