Breeder reactors


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Today, we certainly need thinking of new and infinite ways for generating energy. one of the most beneficial ways is using reactors.As we have a lot of power reactors in fission and fusion fields we can response to this limitation hereabout breeder reactors are those that though their benefits, have less attention, therefore I've decided to describe them at first and answer to this reason.

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Breeder reactors

  1. 1. Breeder reactors Abstract As everyone knows, reactors are special systems for controlling and striking a nuclear chain reaction up. Today, we use reactors for many different goals with this aim to answer to many human beings limitations, in case they have been disported by their different benefits. Some of their most important ones are: Power reactors which are using for generating electricity. Burner reactors, breeder ones and etc. The fact is, thermal nuclear reactors use uranium – 235 as their fuel because of the high activity that they have, unfortunately uranium – 235 includes only less than 0.7 percent of the whole uranium storage that we have in nature other relates to uranium – 238. The most problem begins where uranium – 238 isn’t a suitable fuel because of its less activity. Therefore it cannot be used in thermal reactors, however if it used as fuel certainly won’t be a useful fuel for 100 years because of its high storage. This declaration was a beginning for thinking of producing reactors with high efficiency of uranium – 238. Finally these successive endeavors trepan breeder reactors producing. Introduction Even though, nowadays we use many other reactors that maybe the most current one is PWRs, but the word “breed” in these kinds of reactors is talking about the special ones that produce more fuels than they use and finally for this reason they are being called “breeder” because they are the producers of their own fuel. Mechanism of breeder reactors If we say that the core of reactors is a place for keeping moderator and fuel elements, inside this core we will have fissile materials like: uranium -235 or plutonium – 239. These isotopes have high activity which can release neutrons during their fission.
  2. 2. Since uranium – 235 or plutonium – 239 have been surrounded by a fertile cover of uranium – 238; contemporaneously, neutrons which are being released by fissile materials turn uranium – 238 to plutonium – 239 during the fission reaction. In other words if we call some isotopes like uranium – 238 or thorium – 232 fertile materials, the cause will be their breeding reaction. Breeder=Being fertile After turning of all uranium – 238 to plutonium – 239; reactors refuel again. On the other hand produce more plutonium – 239 than its using. The final mass of produced plutonium – 239 is relating to its “breeding rate” which means:” the mount of final produced plutonium – 239 than that much has been used at first”. This rate for “LMFBRs – liquid fast breeder reactors “is about “1.4” which estimated about “1.2” experimentally. These reactors won’t be moderated by used current moderators because the base of their working is on fast neutrons, therefore they can be called “fast reactors”. Released neutrons turn uranium – 238 in to plutonium – 239 which then can be used in other reactors as fuel. Idea of manufacturing This opinion advanced from the first time of using reactors. Designers of this structure were interested in producing a special mechanism in order to utilize the high storage of uranium in its best way. The ascendancy of using breeders is exploiting near 80 percent of uranium thermal energy whereas PWRs use only near 2 percent of this energy. Way of cooling The main question about breeders is: How can these reactors be cooled after each experiment? Hereof Liquid sodium has been decided. One of the most popular characteristic of sodium is being a good conduction for temperature which don’t reduce neutrons velocity a lot, however it is alkali besides being so reactive especially with air and water, therefore it has two circuits of liquid sodium instead of one with a “heat exchanger” between them. Breeder reactors can be parted to two main groups: 1. LMFBR (liquid moderator fast breeder reactor) 2. Thermal breeder reactors
  3. 3. LMFBR In these kinds of reactors fast neutrons have enough energy for breaking actinides nucleus in to a lot of protons and neutrons. As said, their moderator can be current liquid sodium, however sometimes we can use lithium as an alkali in its structure. Thermal These reactors are based on thermal neutrons which can use moderators like water as a coolant. What are the differences among breeders and other fission or fusion reactors? As an answer we can say that breeders are based on fission than fusion reactors are using fusion for joining two light nuclei, therefore we never ever can find any similarities among breeders and fusion reactors but if we compare breeders and fission reactors we can say that: The highest benefit of using breeders is producing more fissile fuels, in case we cannot do this action in other fission reactors. Now the fact is which of them is more beneficial? Breeder or fission? As these doctrines, breeders should be more beneficial because it can breed those fuels that have the less storage of our nature like: plutonium – 239, however plutonium – 239 is an important isotope for designing bombs, therefore many scientists are against using this structure. The half – life of plutonium is about 25000 years. One sample of this element is so powerful for remaining about 100000 years dangerously. Conclusion Although breeders are very useful but unfortunately their defects out foot their beneficial. Plutonium is one of these defects, however complex structure, high disbursement for manufacturing, intense protection for alkali elements because of their high reactivity and etc. can be some other defects of breeder reactors. By : Mahsa Mehrangiz