دورات هندسية

 

 

Nuclear power plant (محطات الطاقة النووية )

صفحة 1 من 4 12 3 4 الأخيرةالأخيرة
النتائج 1 إلى 10 من 32
  1. [1]
    الصورة الرمزية حسن هادي
    حسن هادي
    حسن هادي غير متواجد حالياً

    عضو متميز

    تاريخ التسجيل: Nov 2006
    المشاركات: 1,338
    Thumbs Up
    Received: 7
    Given: 0

    Nuclear power plant (محطات الطاقة النووية )

    بعد التحية /اخواني الاعزاء نقدم اليوم موضوع محطات الطاقة النووية وفي هذا الموضوع لست سوى باحث واردت ان اكون باحثا معكم بماان هذا الموضوع من المواضيع المهمة جدا ومن وجت نظرنا المتواضعة نرى انه على الاقل لا بد لنا من الاطلاع على هذه التقنيات ولو من باب المعرفة السطحية ومن اراد اراد التبحر والولوج في هذا العلم فاعانه الله على ذلك خدمة لدينه وامته *ولنسال انفسنا اليس من حقنا ان نمتلك هذه التقنيات ولا اريد ان اطيل عليكم لان الموضوع يكاد يكون سطحيا وهو من باب القول ((اعرف شئ عن كل شئ ولا تعرف كل شئ عن شئ ))
    ولكوننا قد ادرجنا موضوع محطات القدرة الحرارية والحقناه بالمحطات التي تعمل بالوقود الصلب نقدم لكم الموضوع التالي والله ولي التوفيق
    ************************************************** ***********************************


  2. [2]
    حسن هادي
    حسن هادي غير متواجد حالياً
    عضو متميز
    الصورة الرمزية حسن هادي


    تاريخ التسجيل: Nov 2006
    المشاركات: 1,338
    Thumbs Up
    Received: 7
    Given: 0
    الاخوة الاعزاء قبل ان نلج الموضوع نشير الى الطاقة النووية في سطور من خلال موسوعة الويكابيديا وبامكانكم متابعة الروابط مع كل التقدير
    ************************************************** *******************************
    Nuclear power is a type of nuclear technology involving the controlled use of nuclear fission to release energy for work including propulsion, heat, and the generation of electricity. Nuclear energy is produced by a controlled nuclear chain reaction and creates heat—which is used to boil water, produce steam, and drive a steam turbine. The turbine can be used for mechanical
    *********
    Use

    Historical and projected world energy use by energy source, 1980-2030, Source: International Energy Outlook 2007, EIA.



    The status of nuclear power globally. Nations in dark green have reactors and are constructing new reactors, those in light green are constructing their first reactor, those in dark yellow are considering new reactors, those in light yellow are considering their first reactor, those in blue have reactors but are not constructing or decommissioning, those in light blue are considering decommissioning and those in red have decommissioned all their commercial reactors.


    See also: Nuclear power by country and List of nuclear reactors As of 2004, nuclear power provided 6.5% of the world's energy and 15.7% of the world's electricity, with the U.S., France, and Japan together accounting for 57% of all nuclear generated electricity.[1] As of 2007, the IAEA reported there are 435 nuclear power reactors in operation in the world,[2] operating in 31 different countries.[3]
    The United States produces the most nuclear energy, with nuclear power providing 20% of the electricity it consumes, while France produces the highest percentage of its electrical energy from nuclear reactors—80% as of 2006.[4][5] In the European Union as a whole, nuclear energy provides 30% of the electricity.[6] Nuclear energy policy differs between European Union countries, and some, such as Austria and Ireland, have no active nuclear power stations. In comparison France has a large number of these plants, with 16 currently in use throughout the country.
    Many military and some civilian (such as some icebreakers) ships use nuclear marine propulsion, a form of nuclear propulsion.
    International research is ongoing into different safety improvements such as passively safe plants, the use of nuclear fusion, and additional uses of produced heat such as the hydrogen production (in support of a hydrogen economy), for desalinating sea water, and for use in district heating systems.

    [edit] History


    [edit] Origins

    Nuclear fission was first experimentally achieved by Enrico Fermi in 1934 when his team bombarded uranium with neutrons, however neither Fermi nor many others properly understood the results. In 1938, the Germany physicists Otto Hahn, Lise Meitner, Fritz Strassmann, and Otto Robert Frisch conducted experiments with the products of neutron-bombarded uranium and determined that in fact the nucleus of the massive uranium atoms had been split into two roughly equal pieces by the relatively tiny neutron, an almost incredible result. The recognition by numerous scientists (Leo Szilard being one of the first) that if the fission reactions released additional neutrons that they could be used to generate a self-sustaining nuclear chain reaction spurred scientists in many countries (including the United States, the United Kingdom, France, Germany, and the Soviet Union) to petition their government to support fission research.
    In the United States, where Fermi and Szilard had both emigrated, this led to the creation of the first man-made reactor, known as Chicago Pile-1, which achieved criticality on December 2, 1942. This work became part of the Manhattan Project, which built giant reactors at Hanford, Washington in order to breed plutonium for use in the first nuclear weapons. (A parallel uranium enrichment effort was also pursued.)
    After World War II, the fear that reactor research would encourage the rapid spread of nuclear weapons and nuclear "know-how", combined with what many scientists thought would be a long road of development, created a situation in which reactor research was kept under very strict government control and classification. Additionally, most reactor research centered on purely military purposes. Electricity was generated for the first time by a nuclear reactor on December 20, 1951 at the EBR-I experimental station near Arco, Idaho, which initially produced about 100 kW (the Arco Reactor was also the first to experience partial meltdown, in 1955). In 1952, a report by the Paley Commission (The President's Materials Policy Commission) for President Harry Truman made a "relatively pessimistic" assessment of nuclear power, and called for "aggressive research in the whole field of solar energy".[7] A December 1953 speech by President Dwight Eisenhower, "Atoms for Peace", set the U.S. on a course of strong government support for the international use of nuclear power.

    [edit] Early years


    The Shippingport Atomic Power Station in Shippingport, Pennsylvania was the first commercial reactor in the USA and was opened in 1957.


    In 1954, Lewis Strauss, then chairman of the United States Atomic Energy Commission (forerunner of the U.S. Nuclear Regulatory Commission) famously spoke of electricity in the future being "too cheap to meter." [8] While few doubt he was thinking of atomic energy when he made the statement, he may have been referring to hydrogen fusion, rather than uranium fission. [6] Actually, the consensus of government and business at the time was that nuclear (fission) power might eventually become merely economically competitive with conventional power sources.
    On June 27, 1954, the USSRs Obninsk Nuclear Power Plant became the world's first nuclear power plant to generate electricity for a power grid, and produced around 5 megawatts electric power.[9][10]
    In 1955 the United Nations' "First Geneva Conference", then the world's largest gathering of scientists and engineers, met to explore the technology. In 1957 EURATOM was launched alongside the European Economic Community (the latter is now the European Union). The same year also saw the launch of the International Atomic Energy Agency (IAEA).
    The world's first commercial nuclear power station, Calder Hall in Sellafield, England was opened in 1956 with an initial capacity of 50 MW (later 200 MW).[11] The Shippingport Reactor (Pennsylvania, 1957) was the first commercial nuclear generator to become operational in the United States.
    One of the first organizations to develop utilitarian nuclear power was the U.S. Navy, for the purpose of propelling submarines and aircraft carriers. It has a good record in nuclear safety, perhaps because of the stringent demands of Admiral Hyman G. Rickover, who was the driving force behind nuclear marine propulsion as well as the Shippingport Reactor. The U.S. Navy has operated more nuclear reactors than any other entity, including the Soviet Navy, with no publicly known major incidents. The first nuclear-powered submarine, USS Nautilus (SSN-571), put to sea in 1955. Two U.S. nuclear submarines, USS Scorpion and Thresher, have been lost at sea, though for reasons not related to their reactors, and their wrecks are situated such that the risk of nuclear pollution is considered low.
    Enrico Fermi and Leó Szilárd in 1955 shared U.S. Patent 2,708,656 for the nuclear reactor, belatedly granted for the work they had done during the Manhattan Project.

    [edit] Development


    History of the use of nuclear power (top) and the number of active nuclear power plants (bottom).


    Installed nuclear capacity initially rose relatively quickly, rising from less than 1 gigawatt (GW) in 1960 to 100 GW in the late 1970s, and 300 GW in the late 1980s. Since the late 1980s capacity has risen much more slowly, reaching 366 GW in 2005, with the largest expansion being in China. Between around 1970 and 1990, more than 50 GW of capacity was under construction (peaking at over 150 GW in the late 70s and early 80s) — in 2005, around 25 GW of new capacity was planned. More than two-thirds of all nuclear plants ordered after January 1970 were eventually cancelled.[12]

    Washington Public Power Supply System Nuclear Power Plants 3 and 5 were never completed


    During the 1970s and 1980s rising economic costs (related to vastly extended construction times largely due to regulatory changes and pressure-group litigation) and falling fossil fuel prices made nuclear power plants then under construction less attractive. In the 1980s (U.S.) and 1990s (Europe), flat load growth and electricity liberalization also made the addition of large new baseload capacity unattractive.
    The 1973 oil crisis had a significant effect on countries, such as France and Japan, which had relied more heavily on oil for electric generation (39% and 73% respectively) to invest in nuclear power.[13][14] Today, nuclear power supplies about 80% and 30% of the electricity in those countries, respectively.
    A general movement against nuclear power arose during the last third of the 20th century, based on the fear of a possible nuclear accident, fears of radiation, nuclear proliferation, and on the opposition to nuclear waste production, transport and final storage. Perceived risks on the citizens' health and safety, the 1979 accident at Three Mile Island and the 1986 Chernobyl disaster played a part in stopping new plant construction in many countries,[15] although the Brookings Institution suggests that new nuclear units have not been ordered in the US primarily for economic reasons rather than fears of accidents.[16]
    Unlike the Three Mile Island accident, the much more serious Chernobyl accident did not increase regulations affecting Western reactors since the Chernobyl reactors were of the problematic RBMK design only used in the Soviet Union, for example lacking containment buildings.[17] An international organization to promote safety awareness and professional development on operators in nuclear facilities was created: WANO; World Association of Nuclear Operators.
    Opposition in Ireland and New Zealand prevented nuclear programs there, while Austria (1978), Sweden (1980) and Italy (1987) (influenced by Chernobyl) voted in referendums to oppose or phase out nuclear power.

    0 Not allowed!



  3. [3]
    حسن هادي
    حسن هادي غير متواجد حالياً
    عضو متميز
    الصورة الرمزية حسن هادي


    تاريخ التسجيل: Nov 2006
    المشاركات: 1,338
    Thumbs Up
    Received: 7
    Given: 0
    الانشطار النووي:- الاخوة الاعزاء لكي اسهل على من فاته ان يتابع الروابط ولكون هذا الموضوع وحسب اعتقادي المتواضع (الانشطارالنووي ) ارتايت ان اجعله في هذه المشاركة مع كل احترامي وتقديري


    ************************************************** ****************************
    الانشطار النووي
    Nuclear physicsKey topicsRadioactive decay
    Nuclear fission
    Nuclear fusionClassical decaysAlpha decay · Beta decay · Gamma radiation · Cluster decayAdvanced decaysDouble beta decay · Double electron capture · Internal conversion · Isomeric transitionEmission processesNeutron emission · Positron emission · Proton emissionCapturingElectron capture · Neutron capture
    R · S · P · RpFissionSpontaneous fission · Spallation · Cosmic ray spallation · PhotodisintegrationNucleosynthesisStellar Nucleosynthesis
    Big Bang nucleosynthesis
    Supernova nucleosynthesisScientistsMarie Curie · others
    This box: view talk edit

    Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing photons (in the form of gamma rays), free neutrons and other subatomic particles as by-products. Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). Fission is a form of elemental transmutation because the resulting fragments are not the same element as the original atom.
    Nuclear fission produces energy for nuclear power and to drive the explosion of nuclear weapons. Both uses are made possible because certain substances called nuclear fuels undergo fission when struck by free neutrons and in turn generate neutrons when they fission. This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon. The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very tempting source of energy; however, the products of nuclear fission are radioactive and remain so for significant amounts of time, giving rise to a nuclear waste problem. Concerns over nuclear waste accumulation and over the destructive potential of nuclear weapons may counterbalance the desirable qualities of fission as an energy source, and give rise to ongoing political debate over nuclear power.

    الروابط فعالة

    0 Not allowed!



  4. [4]
    حسن هادي
    حسن هادي غير متواجد حالياً
    عضو متميز
    الصورة الرمزية حسن هادي


    تاريخ التسجيل: Nov 2006
    المشاركات: 1,338
    Thumbs Up
    Received: 7
    Given: 0
    Physical overview
    Nuclear fission differs from other forms of radioactive decay in that it can be harnessed and controlled via a chain reaction: free neutrons released by each fission event can trigger yet more events, which in turn release more neutrons and cause more fissions. Chemical isotopes that can sustain a fission chain reaction are called nuclear fuels, and are said to be fissile. The most common nuclear fuels are 235U (the isotope of uranium with an atomic mass of 235 and of use in nuclear reactors, 238) and 239Pu (the isotope of plutonium with an atomic mass of 239). These fuels break apart into a range of chemical elements with atomic masses near 100 (fission products). Most nuclear fuels undergo spontaneous fission only very slowly, decaying mainly via an alpha/beta decay chain over periods of millennia to eons. In a nuclear reactor or nuclear weapon, most fission events are induced by bombardment with another particle such as a neutron.
    Typical fission events release several hundred eV of energy for each fission event. By contrast, most chemical oxidation reactions (such as burning coal or TNT) release at most a few tenths of an eV per event, so nuclear fuel contains at least ten million times more usable energy than does chemical fuel. The energy of nuclear fission is released as kinetic energy of the fission products and fragments, and as electromagnetic radiation in the form of gamma rays; in a nuclear reactor, the energy is converted to heat as the particles and gamma rays collide with the atoms that make up the reactor and its working fluid, usually water or occasionally heavy water.
    Nuclear fission of heavy elements produces energy because the specific binding energy (binding energy per mass) of intermediate-mass nuclei with atomic numbers and atomic masses close to 61Ni and 56Fe is greater than the specific binding energy of very heavy nuclei, so that energy is released when heavy nuclei are broken apart.
    The total rest masses of the fission products (Mp) from a single reaction is less than the mass of the original fuel nucleus (M). The excess mass Δm = M - Mp is the invariant mass of the energy that is released as photons (gamma rays) and kinetic energy of the fission fragments, according to the mass-energy equivalence formula E = mc².
    In nuclear fission events the nuclei may break into any combination of lighter nuclei, but the most common event is not fission to equal mass nuclei of about mass 120; the most common event (depending on isotope and process) is a slightly unequal fission in which one daughter nucleus has a mass of about 90 to 100 u and the other the remaining 130 to 140 u [1]. Unequal fissions are energetically more favorable because this allows one product to be closer to the energetic minimum near mass 60 u (only a quarter of the average fissionable mass), while the other nucleus with mass 135 u is still not far out of the range of the most tightly bound nuclei (another statement of this, is that the atomic binding energy curve is slightly steeper to the left of mass 120 u than to the right of it).

    The variation in specific binding energy with atomic number is due to the interplay of the two fundamental forces acting on the component nucleons (protons and neutrons) that make up the nucleus. Nuclei are bound by an attractive strong nuclear force between nucleons, which overcomes the electrostatic repulsion between protons. However, the strong nuclear force acts only over extremely short ranges, since it follows a Yukawa potential. For this reason large nuclei are less tightly bound per unit mass than small nuclei, and breaking a very large nucleus into two or more intermediate-sized nuclei releases energy.
    Because of the short range of the strong binding force, large nuclei must contain proportionally more neutrons than do light elements, which are most stable with a 1-1 ratio of protons and neutrons. Extra neutrons stabilize heavy elements because they add to strong-force binding without adding to proton-proton repulsion. Fission products have, on average, about the same ratio of neutrons and protons as their parent nucleus, and are therefore usually unstable because they have proportionally too many neutrons compared to stable isotopes of similar mass. This is the fundamental cause of the problem of radioactive high level waste from nuclear reactors. Fission products tend to be beta emitters, emitting fast-moving electrons to conserve electric charge as excess neutrons convert to protons inside the nucleus of the fission product atoms.
    The most common nuclear fuels, 235U and 239Pu, are not major radiologic hazards by themselves: 235U has a half-life of approximately 700 million years, and although 239Pu has a half-life of only about 24,000 years, it is a pure alpha particle emitter and hence not particularly dangerous unless ingested. Once a fuel element has been used, the remaining fuel material is intimately mixed with highly radioactive fission products that emit energetic beta particles and gamma rays. Some fission products have half-lives as short as seconds; others have half-lives of tens of thousands of years, requiring long-term storage in facilities such as Yucca mountain until the fission products decay into non-radioactive stable isotopes.

    [edit] Chain reactions


    A schematic nuclear fission chain reaction. 1. A uranium-235 atom absorbs a neutron, and fissions in two new atoms (fission fragments), releasing three new neutrons and some binding energy. 2. One of those neutrons is absorbed by an atom of uranium-238, and does not continue the reaction. Another neutron is simply lost and does not collide with anything, also not continuing the reaction. However one neutron does collide with an atom of uranium-235, which then fissions and releases two neutrons and some binding energy. 3. Both of those neutrons collide with uranium-235 atoms, each of which fission and release between one and three neutrons, which can then continue the reaction.


    Main article: Nuclear chain reaction
    Many heavy elements, such as uranium, thorium, and plutonium, undergo both spontaneous fission, a form of radioactive decay and induced fission, a form of nuclear reaction. Elemental isotopes that undergo induced fission when struck by a free neutron are called fissionable; isotopes that undergo fission when struck by a thermal, slow moving neutron are also called fissile. A few particularly fissile and readily obtainable isotopes (notably 235U and 239Pu) are called nuclear fuels because they can sustain a chain reaction and can be obtained in large enough quantities to be useful.
    All fissionable and fissile isotopes undergo a small amount of spontaneous fission which releases a few free neutrons into any sample of nuclear fuel. Such neutrons would escape rapidly from the fuel and become a free neutron, with a half-life of about 15 minutes before they decayed to protons and beta rays. However, neutrons almost invariably impact and are absorbed by other nuclei in the vicinity long before this happens (newly-created fission neutrons are moving at about 7% of the speed of light, and even moderated neutrons are moving at about 8 times the speed of sound). Some neutrons will impact fuel nuclei and induce further fissions, releasing yet more neutrons. If enough nuclear fuel is assembled into one place, or if the escaping neutrons are sufficiently contained, then these freshly generated neutrons outnumber the neutrons that escape from the assembly, and a sustained nuclear chain reaction will take place.
    An assembly that supports a sustained nuclear chain reaction is called a critical assembly or, if the assembly is almost entirely made of a nuclear fuel, a critical mass. The word "critical" refers to a cusp in the behavior of the differential equation that governs the number of free neutrons present in the fuel: if less than a critical mass is present, then the amount of neutrons is determined by radioactive decay, but if a critical mass or more is present, then the amount of neutrons is controlled instead by the physics of the chain reaction. The actual mass of a critical mass of nuclear fuel depends strongly on the geometry and surrounding materials.
    Not all fissionable isotopes can sustain a chain reaction. For example, 238U, the most abundant form of uranium, is fissionable but not fissile: it undergoes induced fission when impacted by an energetic neutron with over 1 MeV of kinetic energy. But too few of the neutrons produced by 238U fission are energetic enough to induce further fissions in 238U, so no chain reaction is possible with this isotope. Instead, bombarding 238U with slow neutrons causes it to absorb them (becoming 239U) and decay by beta emission to 239Np which then decays again by the same process to 239Pu; that process is used to manufacture 239Pu in breeder reactors, but does not contribute to a neutron chain reaction.
    Fissionable, non-fissile isotopes can be used as fission energy source even without a chain reaction. Bombarding 238U with fast neutrons induces fissions, releasing energy as long as the external neutron source is present. That effect is used to augment the energy released by modern thermonuclear weapons, by jacketing the weapon with 238U to react with neutrons released by nuclear fusion at the center of the device.

    [edit] Fission reactors

    Critical fission reactors are the most common type of nuclear reactor. In a critical fission reactor, neutrons produced by fission of fuel atoms are used to induce yet more fissions, to sustain a controllable amount of energy release. Devices that produce engineered but non-self-sustaining fission reactions are subcritical fission reactors. Such devices use radioactive decay or particle accelerators to trigger fissions.
    Critical fission reactors are built for three primary purposes, which typically involve different engineering trade-offs to take advantage of either the heat or the neutrons produced by the fission chain reaction:
    • power reactors are intended to produce heat for nuclear power, either as part of a generating station or a local power system such as a nuclear submarine.
    • research reactors are intended to produce neutrons and/or activate radioactive sources for scientific, medical, engineering, or other research purposes.
    • breeder reactors are intended to produce nuclear fuels in bulk from more abundant isotopes. The better known fast breeder reactor makes 239Pu (a nuclear fuel) from the naturally very abundant 238U (not a nuclear fuel). Thermal breeder reactors previously tested using 232Th continue to be studied and developed.
    While, in principle, all fission reactors can act in all three capacities, in practice the tasks lead to conflicting engineering goals and most reactors have been built with only one of the above tasks in mind. (There are several early counter-examples, such as the Hanford N reactor, now decommissioned). Power reactors generally convert the kinetic energy of fission products into heat, which is used to heat a working fluid and drive a heat engine that generates mechanical or electrical power. The working fluid is usually water with a steam turbine, but some designs use other materials such as gaseous helium. Research reactors produce neutrons that are used in various ways, with the heat of fission being treated as an unavoidable waste product. Breeder reactors are a specialized form of research reactor, with the caveat that the sample being irradiated is usually the fuel itself, a mixture of 238U and 235U.
    NucleosynthesisRelated topicsedit


    For a more detailed description of the physics and operating principles of critical fission reactors, see nuclear reactor physics. For a description of their social, political, and environmental aspects, see nuclear reactor.

    0 Not allowed!



  5. [5]
    حسن هادي
    حسن هادي غير متواجد حالياً
    عضو متميز
    الصورة الرمزية حسن هادي


    تاريخ التسجيل: Nov 2006
    المشاركات: 1,338
    Thumbs Up
    Received: 7
    Given: 0
    حفظ الله بلاد المسلمين وكل المسلمين وجميع البشرية من كل سوء آمين رب العالمين

    القنابل الذرية في سطور
    ********************
    Fission bombs
    One class of nuclear weapon, a fission bomb (not to be confused with the fusion bomb), otherwise known as an atomic bomb or atom bomb, is a fission reactor designed to liberate as much energy as possible as rapidly as possible, before the released energy causes the reactor to explode (and the chain reaction to stop). Development of nuclear weapons was the motivation behind early research into nuclear fission: the Manhattan Project of the U.S. military during World War II carried out most of the early scientific work on fission chain reactions, culminating in the Little Boy and Fat Man and Trinity bombs that were exploded over test sites, Hiroshima, and Nagasaki, Japan in August of 1945.
    Even the first fission bombs were thousands of times more explosive than a comparable mass of chemical explosive. For example, Little Boy weighed a total of about four tons (of which 60 kg was nuclear fuel) and was 11 feet long; it also yielded an explosion equivalent to about 15,000 tons of TNT, destroying a large part of the city of Hiroshima. Modern nuclear weapons (which include a thermonuclear fusion as well as one or more fission stages) are literally hundreds of times more energetic for their weight than the first pure fission atomic bombs, so that a modern single missile warhead bomb weighing less than 1/8th as much as Little Boy (see for example W88) has a yield of 475,000 tons of TNT, and could bring destruction to 10 times the city area.
    While the fundamental physics of the fission chain reaction in a nuclear weapon is similar to the physics of a controlled nuclear reactor, the two types of device must be engineered quite differently (see nuclear reactor physics). It would be extremely difficult to convert a nuclear reactor to cause a true nuclear explosion (though partial fuel meltdowns and steam explosions have occurred), and similarly difficult to extract useful power from a nuclear explosive (though at least one rocket propulsion system, Project Orion, was intended to work by exploding fission bombs behind a massively padded vehicle!).
    The strategic importance of nuclear weapons is a major reason why the technology of nuclear fission is politically sensitive. Viable fission bomb designs are within the capabilities of bright undergraduates (see John Aristotle Phillips) being incredibly simple, but nuclear fuel to realize the designs is thought to be difficult to obtain being rare (see uranium enrichment and nuclear fuel cycle).

    [edit] History

    The results of the bombardment of uranium by neutrons had proved interesting and puzzling. First studied by Enrico Fermi and his colleagues in 1934, they were not properly interpreted until several years later.
    After the Fermi publication, Lise Meitner, Otto Hahn and Fritz Strassmann began performing similar experiments in Germany. Meitner, an Austrian Jew, lost her citizenship with the Anschluss in 1938. She fled and wound up in Sweden, but continued to collaborate by mail and through meetings with Hahn in Sweden. By coincidence her nephew Otto Robert Frisch, also a refugee, was also in Sweden when Meitner received a letter from Hahn describing his chemical proof that some of the product of the bombardment of uranium with neutrons was barium (barium's atomic weight is half that of uranium). Frisch was skeptical, but Meitner believed Hahn was too good a chemist to have made a mistake. According to Frisch:
    Was it a mistake? No, said Lise Meitner; Hahn was too good a chemist for that. But how could barium be formed from uranium? No larger fragments than protons or helium nuclei (alpha particles) had ever been chipped away from nuclei, and to chip off a large number not nearly enough energy was available. Nor was it possible that the uranium nucleus could have been cleaved right across. A nucleus was not like a brittle solid that can be cleaved or broken; George Gamow had suggested early on, and Bohr had given good arguments that a nucleus was much more like a liquid drop. Perhaps a drop could divide itself into two smaller drops in a more gradual manner, by first becoming elongated, then constricted, and finally being torn rather than broken in two? We knew that there were strong forces that would resist such a process, just as the surface tension of an ordinary liquid drop tends to resist its division into two smaller ones. But nuclei differed from ordinary drops in one important way: they were electrically charged, and that was known to counteract the surface tension.
    The charge of a uranium nucleus, we found, was indeed large enough to overcome the effect of the surface tension almost completely; so the uranium nucleus might indeed resemble a very wobble unstable drop, ready to divide itself at the slightest provocation, such as the impact of a single neutron. But there was another problem. After separation, the two drops would be driven apart by their mutual electric repulsion and would acquire high speed and hence a very large energy, about 200 MeV in all; where could that energy come from? ...Lise Meitner... worked out that the two nuclei formed by the division of a uranium nucleus together would be lighter than the original uranium nucleus by about one-fifth the mass of a proton. Now whenever mass disappears energy is created, according to Einstein's formula E=mc2, and one-fifth of a proton mass was just equivalent to 200MeV. So here was the source for that energy; it all fitted!
    The basic discovery and chemical proof of Otto Hahn and Fritz Strassmann that an isotope of barium was produced by neutron bombardment of uranium was published in a paper in Germany in the Journal Naturwissenschaften, January 6, 1939) and earned Hahn a Nobel Prize [1]
    Frisch rapidly confirmed experimentally by means of a cloud chamber that the uranium atom had indeed been split by the action of neutrons. A fundamental idea of this experiment was suggested to Frisch by George Placzek[2] [3] . Two papers were mailed to England on January 16, 1939, the first on the interpretation of the barium appearance as atom splitting by Meitner and Frisch, the second on the experimental confirmation by Frisch (strangely omitting Placzek's important contribution, however). The first paper appeared on February 11, the second on February 28. [4]
    Meitner and Frisch's theory and mathematical proof of Hahn's discovery and chemical proof of barium products from the bombardment of uranium was the foundation of the later research on nuclear fission. The awarding of the 1944 Nobel Prize in Chemistry to Hahn alone is a longstanding controversy.[5]
    On January 16, 1939, Niels Bohr of Copenhagen, Denmark, arrived in the United States to spend several months in Princeton, New Jersey, and was particularly anxious to discuss some abstract problems with Albert Einstein. (Four years later Bohr was to escape to Sweden from Nazi-occupied Denmark in a small boat, along with thousands of other Danish Jews, in large scale operation.) Just before Bohr left Denmark, Frisch and Meitner gave him their calculations.
    Bohr had promised to keep the Meitner/Frisch paper secret until it was published to preserve priority, but on the boat he discussed it with Léon Rosenfeld, and forgot to tell him to keep it secret. Rosenfeld immediately upon arrival told everyone at Princeton University, and from them the news spread by word of mouth to neighboring physicists including Enrico Fermi at Columbia University. Fermi upon traveling to receive the Nobel Prize for his earlier work. headed to the USA rather than return to Fascist Italy with his Jewish wife. As a result of conversations among Fermi, John R. Dunning, and G. B. Pegram, a search was undertaken at Columbia for the heavy pulses of ionization that would be expected from the flying fragments of the uranium nucleus. On January 26, 1939, there was a conference on theoretical physics at Washington, D.C., sponsored jointly by the George Washington University and the Carnegie Institution of Washington. Before the meeting in Washington was over, several other experiments to confirm fission had been initiated, and positive experimental confirmation was reported.
    Frédéric Joliot-Curie's team in Paris discovered that secondary neutrons are released during uranium fission thus making a chain reaction feasible. About two neutrons being emitted with nuclear fission of uranium was verified independently by Leo Szilard and Walter Zinn. The number of neutrons emitted with nuclear fission of 235uranium was then reported at 3.5/fission, and later corrected to 2.6/fission by Frédéric Joliot-Curie, Hans von Halban and Lew Kowarski.
    "Chain reactions" at that time were a known phenomenon in chemistry, but the analogous process in nuclear physics using neutrons had been foreseen as early as 1933 by Leo Szilard, although Szilard at that time had no idea with what materials the process might be initiated. Szilard, a Hungarian born Jew, also fled mainland Europe after Hitler's rise, eventually landing in the US.
    In the summer Fermi and Szilard proposed the idea of a nuclear reactor (pile) with natural uranium as fuel and graphite as moderator of neutron energy.
    In August Hungarian-Jewish refugees Szilard, Teller and Wigner persuaded Austrian-Jewish refugee Einstein to warn President Roosevelt of the German menace. The letter suggested the possibility of uranium bomb deliverable by ship. The President received it on 1939.10.11 shortly after WWII began.
    In England James Chadwick proposed an atomic bomb utilizing natural uranium based on a paper by Rudolf Peierls with the mass needed for critical state being 30-40 tons.
    In December, Heisenberg delivered a report to the Germany Department of War on the possibility of a uranium bomb.
    In Birmingham, England Otto Robert Frisch teamed up with Rudolf Peierls who had also fled German anti-Jewish race laws. They conceived the idea of utilizing a purified isotope of uranium, uranium-235, and worked out that an enriched uranium bomb could have a critical mass of only 600 g. instead of tons, and that the resulting explosion would be tremendous. (the amount actually turned out to be 15 kg.) In February 1940 they delivered the Frisch-Peierls memorandum, however, they were officially considered "enemy aliens" at the time.
    Uranium-235 is separated by Nier and fission with slow neutron is confirmed by Dunning.
    German-Jewish refugee Francis Simon at Oxford quantified the gaseous diffusion separation of U-235.
    In 1941 American Physicist Ernest O. Lawrence proposed electromagnetic separation.
    Glenn Seaborg, Joe Kennedy, Art Wahl and Italian-Jewish refugee Emilio Segre discovered plutonium and determined it to be fissionable like U-235. (Lawrence controversially dropped Segre's pay by half when he learned he was trapped in the US by Mussolini's race laws.)
    On June 28 1941, the Office of Scientific Research and Development was formed to mobilize scientific resources and apply the results of research to national defense. In September Fermi assembled his first nuclear pile in an attempt to create a slow neutron induced chain reaction in uranium. but the experiment failed.
    Producing a fission chain reaction in uranium fuel is far from trivial. Early nuclear reactors did not use isotopically enriched uranium, and in consequence they were required to use large quantities of highly purified graphite as neutron moderation materials. Use of ordinary water (as opposed to heavy water) in nuclear reactors requires enriched fuel--- the partial separation and relative enrichment of the rare 235U isotope from the far more common 238U isotope. Typically, reactors also require inclusion of extremely chemically pure neutron moderator materials such as deuterium (in heavy water), helium, beryllium, or carbon, usually as the graphite. (The high purity is required because many chemical impurities such as the boron-10 component of natural boron, are very strong neutron absorbers and thus poison the chain reaction.)
    Production of such materials at industrial scale had to be solved for nuclear power generation and weapons production to be accomplished. Up to 1940, the total amount of uranium metal produced in the USA was not more than a few grams and even this was of doubtful purity; of metallic beryllium not more than a few kilograms; concentrated deuterium oxide (heavy water) not more than a few kilograms; and finally carbon had never been produced in quantity with anything like the purity required of a moderator.
    The problem of producing large amounts of high purity uranium was solved by Frank Spedding using the thermite process. Ames Laboratory was established in 1942 to produce the large amounts of natural (unenriched) uranium that would be necessary for the research to come. The success of the Chicago Pile-1 which used unenriched (natural) uranium, like all of the atomic "piles" which produced the plutonium for the atomic bomb, was also due specifically to Szilard's realization that very pure graphite could be used for the moderator of even natural uranium "piles". In wartime Germany, failure to appreciate the qualities of very pure graphite led to reactor designs dependent on heavy water, which in turn was denied the Germans by allied attacks in Norway, where heavy water was produced. These difficulties prevented the Nazis from building a nuclear reactor capable of criticality during the war.
    Unknown until 1972 (but postulated by Paul Kuroda in 1956), when French physicist Francis Perrin discovered the Oklo Fossil Reactors, nature had beaten humans to the punch by engaging in large-scale uranium fission chain reactions, some 2,000 million years in the past. This ancient process was able to use normal water as a moderator, only because 2,000 million years in the past, natural uranium was "enriched" with the shorter-lived fissile isotope 235U, as compared with the natural uranium available today.
    For more detail on the early development of nuclear reactors and nuclear weapons, see Manhattan Project.

    0 Not allowed!



  6. [6]
    حسن هادي
    حسن هادي غير متواجد حالياً
    عضو متميز
    الصورة الرمزية حسن هادي


    تاريخ التسجيل: Nov 2006
    المشاركات: 1,338
    Thumbs Up
    Received: 7
    Given: 0
    The future of the industry
    See also: Nuclear energy policy, Mitigation of global warming, and Economics of new nuclear power plants As of March 1, 2007, Watts Bar 1, which came on-line in 1997, was the last U.S. commercial nuclear reactor to go on-line. This is often quoted as evidence of a successful worldwide campaign for nuclear power phase-out. However, political resistance to nuclear power has only ever been successful in parts of Europe, in New Zealand, in the Philippines, and in the United States. Even in the US and throughout Europe, investment in research and in the nuclear fuel cycle has continued, and some experts predict that electricity shortages, fossil fuel price increases, global warming from fossil fuel use, new technology such as passively safe plants, and national energy security will renew the demand for nuclear power plants.
    Many countries remain active in developing nuclear power, including Japan, China and India, all actively developing both fast and thermal technology, South Korea and the United States, developing thermal technology only, and South Africa and China, developing versions of the Pebble Bed Modular Reactor (PBMR). Finland and France actively pursue nuclear programs; Finland has a new European Pressurized Reactor under construction by Areva. Japan has an active nuclear construction program with new units brought on-line in 2005. In the U.S., three consortia responded in 2004 to the U.S. Department of Energy's solicitation under the Nuclear Power 2010 Program and were awarded matching funds—the Energy Policy Act of 2005 authorized subsidies for up to six new reactors, and authorized the Department of Energy to build a reactor based on the Generation IV Very-High-Temperature Reactor concept to produce both electricity and hydrogen. As of the early 21st century, nuclear power is of particular interest to both China and India to serve their rapidly growing economies—both are developing fast breeder reactors. See also energy development. In the energy policy of the United Kingdom it is recognized that there is a likely future energy supply shortfall, which may have to be filled by either new nuclear plant construction or maintaining existing plants beyond their programmed lifetime.
    On September 22, 2005 it was announced that two sites in the U.S. had been selected to receive new power reactors (exclusive of the new power reactor scheduled for INL)—see Nuclear Power 2010 Program.
    ************************************************** **************
    المفاعلات النووية
    Nuclear reactor technology
    Main article: Nuclear reactor technology

    Cattenom Nuclear Power Plant.


    Conventional thermal power plants all have a fuel source to provide heat. Examples are gas, coal, or oil. For a nuclear power plant, this heat is provided by nuclear fission inside the nuclear reactor. When a relatively large fissile atomic nucleus is struck by a neutron it forms two or more smaller nuclei as fission products, releasing energy and neutrons in a process called nuclear fission. The neutrons then trigger further fission. And so on. When this nuclear chain reaction is controlled, the energy released can be used to heat water, produce steam and drive a turbine that generates electricity. While a nuclear power plant uses the same fuel, uranium-235 or plutonium-239, a nuclear explosive involves an uncontrolled chain reaction, and the rate of fission in a reactor is not capable of reaching sufficient levels to trigger a nuclear explosion because commercial reactor grade nuclear fuel is not enriched to a high enough level. Naturally found uranium is less than 1% U-235, the rest being U-238. Most reactor fuel is enriched to only 3-4%, but some designs use natural uranium or highly enriched uranium. Reactors for nuclear submarines and large naval surface ships, such as aircraft carriers, commonly use highly enriched uranium. Although highly enriched uranium is more expensive, it reduces the frequency of refueling, which is very useful for military vessels. CANDU reactors are able to use unenriched uranium because the heavy water they use as a moderator and coolant does not absorb neutrons like light water does.
    The chain reaction is controlled through the use of materials that absorb and moderate neutrons. In uranium-fueled reactors, neutrons must be moderated (slowed down) because slow neutrons are more likely to cause fission when colliding with a uranium-235 nucleus. Light water reactors use ordinary water to moderate and cool the reactors. When at operating temperatures if the temperature of the water increases, its density drops, and fewer neutrons passing through it are slowed enough to trigger further reactions. That negative feedback stabilizes the reaction rate.
    The current types of plants (and their common components) are discussed in the article nuclear reactor technology.
    A number of other designs for nuclear power generation, the Generation IV reactors, are the subject of active research and may be used for practical power generation in the future. A number of the advanced nuclear reactor designs could also make critical fission reactors much cleaner, much safer and/or much less of a risk to the proliferation of nuclear weapons.
    Controlled nuclear fusion could in principle be used in fusion power plants to produce power without the complexities of handling actinides, but significant scientific and technical obstacles remain. Several fusion reactors have been built, but as yet none has 'produced' more thermal energy than electrical energy consumed. Despite research having started in the 1950s, no commercial fusion reactor is expected before 2050. The ITER project is currently leading the effort to commercialize fusion power.



    0 Not allowed!



  7. [7]
    حسن هادي
    حسن هادي غير متواجد حالياً
    عضو متميز
    الصورة الرمزية حسن هادي


    تاريخ التسجيل: Nov 2006
    المشاركات: 1,338
    Thumbs Up
    Received: 7
    Given: 0
    Safety
    Main article: Nuclear safety
    See also: Nuclear safety in the U.S. The topic of nuclear safety covers:
    • The research and testing of the possible incidents/events at a nuclear power plant,
    • What equipment and actions are designed to prevent those incidents/events from having serious consequences,
    • The calculation of the probabilities of multiple systems and/or actions failing thus allowing serious consequences,
    • The evaluation of the worst-possible timing and scope of those serious consequences (the worst-possible in extreme cases being a release of radiation),
    • The actions taken to protect the public during a release of radiation,
    • The training and rehearsals performed to ensure readiness in case an incident/event occurs.
    Many different safety features have been added to nuclear power plants and the NRC is responsible for this.

    [edit] Economics

    Main article: Economics of new nuclear power plants
    This is a controversial subject, since multi-billion dollar investments ride on the choice of an energy source.
    Which power source (generally coal, natural gas, nuclear or wind) is most cost-effective depends on the assumptions used in a particular study—several are quoted in the main article.

    [edit] Life cycle


    The Nuclear Fuel Cycle begins when uranium is mined, enriched, and manufactured into nuclear fuel, (1) which is delivered to a nuclear power plant. After usage in the power plant, the spent fuel is delivered to a reprocessing plant (2) or to a final repository (3) for geological disposition. In reprocessing 95% of spent fuel can be recycled to be returned to usage in a power plant (4).



    Nuclear fuel — a compact, inert, insoluble solid.


    Main article: Nuclear fuel cycle
    A nuclear reactor is only part of the life-cycle for nuclear power. The process starts with mining. Generally, uranium mines are either open-pit strip mines, or in-situ leach mines. In either case, the uranium ore is extracted, usually converted into a stable and compact form such as yellowcake, and then transported to a processing facility. Here, the yellowcake is converted to uranium hexafluoride, which is then enriched using various techniques. At this point, the enriched uranium, containing more than the natural 0.7% U-235, is used to make rods of the proper composition and geometry for the particular reactor that the fuel is destined for. The fuel rods will spend about 3 years inside the reactor, generally until about 3% of their uranium has been fissioned, then they will be moved to a spent fuel pool where the short lived isotopes generated by fission can decay away. After about 5 years in a cooling pond, the spent fuel is radioactively cool enough to handle, and it can be moved to dry storage casks or reprocessed.

    [edit] Fuel resources

    Main article: Uranium market
    Main article: Energy development - Nuclear energy
    Uranium is a common element, approximately as common as tin or zinc, and it is a constituent of most rocks and of the sea. The world's present measured resources of uranium, economically recoverable at a price of 130 USD/kg, are enough to last for some 70 years at current consumption. This represents a higher level of assured resources than is normal for most minerals. On the basis of analogies with other metallic minerals, a doubling of price from present levels could be expected to create about a tenfold increase in measured resources, over time. The fuel's contribution to the overall cost of the electricity produced is relatively small, so even a large fuel price escalation will have relatively little effect on final price. For instance, typically a doubling of the uranium market price would increase the fuel cost for a light water reactor by 26% and the electricity cost about 7% (whereas doubling the gas price would typically add 70% to the price of electricity from that source). At higher prices eventually extraction from sources such as granite and seawater become economically feasible.[18][19]
    Current light water reactors make relatively inefficient use of nuclear fuel, leading to energy waste. But nuclear reprocessing makes this waste reusable (except in the USA, where this is not allowed) and more efficient reactor designs would allow better use of the available resources (and reduce the amount of waste material).[20]
    As opposed to current light water reactors which use uranium-235 (0.7% of all natural uranium), fast breeder reactors use uranium-238 (99.3% of all natural uranium). It has been estimated that there is up to five-billion years’ (also the estimated remaining life of the Sun) worth of uranium-238 for use in these power plants.[21] Breeder technology has been used in several reactors, but requires higher uranium prices before becoming justified economically.[22] As of December 2005, the only breeder reactor producing power is BN-600 in Beloyarsk, Russia. (The electricity output of BN-600 is 600 MW — Russia has planned to build another unit, BN-800, at Beloyarsk nuclear power plant.) Also, Japan's Monju reactor is planned for restart (having been shut down since 1995), and both China and India intend to build breeder reactors.
    Another alternative would be to use uranium-233 bred from thorium as fission fuel — the thorium fuel cycle. Thorium is three times more abundant in the Earth's crust than uranium, and (theoretically) all of it can be used for breeding, making the potential thorium resource orders of magnitude larger than the uranium fuel cycle operated without breeding.[23] Unlike the breeding of U-238 into plutonium, fast breeder reactors are not necessary — it can be performed satisfactorily in more conventional plants.
    Fusion power commonly propose the use of deuterium, an isotope of hydrogen, as fuel and in many current designs also lithium. Assuming a fusion energy output equal to the current global output and that this does not increase in the future, then the known current lithium reserves would last 3000 years, lithium from sea water would last 60 million years, and a more complicated fusion process using only deuterium from sea water would have fuel for 150 billion years.[24]

    [edit] Depleted uranium

    Main article: Depleted uranium
    Uranium enrichment produces many tons of depleted uranium (DU) which consists of U-238 with most of the easily fissile U-235 isotope removed. U-238 is a tough metal with several commercial uses — for example, aircraft production, radiation shielding, and making bullets and armor — as it has a higher density than lead. There are concerns that U-238 may lead to health problems in groups exposed to this material excessively, like tank crews and civilians living in areas where large quantities of DU ammunition have been used.

    [edit] Solid waste

    For more details on this topic, see Radioactive waste.
    The safe storage and disposal of nuclear waste is a significant challenge. The most important waste stream from nuclear power plants is spent fuel. A large nuclear reactor produces 3 cubic metres (25-30 tonnes) of spent fuel each year.[25] It is primarily composed of unconverted uranium as well as significant quantities of transuranic actinides (plutonium and curium, mostly). In addition, about 3% of it is made of fission products. The actinides (uranium, plutonium, and curium) are responsible for the bulk of the long term radioactivity, whereas the fission products are responsible for the bulk of the short term radioactivity.
    Spent fuel is highly radioactive and needs to be handled with great care and forethought. However, spent nuclear fuel becomes less radioactive over time. After 40 years, the radiation flux is 99.9% lower than it was the moment the spent fuel was removed, although still dangerously radioactive.[20]
    Spent fuel rods are stored in shielded basins of water (spent fuel pools), usually located on-site. The water provides both cooling for the still-decaying uranium, and shielding from the continuing radioactivity. After a few decades some on-site storage involves moving the now cooler, less radioactive fuel to a dry-storage facility or dry cask storage, where the fuel is stored in steel and concrete containers until its radioactivity decreases naturally ("decays") to levels safe enough for other processing. This interim stage spans years or decades, depending on the type of fuel. Most U.S. waste is currently stored in temporary storage sites requiring oversight, while suitable permanent disposal methods are discussed.
    As of 2003, the United States had accumulated about 49,000 metric tons of spent nuclear fuel from nuclear reactors. Underground storage at Yucca Mountain in U.S. has been proposed as permanent storage. After 10,000 years of radioactive decay, according to United States Environmental Protection Agency standards, the spent nuclear fuel will no longer pose a threat to public health and safety.
    The amount of waste can be reduced in several ways, particularly reprocessing. Even so, the remaining waste will be substantially radioactive for at least 300 years even if the actinides are removed, and for up to thousands of years if the actinides are left in. Even with separation of all actinides, and using fast breeder reactors to destroy by transmutation some of the longer-lived non-actinides as well, the waste must be segregated from the environment for one to a few hundred years, and therefore this is properly categorized as a long-term problem. Subcritical reactors or fusion reactors could also reduce the time the waste has to be stored.[26] It has been argued that the best solution for the nuclear waste is above ground temporary storage since technology is rapidly changing. The current waste may well become a valuable resource in the future.
    The nuclear industry also produces a volume of low-level radioactive waste in the form of contaminated items like clothing, hand tools, water purifier resins, and (upon decommissioning) the materials of which the reactor itself is built. In the United States, the Nuclear Regulatory Commission has repeatedly attempted to allow low-level materials to be handled as normal waste: landfilled, recycled into consumer items, et cetera. Most low-level waste releases very low levels of radioactivity and is only considered radioactive waste because of its history. For example, according to the standards of the NRC, the radiation released by coffee is enough to treat it as low level waste.
    In countries with nuclear power, radioactive wastes comprise less than 1% of total industrial toxic wastes, which remain hazardous indefinitely unless they decompose or are treated so that they are less toxic or, ideally, completely non-toxic.[20] Overall, nuclear power produces far less waste material than fossil-fuel based power plants. Coal-burning plants are particularly noted for producing large amounts of toxic and mildly radioactive ash due to concentrating naturally occurring metals and radioactive material from the coal. Contrary to popular belief, coal power actually results in more radioactive waste being released into the environment than nuclear power. The population effective dose equivalent from radiation from coal plants is 100 times as much as nuclear plants.[27]

    [edit] Reprocessing

    For more details on this topic, see Nuclear reprocessing.
    Reprocessing can potentially recover up to 95% of the remaining uranium and plutonium in spent nuclear fuel, putting it into new mixed oxide fuel. This would produce a reduction in long term radioactivity within the remaining waste, since this is largely short-lived fission products, and reduces its volume by over 90%. Reprocessing of civilian fuel from power reactors is currently done on large scale in Britain, France and (formerly) Russia, will be in China and perhaps India, and is being done on an expanding scale in Japan. The potential of reprocessing has not been achieved because it requires breeder reactors, which are not yet commercially available. France is generally cited as the most successful reprocessor, but it presently only recycles 28% (by weight) of the yearly fuel use, 7% within France and another 21% in Russia.[28]
    Unlike other countries, the US has stopped civilian reprocessing as one part of US non-proliferation policy, since reprocessed material such as plutonium can be used in nuclear weapons. Spent fuel is all currently treated as waste.[29] In February, 2006, a new U.S. initiative, the Global Nuclear Energy Partnership was announced. It would be an international effort to reprocess fuel in a manner making nuclear proliferation unfeasible, while making nuclear power available to developing countries.[30]

    0 Not allowed!



  8. [8]
    حسن هادي
    حسن هادي غير متواجد حالياً
    عضو متميز
    الصورة الرمزية حسن هادي


    تاريخ التسجيل: Nov 2006
    المشاركات: 1,338
    Thumbs Up
    Received: 7
    Given: 0
    Debate on nuclear power
    Since Global warming has become high on the Environmentalist agenda, environmental groups are split on the issue of nuclear power, though they used to be more united against it in the 70s and 80s.[31] Arguments of economics and safety are used by both sides of the debate.
    Critics claim that nuclear power is an uneconomic and potentially dangerous energy source with a limited fuel supply compared to renewable energy, and dispute whether the costs and risks can be reduced through new technology. Critics also point to the problem of storing radioactive waste, the potential for possibly severe radioactive contamination by accident or sabotage, and the possibility of nuclear proliferation. Greenpeace, for instance, has never changed its anti-nuclear position, Greenpeace-US positions themselves with this statement on their website:
    We have always fought - and will continue to fight - vigorously against nuclear power because it is an unacceptable risk to the environment and to humanity[32]
    Proponents of nuclear energy respond that nuclear power is a sustainable energy source that reduces carbon emissions and increases energy security by decreasing dependence on foreign countries for energy sources. Proponents also claim that the risks of storing waste are small and can be further reduced by the technology in the new reactors and the operational safety record is already good when compared to the other major kinds of power plants. Many go on to argue that renewables are limited to a minority share of energy production because they are Intermittent power sources and have questionable economics themselves as well as demanding too much money for development. James Lovelock, a nuclear supporter, of the Environmentalists for Nuclear Energy has said:
    We have no time to experiment with visionary energy sources; civilisation is in imminent danger and has to use nuclear -- the one safe, available, energy source[33]

    [edit] Accidents

    Main article: Nuclear and radiation accidents
    The International Nuclear Event Scale (INES), developed by the International Atomic Energy Agency (IAEA), is used to communicate the severity of nuclear accidents on a scale of 0 to 7. The two most well-known events are the Three Mile Island accident and the Chernobyl disaster.
    The 1979 accident at Three Mile Island Unit 2 was the worst civilian nuclear accident outside the Soviet Union (INES score of 5). The reactor experienced a partial core meltdown. However, the reactor vessel and containment building were not breached and little radiation was released to the environment. [34] The event resulted in fundamental changes in how plants in the West were to be maintained and operated.
    The Chernobyl disaster in 1986 at the Chernobyl Nuclear Power Plant in the Ukrainian Soviet Socialist Republic (now Ukraine) was the worst nuclear accident in history and is the only event to receive an INES score of 7. The power excursion and resulting steam explosion and fire spread radioactive contamination across large portions of Europe. A large 2005 study found that the death toll includes the 50 workers who died of acute radiation syndrome, nine children who died from thyroid cancer, and an estimated 4000 excess cancer deaths in the future, added to an estimated 100,000 cancer deaths in this population due to other factors.[35] Supporters of nuclear power argue that this accident occurred due to several critical design flaws in the Soviet RBMK reactors, such as lack of a containment building which would have stopped radioactive emissions from that accident, and that security in the remaining RBMK reactors have greatly improved.[7]
    Design changes are being pursued to lessen the risks of fission reactors; in particular, passively safe plants (such as the ESBWR) are available to be built and inherently safe designs are being pursued. Fusion reactors which may come to exist in the future theoretically have very little risk.
    The World Nuclear Association provides a comparison of deaths due to accidents among different forms of energy production. In their comparison, deaths per TWy of electricity produced are 885 for hydropower, 342 for coal, 85 for natural gas, and 8 for nuclear.[36] Air pollution from fossil fuels is argued to cause tens of thousands of additional deaths each year in the US alone.[37] Furthermore, a 2004 news article from the BBC stated, "The World Health Organization (WHO) says 3 million people are killed worldwide by outdoor air pollution annually from vehicles and industrial emissions, and 1.6 million indoors through using solid fuel. Most are in poor countries."[38]

    [edit] Vulnerability of plants to attack

    Nuclear power plants are generally (although not always) considered "hard" targets. In the US, plants are surrounded by a double row of tall fences which are electronically monitored. The plant grounds are patrolled by a sizeable force of armed guards.[39] The NRC's "Design Basis Threat" criteria for plants is a secret, and so what size attacking force the plants are able to protect against is unknown. However, to scram a plant takes less than 5 seconds while unimpeded restart takes hours, severely hampering a terrorist force in a goal to release radioactivity.
    Attack from the air is a more problematic concern. The most important barrier against the release of radioactivity in the event of an aircraft strike is the containment building and its missile shield. The NRC's Chairman has said "Nuclear power plants are inherently robust structures that our studies show provide adequate protection in a hypothetical attack by an airplane. The NRC has also taken actions that require nuclear power plant operators to be able to manage large fires or explosions—no matter what has caused them." [40]
    In addition, supporters point to large studies carried out by the US Electric Power Research Institute that tested the robustness of both reactor and waste fuel storage, and found that they should be able to sustain a terrorist attack comparable to the September 11 terrorist attacks in the USA.[36] Spent fuel is usually housed inside the plant's "protected zone"[41] or a spent nuclear fuel shipping cask; stealing it for use in a "dirty bomb" is extremely difficult. Exposure to the intense radiation would almost certainly quickly incapacitate or kill any terrorists who attempt to do so.[42]
    Nuclear power plants are designed to withstand threats deemed credible at the time of licensing. However, as weapons evolve it cannot be said unequivocably that within the 60 year life of a plant it will not become vulnerable. In addition, the future status of storage sites may be in doubt. Other forms of energy production are also vulnerable to attack, such as hydroelectric dams and LNG tankers.

    [edit] Use of waste byproduct as a weapon

    An additional concern with nuclear power plants is that if the by-products of nuclear fission—the nuclear waste generated by the plant—were to be unprotected it could be used as a radiological weapon, colloquially known as a "dirty bomb". There have been incidents of nuclear plant workers attempting to sell nuclear materials for this purpose (for example, there was such an incident in Russia in 1999 where plant workers attempted to sell 5 grams of radioactive material on the open market,[43] and an incident in 1993 where Russian workers were caught attempting to sell 4.5 kilograms of enriched uranium.[44][45][46]), and there are additional concerns that the transportation of nuclear waste along roadways or railways opens it up for potential theft. The UN has since called upon world leaders to improve security in order to prevent radioactive material falling into the hands of terrorists,[47] and such fears have been used as justifications for centralized, permanent, and secure waste repositories and increased security along transportation routes.[48]

    [edit] Health effect on population near nuclear plants


    A couple fishermen near the Trojan Nuclear Power Plant. The reactor dome is visible on the left, and the massive cooling tower on the right.


    Most of human exposure to radiation comes from natural background radiation. Most of the remaining exposure comes from medical procedures. Several large studies in the US, Canada, and Europe have found no evidence of any increase in cancer mortality among people living near nuclear facilities. For example, in 1991, the National Cancer Institute (NCI) of the National Institutes of Health announced that a large-scale study, which evaluated mortality from 16 types of cancer, found no increased incidence of cancer mortality for people living near 62 nuclear installations in the United States. The study showed no increase in the incidence of childhood leukemia mortality in the study of surrounding counties after start-up of the nuclear facilities. The NCI study, the broadest of its kind ever conducted, surveyed 900,000 cancer deaths in counties near nuclear facilities.[8]
    Some areas of Britain near industrial facilities, particularly near Sellafield, have displayed elevated childhood leukemia levels, in which children living locally are 10 times more likely to contract the cancer. One study of those near Sellafield has ruled out any contribution from nuclear sources, and the reasons for these increases, or clusters, are unclear. Apart from anything else, the levels of radiation at these sites are orders of magnitude too low to account for the excess incidences reported. One explanation is viruses or other infectious agents being introduced into a local community by the mass movement of migrant workers.[49][50] Likewise, small studies have found an increased incidence of childhood leukemia near some nuclear power plants has been found in Germany[51] and France.[52] Nonetheless, the results of larger multi-site studies in these countries invalidate the hypothesis of an increased risk of leukemia related to nuclear discharge. The methodology and very small samples in the studies finding an increased incidence has been criticized.[53] [54] [55] [56] Also, one study focusing on leukemia clusters in industrial towns in England indicated a link to high-capacity electricity lines suggesting that the production or distribution of the electricity, rather than the nuclear reaction, may be a factor.[dubiousdiscuss][citation needed]

    [edit] Nuclear proliferation

    For more details on this topic, see Nuclear proliferation.
    Nuclear proliferation is the spread of nuclear weapons and related technology to nations not recognized as "Nuclear Weapon States" by the Nuclear Nonproliferation Treaty. Since the days of the Manhattan Project it has been known that reactors could be used for weapons-development purposes—the first nuclear reactors were developed for exactly this reason—as the operation of a nuclear reactor converts U-238 into plutonium. As a consequence, since the 1950s there have been concerns about the possibility of using reactors as a dual-use technology, whereby apparently peaceful technological development could serve as an approach to nuclear weapons capability.
    Original impetus for development of nuclear power came from the military nuclear programs, including the early designs of power reactors that were developed for nuclear submarines. In many countries nuclear and civilian nuclear programs are linked, at least by common research projects and through agencies such as the US DOE. In the U.S., for example, the first goal of the Department of Energy is "to advance the national, economic, and energy security of the United States; to promote scientific and technological innovation in support of that mission; and to ensure the environmental cleanup of the national nuclear weapons complex."[57]
    To prevent weapons proliferation, safeguards on nuclear technology were published in the Nuclear Non-Proliferation Treaty (NPT) and monitored since 1968 by the International Atomic Energy Agency (IAEA). Nations signing the treaty are required to report to the IAEA what nuclear materials they hold and their location. They agree to accept visits by IAEA auditors and inspectors to verify independently their material reports and physically inspect the nuclear materials concerned to confirm physical inventories of them in exchange for access to nuclear materials and equipment on the global market.
    Several states did not sign the treaty and were able to use international nuclear technology (often procured for civilian purposes) to develop nuclear weapons (India, Pakistan, Israel, and South Africa). Of those who have signed the treaty and received shipments of nuclear paraphernalia, many states have either claimed to, or been accused of, attempting to use supposedly civilian nuclear power plants for developing weapons. Certain types of reactors may be more conducive to producing nuclear weapons materials than others, such as possible future fast breeder reactors, and a number of international disputes over proliferation have centered on the specific model of reactor being contracted for in a country suspected of nuclear weapon ambitions.
    There is concern in some countries over North Korea and Iran operating research reactors and fuel enrichment plants, since those countries refuse adequate IAEA oversight and are believed to be trying to develop nuclear weapons. In 2006, North Korea detonated what they claimed was a functioning nuclear weapon, which analysis has indicated was fueled by plutonium, presumably diverted from their Yongbyon nuclear reactor.[58] Iran maintains that its nuclear program is solely for peaceful purposes, though this has been disputed.[59]
    Aside from their plutonium-producing potential, some research reactors are considered proliferation threats because of their use of highly-enriched uranium (HEU) as their fuel. According to the IAEA, there are over 100 reactors in the world which continue to be fueled by HEU, though for decades work has pursued to convert these to operate with low-enriched uranium (LEU). In this case, the threat is not considered to be based on surrepticious weapons development, but rather that of theft of the enriched nuclear materials, which would help potential bomb makers subvert the largest hurdle in developing an enriched-uranium weapon.[60]

    0 Not allowed!



  9. [9]
    حسن هادي
    حسن هادي غير متواجد حالياً
    عضو متميز
    الصورة الرمزية حسن هادي


    تاريخ التسجيل: Nov 2006
    المشاركات: 1,338
    Thumbs Up
    Received: 7
    Given: 0
    Floating nuclear power plants
    Main article: Russian floating nuclear power station
    Russia has begun building floating nuclear power plants. The £100 million vessel, the Lomonosov, to be completed in 2010, is the first of seven plants that Moscow says will bring vital energy resources to remote Russian regions. While producing only a small fraction of the power of a standard Russian land-based plant, it can supply power to a city of 200,000, or function as a desalination plant. The Russian atomic energy agency said that at least 12 countries were also interested in buying floating nuclear plants. [61]
    Environmental groups and nuclear experts are concerned that floating nuclear plants will be more vulnerable to accidents and terrorism than land-based stations. They point to a history of naval and nuclear accidents in Russia and the former Soviet Union, including the Chernobyl disaster of 1986.[61] Russia does have 50 years of experience operating a fleet of nuclear powered icebreakers that are also used for scientific and Arctic tourism expeditions. The Russians have commented that a nuclear reactor that sinks, such as the similar reactor involved in the Kursk explosion, can be raised and probably put back into operation.[61] At this time it is not known what, if any, containment structure or associated missile shield will be built on the ship. According to MosNews, a Russian news outlet, there is no way an airliner striking the ship would destroy the reactor.[62]

    [edit] Environmental effects


    [edit] Air pollution

    Further information: Environmental concerns with electricity generation Nuclear generation does not directly produce sulfur dioxide, nitrogen oxides, mercury or other pollutants associated with the combustion of fossil fuels (pollution from fossil fuels is blamed for many deaths each year in the U.S. alone[63]). It also does not directly produce carbon dioxide, which has led some environmentalists to advocate increased reliance on nuclear energy as a means to reduce greenhouse gas emissions (which contribute to global warming). Non-radioactive water vapor is the significant operating emission from nuclear power plants.[64]
    According to a 2007 story broadcast on 60 Minutes,[65] nuclear power gives France the cleanest air of any industrialized country, and the cheapest electricity in all of Europe.
    Like any power source (including renewables like wind and solar energy), the facilities to produce and distribute the electricity require energy to build and subsequently decommission. Mineral ores must be collected and processed to produce nuclear fuel. These processes either are directly powered by diesel and gasoline engines, or draw electricity from the power grid, which may be generated from fossil fuels. Life cycle analyses assess the amount of energy consumed by these processes (given today's mix of energy resources) and calculate, over the lifetime of a nuclear power plant, the amount of carbon dioxide saved (related to the amount of electricity produced by the plant) vs. the amount of carbon dioxide used (related to construction and fuel acquisition).
    In a study conducted in 2006 by the UK's Parliamentary Office of Science and Technology (POST), nuclear power's lifecycle was evaluated to emit the least amount of carbon dioxide (very close to wind power's lifecycle emissions) when compared to the other alternatives (fossil oil, coal, and some renewable energy including biomass and PV solar panels). [66] In 2006, a UK government advisory panel, The Sustainable Development Commission, concluded that if the UK's existing nuclear capacity were doubled, it would provide an 8% decrease in total UK CO2 emissions by 2035. This can be compared to the country's goal to reduce greenhouse gas emissions by 60 % by 2050. As of 2006, the UK government was to publish its official findings later in the year.[67][68] On 21 September 2005 the Oxford Research Group published a report, in the form of a memorandum to a committee of the British House of Commons, which argued that, while nuclear plants do not generate carbon dioxide while they operate, the other steps necessary to produce nuclear power, including the mining of uranium and the storing of waste, result in substantial amounts of carbon dioxide pollution.[69]
    According to one life cycle study from 2001–2005, carbon dioxide emissions from nuclear power per kilowatt hour could range from 20% to 120% of those for natural gas-fired power stations depending on the availability of high grade ores.[70] The study was strongly criticized by the World Nuclear Association (WNA), rebutted in 2003, then dismissed by the WNA in 2006 based on its own life-cycle-energy calculation (with comparisons). The WNA also listed several other independent life cycle analyses which show similar emissions per kilowatt-hour from nuclear power and from renewables such as wind power

    0 Not allowed!



  10. [10]
    حسن هادي
    حسن هادي غير متواجد حالياً
    عضو متميز
    الصورة الرمزية حسن هادي


    تاريخ التسجيل: Nov 2006
    المشاركات: 1,338
    Thumbs Up
    Received: 7
    Given: 0
    بامكانكم متابعة الروابط وسوف نسترسل بالموضوع لاكماله تحياتي اخوكم حسن

    0 Not allowed!



  
صفحة 1 من 4 12 3 4 الأخيرةالأخيرة
الكلمات الدلالية لهذا الموضوع

عرض سحابة الكلمة الدلالية

RSS RSS 2.0 XML MAP HTML