Amit Chemistry

LOVELY PROFESSIONAL UNIVERSITY PHAGWARA, PUNJAB

TERM PAPER OF CHEMISTRY TOPIC:-

ENRICHMENT OF NUCLEAR FUEL.

D.O.A. :- 9TH SEPTEMBER 2009. D.O.R. :- 20TH OCTOBER 2009. D.O.S. :- 7TH DECEMBER 2009.

SUBMITTED TO :BY:MR. HARMANJEET SINGH DOSANG.

SUBMITTED AMIT KUMAR.

ROLL NO. :-

RB6903B63.

CHEMISTRY DEPPT. 10908297.

L.P.U. PHAGWARA.

REG. NO. :-

ACKNOWLEDGEMENT

With great pleasure and gratitude, I take this privilege to thank Almighty God for the blessings which, He has showered on me to complete this venture successfully. I also thank my parents for their blessings and prayers and love which led me to success. I express my sincere thanks to MR. HARMANJEET SINGH DOSANG for this valuable guidance, constrictive and creative criticisms and copious encouragement. Finally, my heartful thanks to my friends & all member of CHEMISTRY department, which provided good facility for editing the contents of my project.

A MIT KUMAR

ABSTRACT:Every intellectual of present age is well familier with the importance of “nuclear energy” in rapidly exploding world. My this report also deals with the same matter and I have tried my best to present the most relevant and latest matter related to “enrichment of nuclear fuel”. In my this project report I have tried to explain the theory and principle on which a nuclear power plant works. I have also included the latest applications and limitations of using nuclear power as a source of energy. Some relevant datas are also given which are available on internet in the form of tables and figures.

Introduction:In 1953, in a search for a cheap and efficient energy source, nuclear energy was introduced into America. . Nuclear power became quickly popular over increasingly scarce fossil fuels which were known to cause air pollution. It was quickly accepted by the public since it lowered the cost of electricity. (Bodansky, 21) Nuclear power is produced by splitting a nucleus of an atom is to release a powerful burst of energy. Nuclear power reactors generates heat that is converted into steam. The steam can be used directly for energy. This energy is used in transportation. Most military subs are now run by nuclear energy. The most used purpose of nuclear energy can also be used to generate electric power for example in a commercial nuclear power plant. Another way to produce nuclear energy is by gas-cooled reactors with either carbon dioxide or helium as the coolant instead of water. This method is used mainly in nuclear power plants in the United Kingdom and France due to lack of fresh water.

HISTORY:The first large-scale nuclear reactors were built during World War II. These reactors were designed for the production of plutonium for use in nuclear weapons. The only reprocessing required, therefore, was the extraction of the plutonium (free of fission-product contamination) from the spent natural uranium fuel. In 1943, several methods were proposed for separating the

relatively small quantity of plutonium from the uranium and fission products. The first method selected, a precipitation process called the Bismuth-Phosphate process, was developed and tested at the Oak Ridge National Laboratory (ORNL) in the 1943-1945 period to produce quantities of plutonium for evaluation and use in weapons programs. ORNL produced the first macroscopic quantities (grams) of separated plutonium with these processes. The Bismuth Phosphate process was first operated on a large scale at the Hanford Site, in the latter part of 1944. It was successful for plutonium separation in the emergency situation existing then, but it had a significant weakness: the inability to recover uranium. The first successful solvent extraction process for the recovery of pure uranium and plutonium was developed at ORNL in 1949. The PUREX process is the current method of extraction. Separation plants were also constructed at” Savannah River Site” and a smaller plant at WestValley, New York which closed by 1972 because of its inability to meet new regular requirements. Reprocessing of civilian fuel has long been employed in Europe, at the “COGEMA La Hague site” in France, the Sellafield site in the United Kingdom, the “Mayak Chemical Combine” in Russia, and at sites such as the Tokai plant in Japan, the Tarapur plant in India, and briefly at the “West Valley Reprocessing Plant” in the United States.In October 1976, fear of nuclear weapons proliferation (especially after India demonstrated nuclear weapons capabilities using reprocessing technology) led President “Gerald Ford” to issue a Presidential directive to indefinitely suspend the commercial reprocessing and recycling of plutonium in the U.S. On April 7, 1977 , President “Jimmy Carter” banned the reprocessing of commercial reactor spent nuclear fuel. The key issue driving this policy was the serious threat of nuclear weapons proliferation by diversion of plutonium from the civilian fuel cycle, and to encourage other nations to follow the USA lead. After that, only countries that already had large investments in reprocessing infrastructure continued to reprocess spent nuclear fuel. President Reagan lifted the ban in 1981, but did not provide the substantial subsidy that would have been necessary to start up commercial reprocessing.

THEORY:The nuclear fuel cycle is the series of industrial processes which involve the production of electricity from uranium in nuclear power reactors. Uranium is a relatively common element that is found throughout the world. It is mined in a number of countries and must be processed before it can be used as fuel for a nuclear reactor. Fuel removed from a reactor, after it has reached the end of its useful life, can be reprocessed to produce new fuel. The various activities associated with the production of electricity from nuclear reactions are referred to collectively as the nuclear fuel cycle. The nuclear fuel cycle starts with the mining of uranium and ends with

the disposal of nuclear waste. With the reprocessing of used fuel as an option for nuclear energy, the stages form a true cycle.

THE NUCLEAR FUEL CYCLE:-

SOURCE:- www.world-nuclear.org

Uranium- as nuclear fuel:Uranium is a slightly radioactive metal that occurs throughout the Earth's crust. It is about 500 times more abundant than gold and about as common as tin. It is present in most rocks and soils as well as in many rivers and in sea water. It is, for example, found in concentrations of about

four parts per million (ppm) in granite, which makes up 60% of the Earth's crust. In fertilisers, uranium concentration can be as high as 400 ppm (0.04%), and some coal deposits contain uranium at concentrations greater than 100 ppm (0.01%). Most of the radioactivity associated with uranium in nature is in fact due to other minerals derived from it by radioactive decay processes, and which are left behind in mining and milling. There are a number of areas around the world where the concentration of uranium in the ground is sufficiently high that extraction of it for use as nuclear fuel is economically feasible. Such concentrations are called ore.

Mining of uranium:Both excavation and in situ techniques are used to recover uranium ore. Excavation may be underground and open pit mining. In general, open pit mining is used where deposits are close to the surface and underground mining is used for deep deposits, typically greater than 120 m deep. Open pit mines require large holes on the surface, larger than the size of the ore deposit, since the walls of the pit must be sloped to prevent collapse. As a result, the quantity of material that must be removed in order to access the ore may be large. Underground mines have relatively small surface disturbance and the quantity of material that must be removed to access the ore is considerably less than in the case of an open pit mine. Special precautions, consisting primarily of increased ventilation, are required in underground mines to protect against airborne radiation exposure. An increasing proportion of the world's uranium now comes from in situ leach (ISL) mining, where oxygenated groundwater is circulated through a very porous ore body to dissolve the uranium oxide and bring it to the surface. ISL may be with slightly acid or with alkaline solutions to keep the uranium in solution. The uranium oxide is then recovered from the solution as in a conventional mill. The decision as to which mining method to use for a particular deposit is governed by the nature of the ore body, safety and economic considerations.

Uranium milling:Milling, which is generally carried out close to a uranium mine, extracts the uranium from the ore. Most mining facilities include a mill, although where mines are close together, one mill may process the ore from several mines. Milling produces a uranium oxide concentrate which is shipped from the mill. It is sometimes referred to as 'yellowcake' and generally contains more than 80% uranium. The original ore may contain as little as 0.1% uranium, or even less. In a mill, uranium is extracted from the crushed and ground-up ore by leaching, in which either a strong acid or a strong alkaline solution is used to dissolve the uranium oxide. The uranium oxide is then precipitated and removed from the solution. After drying and usually heating it is packed in 200-litre drums as a concentrate, sometimes referred to as 'yellowcake'. The remainder of the ore, containing most of the radioactivity and nearly all the rock material, becomes tailings, which are emplaced in engineered facilities near the mine (often in mined out pit). Tailings need to be isolated from the environment because they contain long-lived

radioactive materials in low concentrations and toxic materials such as heavy metals; however, the total quantity of radioactive elements is less than in the original ore, and their collective radioactivity will be much shorter-lived.

Conversion:The uranium oxide product of a uranium mill is not directly usable as a fuel for a nuclear reactor and additional processing is required. Only 0.7% of natural uranium is 'fissile', or capable of undergoing fission, the process by which energy is produced in a nuclear reactor. The form, or isotope, of uranium which is fissile is the uranium-235 (U-235) isotope. The remainder is uranium-238 (U-238). For most kinds of reactor, the concentration of the fissile uranium-235 isotope needs to be increased - typically to between 3.5% and 5% U-235. This is done by a process known as enrichment, which requires the uranium to be in a gaseous form. The uranium oxide concentrate is therefore first converted to uranium hexafluoride, which is a gas at relatively low temperatures. At a conversion facility, the uranium oxide is first refined to uranium dioxide, which can be used as the fuel for those types of reactors that do not require enriched uranium. Most is then converted into uranium hexafluoride, ready for the enrichment plant. The main hazard of this stage of the fuel cycle is the use of hydrogen fluoride. The uranium hexafluoride is then shipped in strong metal containers to the enrichment plant.The enrichment process separates gaseous uranium hexafluoride into two streams, one being enriched to the required level and known as low-enriched uranium; the other stream is progressively depleted in U-235 and is called 'tails'. In the dry process, uranium oxide concentrates are first calcined (heated strongly) to drive off some impurities, then agglomerated and crushed. For the wet process, the concentrate is dissolved in nitric acid. The resulting solution of uranyl nitrate UO2(NO3)2.6H2O is fed into a countercurrent solvent extraction process, using tributyl phosphate dissolved in kerosene or dodecane. The uranium is collected by the organic extractant, from which it can be washed out by dilute nitric acid solution and then concentrated by evaporation. The solution is then calcined in a fluidised bed reactor to produce UO3 (or UO2 if heated sufficiently). Purified U3O8 from the dry process and purified uranium oxide UO3 from the wet process are then reduced in a kiln by hydrogen to UO2: U3O8 + 2H2 ===> 3UO2 + 2H2O or UO3 + H2 ===> UO2 + H2O

deltaH = -109 kJ/mole deltaH = -109 kJ/mole

This reduced oxide is then reacted in another kiln with gaseous hydrogen fluoride (HF) to form uranium tetrafluoride (UF4), though in some places this is made with aqueous HF by a wet process: UO2 + 4HF ===> UF4 + 2H2O

deltaH = -176 kJ/mole

The tetrafluoride is then fed into a fluidised bed reactor or flame tower with gaseous fluorine to produce uranium hexafluoride, UF6. Hexafluoride ("hex") is condensed and stored. Removal of impurities takes place at each step. UF4 + F2 ===> UF6 The UF6, particularly if moist, is highly corrosive. When warm it is a gas, suitable for use in the enrichment process. At lower temperature and under moderate pressure, the UF6 can be liquefied. The liquid is run into specially designed steel shipping cylinders which are thick walled and weigh over 15 tonnes when full. As it cools, the liquid UF6 within the cylinder becomes a white crystalline solid and is shipped in this form. The siting of environmental and security management of a conversion plant is subject to the regulations that are in effect for any chemical processing plant involving fluorine-based chemicals.

World Primary Conversion capacity:Company

Capacity (tonnes U as UF6)

Cameco, Port Hope, Ont

12,500

Cameco, Springfields, UK

6000

JSC Enrichment & Conversion Co (Atomenergoprom), Irkutsk & Seversk, Ru

25,000*

Comurhex (Areva), Pierrelatte, Fr

14,500

Converdyn, Metropolis, USA

15,000

CNNC, Lanzhou IPEN, Brazil Total

3000 90 76,090 nameplate

WNA Market Report 2009

* operating capacity estimated at 12,000 to 18,000 tU/yr

ENRICHMENT:There are two enrichment processes in large scale commercial use, each of which uses uranium hexafluoride gas as feed: diffusion and centrifuge. These processes both use the physical properties of molecules, specifically the 1% mass difference between the two uranium isotopes,

to separate them. The product of this stage of the nuclear fuel cycle is enriched uranium hexafluoride, which is reconverted to produce enriched uranium oxide. • Most of the 470 commercial nuclear power reactors operating or under construction in the world today require uranium 'enriched' in the U-235 isotope for their fuel. 1. The main commercial processes employed for this enrichment involves gaseous uranium in centrifuges. An Australian process based on laser excitation is under development in the USA. 2. Prior to enrichment, uranium oxide must be converted to a fluoride. Uranium found in nature consists largely of two isotopes, U-235 and U-238. The production of energy in nuclear reactors is from the 'fission' or splitting of the U-235 atoms, a process which releases energy in the form of heat. U-235 is the main fissile isotope of uranium. Natural uranium contains 0.7% of the U-235 isotope. The remaining 99.3% is mostly the U-238 isotope which does not contribute directly to the fission process (though it does so indirectly by the formation of fissile isotopes of plutonium). Uranium-235 and U-238 are chemically identical, but differ in their physical properties, particularly their mass. The nucleus of the U-235 atom contains 92 protons and 143 neutrons, giving an atomic mass of 235 units. The U-238 nucleus also has 92 protons but has 146 neutrons - three more than U-235, and therefore has a mass of 238 units. The difference in mass between U-235 and U-238 allows the isotopes to be separated and makes it possible to increase or "enrich" the percentage of U-235. All present enrichment processes, directly or indirectly, make use of this small mass difference. Some reactors, for example the Canadian-designed Candu and the British Magnox reactors, use natural uranium as their fuel. Most present day reactors (Light Water Reactors or LWRs) use enriched uranium where the proportion of the U-235 isotope has been increased from 0.7% to about 3% or up to 5%. (For comparison, uranium used for nuclear weapons would have to be enriched in plants specially designed to produce at least 90% U-235.)

The large Tricastin enrichment plant in France (beyond cooling towers) The four nuclear reactors in the foreground provide over 3000 MWe power for it

Fuel fabrication:Reactor fuel is generally in the form of ceramic pellets. These are formed from pressed uranium oxide which is sintered (baked) at a high temperature (over 1400°C). The pellets are then encased in metal tubes to form fuel rods, which are arranged into a fuel assembly ready for introduction into a reactor. The dimensions of the fuel pellets and other components of the fuel assembly are precisely controlled to ensure consistency in the characteristics of the fuel. In a fuel fabrication plant great care is taken with the size and shape of processing vessels to avoid criticality (a limited chain reaction releasing radiation). With low-enriched fuel criticality is most unlikely, but in plants handling special fuels for research reactors this is a vital consideration.

Power generation and burn-up:Inside a nuclear reactor the nuclei of U-235 atoms split (fission) and, in the process, release energy. This energy is used to heat water and turn it into steam. The steam is used to drive a turbine connected to a generator which produces electricity. Some of the U-238 in the fuel is turned into plutonium in the reactor core. The main plutonium isotope is also fissile and this yields about one third of the energy in a typical nuclear reactor. The fissioning of uranium (and

the plutonium generated in situ) is used as a source of heat in a nuclear power station in the same way that the burning of coal, gas or oil is used as a source of heat in a fossil fuel power plant. Typically, some 44 million kilowatt-hours of electricity are produced from one tonne of natural uranium. The production of this amount of electrical power from fossil fuels would require the burning of over 20,000 tonnes of black coal or 8.5 million cubic metres of gas. An issue in operating reactors and hence specifying the fuel for them is fuel burn-up. This is measured in gigawatt-days per tonne and its potential is proportional to the level of enrichment. Hitherto a limiting factor has been the physical robustness of fuel assemblies, and hence burn-up levels of about 40 GWd/t have required only around 4% enrichment. But with better equipment and fuel assemblies, 55 GWd/t is possible (with 5% enrichment), and 70 GWd/t is in sight, though this would require 6% enrichment. The benefit of this is that operation cycles can be longer - around 24 months - and the number of fuel assemblies discharged as used fuel can be reduced by one third. Associated fuel cycle cost is expected to be reduced by about 20%.As with as a coal-fired power station about two thirds of the heat is dumped, either to a large volume of water (from the sea or large river, heating it a few degrees) or to a relatively smaller volume of water in cooling towers, using evaporative cooling (latent heat of vapourisation).

increases.

Used fuel:With time, the concentration of fission fragments and heavy elements formed in the same way as plutonium in the fuel will increase to the point where it is no longer practical to continue to use the fuel. So after 12-24 months the 'spent fuel' is removed from the reactor. The amount of energy that is produced from a fuel bundle varies with the type of reactor and the policy of the reactor operator. 1. When removed from a reactor, the fuel will be emitting both radiation, principally from the fission fragments, and heat. 2. Used fuel is unloaded into a storage pond immediately adjacent to the reactor to allow the radiation levels to decrease. In the ponds the water shields the radiation and absorbs the heat. Used fuel is held in such pools for several months to several years. 3. Depending on policies in particular countries, some used fuel may be transferred to central storage facilities. Ultimately, used fuel must either be reprocessed or prepared for permanent disposal.

Reprocessing:Used fuel is about 95% U-238 but it also contains about 1% U-235 that has not fissioned, about 1% plutonium and 3% fission products, which are highly radioactive, with other transuranic elements formed in the reactor. In a reprocessing facility the used fuel is separated into its three components: uranium, plutonium and waste, which contains fission products. Reprocessing enables recycling of the uranium and plutonium into fresh fuel, and produces a significantly reduced amount of waste (compared with treating all used fuel as waste). See page on Processing of Used Nuclear Fuel. The uranium from reprocessing, which typically contains a slightly higher concentration of U235 than occurs in nature, can be reused as fuel after conversion and enrichment, if necessary. The plutonium can be directly made into mixed oxide (MOX) fuel, in which uranium and plutonium oxides are combined. In reactors that use MOX fuel, plutonium substitutes for the U235 in normal uranium oxide fuel.

Disposal OF USED FUEL:At the present time, there are no disposal facilities (as opposed to storage facilities) in operation in which used fuel, not destined for reprocessing, and the waste from reprocessing, can be placed. Although technical issues related to disposal have been addressed, there is currently no pressing technical need to establish such facilities, as the total volume of such wastes is relatively small. Further, the longer it is stored the easier it is to handle, due to the progressive

diminution of radioactivity. There is also a reluctance to dispose of used fuel because it represents a significant energy resource which could be reprocessed at a later date to allow recycling of the uranium and plutonium. There is also a proposal to use it in Candu reactors directly as fuel. This proposal, known as DUPIC (direct use of used PWR fuel in Candu reactors) is covered at the end of the page on Processing of Used Nuclear Fuel. A number of countries are carrying out studies to determine the optimum approach to the disposal of used fuel and wastes from reprocessing. The general consensus favours its placement into deep geological repositories, initially recoverable before being permanently sealed.

Wastes:Wastes from the nuclear fuel cycle are categorised as high-, medium- or low-level wastes by the amount of radiation that they emit. These wastes come from a number of sources and include: 1. low-level waste produced at all stages of the fuel cycle; 2. intermediate-level waste produced during reactor operation and by reprocessing; 3. high-level waste, which is waste containing fission products from reprocessing, and in many countries, the used fuel itself. The enrichment process leads to the production of much 'depleted' uranium, in which the concentration of U-235 is significantly less than the 0.7% found in nature. Small quantities of this material, which is primarily U-238, are used in applications where high density material is required, including radiation shielding and some is used in the production of MOX fuel. While U-238 is not fissile it is a low specific activity radioactive material and some precautions must, therefore, be taken in its storage or disposal.

Material balance in the nuclear fuel cycle:The following figures may be regarded as typical for the annual operation of a 1000 MWe nuclear power reactor: Mining

: 20,000 tonnes of 1% uranium ore.

Milling

: 230 tonnes of uranium oxide concentrate (which contains 195 tonnes of U-235).

Conversion

:288 tonnes uranium hexafluoride, UF6 (with 195 t U).

Enrichment

: 35 tonnes enriched UF6 (containing 24 t enriched U) - balance is 'tails'.

Fuel fabrication : 27 tonnes UO2 (with 24 t enriched U).

APPLICATIONS:Nuclear power has many applications and usages in different fields apart from that of energy production. 1. Scientific research:- Scientists can now use nuclear power for biological research to

help understand life more. Radioactive isotopes have been described as the most useful research tool since the invention of the microscope. Physiologists use them to learn where and at what speed physical and chemical processes occur in the human body. 2. Agriculture:- Isotopes are also used for agricultural Biologists use radioactive isotopes to see how plants absorb chemicals as they grow. With radioactive cobalt, botanists can produce new types of plants. Structural variations that normally take years of selective breeding to develop can be made to occur in a few months 3. Energy production:-.Despite this, fossil fuels such as coal, are needed in greater quantities to produce the equivalent amount of electricity produced by nuclear power using Uranium 235 or Plutonium 239. Using nuclear power instead of other sources such as coal, has reduced the carbon dioxide emissions by over 2 billion tons per year. This is a positive effect since it helps to reduce global warming, since carbon dioxide makes up half of all man- made gases which contribute to the Greenhouse Effect. 4. Sustainable Energy:-Nuclear technologies can be used in a wide range of applications to help reduce greenhouse gas emissions and combat climate change, in addition to electricity generation. 5.

Food and agriculture:-Radioisotopes and radiation used in food and agriculture are some of the 800 million people who are chronically malnourished, and tens of thousands who die daily from hunger and hunger-related causes.

6. Insect Control:-Insects are estimated to cause the loss of 25-35% of crops in developing countries. Chemical insecticides have used for many years , but they have not always been effective. 7. Food Preservation :- Some 25-30% of the food harvested is lost as a result of spoilage by microbes and pests. In all parts of the world there is growing use of irradiation technology to preserve food. Food irradiation works by exposing raw foods to high levels of gamma radiation which kills bacteria and other harmful organisms without affecting the nutritional value of food itself or leaving any residue. It is the only means of killing bacterial pathogens in raw and frozen food. Of course, irradiation of food does not make it radioactive.

8. Medical Diagnosis:-Radioisotopes are an essential part of diagnostic treatment. An advantage over x-ray techniques is that both bone and soft tissue can be imaged very successfully. A major use of radioisotopes for diagnosis is in radio-immunoassays for biochemical analysis. Very low concentrations of hormones, enzymes, hepatitis virus, some drugs and a range of other substances in a sample of the patient's blood can be measured with these techniques. The patient never comes in contact with the radioisotopes used in the diagnostic tests. In the USA alone it is estimated that some 40 million such tests are carried out each year . 9. Smoke Detector :-One of the commonest uses of radioisotopes today is in household smoke detectors. These contain a small amount of americium-241 which is a decay product of plutonium-241 originating in nuclear reactors. The Am-241 emits alpha particles which ionize the air and allow a current between two electrodes. If smoke enters the detector it absorbs the alpha particles and interrupts the current, setting off the alarm 10. Radioisotopic Dating:-Analysis of radioisotopes is of vital importance in determining the age of rocks and other materials that are of interest to geologists, anthropologists and archaeologists. .

LIMITATIONS:power is not perfect. There are many problems with of the radioactive waste byproduct. It is a threat to the environment and people around it if it is not contained properly. and temporarily disposed of with maximum security. There are many problems with of the radioactive waste byproduct. 1. It is a threat to the environment and people around it if it is not contained properly. and temporarily disposed off with maximum security. 2. Disposing of nuclear waste is extremely difficult since it takes thousands of years for it to decompose. In addition to the environmental effects of disposing of the nuclear waste, the potential of the disaster of radioactive fallout from a reactor is an extremely dangerous possibility. This has been shown by the effects of the Chernobyl in 1986. This was caused by an unauthorized experiment conducted with the cooling system turned off which lead to the explosion of one of the reactors. The radioactive fallout spread through the atmosphere, going all the way into northern Europeand Great Britain. There were 31 casualties resulting directly from the accident, but the total deaths due to radiation will never be determined. The radiation has even caused genetic mutations in children whose parents were exposed to the radiation. 3. Uranium is only weakly radioactive, and its chemical toxicity - especially as UF6 - is more significant than its radiological toxicity. The protective measures required for an enrichment plant are therefore similar to those taken by other chemical industries concerned with the production of fluorinated chemicals.

4. Uranium hexafluoride forms a very corrosive material (HF - hydrofluoric acid) when exposed to moisture, therefore any leakage is undesirable. Hence in almost all areas of a centrifuge plant the pressure of the UF6 gas is maintained below atmospheric pressure and thus any leakage could only result in an inward flow;

Conclusion:Nuclear power is power (generally electrical) produced from controlled (i.e., non-explosive) nuclear reactions. Commercial plants in use to date use nuclear fission reactions. Electric utility reactors heat water to produce steam, which is then used to generate electricity. In 2007, 14% of the world's electricity came from nuclear power, despite concerns about safety and radioactive waste management. More than 150 naval vessels using nuclear propulsion have been built. Nuclear fusion reactions are widely believed to be safer than fission and appear potentially viable, though technically quite difficult. Fusion power has been under intense theoretical and experimental investigation for many years. Both fission and fusion appear promising for some space propulsion applications in the mid- to distant-future, using low thrust for long durations to achieve high mission velocities. Radioactive decay has been used on a relatively small (few kW) scale, mostly to power space missions and experiments. As of 2007, Watts Bar 1, which came on-line in February 7, 1996, 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, even in the U.S. and throughout Europe, investment in research and in the nuclear fuel cycle has continued, and some nuclear industry experts predict electricity shortages, fossil fuel price increases, global warming and heavy metal emissions from fossil fuel use, new technology such as passively safe plants, and national energy security will renew the demand for nuclear power plants. According to the World Nuclear Association, globally during the 1980s one new nuclear reactor started up every 17 days on average, and by the year 2015 this rate could increase to one every 5 days. Many countries remain active in developing nuclear power, including Pakistan, 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). Several EU member states actively pursue nuclear programs, while some other member states continue to have a ban for the nuclear energy use. 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 loan guarantees 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. 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.

Brunswick Nuclear Plant discharge canal There is a possible impediment to production of nuclear power plants as only a few companies worldwide have the capacity to forge single-piece reactor pressure vessels, which are necessary in most reactor designs. Utilities across the world are submitting orders years in advance of any actual need for these vessels. Other manufacturers are examining various options, including making the component themselves, or finding ways to make a similar item using alternate methods. Other solutions include using designs that do not require single-piece forged pressure vessels such as Canada's Advanced CANDU Reactors or Sodium-cooled Fast Reactor.

Refrences:-

REFRENCES

In the last, I greatfully acknowledge and express my gratitude to all staff members of following sites who supported me in preparing this project. • www.google.com • www.wikkipedia.com • www.WORLD-NUCLEAR.org

BOOKS: • R. CHANG • ADVANCED CHEMISTRY