Stages of the Nuclear Fuel Cycle

The nuclear fuel cycle uses uranium in different chemical and physical forms. As illustrated below, this cycle typically includes the following stages:

• Uranium recovery to extract (or mine) uranium ore, and concentrate (or mill) the ore to produce "yellowcake"
• Conversion of yellowcake into uranium hexafluoride (UF₆)
• Enrichment to increase the concentration of uranium-235 (U²³⁵) in UF₆
• Deconversion to reduce the hazards associated with the depleted uranium hexafluoride (DUF₆), or "tailings," produced in earlier stages of the fuel cycle
• Fuel fabrication to convert enriched UF₆ into fuel for nuclear reactors
• Use of the fuel in reactors (nuclear power, research, or naval propulsion)
• Interim storage of spent nuclear fuel
• Reprocessing (or recycling) of high-level waste (currently not done in the U.S.) ^[1]
• Final disposition (disposal) of high-level waste

^[1]  Neither a recycling/reprocessing facility nor a Federal waste repository is currently approved (licensed) in the United States, and spent fuel is in interim storage. However, the NRC is currently reviewing a license application for a new Mixed-Oxide Fuel Fabrication Facility, which would recycle surplus weapon-grade plutonium, remove impurities, and mix it with uranium oxide to form mixed-oxide (MOX) fuel pellets for use in reactor fuel assemblies. For additional information, see the Backgrounder on Mixed Oxide Fuel and the Frequently Asked Questions About Mixed Oxide Fuel.

Resource: http://www.nrc.gov/materials/fuel-cycle-fac/stages-fuel-cycle.html

What is the Nuclear Fuel Cycle

Uranium, as it is mined from the earth's crust, is not directly useable for power generation. Much processing must be carried out to concentrate the fissile isotope U-235 before uranium can be used efficiently to generate electricity.
More so than other energy resources such as coal, oil and natural gas, uranium has its own distinctive and very complicated fuel cycle. This is called the 'Nuclear Fuel Cycle'. There are several steps in the nuclear fuel cycle - mining and milling, conversion, enrichment, and fuel fabrication. These steps are known as the 'front end' of the cycle.
Once uranium becomes 'spent fuel' (after being used to produce electricity), the 'back end'  of the cycle follows. This may include: temporary storage, reprocessing, recycling, and waste disposal.




Resource:http://www.uraniumsa.org/fuel_cycle/nfcycle.htm

Fukushima Daiichi Incident (details, analysis)

Resource:Fukushima Daiichi Incident (details, analysis)

Fukushima Daiichi incident -11 march 2011

The Great East Japan Earthquake* with magnitude 9.0 at 2.46 pm on Friday 11 March did considerable damage in the region, and the large tsunami it created caused very much more. The earthquake was centred 130 km offshore the city of Sendai in Miyagi prefecture on the eastern cost of Honshu Island (the main part of Japan), and was a rare and complex double quake giving a severe duration of about 3 minutes. Japan moved a few metres east and the local coastline subsided half a metre.  The tsunami inundated about 560 sq km and resulted in a human death toll of over 20,000.

Eleven reactors at four nuclear power plants in the region were operating at the time and all shut down automatically when the quake hit. The operating units which shut down were Tepco's Fukushima Daiichi 1, 2, 3, Fukushima Daini 1, 2, 3, 4, Tohoku's Onagawa 1, 2, 3, and Japco's Tokai, total 9377 MWe net. Fukushima Daiichi units 4-6 were not operating at the time, but were affected, total 2587 MWe net (units 4-6). Onagawa 1 briefly suffered a fire in the turbine building, but the main problem initially centred on Fukushima Daiichi units 1-3. Unit 4 became a problem on day five.

The reactors proved robust seismically, but vulnerable to the tsunami. Power, from grid or backup generators, was available to run the Residual Heat Removal (RHR) system cooling pumps at eight of the eleven units, and despite some problems they achieved 'cold shutdown' within about four days. The other three, at Fukushima Daiichi, lost power at 3.42 pm, almost an hour after the quake, when almost the entire site lost the ability to maintain proper reactor cooling and water circulation functions due to being flooded by the 15-metre tsunami.  This disabled 12 of 13 back-up generators on site, located in the basements of the turbine buildings, and also the heat exchangers for dumping reactor heat to the sea.  Electrical switchgear was also disabled.

Thereafter, many weeks of focused work centred on restoring heat removal from the reactors and coping with overheated spent fuel ponds. This was undertaken by hundreds of Tepco employees as well as some contractors, supported by firefighting and military personnel. Some of the Tepco staff had lost homes, and even families, in the tsunami, and were initially living in temporary accommodation under great difficulties and privation, with some personal risk. Media coverage of the Fukushima drama often ignored the context of the enormous natural disaster which greatly affected how it played out.  A hardened emergency response centre on site proved very helpful in grappling with the situation.

Three Tepco employees at the Daiichi plant were killed directly by the earthquake and tsunami.
Among hundreds of aftershocks, an earthquake with magnitude 7.1, closer to Fukushima than the 11 March one, was experienced on 7 April, but without further damage to the plant.  The epicenter was 120 km from Fukushima but only 20 km from Onagawa, where power supply was affected.  On 11 April a magnitude 7.1 earthquake and on 12 April a magnitude 6.3 earthquake, both with epicenter at Fukushima-Hamadori, caused no further problems.

Resource:Fukushima accident
Additional:Timeline for the Fukushima Daiichi nuclear power plant accident
Picture:Fukushima Daiichi Nuclear Plant Hi-Res Photos

Patchy global support for nuclear new-build

25 November 2011 

A worldwide poll has shown widely varying levels of support for the use of nuclear energy. A large majority in countries that use nuclear want to keep doing so, but only a few nations showed strong support for new build. 

The poll included some 23 countries and gave respondents three options for what should be done regarding the use of nuclear power plants: shut them down as soon as possible; build new ones; or keep using current plants but not build more.

The question on nuclear was one of two on energy that were part of a larger GlobeScan questionnaire conducted by telephone or face-to-face. Half of 23,231 interviewees were asked one or other of the energy questions.

Among the 12 polled nations already using the energy source, countries that expressed dominant anti-nuclear views were Germany, Mexico, Russia and Spain with respective shares of 52%, 43%, 43% and 55% opting to shut nuclear plants as soon as possible. Taking the opposite view were China, Pakistan, the UK and USA with dominant shares of 42%, 39%, 37% and 39% saying new nuclear power plants should be built.

Anti-nuclear views in Russia were noted to have more than doubled since 2005 when the same question was asked, with a corresponding drop of more than half in the number of people supporting new build.

Other countries in this sector included Brazil, France and Japan, which recorded 35%, 25% and 37% wanting nuclear plants shut down against a body of overall support of 60%, 73% and 63% choosing to either keep operating plants or build new ones. In India some 38% of people recorded no opinion with the remainder split quite evenly between the three choices.

In total the 12 countries polled that use nuclear energy counted 61% of people as supporting continued operation or new build (39% and 22%) with 30% saying nuclear should be shut down immediately.

The same question was also asked of people in countries not using nuclear energy: Chile, Ecuador, Egypt, Ghana, Indonesia, Kenya, Nigeria, Panama, Peru, Philippines and Turkey.

Among those are four that are actively preparing to a possible start in nuclear energy. The technology was most opposed in Chile (55% calling for shutdown) and Turkey (41%). Egypt, however, saw 61% overall support for continued operation and new build;  51%.
 
Researched and written
by World Nuclear News

Resource: Patchy global support for nuclear new build

How it works..

This is how the power plant work.

Nuclear power stations work in pretty much the same way as fossil fuel-burning stations, except that a "chain reaction" inside a nuclear reactor makes the heat instead.

The reactor uses Uranium rods as fuel, and the heat is generated by nuclear fission: neutrons smash into the nucleus of the uranium atoms, which split roughly in half and release energy in the form of heat.

Carbon dioxide gas or water is pumped through the reactor to take the heat away, this then heats water to make steam. The steam drives turbines which drive generators.

Modern nuclear power stations use the same type of turbines and generators as conventional power stations.

In Britain, nuclear power stations are often built on the coast, and use sea water for cooling the steam ready to be pumped round again. This means that they don't have the huge "cooling towers" seen at other power stations. 

The reactor is controlled with "control rods", made of boron, which absorb neutrons. When the rods are lowered into the reactor, they absorb more neutrons and the fission process slows down. To generate more power, the rods are raised and more neutrons can crash into uranium atoms. 

Resource:Energy Resources: Nuclear power

Iran vows no retreat on nuclear program

Posted By: TOE, NEW YORK, on 2011-11-09 

Tehran - Iranian President Mahmoud Ahmadinejad says his county will not retreat “an iota” from its nuclear path, in the wake of a report that raises concerns Tehran is seeking to develop nuclear weapons.

He also rejected the findings of the report by the International Atomic Energy Agency while speaking at a rally shown Wednesday on Iranian state television.

On Tuesday, the IAEA said it had “credible” information that Tehran had engaged in activities aimed at developing nuclear weapons.

In its report, the U.N.'s nuclear watchdog agency said it had “serious concern” about the information indicating Iran has worked on a nuclear weapon design, including the “testing of components.”

Some world powers have long suspected that Iran has nuclear weapons ambitions — a charge Tehran has repeatedly denied.

The European Union said Wednesday that the IAEA report “seriously aggravates existing concerns” about Iran's nuclear program.

Meanwhile, France said world powers need to impose “unprecedented” sanctions on Iran if it rejects cooperation on its nuclear program. The U.N. Security Council has already imposed four rounds of sanctions on Iran.

On Tuesday, the U.S. said the report may lead it to impose additional sanctions on Iran.

China and Russia have taken a different stance. China said Wednesday that it is still studying the IAEA report and called for a peaceful resolution of the Iranian nuclear issue. 

Russia criticized the IAEA for distributing the report to the agency's 35-nation governing board. In a statement Tuesday, the Russian foreign ministry said the move appeared to be intended to prevent a diplomatic solution to the dispute at a time when there is a chance for renewed talks between Iran and world powers.

Resource: Times of Earth

Nuclear INFO...

There are several nuclear web link below, check it out...

world-nuclear-news
nuclearinfo.net

Nuclear Fusion

Original Video Link

Chernobyl Accident 1986

The April 1986 disaster at the Chernobyl nuclear power plant in Ukraine was the product of a flawed Soviet reactor design coupled with serious mistakes made by the plant operators.  It was a direct consequence of Cold War isolation and the resulting lack of any safety culture.

 

The accident destroyed the Chernobyl 4 reactor, killing 30 operators and firemen within three months and several further deaths later. One person was killed immediately and a second died in hospital soon after as a result of injuries received. Another person is reported to have died at the time from a coronary thrombosis. Acute radiation syndrome (ARS) was originally diagnosed in 237 people on-site and involved with the clean-up and it was later confirmed in 134 cases. Of these, 28 people died as a result of ARS within a few weeks of the accident. Nineteen more subsequently died between 1987 and 2004 but their deaths cannot necessarily be attributed to radiation exposure. Nobody off-site suffered from acute radiation effects although a large proportion of childhood thyroid cancers diagnosed since the accident is likely to be due to intake of radioactive iodine fallout. Furthermore, large areas of Belarus, Ukraine, Russia and beyond were contaminated in varying degrees.

The Chernobyl disaster was a unique event and the only accident in the history of commercial nuclear power where radiation-related fatalities occurred. However, the design of the reactor is unique and the accident is thus of little relevance to the rest of the nuclear industry outside the then Eastern Bloc.

Read here for more details...
Click here "Chernobyl Accident 1986"

How Nuclear Energy works

Original video link

How a Nuclear Power Plant Works

Original video link

Nuclear Energy

Advantages of Nuclear Energy

1- The Earth has limited supplies of coal and oil. Nuclear power plants could still produce electricity after coal and oil become scarce.

2- Nuclear power plants need less fuel than ones which burn fossil fuels. One ton of uranium produces more energy than is produced by several million tons of coal or several million barrels of oil.

3- Coal and oil burning plants pollute the air. Well-operated nuclear power plants do not release contaminants into the environment.

Disadvantages of Nuclear Energy

The nations of the world now have more than enough nuclear bombs to kill every person on Earth. The two most powerful nations -- Russia and the United States -- have about 50,000 nuclear weapons between them. What if there were to be a nuclear war? What if terrorists got their hands on nuclear weapons? Or what if nuclear weapons were launched by accident?

1-  Nuclear explosions produce radiation. The nuclear radiation harms the cells of the body which can make people sick or even kill them. Illness can strike people years after their exposure to nuclear radiation.
2-  One possible type of reactor disaster is known as a meltdown. In such an accident, the fission reaction goes out of control, leading to a nuclear explosion and the emission of great amounts of radiation.
* In 1979, the cooling system failed at the Three Mile Island nuclear reactor near Harrisburg, Pennsylvania. Radiation leaked, forcing tens of thousands of people to flee. The problem was solved minutes before a total meltdown would have occurred. Fortunately, there were no deaths.
* In 1986, a much worse disaster struck Russia's Chernobyl nuclear power plant. In this incident, a large amount of radiation escaped from the reactor. Hundreds of thousands of people were exposed to the radiation. Several dozen died within a few days. In the years to come, thousands more may die of cancers induced by the radiation.

3-  Nuclear reactors also have waste disposal problems. Reactors produce nuclear waste products which emit dangerous radiation. Because they could kill people who touch them, they cannot be thrown away like ordinary garbage. Currently, many nuclear wastes are stored in special cooling pools at the nuclear reactors.
* The United States plans to move its nuclear waste to a remote underground dump by the year 2010.
* In 1957, at a dump site in Russia's Ural Mountains, several hundred miles from Moscow, buried nuclear wastes mysteriously exploded, killing dozens of people.

4-  Nuclear reactors only last for about forty to fifty years.

The Future of Nuclear Energy

Some people think that nuclear energy is here to stay and we must learn to live with it. Others say that we should get rid of all nuclear weapons and power plants. Both sides have their cases as there are advantages and disadvantages to nuclear energy. Still others have opinions that fall somewhere in between.

What do you think we should do? After reviewing the pros and cons, it is up to you to formulate your own opinion. Read more about the politics of the issues or go to the forum to share your own opinions and see what others think.

Nuclear power plant for Malaysia?

The nuclear energy is the greenest energy currently available on Earth. James Lovelock, a scientist, environmentalist, futurologist and the father of Gaia Hypothesis wrote in his book: “The Vanishing Face of Gaia: A Final Warning”, that the nuclear energy is indeed greener than any other form of power generating plants including solar voltaic and wind energy farm. A 1GW wind farm requires 2 millions tons of concrete, enough to build 30,000 homes for 100,000 people. That quantity of concrete would release 1 million tons of carbon dioxide into the air.

The under-construction Bakun Dam, located in Sarawak on the Balui River, will be the tallest concrete-faced rockfill dam in the world and the largest dam in Asia outside of China. Its powerhouse with 8 penstocks to powertrains comprising 8 vertical shaft Francis turbines of 300MW each, 8 air-cooled generators of 360MVA each and 8 oil-immersed transformers (360MVA each) will generate about 2.4GW of electricity. The dam has 16.71 million cubic meters of filled volume. With catchment area of 14,750 km square, its gross storage capacity is 43,800 million cubic meters. How much concrete is required to build this dam? How much carbon dioxide will be released by the concrete? How much biodiversity would have perished under catchment area that large?

I read from various sources about people’s objections (including politicians’) of this nuclear energy project. This should not be a political issue and never be one. This should be an environmental, safety and social-economic issues at top.

TNB, the sole electricity distributor/supplier in Malaysia is not the sole energy producer. TNB buys, under contract, energy from many other producers. Unfair advantages, unscrupulous practice and increasing fuel cost in the produce-supply chain have contributed to rising energy cost, leading Malaysians to cry foul. The substandard service provided by TNB worsens the situation. As a corporation with revenue of MYR25.75 billion and net income of MYR2.6 billion as of fiscal year 2008, TNB is cutting more corners to reduce its operating costs and to maximize its profit with unhealthy practices, e.g. bi-monthly meter reading practice has stirred uproars in recent week. Being greenest, nuclear energy is more profitable than any other energy production. Could this help to reduce electricity cost for Malaysians considering the unhealthy practices and unfair advantages TNB has in its glossary bag?

I am not going to write more about TNB’s malpractice and sluggish substandard service. Ask any Malaysians, they will be able to tell you stories whole day and night. Instead, I am going to write more about safety.

The next question: Is it really safe to have nuclear power plant in Malaysia? This question does not imply that nuclear power plant is not safe. Rather, the human factors in managing and operating the nuclear power plant.

Alongside the nuclear physics in the power plant is the safety critical computer system, which includes both hardware and software, that is used to control and monitor the nuclear power plant. This safety critical system is the most crucial part and the entire operation of a nuclear power plant heavily relies on it.

Safety critical system is a computer (including software), electronic or electromechanical system whose failure may be a catastrophe, causing injury or death to human beings. This safety critical system comprises high integrity software. The safety critical system, both hardware and software, will likely be integrated and maintained by foreign contractors.

Nuclear power plant software are developed using Ada and/or SPARK programming language. SPARK is a subset of Ada. In the mid 1990s, UTM (University Technology Malaysia) KL campus was teaching Ada in CASE (Center for Advanced Software Engineering). At that time, CASE was a collaboration between UTM and Thomson CSF under special arrangement between the government of France and Malaysia. The Ada course was not long lived. Two years later, it was replaced by Java due to ignorance and market driven trends. Java is not a suitable candidate for high integrity, safety critical, real-time and distributed application development. Today, none of the universities in Malaysia is teaching Ada. According to my hitherto knowledge, apparently none of the Malaysia academies have submitted any high integrity and safety critical system related papers in international conferences and scientific journals.

It does not only require software engineers with Ada or SPARK knowledge. In safety critical software engineering, the individual developers, the entire team and organization are required to go through rigorous software development and safety critical validation processes. It takes years to achieve Carnegie-Mellon’s SEI (Software Engineering Institute) CMM (Capability Maturity Model) Level 5. Safety critical system development requires utterly strong discipline and engineering ethics in every requirement, design, development, testing and maintenance process and every process needs to be validated. Other than software process, there are many other non-software related risk assessments to comply.

Malaysia lacks qualified software engineers of such competency to develop and to maintain high integrity software system. It is costly to maintain such system by contract. The maintenance will increase the cost of energy production and hence will be borne by consumers.

The safety critical system of a nuclear power plant must be thoroughly tested with proven track records. With the loosey-goosey attitude of many Malaysians, will they have capability to manage the system and safety critical issues? Will they be effective to respond to emergencies, for example, system shutdown or nuclear melt down?

The disposal of nuclear waste poses another safety issue. If the engine of a RMAF (Royal Malaysia Air Force) fighter jet could go missing and be exported, can you imagine the potential hazard of missing nuclear waste?

Objection should be rational, not emotional. It is imbecilic to politicize the objection without scrutinizing facts. I, in my book, embrace nuclear energy for it is the greenest energy. On the contrary, I do not have any confidence in the management of safety related issues in Malaysia.

Suggest way forward for Malaysia

Malaysia is actually blessed with plenty of natural sources of renewable energy, being located in a tropical region. Solar, wind and hydro energies could be utilised to complement the current fossil fuel power plants for power generation

Renewable energy should be the way to go when seeking for alternatives to fossil fuel power generation. It is also because we need to ensure that the environment is taken into consideration in this matter.
Nuclear power plants are more efficient compare to other plant. New technology developed has made them more reliable and safer. Based of that reason,more and more nations developed nuclear plant in their country.Besides,nuclear power plant can reduce greenhouse gas emissions. This is remain as big issue since most of the people that support nuclear power plant believed that no carbon dioxide is released into the air as no coal or fossil fuels are burnt. Since there are no carbon emissions nuclear power is also considered clean energy source just like solar, wind or geothermal energy.

Another reason why we must consider to develop nuclear power plant is that the initial cost of building nuclear plants is high but the running costs are relatively low. One reason the costs are low is that nuclear plants need only a small amount of uranium to produce a lot of energy. In fact, if the cost of uranium doubled, costs would only be increased by 7%. It is believed that 1 truck of uranium produces as much energy as 1000 trucks of coal.Besides,it also can reduces our dependences on foreign oils and natural gas like biofuels. America, for example imports a lot of oil and natural gas from other countries. The price of these products is not fixed and change very quickly. If the price increases quickly, consumers have to pay more for their electricity (which they may not be able to afford). All newly built nuclear power plants need to satisfy maximum safety standards, and the newest nuclear reactor designs really ensure maximum safety by applying the concept of the negative feedback loop, which ensures that as the nuclear reactor's power output increases, it becomes more and more harder to squeeze any more power out of it, meaning that nuclear chain reaction that could lead to nuclear reactor explosion is almost impossible to happen. Though this design is not totally foolproof it is much safer compared to the older designs.

Nuclear power plants do not need fossil fuels to produce electricity, and this means that they do not release harmful carbon emissions that contribute to pollution and climate change problem.In order to properly operate nuclear power plants require nuclear fuel. Nuclear fuel mostly used in nuclear power plants in uranium though some nuclear power plants also use plutonium. Uranium is plentiful in United States, and building more nuclear power plants would therefore contribute to better energy independence as there would be reduced need for importing expensive foreign fuels.Nuclear power plants operate very efficiently and reliably. Their efficiency is comparable to coal power plants, and once they are built they are extremely reliable given that there's enough uranium to feed them, and as already said there is plenty of uranium in United States.

The main disadvantage of nuclear power plants is no doubt nuclear radioactive waste that has lifespan of more than 5000 years so more new nuclear power plants will mean more radioactive waste, and current nuclear waste storage options definitely do not ensure totally safe storage for the next 5000 years or so. Another challenge is how to protect a nuclear power plant from earthquakes, which can damage reactor containment structures and expose the nation to the risk of radiation leaks. Areas around Janda Baik and Bentong, towns in the Malaysian state of Pahang, have experienced minor quakes twice in the past few years. Volcanic eruptions in nearby Indonesia have also shaken some areas, although Malaysia is not located in the Pacific "ring of fire" that is home to most of the world's volcanoes. Malaysia cannot afford to risk building a nuclear plant in an area that could be vulnerable to a volcano or earthquake; the consequences would be too devastating.

Proponents of nuclear power point to the current energy situation in Malaysia as evidence that new energy sources must be developed. Government officials believe that Malaysia's current energy sources will not be sustainable beyond 2020, and that the depletion of the nation's fossil-fuel resources is a threat to national security.

Analysts predict that escalating global oil prices will force Malaysia to become a net oil importer in the years to come. Malaysia uses oil mainly in the transportation sector, and relies on natural gas and coal (along with hydropower) to generate electricity. However, government officials have expressed concern that the cost of coal and gas is likely to soar in the coming decades, as supply fails to keep up with demand. Malaysia's coal imports, which held steady for many years, have grown rapidly in the past two years. Natural gas is currently the largest energy source for the country, but national gas fields may be depleted by 2027, which would leave the country unable to meet petrochemical industry demand and commitments for exports of liquefied natural gas.

Because of these gathering storms, there is no doubt that Malaysia urgently needs new sources of energy to assuage its future energy demands, and nuclear energy seems a very attractive alternative -- particularly since the neighboring countries of Vietnam and Thailand have already announced plans to bring their first nuclear plants online by 2020, and Indonesia intends to construct a plant on Java Island by 2015. Nevertheless, for Malaysia, the prudent management of current energy resources -- to ensure that they are sustainable over the long term -- deserves serious consideration as an alternative to nuclear energy.And the other futuer we need the nuclear power plan to source the energy for our country.

Nuclear Fission Basics

The debate over nuclear power plants has been going on for some time, with nuclear physicists and lawmakers alike throwing around terms like nuclear fission, critical mass, and chain reaction. But how does nuclear fission work, exactly?

In the 1930s, scientists discovered that some nuclear reactions can be initiated and controlled. Scientists usually accomplished this task by bombarding a large isotope with a second, smaller one — commonly a neutron. The collision caused the larger isotope to break apart into two or more elements, which is called nuclear fission. Figure 1 shows the equation for the nuclear fission of uranium-235.

Figure 1: The equation for nuclear fission.

Reactions of this type also release a lot of energy. Where does the energy come from? Well, if you make very accurate measurement of the masses of all the atoms and subatomic particles you start with and all the atoms and subatomic particles you end up with, and then compare the two, you find that there's some "missing" mass. Matter disappears during the nuclear reaction. This loss of matter is called the mass defect. The missing matter is converted into energy.

You can actually calculate the amount of energy produced during a nuclear reaction with a fairly simple equation developed by Einstein: E = mc2. In this equation, E is the amount of energy produced, m is the "missing" mass, or the mass defect, and c is the speed of light, which is a rather large number. The speed of light is squared, making that part of the equation a very large number that, even when multiplied by a small amount of mass, yields a large amount of energy.

Take another look at the equation for the fission of U-235. Notice that one neutron was used, but three were produced. These three neutrons, if they encounter other U-235 atoms, can initiate other fissions, producing even more neutrons. It's the old domino effect. In terms of nuclear chemistry, it's a continuing cascade of nuclear fissions called a chain reaction. The chain reaction of U-235 is shown in Figure 2.

Figure 2: Chain reaction.

This chain reaction depends on the release of more neutrons than were used during the nuclear reaction. If you were to write the equation for the nuclear fission of U-238, the more abundant isotope of uranium, you'd use one neutron and only get one back out. You can't have a chain reaction with U-238. But isotopes that produce an excess of neutrons in their fission support a chain reaction. This type of isotope is said to be fissionable, and there are only two main fissionable isotopes used during nuclear reactions — uranium-235 and plutonium-239.

A certain minimum amount of fissionable matter is needed to support a self-sustaining chain reaction, and it's related to those neutrons. If the sample is small, then the neutrons are likely to shoot out of the sample before hitting a U-235 nucleus. If they don't hit a U-235 nucleus, no extra electrons and no energy are released. The reaction just fizzles. The minimum amount of fissionable material needed to ensure that a chain reaction occurs is called the critical mass. Anything less than this amount is called subcritical.

Original link from:
www.dummies.com/how-to/content/nuclear-fission-basics

Nuclear Reactor Evolution

History of Nuclear Power Plant

1940’s
1942: World’s first nuclear reactor, Chicago Pile 1 (CP1), achieved criticality.
1944: World’s first plutonium production reactor operational in Hanford, USA.

1950’s
1951: World’s first nuclear electricity generation with EBR-1 (FBR) in Idaho, USA.
1954: World’s first nuclear power submarine, USS Nautilus, launched by the USA & world’s first nuclear power plant (LWGR) operational at Obninsk in Russia.
1956: First UK nuclear power plant (Magnox), Calder Hall, operational in Sell afield & first nuclear power plant (similar to Magnox) operational in France.
1957: First US nuclear power plant (PWR) operational in Shippingport.
1959: World’s first nuclear powered merchant ship, NS Savannah, launched in USA.

1960’s
1960: First BWR nuclear power plant operational in Dresden, USA.
1961: World’s first nuclear powered aircraft carrier, USS Enterprise, launched.
1962: First CANDU PHWR nuclear power plant operational in Canada.
1965: World’s first nuclear powered satellite, SNAP-10A, launched into orbit by USA.

1970’s
1972: World’s first prototype fast breeder reactor (FBR) power plant, BN-350, operational in Shevchenko, Kazakhstan, in former Soviet Union.
1979: Three Mile Island II nuclear power plant (PWR) accident in Pennsylvania, USA.

1980’s
1986: Chernobyl nuclear power plant (LWGR) accident in Ukraine, former Soviet Union.

1990’s
1997: First third generation nuclear power plant (Advanced BWR) operational, in Kashiwazaki Kariwa, Japan.

Nuclear energy..

Is the energy released by the nucleus of an atom as the result of nuclear fission, nuclear fusion, or radioactive decay. Although they are tiny, atoms have a large amount of energy holding their nuclei together. Certain isotopes of some elements can be split and will release part of their energy as heat. This splitting is called fission. The heat released in fission can be used to help generate electricity in power plants.

Uranium-235 (U-235) is one of the isotopes that fissions easily. During fission, U-235 atoms absorb loose neutrons.  This causes U-235 to become unstable and split into two light atoms called fission products.

The combined mass of the fission products is less than that of the original U-235. The reduction occurs because some of the matter changes into energy. The energy is released as two or three neutrons are released along with the heat. These neutrons may hit other atoms, causing more fission.

A series of fissions is called a chain reaction. If enough uranium is brought together under the right conditions, a continuous chain reaction occurs. This is called a self-sustaining chain reaction.  A self-sustaining chain reaction creates a great deal of heat, which can be used to help generate electricity.

Nuclear power plants generate electricity like any other steam-electric power plant. Water is heated, and steam from the boiling water turns turbines and generates electricity. The main difference in the various types of steam-electric plants is the heat source.  Heat from a self- sustaining chain reaction boils the water in a nuclear power plant.  Coal, oil, or gas is burned in other power plants to heat the water.