Nuclear Energy General Concept

In 2001, total US generation of electricity was 3,777 billion kilowatt-hours.

Horizontal Axis stands for years Vertical Axis stands for total nuclear output in billion kilowatt hours

Statistics In 2000, there were 438 commercial nuclear generating units throughout the world, with a total capacity of about 351 gigawatts. In 2001, there were 104 (69 pressurized water reactors, 35 boiling water reactors) commercial nuclear generating units in U.S, and it is producing 20 percent of the nation’s total electric energy consumption. In France, 2001, 80% of all electric power comes from nuclear reactors.

Energy from atoms The process that produces the heat in a nuclear plant is the fissioning or splitting of uranium atoms. That heat boils water to make the steam that turns the turbine-generator. Uranium known as uranium-235 (U-235 or U235), which is the fuel used in most types of nuclear reactors today.

Fission of one U-235 nucleus, approximately 3.2*10-11 J energy is released.

Nuclear chain reaction

Uranium Fuel Cycle Uranium ore is mined. Milled into yellowcake Yellowcake is turned into gas. Gas is filtered to increase the amount of U-235. U-235 is made into ceramic fuel pellets. Pellets are put in fuel rods and make electricity. Spent fuel is stored at the power plant site. In the future, the spent fuel will be buried in an underground repository.

Types of Reactors Nuclear reactors are basically machines that contain and control chain reactions, while releasing heat at a controlled rate. In electric power plants, the reactors supply the heat to turn water into steam, which drives the turbine-generators. Two types are used in the United States: boiling-water reactors (BWRs), and pressurized-water reactors (PWRs).

Boiling-Water Reactors In the BWR, the water heated by the reactor core turns directly into steam in the reactor vessel and is then used to power the turbine-generator.

Pressurized Water Reactors Diagram of pressurized nuclear reactor’s steam supply system. In a PWR, the water passing through the reactor core is kept under pressure so that it does not turn to steam at all -- it remains liquid. Roughly seventy percent of the reactors operating in the U.S. are PWR, in 2003.

Map of Power Reactor Sites Last revised Friday, September 12, 2003

Benefits of Nuclear Energy Nuclear energy preserves the environment because it does not emit harmful gases, and requires less area to produce the same amount of electricity as other sources. Nuclear energy provides reliable electricity because of the large size of the plants, their long periods of operation, and the expertise with which they are run. Nuclear energy is an economical energy source – because of stable fuel prices, high plant performance, modernized plants, and renewal of plant licenses. Nuclear energy contributes to national energy security --nuclear energy is not subject to unreliable weather or climate conditions, unpredictable cost fluctuations, or dependence on foreign suppliers

A little goes a long way one uranium fuel pellet—the size of the tip of your little finger—is the equivalent of 17,000 cubic feet of natural gas, 1,780 pounds of coal, or 149 gallons of oil.

Long periods of operation. Nuclear power plants are designed to operate continuously for long periods of time. They can run about 540 days before they are shut down for refueling. Reduced refueling outage time. U.S nuclear power plants have been steadily reducing the period of time it takes to refuel, greatly cutting down on the time that they are not producing electricity.

Average Duration of Nuclear Refueling Outages in the US ( ) Source: Institute of Nuclear Power Operators (INPO) Note: Average Values do not include data from shutdown units

Safety systems Nuclear generation of electricity has an excellent safety record. The general strategy used can be described as 'defence in depth'. In other words, there are multiple levels of provision to ensure safety. If any system or procedure fails there is another that provides backup. a facility is designed so that, in the unlikely event of all systems failing, at least the release of contamination will be limited.

To achieve optimum safety, nuclear plants operate using a 'defence-in-depth' approach high-quality design & construction equipment which prevents operational disturbances developing into problems redundant and diverse systems to detect problems, control damage to the fuel and prevent significant radioactive releases provision to confine the effects of severe fuel damage to the plant itself.

Accidents At the Three Mile Island nuclear plant in 1979, a situation developed that led to a reactor being destroyed, but there were no off-site physical health impacts and the automatic safety systems responded properly. Even when the operators shut down some automatic systems, the containment was sufficient to prevent any elevated radiation doses to anyone.Three Mile Island

Radiation the fission process that takes place in a nuclear reactor leads to the creation of substantial amounts of new radioactivity. Radiation doses to workers are controlled by employing all three factors that reduce exposure: Workers are kept at a distance from radiation sources, whenever possible, with robotics and remote handling techniques frequently being employed. Shielding is used to reduce radiation levels. The time spent by workers in high radiation areas is limited.

Radioactive wastes Spent fuel is produced by a power reactor throughout its working life. This material is highly radioactive and is subject to a management regime that ensures that it is safely handled and stored. There are other wastes that are much less radioactive, such as process wastes (from treatment, purification and filtration systems), technological wastes (contaminated clothing, rags and scrap materials) and decommissioning wastes. Such materials are handled in the same manner as similar wastes that arise in other segments of the nuclear fuel cycle.

Nuclear Fuel Cycle

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