Nuclear Energy
The Process: From Atom to Outlet
Nuclear energy is just one of the many forms of electrical power in the world. It has become a safe, economical, and environmentally healthy source of energy. Strict licensing policies and national regulations have eased the public's opinion of the value of nuclear energy as well. In order to understand the importance of nuclear energy and its role in providing the public with electrical power, the entire process - from atom to outlet - must be examined.
Electricity from nuclear energy is made available from a nuclear reactor. A nuclear reactor is a complex machine designed to heat water, producing steam that runs a turbine that generates electricity.
The heat for the water or steam comes from a process called fission in which atoms are split, specifically, uranium-235. The uranium nucleus, like any atomic nucleus, contains protons with a positive electric charge and neutrons that are electrically neutral. These positively charged neutrons provide the reaction for successful fission.
The uranium is contained in small ceramic pellets, about the size of the end of a finger. These pellets are placed in zirconium tubes or rods. The rods are contained in a reactor. Neutrons bombard the uranium causing it to break down. Neutrons of uranium split apart, causing a chain reaction as they collide with other atoms of uranium, splitting off more neutrons. This chain reaction, fission, produces heat.
The flow of water into the reactor as well as the addition and removal of the zirconium tubes or rods can control the speed of the chain reaction. Some rods absorb the uranium neutrons as well, aiding in the control of the fission. At all times, precise heating temperatures are maintained to produce the proper amount of steam used to power the turbines, thus providing a constant and even supply of electricity.
The amount of heat that one pellet produces is equivalent to heat created by 149 gallons of oil, 157 gallons of gasoline, 1,780 lbs. of coal, or 19,200 cubic feet of natural gas. Each reactor holds 18,000,000 pellets.
Nuclear Energy Landmarks
- 1938 - the process of fission was discovered.
- 1942 - Enrico Fermi creates the atomic pile - blocks of uranium and graphite (uranium metal and uranium oxide fuel) with cadmium control rods interspersed among the blocks.
- 1946 - the development of nuclear reactors for submarines began.
- 1955 - first nuclear reactor developed for electricity in Pennsylvania, operating from 1957-1982.
- 1957 - congress passed the Price-Anderson Act, protecting the nuclear industry, and providing insurance coverage against liability claims and accidents.
Modern Reactors: Core Facts
As of 1993, there were 109 nuclear reactor facilities in the United States with operating licenses. A reactor typically can operate for 1 year on 20 tons of uranium. In the United States, 20% of electrical power is generated by nuclear reactors. Approximately 17% of the world's electricity are produced by nuclear reactors. Lithuania, having the highest level of 87%, Canada with the lowest, 17%.
World wide there are 6 types of reactors:
- Boiling Water Reactor
- Pressurized Water Reactor
- High-Temperature Gas-Cooled Reactor
- Canadian Deuterium Uranium Reactor
- Liquid Metal Fast Breeder Reactor
- RBMK Reactor
All reactors in the United States are either Boiling Water or Pressurized Water Reactors.
Boiling Water Reactor
Pressurized Water Reactor
Safe and Secure in the Nuclear Reactor
A nuclear explosion cannot happen with a reactor. A reactor uses different materials than a bomb. The reactor is also housed within concrete and steel walls, several feet thick.
Radiation: Real or Rumor
Radiation is a by-product of nuclear power. Radiation is measured in rem, or roentgen equivalent man. The effects of radiation on humans vary, depending on the length of exposure and the level of rem. It is estimated that people are exposed to 360 millirem daily, mostly from naturally occurring radon gas. 27 % of this exposure is from cosmic radiation from space, rocks and soil, and internal radiation from the human body. 18% of radiation exposure comes from man-made sources, 7% from medical diagnosis including x-rays, and 3% from consumer products like smoke detectors. 0.1% of the world's exposure to radiation comes from nuclear energy.
However, in rare and extreme situations, people exposed to 500 rem are in immediate risk of death. Exposure to levels at 100 rem produces radiation sickness. 50 rem is equivalent to the radiation level experienced at Hiroshima and Nagasaki when the atom bomb was used on Japan in WWII.
Economics: The Future of Nuclear Power
Nuclear and coal plants are built to provide baseload power, the electricity for everyday needs. Unlike other energy plants, no air pollutants are produced by nuclear reactors and uranium is abundant all over the world. However, for the next decade, it appears unlikely that any new nuclear or coal baseload generating plants will be built.
If inefficient plants are replaced in the future by the construction of new baseload energy plants, several factors must be considered: capital cost per kilowatt of the plant, cost of fuel (coal, gas, or uranium), maintenance costs (personnel, equipment, etc.), plant performance, and the environment. Issues concerning the environment include: developing a decommissioning fund to effectively shut down the plant, and how the ozone layer will be affected, specifically carbon dioxide and the Greenhouse Effect.
Nuclear Waste and Disposal
When nuclear fuel is first placed in a commercial reactor, it consists of uranium oxide. After the fuel has been used for 3 to 4 years, it consists of about 96% uranium oxide and about 3% other elements - including iodine, strontium, carbon, xenon, cesium, silver, and palladium. These are nuclear wastes.
Spent nuclear fuel is termed "high-level waste" since it is considerably more radioactive than new fuel. A person can handle new fuel pellets of uranium oxide without risk of harm. In contrast, spent fuel is dangerously radioactive, although much of the radioactivity dissipates quickly - almost 98% within 6 months. 40 to 50 years after spent fuel is removed from the reactor, its radioactivity has decreased by a factor of 100. A very small percentage of nuclear wastes remain radioactive for thousands of years.
In addition to high-level waste, another category of nuclear waste associated with nuclear power is called "low-level waste." Low-level waste is generally anything that becomes contaminated with radioactive materials during its use. Such items include rags, papers, cleaning materials, protective clothing, tools, and contaminated liquids.
The residue, sludge, and sand from uranium mining and milling operations are also considered nuclear wastes because they contain very small concentrations of natural radioactive elements.
Typically commercial reactor plants produce 40,000 tons of waste. Military plants produce 100 times more. Overall, 180 million tons of low-level waste have been produced and disposed of on site.
Nuclear wastes can be isolated from the environment so that they do not pose a danger to today's or future generations. First, wastes are placed deep underground in a stable geological environment. Second, a multi-barrier approach is used to ensure that none of the radioactivity escapes. The wastes are immobilized by imbedding them in stable indissolvable solid ceramic or glassy materials. They then are sealed in ceramic or metal canisters, with absorbent mineral fillings packed around them. The entire assembly is sealed in deep bedrock.
One of the fears expressed about nuclear waste storage is that the buried waste canisters might somehow, over time, become damaged allowing radioactive materials to enter underground water. In fact, the toxicity of nuclear plant wastes after 1,000 years is about equal to the toxicity of the uranium ore from which the fuel was originally obtained. After about 4,000 years, the nuclear waste is no more toxic than natural mercury, chromium, cadmium, silver, and many other ores. The multiple barriers are selected, designed, and constructed to retain the radioactive wastes for at least 10,000 years.
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