Download
1 / 39
390 likes | 641 Views
Nuclear Energy. “Nuclear power is a hell of a way to boil water.” - Albert Einstein. The 100 Ton Test. On May 7, 1945, 108 tons of TNT stacked and threaded with radioactive material was detonated in the White Sands desert in New Mexico.
E N D
Nuclear Energy “Nuclear power is a hell of a way to boil water.” - Albert Einstein
The 100 Ton Test • On May 7, 1945, 108 tons of TNT stacked and threaded with radioactive material was detonated in the White Sands desert in New Mexico. • This explosion was meant to calibrate the instruments that would measure the actual nuclear bombs to be tested later.
Atomic Structure • Nuclear technology takes advantage of the power locked in structure of atoms, the basic particle of matter. • The nucleus of an atom contains all of its positively-charged protonsand non-charged neutrons. • Negatively-charged electronsorbit the nucleus. • Atoms always contain equal numbers of protons and electrons, , making them electrically neutral.
Atoms can have different numbers of neutrons in their nuclei. • Nuclei from the same element with different numbers of neutrons are called isotopes. • Most isotopes are stable, but some can spontaneously break apart, emitting energy and particles. • This is radiation.
Nuclear weapons harness a specific type of decay called nuclear fission. • This is the splitting of the nucleus into two smaller fragments. • The fuel used by the first nuclear weapons was Uranium-235, a naturallyoccurring isotope. • Uranium-235 has an extremely large nucleus that can be split when it is hit with a high-speed neutron.
In a nuclear bomb, a large amount of uranium-235 is clustered together, so that when fission is initiated in one of the atoms, it splits and released more neutrons, which then cause fission in other atoms. • This creates a fission chain reaction. • Each time a nucleus splits, a large amount of energy is released. • Multiplied across the entirechain reaction…
Trinity • The first nuclear test detonation used a device that was an exact replica of “Fat Man”, which would later be dropped on Nagasaki, Japan. • The heat of the explosion fused the desert sands together, forming a layer of radioactive green glass.
Two atomic bombs were dropped during World War II – Hiroshima and Nagasaki, Japan. • Each had yields of 15-21 kilotons of TNT. • These blasts ended World War II. Hiroshima, March 1946.
Following World War 2, additional nuclear weapons testing was moved to part of the Marshall Islands, called the Bikini Atoll (11°N, 165°E). • This testing was codenamed “Operation Crossroads.”
Two nuclear devices were detonated at sea as part of Operation Crossroads. • The purpose was to study the effects of a nuclear blast on an armada of naval ships. • The first blast, called Shot Able, was dropped from a plane. The second, Shot Baker, was detonated underwater, beneath the ships. • Different species of lab animals were placed on several ships, to test for radiation poisoning following the blast.
Operation Crossroads Fallout • Glenn Seaborg, chairman of the Atomic Energy Commission, called Baker “the world’s first nuclear disaster.” • The target ships of Shot Baker were all heavily contaminated with radioactive fallout. • Some were so “hot” that they could not be safely decontaminated and had to be sunk.
Operation Castle • In 1954, six large nuclear tests were conducted. The largest was code named Castle Bravo. • This tested a new design, called a hydrogen bomb.
Castle Bravo Fallout • Castle Bravo was a much more powerful blast than expected. • Residents of nearby atolls were exposed to toxic levels of radioactive fallout. • A Japanese tuna fishing boat called the Lucky Dragon 5 was also caught in the blast radius.
Nuclear fallout is dust and ash propelled into the atmosphere following a nuclear blast. • Radiation exposure from fallout is measured in rems. • 100-200 rems causes mild symptoms, such as nausea and vomiting. • 400-600 rems has about a 50% mortality rate. • 600-1000 rems will usually cause death. • Over 1000 rems will cause death in a few hours or less. • Interior exposure of fallout, from breathing or ingesting the dust and ash, would have even more severe effects. • An average person will be exposed to about 620 millirems of radiation per year from natural and man-made sources.
Radioactive coral dust fell on the Lucky Dragon 5. • Fishermen touched the dust with their bare skin, inhaled it, and in some cases, tasted it. • One crewmember died from exposure.
Atoms for Peace • As the Bikini nuclear testing continued, President Dwight Eisenhower gave a famous speech to the United Nations: “My country wants to be constructive, not destructive.” “…the United States pledges before you…its determination to help solve the fearful atomic dilemma--to devote its entire heart and mind to find the way by which the miraculous inventiveness of man shall not be dedicated to his death, but consecrated to his life."
Equipment and technology were provided to schools, hospitals, and research institutions to help develop nuclear technology towards more peaceful goals. • The primary goal: electricity generation. • Optimism for the new technology was very high. • Lewis Strauss, chairman of the Atomic Energy Commission, predicted that, “Our children will enjoy in their homes electrical energy too cheap to meter.”
Nuclear Reactors • The process of converting nuclear energy into electricity is similar to that of using fossil fuels. • Water is boiled, the steam is passed through a turbine, which spins a generator.
As with nuclear bombs, the primary fuel is uranium-235. • Uranium ore is enriched and formed into fuel pellets. • The fuel pellets are stacked into long, cylindrical fuel rods. • Control rods, made of a neutron-absorbing material, are placed amongst the fuel rods. • Can be removed and inserted to adjust the rate of the chain reaction. Withdraw control rods, reaction increases Insert control rods, reaction decreases
One big advantage to nuclear power is that, under normal conditions, it does not release any air pollution, only steam. Cooling Tower in Byron, Illinois
Kinds of Reactors Cont’d • Both reactor vessel and steam generator are housed in a special containment building preventing radiation from escaping, and providing extra security in case of accidents. • Under normal operating conditions, a reactor releases very little radioactivity.
Through the late 1970s, many new reactors were constructed all over the United States. • Since that initial boom, few new reactors have come online.
Nuclear Accidents • In 1979, a movie called “The China Syndrome” was released. • Fictional story about a California nuclear plant that experienced a near-meltdown of its nuclear core. • The title of the movie is an exaggeration of what happens during a meltdown – the nuclear core becomes so hot that it melts, even melting through the floor of the reactor vessel.
Ten days following the movie’s release, the Three Mile Island partial meltdown occurred. • A relief water valve stuck open, allowing water to escape from the core. • A meltdown, when the fuel and control rods physically begin to melt due to the heat surge within the reactor, partially occurred. • No major leak to theenvironment occurred.
In 1986, a full meltdown occurred at the Chernobyl nuclear plant located in Ukraine (formerly Soviet Union). • A test was being conducted on the reactor to see how the backup water pump generators would respond to a full power outage. • The control rods were fully removed. • At some point, the fission chain reaction began occurring uncontrollably. • An explosion ripped apart the containment building, spreading radioactive fallout throughout the area and into the atmosphere.
There were multiple design flaws at the Chernobyl plant: • The containment building was inadequate. • Graphite was used as a moderator instead of water. When the meltdown occurred, it ignited, releasing more fallout. • A water storage pool was located under the reactor. If the core had melted down into this pool, an even greater explosion would have occurred.
The burning core was eventually extinguished. • The nearby employees’ town, Pripyat, was permanently evacuated. • A 30km radius around the plant, called the exclusion zone, has been designated as uninhabitable to people.
Fukushima • The most recent meltdown occurred following a massive earthquake and tidal wave off the coast of Japan. • The generators powering the water pumps of some of the Fukushima Daiichi reactors were flooded. • Without cooling water, the core overheated and experienced a meltdown.
Contaminated water from the plant leaked into the Pacific. • Top predators, like bluefin tuna, caught in the Pacific have positively tested for small amounts of radioactive fallout. • A single serving of tuna has less than half of the exposure from an arm x-ray.
Radioactive Waste Management • About 100,000 tons of low-level waste (clothing) and about 15,000 tons of high-level waste (spent-fuel) waste is stored in the U.S. from reactor usage. • Spent fuel rods are temporarily placed in deep water pools while they cool down and the fission reaction slows. • Waste is then moved to large casks of metal and concrete near the reactor.
The U.S. Department of Energy announced plans to build a high-level waste repository near Yucca Mountain, Nevada in 1987. • The facility met three important criteria for long-term waste storage: • Low moisture. • Geologically stable. • Far away from major population centers. • Plans to use Yucca have since been halted, due to objections from Nevada residents. • No long-term storage plan has been accepted by the U.S.
Some alternative methods of nuclear waste disposal have been researched. • Transmutation uses the waste as fuel in a different type of reactor, which converts it to a less-dangerous waste. • Geologic disposal involves depositing the waste deep below the Earth’s crust in stable rock formations.
Nuclear energy makes up only a fraction of our total energy generation. • Its use may increase in the future, as fossil fuels become more scarce or are considered too environmentally damaging.
