Most of the hydrogen in the universe consists of a single proton orbited by a single electron and is also known as H-1 or protium. A small percentage of hydrogen atoms contain a neutron in the nucleus as well as the proton. This form of hydrogen is referred to as H-2, heavy hydrogen or deuterium. It is a stable atom like H-1. In the Earth's crust, for every six thousand four hundred and twenty H-1 atoms, there is a single H-2 atom.
Most of the hydrogen in the universe consists of a single proton orbited by a single electron and is also known as H-1 or protium. A small percentage of hydrogen atoms contain a neutron in the nucleus as well as the proton. This form of hydrogen is referred to as H-2, heavy hydrogen or deuterium. It is a stable atom like H-1. In the Earth's crust, for every six thousand four hundred and twenty H-1 atoms, there is a single H-2 atom.
Most of the water molecules in the universe contain two of these ordinary hydrogen atoms combined with an oxygen atom. A few of the water molecules will have H-2 atoms combined with oxygen. In all the water on Earth, in ten thousand water molecules there will be about 2 with H-2 atoms instead of H-1 atoms. Water with H-2 atoms is referred to as heavy water.
Just about all the deuterium in the universe is thought to have been created in the big bang. Heat can be used to separate the isotopes of hydrogen. The ratio of H1 to H-2 in gas giants and comets varies because of the effects of internal heat and solar heating. The fact that the ratio of H1 to H2 found in comets is close to that found in the oceans on Earth has been used to argue that the oceans were created by cometary impacts on the young Earth.
Deuterium was identified in the early 1930 soon after the discovery of the neutron. Harold Urey won a Nobel Prize in 1934 for discovering and naming deuterium. Since the discovery of deuterium, water containing deuterium in its molecules has been extracted from ordinary water through a steam distillation process. Canada used to be the leading world supplier of deuterium until its last heavy water production plant was closed in 1997.
The chemical and physical properties of compounds containing deuterium are similar to the behavior of the same compound without deuterium. However, there are still differences that are greater that those caused by any other change of particular isotopes in compounds. Heavy water is more viscous than ordinary water and ice created from heavy water will sink in ordinary water in contrast to ordinary ice which floats.
Heavy water is slightly toxic to multi-cellular creatures and single cell life forms whose cells contain a nucleus. More primitive single cell life that has no nucleus appear to not be harmed by it. A average person could consume five quarts of heavy water without serious injury but it half the water in the body was replace with heavy water, death would result.
Deuterium is used in experimental fusion reactors. When fusing hydrogen to helium, neutrons must be part of the mix because even though most hydrogen does not include neutrons, all helium nuclei do include neutrons. Heavy water is used as a moderator to slow neutrons in some nuclear reactor designs because it does not absorb neutrons like ordinary water. The Canada reactor design CANDU uses heavy water as a moderator. Deuterium is a useful tracer for chemistry and biochemistry because it is a non-radioactive and easily identified.
About two thirds of the heat generated by nuclear reactors is dumped into the cooling system. Ordinary water is a popular coolant for reactors. The water for cooling is drawn from either a large river or the ocean. While this makes it convenient to locate reactors near a river or the ocean, it also makes them more vulnerable to floods and tidal waves such as the recent disaster at Fukushima.
So far we have focused on uranium and plutonium in our discussion of nuclear fuel and reactors because they are the fuels for most of the world's reactors. There are other nuclear fuels used in existing reactors and atomic batteries or suggested for use in new designs. One of these alternative nuclear fuels that holds great promise is thorium.
When spent fuel rods are removed from a nuclear reactor, they are giving off heat and emitting radiation, primarily from fission products. They are stored in special pools of water or boric acid to allow the heat and radiation to diminish. The cooling fluid absorbs the radiation and is circulated through heat exchangers to get rid of the heat. It can take several years for the heat and radiation to drop to a safer level.
After manufacture, nuclear fuel is transported from the production facility to a nuclear power plant for use in a reactor. Specialized transport companies transport nuclear fuel assemblies which release little radioactivity and do not require special shielding.
In a typical nuclear reactor, sets of fuel rods called cells surround a control rod which can be inserted or withdrawn to control the neutron flux and thus, the rate of the chain reaction.
U-235 atoms are bombarded by neutrons and fission which produces heat and more neutrons. Some of the U-235 transmutes into plutonium which also undergoes fission producing about one third of the heat in the reactor core. The heat from the core is used to produce steam which drives the turbines that produce the electricity.
As the nuclear fuel in the rods fissions, the heat generated causes thermal expansion which can cause cracking. The nuclear fuel reacts with cladding materials such zirconium alloy which forms the shell of the fuel rod. The chemical composition of the fuel near the edge of the pellet changes as does its thermal conductivity. The purer uranium oxide in the center of the pellet will reach higher temperatures than the fuel near the outer edge of the pellet.
One ton of natural uranium can generate about fourty four million kilowatt hours. It would require over twenty thousand tons of coal or eight million cubic meters of natural gas to generate the same amount of electricity.
The rate at which the fuel is consumed is measured in gigawatt-days per ton of fuel and it is proportional to the level of concentration of U-235 in the nuclear fuel contained in the rods. The level of heat generation that can be safely handled by the current reactors limits the enrichment to about four percent which will yield a burn up rate of fourty gigawatt-days per ton. With improvements in materials and design, enrichment as high as five percent can be utilized, ultimately producing seventy gigawatt-days per ton.
Only a third of the heat produced by the core is captured in steam production. The other two thirds of the heat is passed to the water of the cooling system and either released in into a body of water such as a large river or the ocean. Alternatively, the water may be sent into cooling towers for evaporative cooling. Normally, a small amount of radioactivity is released into the cooling water.
The progression of nuclear fuel through a series of stages of production, use and disposal is referred to as the nuclear fuel cycle. When the spent fuel is used once and then disposed of, the cycle is called open or once-through. When the spent fuel is reprocessed and used again, the cycle is called closed.
The common nuclear fuel uranium oxide also known as UOX is usually compressed and cooked into cylindrical ceramic pellets. These pellets manufactured to exacting standards and are machined to precise dimensions. The pellets are then sealed into long metal tubes called fuel rods
There are a number of different types of nuclear fuel in terms of what isotope is used, what other materials are mixed with the isotope and the physical configuration of the fuel. Nuclear reactors are designed to use a specific isotope in a specific shape
There are a number of different types of nuclear fuel in terms of what isotope is used, what other materials are mixed with the isotope and the physical configuration of the fuel. Nuclear reactors are designed to use a specific isotope in a specific shape
In order to control how much power is generated in a nuclear reactor, the number of neutrons available to cause nuclei to fission must be controlled. Control rods which absorb neutrons must be inserted into or withdrawn from the core in order to control the chain reaction.
A nuclear reactor is a complex device that is designed to start and sustain a controlled nuclear chain reaction. They are usually utilized to generate electrical power or to provide propulsion for ships and submarines. Controlled nuclear fission is used to heat either water or a gas which is then passed through a turbine. The turbine in turn either spins the propellers of a ship or the generators of an electrical power station.
The stagnation of the nuclear power industry extended into the 1990s with few new plants being ordered and many ordered plants being cancelled. However, during the 90s a third generation of power plants were being designed to replace the second generation plants constructed in the 70s and 80s. This new design moved the moderator rods to a different location in the plant in order to minimize leaks. Plants with the new design were ordered in the late 90s.
The Kyoto Protocols first signed by several nations in 1997 called for the reduction of carbon dioxide emissions by to 5% below the emissions in 1990. This demand for carbon dioxide reduction much of which comes from oil and coal fired power plants and the need to replace old second generation reactors which were scheduled for decommissioning led to pressure for the adoption of nuclear power. While nuclear power stations do not emit carbon dioxide, their construction involves huge quantities of cement which does emit a great deal of carbon dioxide.
The election of George W. Bush, an enthusiastic supporter of nuclear energy to the US Presidency stimulated renewed interest in the expansion of nuclear power generation. In 2004, Bush signed a resolution to allow the US Department of Energy to move forward on the construction of a long term nuclear waste depository at Yucca Mountain in Nevada. In 2005, Bush signed the first new US energy bill in more than a decade. The bill included funding for nuclear research, decommissioning of old nuclear power plants, tax credits and loan guarantees for the nuclear industry, and a liability cap in case of serious nuclear accidents. A number of consortia of companies were created to build more nuclear power plants.
In the first decade of the Twenty First Century, design evolution continued with the development of new passive nuclear power plants that relied on natural processes such as gravity, convection, evaporation and condensation to achieve cooling instead of active systems of pumps. Emergency cooling water pools were built above the core so that in an emergency, the water could be easily dropped into the core. Other reactor designs relied on balls of graphite instead of graphite rods or water and were gas cooled.
By 2007, there were over four hundred nuclear power reactions in the world in thirty one countries. France, Japan and the U.S. accounted for over fifty percent of nuclear generated electricity. As of 2010, China had over twenty five reactors under construction with plans to build many more. In the United States almost half of the operating reactors have had their licenses extended to sixty years.
Worldwide, there are currently four hundred and thirty six nuclear reactors generating three hundred and seventy gigawatts of electrical power. Another sixty three are under construction with a combined capacity of sixty gigawatts.
The terrible nuclear accident at Fukushima where a tsunami caused by an earthquake destroyed four reactors a coastal nuclear power plant has caused many countries to reevaluate their reliance on nuclear power generation and their plans for expansion. Most of the power plants in Japan have been shut down for maintenance and then not restarted. Germany has decide to phase out all nuclear power plants by 2022 and Italy has banned nuclear power. The International Atomic Energy Commission has cut its estimated of new nuclear power generation by 2035 in half. However, in the United States, two new reactors were recently licensed for construction in Georgia and there are orders for more reactors.
As nuclear power plants were built and produced power in the 1960s, local protests began to appear. Some scientists also started to raise concerns about nuclear power. There were fears of nuclear accidents, spread of nuclear weapons, cost overruns on power plant construction, terrorist use of nuclear materials and nuclear waste. By 1970, world production f nuclear power had reached one gigawatt or one billions watts).
In the early 70s, big protests broke out against the construction of a nuclear power plant in Wyhl, Germany. The cancellation of the plant in 1975 inspired protests in other parts of Europe and in North America. The oil crisis in 1973 put pressure on countries such as Japan and France to find an alternative to oil fired power plants. They turned to nuclear energy as a substitute. Hundreds of thousands of people participated in multiple protests in France and Germany in the late 70s.
In 1979, there was an accident at the Three Mile Island nuclear power plant in Dauphin County, Pennsylvania. Confusing controls and operator error led to the loss of large amounts of coolant which resulted in a partial meltdown of the fuel rods. This caused a release of small amounts of radioactive gases and iodine-131 into the environment. For days, the owners of the plant and government authorities floundered as they tried to deal with the crisis. Poor communication with the public, confusion over the possible need for an evacuation and authorization of the release of fourty thousand gallons of radioactive waste water into the Susquehanna River undermined the credibility of the plant owners and the government with the public. An extended investigation led to the conclusion that there was no health danger from the accident. Clean up ultimately cost one billion dollars.
World wide nuclear power production reached one hundred gigawatts by 1979. Rising construction costs due to construction delays and regulatory problems, dropping fossil fuel costs, public fears stoked by the Three Mile Island accident, law suits brought by groups opposing nuclear power and a lowering of demand for electrical power in the late 70s had major impacts on plant construction in the 70s. Sixty three nuclear power units were cancelled between 1975 and 1980.
Nuclear power plant construction slowed in the 1980s due to the problems mentioned above. Many proposed plants were cancelled in the face of protests, law suits, rising costs and lower energy demands.
In 1986, there was a terrible accident at the Chernobyl Nuclear Power Plant in Ukraine. A power surge triggered an attempt to run an emergency shut down which resulted in a greater power surge. This second surge ruptured a reactor vessel and exposed graphite moderator rods to the air. The resulting explosion and fire released large amounts of radioactive contamination into the atmosphere in the form of dust and smoke. The prevailing winds carried the radioactivity over much of the Western Soviet Union and Western Europe. Over three hundred thousand people were evacuated from parts of Belarus, Russia and Ukraine. More that half of the radioactive fallout fell on Balarus.
While the Chernobyl accident had a huge impact on public fear of nuclear power, it did not have a great effect on the regulation in Europe and the United States because the design of the Chernobyl reactor was a uniquely Soviet design.
The World Association of Nuclear Operators was created in 1989 as a direct result of the Chernobyl accident to help the operators of nuclear power plants achieve the highest levels of safety and reliability.
Where the 70s saw a huge increase in nuclear power generation, in the 80s the world capacity only tripled from one hundred gigawatts to three hundred gigawatts.
In the early Twentieth Century, it was discovered that radioactive elements could release great amounts of energy according to Albert Einstein's famous equation, E = MC2. This equation says that the energy in a quantity of matter is equal to that quantity of matter multiplied by the speed of light squared. There are approximately twenty five million kilowatt hours of energy in one gram of matter.
Unstable atomic nuclei undergo spontaneous decay involving the emission of gamma rays, electrons (beta particles), helium nuclei (alpha particles), protons and neutron. In this process, only a few elementary particles escape the nuclei of the decaying atom. There is another nuclear process that involves the decomposition of atoms. This process is called nuclear fission.
The biological damage of ionizing radiation occurs at the level of the cell. Radiation can tear apart the DNA in the nucleus of the cell. Most breaks in DNA are repaired within twenty four hours but twenty four percent of those repairs are incorrect. If the damage is severe enough, it will kill the cell in a process called apoptosis where the cell go through a process of programmed cell death. If the damage to DNA does not kill the cell, it can cause changes in the DNA sequence known as mutations. These can be passed to daughter cells when the damaged cell divides and cause cancerous tumors. Since the DNA contains the recipe for all the proteins in the human body as well as instructions for the manufacture of proteins, abnormal proteins or abnormal protein production can be the result leading to premature aging and cancer.
Radioactivity is definitely a threat to our health. It has been said that there is no safe minimum dose of radiation but we seem to survive in a natural environment with many different sources of radiation both outside and inside our bodies. On the average, there are over 800 radioactive events in the human body every second. Here is a list of the radioactive isotopes in our bodies.
(There are 28.3 grams in one ounce, one thousand milligrams in a gram, on million micrograms in a gram, one billion nanograms in a gram, one trillion picograms in a gram, and one quadrillion femto grams in a gram, and one thousand grams in a kilogram)
Potassium-40 - 16.5 milligrams - 4,340 disintegrations per second
Carbon-14 - 16 nanograms - 3080 disintegrations per second
Rubidium-87 - 190 milligrams - 600 disintegrations per second
Lead-210 - 5400 picograms - 15 disintegrations per second
Helium-3 - 20 femtograms - 7 disintegrations per second
Uranium-238 - 100 micrograms - 3-5 disintegrations per second
Radium-228 - 46 femtograms - 5 disintegrations per second
Radium-226 36 micrograms - 3 disintegrations per second
The uranium, potassium and rubidium in our bodies were created in stellar explosions before the Earth was formed. The lead and radium isotopes were created by thorium and uranium decay. Helium-3 and Carbon-14 are being continuously created by cosmic rays bombarding the atmosphere of the Earth.
Potassium-40 is present in all the food that we eat in tiny quantities. Potassium is abundant in our environment and plants take it up from the soil. We consume about two and one half grams of potassium every day. It is an essential part of our diet and our bodies maintain a constant level.
Carbon-14 makes up a tiny amount of the roughly 16 kilograms of carbon in our bodies. It is constantly being created by cosmic rays interacting with nitrogen in the atmosphere. All living things breath in tiny amounts of carbon-14 as their bodies constantly replace carbon. Carbon-14 can be used to date the age of a biological material because when something dies, it stops taking in carbon-14 which decays and slowly disappears.
Radioactive contamination of food has become a big concern since the Fukushima. This articles will explore how radioactivity finds it's way into the food chain.
In the course of the evolution of civilization, mankind has created a number of sources of radiation which contribute to radiation exposure of people. These include substances, medical equipments, consumer devices and building materials.
Sources of radiation that impact the average individual in industrialized countries include tobacco which contains thorium and uranium, televisions which emit x-rays, medical X-rays, smoke detectors which contain americium, and lantern mantles which contain thorium.
Modern medicine utilizes a large variety of radioactive isotopes which include: bismuth-213, cesium-137, carbon-11, chromium-51, cobalt-57, cobalt-60, copper-64, dysprosium-165, erbium-169, fluorine-18, gallium-67, gold-198, holmium-166, indium-111, iodine-123, iodine-125, iridium-192, iron-59, krypton-81, lutetium-177, nitrogen-13, oxygen-15, palladium-103, phosphorus-32, potassium-42, rhenium-188, rubidium-82, samarium-153, selenium-75, sodium-24, strontium-89, strontium-92, technetium-99, thallium-201, xenon-133 (5 d), ytterbium-169, and yttrium-90. These isotopes, with the exception of cesium, have half lives for seconds to days. They are used for diagnosis of many conditions, imaging of different parts of the body and treatment of a variety of disease.
Most building materials from natural sources contain small quantities of radium 226, uranium 238 and Thorium 232 as well as radionuclides which are the result of decay of these isotopes. Radon 22 and radon 220 are gases which are injected into the interior air of builds from the decay in the building materials.
Recycled industrial by-products contain radioactive isotopes which have been concentrated above normal background levels in industrial processes. These include coal ash from the burning of coal which is an additive in cement, coal slag is used in floors as an insulating fill, phosphogypsum which is a by-product of the production of phosphorous fertilizers and red mud which is a waste product in aluminum manufacture used in bricks, ceramics and tiles.
Some professions expose workers to radioactivity. Workers who mine uranium and process uranium are exposed to the natural radioactivity of uranium. Nuclear power plant workers and power plant inspectors can be exposed to uranium 235 and plutonium. Nuclear medicine technician can be exposed to any of the radioisotopes mentioned in the paragraph above on nuclear medicine. Radiography and X-ray technicians are exposed to x-rays.
