After reading this essay you will learn about:- 1. Scope of Nuclear Energy 2. Effects of Nuclear Energy on the Environment 3. Environmental Benefits of Nuclear Power Generation Safety.
Scope of Nuclear Energy:
i. Economical Source of Energy:
a. Abundant Fuel with Low Cost and Stable Price:
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U.S. nuclear power plants use an enriched form of uranium for fuel. Uranium is a relatively abundant element that occurs naturally in the earth’s crust. Uranium oxide is about as common as tin. In 1998, 16 countries produced over 99 per cent of the world’s total uranium production.
Canada’s and Australia’s uranium mines account for 46 per cent. Compared to natural gas, a fuel also used to generate electricity, uranium is already relatively low in cost and less sensitive to fuel price increases. And 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.
b. Improving Plant Performance:
Greater nuclear plant performance means more electricity for less money. Plant operators routinely take a variety of measures to increase performance, such as improving the design of systems, installing more reliable equipment, using better information systems, enhancing integration of systems and co-ordination of their operations, observing better work planning and work management, sharing lessons learned about plant operations throughout the industry, and providing higher levels of training.
c. Continual Plant Modernization:
Although the first commercial nuclear power plant began commercial operations in 1969, there is really no “old” nuclear power plant. Systems are continually being redesigned and replaced such that the original plant is substantially new and improved.
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Moreover, the collective wisdom of the entire nuclear industry is brought to bear on this improvement process. All plant operators share best practices and operating experiences through industry’s wide lessons, learned procedures, benchmarking projects and the Top Industry Practice Awards program me.
d. Plant Longevity through License Renewal:
Nuclear power plants are a valuable asset to their owners because their initial license period can be extended. The initial license period of 40 years can be renewed for an additional 20 years. So far, eight plants have applied for license renewal and an additional 22 have announced intentions to do so-almost one-third of all U.S. plants.
This renewed life of a plant translates into additional savings for customers because the expense of building a new power plant can be avoided.
ii. Environmental Preservation:
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Nuclear energy has perhaps the lowest impact on the environment—including air, land, water, and wildlife—of any energy source, because it does not emit harmful gases, isolates its waste from the environment, and requires less area to produce the same amount of electricity as other sources.
iii. Economic Performance:
The average electricity production cost in 2000 for nuclear energy was 1.76 cents per kilowatt-hour, for coal-fired plants 1.79 cents, for oil 5.28 cents, and for gas 5.69 cents. In the United States, six of the nine largest investor-owned utilities by revenue were nuclear utilities in 1998. The top investor owned utility by profit was a nuclear utility, and eight of the next nine profit leaders were nuclear utilities.
Eight of the top ten “market value-added” energy companies between 1995 and 1998 operate nuclear plants, a measure of shareholder wealth creation, according to a study by Resource Data International and Deloitte Consulting. (Market value-added is the market capitalization of a company less the amount of capital invested in the company.)
Nuclear power plants provide low-cost, predictable power at stable prices and are essential in maintaining the reliability of the U.S. electric power system.
iv. Environmental Protection:
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Of all energy sources, nuclear energy has perhaps the lowest impact on the environment, including water, land, habitat, species and air resources. Nuclear energy is the most eco-efficient of all energy sources because it produces the most electricity in relation to its minimal environmental impact.
Nuclear energy is the world’s largest source of emission-free energy. Nuclear power plants produce no controlled air pollutants, such as sulphur and particulates, or greenhouse gases.
The use of nuclear energy in place of other energy sources helps to keep the air clean, preserves the Earth’s climate, avoids ground-level ozone formation and prevents acid rain. Between 1973 and 2000, nuclear generation avoided the emission of 66.1 million tons of sulphur dioxide and 33.6 million tons of nitrogen oxides.
Each year, U.S. nuclear power plants prevent 5.1 million tons of sulphur dioxide, 2.4 million tons of nitrogen oxides, and 164 million metric tons of carbon from entering the earth’s atmosphere. Nuclear power plants were responsible for nearly half of the total voluntary reductions in greenhouse gas emissions reported by U.S companies in 1998, the Energy Information Administration reported on January 4,2000.
“Emission reductions from nuclear energy usage reported by the electric power sector increased by 43 per cent from an estimated 70 million metric tons carbon dioxide equivalent for 1997 to 100 million metric tons carbon dioxide equivalent for 1998.” That 100 million metric tons equals 47 per cent of the 212 million metric tons of carbon emissions reductions reported nationwide, according of EIA.
Throughout the nuclear fuel cycle, the small volume of waste by-products actually created is carefully contained, packaged and safely stored. As a result, the nuclear energy industry is the only industry established since the industrial revolution that has managed and accounted for all of its waste, preventing adverse impacts to the environment.
Water discharged from a nuclear power plant contains no harmful pollutants and meets regulatory standards for temperature designed to protect aquatic life.
Effects of Nuclear Energy on the Environment:
Nuclear power stations and their supporting plants such as those for fuel reprocessing are associated with a number of an environmental effects. These stations, however, avoid many of the routine environmental effects associated with fossil – fuelled power stations.
Thus there is no thermal pollution from the emission of carbon dioxide and associated long – term threat to the worlds climate; there are no emissions of sulphur dioxide or fly ash; no coal tip; and the power station is smaller.
Environmental dangers related to nuclear power vary from low level radiation emissions to reactor explosions. The principal environmental effect is that of radiation. Unlike any of the environmental hazards associated with fossil fuels, radiation effects are mostly restricted to man.
These effects are both somatic (to the individuals exposed to the radiations) and genetic (to their offspring). Because of these dual effects, it is usual to measure radiation dose rates for both the bone marrow and for the reproductive organs. The principal long-term effect of radiation is the induction of cancers.
Some of the main worries concerning the large scale development of nuclear power relate to the problems of storing radioactive wastes, the security measures required to ensure that Plutonian is not acquired by terrorists and criminals, the proliferation of nuclear weapons, and the probability of catastrophic nuclear accidents.
Nearly all the radioactive material produced by nuclear power stations is in concentrated form and must be isolated from man’s environment. The question of the probability of large-scale nuclear accidents is very controversial.
To date, reactor accidents have been rare. The only known large-scale escape of a radioactivity to the surrounding ecosystem occurred as a result of a fire at the U.K. Atomic Energy Authority’s No.1 pile at Wind scale in 1957. There have been two other major accidents which took place at Chernobyl, Ukraine and Three Mile Island, Pennsylvania.
There are a number of possible policy instruments available to governments to reduce levels of pollution. These include the use of economic instruments, such as pollution charges or taxes, and regulatory instruments like the laying down of emission standards, the control of firms locations and the prohibition of the use of some fuels.
i. Health Effects:
Detailed studies of the radiological consequences of the accident have been conducted by the NRC, the Environmental Protection Agency, the Department of Health, Education and Welfare (now Health and Human Services), the Department of Energy, and the State of Pennsylvania.
Several independent studies have also been conducted. Estimates are that the average dose to about 2 million people in the area was only about 1 millirem. To put this into context, exposure from a full set of chest x-rays is about 6 millirem.
Compared to the natural radioactive background dose of about 100-125 millirem per year for the area, the collective dose to the community from the accident was very small. The maximum dose to a person at the site boundary would have been less than 100 millirem.
In the months following the accident, although questions were raised about possible adverse effects from radiation on human, animal, and plant life in the TMI area, none could be directly correlated to the accident.
Thousands of environmental samples of air, water, milk, vegetation, soil, and foodstuffs were collected by various groups monitoring the area. Very low levels of radionuclides could be attributed to releases from the accident.
However, comprehensive investigations and assessments by several well- respected organizations have concluded that in spite of serious damage to the reactor, most of the radiation was contained and that the actual release had negligible effects on the physical health of individuals or the environment.
The causes of the accident continue to be debated to this day.
However, based on a series of investigations, the main factors appear to have been a combination of personnel error, design deficiencies, and component failures. There is no doubt that the accident at Three Mile Island permanently changed both the nuclear industry and NRC.
Public fear and distrust increased, NRC’s regulations and oversight became broader and more robust, and management of the plants was scrutinized more carefully. The problems identified from careful analysis of the events during those days have led to permanent and sweeping changes in how NRC regulates its licensees – which, in turn, has strengthened public health and safety.
Environmental Benefits of Nuclear Power Generation Safety:
While no source of electrical power generation is completely safe, nuclear power has a remarkable record. About 20% of electricity generated in the U.S. comes from nuclear power, and in the last forty years of this production, not one single fatality has occurred as a result of the operation of a civilian nuclear power plant in the United States, Western Europe, Japan, or South Korea. No other form of energy production can even come close.
i. Zero Risk of Large Scale Oil Spills:
Incidentally, getting rid of our dependence on imported oil is desirable not only from an environmental standpoint, but from a political one. The largest single activity of our military today is ensuring the security of the Middle East for U.S. interests. As far as the risk of large oil spills, the Exxon Valdez spill of 1989 was one of the worst environmental disasters in history.
ii. Protection of Salmon Habitat:
No salmon have died as a result of nuclear power plant operation. The same cannot be said for hydro-electric power. As a result of the near-eradication of salmon runs, breaching hydro-electric dams on the Snake River in Washington is being seriously considered.
iii. Economical:
Nuclear power plants are one of the most economical forms of energy production. Fuel costs for an equivalent amount of power run from 1/3rd to 1/6th the cost for fossil production, and capital and non-fuel operating costs are roughly equivalent, resulting in the overall cost of nuclear generation of electricity running 50% to 80% that of other sources. This is in spite of the fact that capital costs have been hugely inflated due to lawsuits, court injunctions, and other delaying tactics used by individuals and organizations opposed to nuclear power.
iv. Reliability:
Nuclear power plant capacity factors average about 75% . This is about equivalent to those of fossil fired plants, and since nuclear plants are required by the NRC to shut down for what often amounts to trivial reasons, that would indicate they are actually more reliable than fossil plants. Wind and Solar power can’t come close to the capacity factors of nuclear power, for obvious reasons.
v. Sustainability:
Even if Uranium mining were stopped today, the use of breeder readers (which create more fuel than they use) would permit us to continue generating electricity at present levels for over a thousand years into the future. The Integral Fast Reactor, developed by Argonne National Laboratory, would have had this feature in addition to on- site fuel recycling, thus avoiding transport of spent fuel.
The population of the United States and the World is growing rapidly, and even with significant conservation measures, demand for electricity will increase.
This is particularly true if we can move a significant number of people from gasoline powered cars to light rail and electric automobiles, both of which require large amounts of electricity. Nuclear power is a proven, safe, and effective technology for production of electricity, and the technical issues of radiation control and waste management have long since been resolved.
Case Study-1 Chernobyl, Ukraine:
On 25 April 1986, prior to a routine shut-down, the reactor crew at Chernobyl-4 began preparing for a test to determine how long turbines would spin and supply power following a loss of main electrical power supply. Similar tests had already been carried out at Chernobyl and other plants, despite the fact that these reactors were known to be very unstable at low power settings.
A series of operator actions, including the disabling of automatic shutdown mechanisms, preceded the attempted test early on April 26. As flow of coolant water diminished, power output increased. When the operator moved to shut down the reactor from its unstable condition arising from previous errors, a peculiarity of the design caused a dramatic power surge.
The fuel elements ruptured and the resultant explosive force of steam lifted off the cover plate of the reactor, releasing fission products to the atmosphere.
A second explosion threw out fragments of burning fuel and graphite from the core and allowed air to rush in, causing the graphite moderator to burst into flames. There is some dispute among experts about the character of this second explosion. The graphite burned for nine days, causing the main release of radioactivity into the environment.
Some 5000 tonnes of boron, dolomite, sand, clay and lead were dropped on to the burning core by helicopter in an effort to extinguish the blaze and limit the release of radioactive particles. It is estimated that all of the xenon gas, about half of the iodine and cesium, and at least 5% of the remaining radioactive material in the Chernobyl-4 reactor core was released in the accident.
Most of the released material was deposited close by as dust and debris, but the lighter material was carried by wind over the Ukraine, Belarus, Russia and to some extent over Scandinavia and Europe.
The main casualties were among the fire-fighters, including those who attended the initial small fires on the roof of the turbine building. All these were put out in a few hours. Many children in the surrounding areas were exposed to radiation doses sufficient to lead to thyroid cancers (usually not fatal if diagnosed and treated early).
The Chernobyl accident at Chernobyl, Ukraine, was the worst accident in the history of nuclear energy, worse than all others put together. The following factors made the accident worse than is likely to happen in other plants.
1. The 16 RBMK reactors, of which the Chernobyl plant was one, are built without containment shells. In other reactors, the containment shell will keep almost all radioactive material from spreading in case of an accident.
2. RBMK reactors were intended to produce power and also to produce plutonium for military use. This required that it be possible to remove fuel rods for reprocessing by means of a crane on top of the reactor at short intervals in order to get Pu-239 without substantial admixture of Pu-240. These facilities made the reactor too tall for a containment structure used in Western and other Soviet reactors.
3. The reactor had several other features which were regarded as unsafe in the Soviet Union as well by experts from other countries.
The Soviet Union never exported RBMK reactors.
Positive void coefficient. If the water in the reactor boils in some spot a bubble of steam is produced. In PWR and BWR reactors, this reduces reactivity, causing the nuclear reaction to slow down. In RBMK reactors it causes the nuclear reaction to speed up.
Carbon moderator. This can catch fire in case of an accident and did at Chernobyl.
4. Making an experiment with the reactor which involved disabling its safety features. This is the single main cause of the accident. The safety features would have safely shut down the reactor if they hadn’t been disabled.
In order to prevent the reactor from shutting itself off from xenon poisoning, the operators pulled the control rods almost all the way out. This caused an enormous increase in the nuclear reaction to many times the reactor’s normal power level. This caused a steam explosion that blew the top off the reactor, probably stopping the nuclear reaction.
Then the carbon caught fire and burned for about nine days. This scattered the reactor contents and large amounts of radioactivity. 32 people died in the accident and in efforts to put out the fire. 38 more people died of acute radiation sickness in the following months. There were measureable health effects in Ukraine and Belarus.
The radioactivity spread over northern Europe caused some plants and wild animals to be more radioactive than was legal for human consumption.
However, there were no identifiable illnesses outside the Soviet Union.
(i) The Chernobyl accident in 1986 was the result of a flawed reactor design that was operated with inadequately trained personnel and without proper regard for safety.
(ii) The resulting steam explosion and fire released at least five percent of the radioactive reactor core into the atmosphere and downwind.
(iii) Some 31 people were killed, and there have since been around ten deaths from thyroid cancer due to the accident.
(iv) An authoritative UN report in 2000 concluded that there is no scientific evidence of any significant radiation-related health effects to most people exposed.
Leaving aside the verdict of history on its role in melting the Soviet iron curtain, some very tangible practical benefits have resulted from the Chernobyl accident. The mam ones concern reactor safety. While no one in the West was under any illusion about the safety of early Soviet reactor designs, some lessons learned have also been applicable to western plants.
Certainly the safety of all Soviet-designed reactors has improved vastly. This is due largely to the development of a culture of safety encouraged by increased collaboration between East and West, and substantial investment in improving the reactors.
Case Study-2 Three Mile Island, Pennsylvania:
The accident at the Three Mile Island Unit 2 (TMI-2) nuclear power plant near Middletown, Pennsylvania, on March 28,1979, was the most serious in U.S. commercial nuclear power plant operating history, even though it led to no deaths or injuries to plant workers or members of the nearby community.
But it brought about sweeping changes involving emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations. It also caused the U.S. Nuclear Regulatory Commission to tighten and heighten its regulatory oversight. Resultant changes in the nuclear power industry and at the NRC had the effect of enhancing safety.
The sequence of certain events – equipment malfunctions, design related core but only very small off-site releases of radioactivity, problems and worker errors – led to significant damage to the TMI-2 reactor Summary of Events
The accident began at about 4.00 a.m. on March 28,1979, when the plant experienced a failure in the secondary, non-nuclear section of the plant. The main feed water pumps stopped running, caused by either a mechanical or electrical failure, which prevented the steam generators from removing heat.
First the turbine, then the reactor automatically shut down. Immediately, the pressure in the primary system (the nuclear portion of the plant) began to increase. In order to prevent that pressure from becoming excessive, the pressurizer relief valve (a valve located at the top of the pressurizer) opened.
The valve should have closed when the pressure decreased by a certain amount, but it did not. Signals available to the operator failed to show that the valve was still open. As a result, the stuck-open valve caused the pressure to continue to decrease in the system.
Meanwhile, another problem appeared elsewhere in the plant. The emergency feed water system (backup to main feed water) was tested 42 hours prior to the accident. As part of the test, a valve is closed and then reopened at the end of the test. But this time, through either an administrative or human error, the valve was not reopened – preventing the emergency feed water system from functioning.
The valve was discovered closed about eight minutes into the accident. Once it was reopened, the emergency feed water system began to work correctly, allowing cooling water to flow into the steam generators.
As the system pressure in the primary system continued to decrease, voids (areas where no water is present) began to form in portions of the system other than the pressurizer. Because of these voids, the water in the system was redistributed and the pressurizer became full of water.
The level indicator, which tells the operator the amount of coolant capable of heat removal, incorrectly indicated the system was full of water. Thus, the operator stopped adding water. He was unaware that, because of the stuck valve, the indicator can, and in this instance did provide false readings.
Because adequate cooling was not available, the nuclear fuel overheated to the point where some of the zirconium cladding (the long metal tubes or jackets which hold the nuclear fuel pellets) reacted with the water and generated hydrogen.
This hydrogen was released into the reactor containment building. By March 30, two days after the start of the chain of events, some hydrogen remained within the primary coolant system in the vessel surrounding the reactor, forming a “hydrogen bubble” above the reactor core.
The concern was that if reactor pressure decreased, the hydrogen bubble would expand and thus interfere with the flow of cooling water through the core. Over the next few days, the bubble was reduced by “degassing” the pressurizer adjusting air and water pressure.
Without water to cool it, and with the top of the reactor core uncovered, the primary damage to the reactor occurred two to three hours into the accident. Although no “meltdown” occurred in the classic sense of the word, in that fuel did not “melt” through the floor beneath the containment or through the steel reactor vessel, a significant amount of fuel did in fact melt.
Radioactivity in the reactor coolant increased dramatically, and there were small leaks in the reactor coolant system which caused high radiation levels in other parts of the plant and small releases into the environment. Shortly after the accident began, some of the water, carrying fuel debris and fission products, escaped from the reactor coolant system and flowed into the reactor building basement.
By the time the accident had ended, the water in the basement had been heated by residual heat from the reactor vessel, evaporated, condensed on the walls, and drained down onto the floors and back into the basement.
The radionuclides then permeated into the porous surfaces of concrete and layers of iron which later became corroded (this area of the plant became a major focus of the subsequent clean-up and decontamination).
Conclusion:
Twenty years ago, on March 28th 1979, the reactor in Unit#2 at Three Mile Island near Harrisburg, Pennsylvania, suffered a malfunction, which, coupled with operator errors, resulted in the partial meltdown of the reactor core and release of radioactive coolant to the atmosphere. Although nobody was injured, this accident triggered widespread fear of nuclear energy in the public and calls for the abandonment of nuclear power.
Twenty years later, the nuclear energy industry is on the brink of a renaissance as the safety and economical production of electricity from nuclear plants reaches all-time highs. The entire nuclear power industry generates approximately 2,000 tons of solid waste annually in the United States. All technical and safety issues have been resolved in creation of a high-level waste repository in the United States.
Coal fired power produces 100,000,000 tons of ash and sludge annually, and this ash is laced with poisons such as mercury and nitric oxide. Industry generates 36,000,000 tons of hazardous waste, and the kind they make will be with us forever, not decaying away.
Also, this waste does not receive nearly the care and attention in disposal that radioactive waste does. This is not to say that radioactive waste is more dangerous; it is not.