Nuclear power: benefits and challenges

Environmental Science

Nuclear Power

Technical Summary

To eventually produce electricity with nuclear energy, a mining company must first find, purify, supplement, and make fuel-grade uranium pellets. Uranium is an element that exists in somewhat different forms in nature. All uranium atoms have the same number of protons, but not all uranium atoms have the same number of neutrons. The heat that is fashioned by uranium comes from nuclear fission, a process that causes an atom to split into pieces. When uranium naturally decomposes, it emits neutrons. Loose neutrons will have a collision with other uranium atoms and cause them to split. In turn, more neutrons are released that have a collision with even more uranium atoms. This chain reaction can keep expanding exponentially until a huge nuclear explosion takes place. However, in a nuclear power plant, this chain reaction is controlled such that it does not produce more heat than the containment building and the reactor equipment can endure (Energy Information Administration, 2007).

There are two basic segments at the heart of a nuclear power plant. One major part is the reactor. The second major part is the generator. The reactor has a core, and the core consists of the fuel assembly with the tubes of uranium pellets, control rods, and circulating, highly purified water. The purpose of the fuel assembly is to place uranium in water so its nuclear fission will heat the water. The function of the control rods is to soak up more or fewer neutrons depending on whether more or less heat is needed. The more the control rods absorb, the slower the rate of fission. The closer the control rods are positioned to the fuel assembly, the more the control rods absorb neutrons (Childress, 2009.)

The generator, itself, has two basic parts, the stator, which is stationary, and the rotor, which rotates. The magnetic field is produced using electromagnets carefully positioned at different locations in the stator. The electricity that is used to produce the magnetism in these field magnets comes from the same power grid that serves other industries and commercial operations in the area. Electromagnets are coils of wire wrapped around an armature or metal frame that helps to structure the magnetic field (Childress, 2008).

Spent nuclear fuel remains radioactive for hundreds of thousands of years. Nuclear power plants have to alter out about one-third of their fuel assemblies yearly, producing an estimated two thousand metric tons of radioactive waste. Thus far, the United States has stored spent nuclear fuel deep underground in the Yucca Mountain storage facility, but Yucca Mountain is filled to its current legal capacity. The quantity of nuclear material that can be safely stored using current technology is limited because the spent nuclear fuel generates significant amounts of heat even after its initial cooling period. Argonne National Laboratory suggests that there are three options for the storage of nuclear waste from power plants. One option is to find another place similar to Yucca Mountain that will be free of significant earthquakes and cave-ins for more than one hundred thousand years. The other two options are partial recycling and full recycling. Recycling nuclear fuel means extracting remaining radioactive isotopes from the fuel pellets, but this is an area of critical research. There presently exists no way to prevent nuclear waste from remaining dangerously radioactive for generation after generation (Childress, 2008).

With Yucca Mountain at capacity, nuclear power plants are storing their own fuel assemblies on power plant premises. There are tons of stored fuels at plants across the country. There are two basic ways to store fuel on premises. One is in cooling pools, and the other is in large metal casks. The cooling pools are about twenty feet deep with water, and fuel assemblies are moved from the reactor to the cooling pool by moving them along a canal. Once a fuel assembly is sufficiently cool, it may be stored in a cask. Typical casks are about the size of a semi-trailer. They have double metal walls and are bolted shut (Childress, 2008).

Resources

Childress, V.W. (2008). Resources in technology: Energy perspective: Is hydroelectricity green? The TechnologyTeacher, 68(5), 4-9.

Childress, V.W. (2009). Producing Nuclear Power. Technology Teacher, 69(4), 5-10.

Energy Information Administration. (2007). Energy generating capacity. Washington, DC:

U.S. Department of Energy. Retrieved from http://www.eia.gov/cneaf/electricity/page/capacity/capacity.html

In 2002, nuclear power supplied twenty percent of United States and seventeen percent of world electricity consumption. Experts' estimate worldwide electricity consumption will augment considerably in the coming decades, particularly in the developing world, accompanying economic growth and social progress. Nevertheless, official forecasts call for a mere five percent increase in nuclear electricity generating capacity worldwide by 2020 and even this is questionable, while electricity use could grow by as much as seventy five percent (Chapter 1 -- The future of nuclear power -- overview and conclusions, n.d.)

Today, nuclear power is not an economically competitive choice. Furthermore, unlike other energy technologies, nuclear power necessitates considerable government involvement because of safety, proliferation, and waste concerns. If in the future carbon dioxide emissions carry a significant price, though, nuclear energy could be an important and maybe even fundamental option for generating electricity. It is not known whether this will take place or not. But it is thought that the nuclear options should be kept, precisely because it is an important carbon free source of power that can potentially make an important contribution to future electricity supply. In order to keep the nuclear option for the future requires overcoming the challenges of costs, safety, proliferation, and wastes. These challenges will go up if a considerable number of new nuclear generating plants are built in a growing number of countries. The effort to conquer these challenges, though, is justified only if nuclear power can potentially add significantly to dropping global warming, which involves major development of nuclear power. In effect, preserving the nuclear option for the future means planning for growth, as well as for a future in which nuclear energy is a spirited, safer, and more secure source of power (Chapter 1 -- The future of nuclear power -- overview and conclusions, n.d.)

A vital factor for the future of an expanded nuclear power industry is the choice of the fuel cycle to include what type of fuel is used, what types of reactors burn the fuel, and the method of disposal of the spent fuel. This option affects all four key problems that confront nuclear power. "There are three main types of nuclear fuel cycle deployments:

conventional thermal reactors operating in a once through mode, in which discharged spent fuel is sent straight to disposal thermal reactors with reprocessing in a closed fuel cycle, which means that waste products are divided from unused fissionable material that is re-cycled as fuel into reactors. This includes the fuel cycle currently used in some countries in which plutonium is divided from spent fuel, fabricated into an assorted plutonium and uranium oxide fuel, and recycled to reactors for one pass fast reactors with reprocessing in a balanced closed fuel cycle, which means thermal reactors operated globally in once-through mode and a balanced number of fast reactors that obliterate the actinides separated from thermal reactor spent fuel. The fast reactors, reprocessing, and fuel fabrication facilities would be co-located in secure nuclear energy parks in industrial countries" (Chapter 1 -- The future of nuclear power -- overview and conclusions, n.d.)

Closed fuel cycles extend fuel supplies. The feasibility of the once-through option in a global growth scenario depends upon the quantity of uranium resource that is available at economically attractive prices. It is thought that the universal supply of uranium ore is sufficient to fuel the deployment of one thousand reactors over the next half century and to uphold this level of deployment over a forty year lifetime of this fleet (Chapter 1 -- The future of nuclear power -- overview and conclusions, n.d.)

Operational security is a major concern for those working in nuclear plants. Radiation doses are controlled by the use of distant handling equipment for a lot of operations in the core of the reactor. Other controls include physical protecting and restricting the time workers spend in areas with significant radiation levels. These are supported by constant monitoring of individual doses and of the work environment to make sure very low radiation exposure compared with other industries (Safety of nuclear power reactors, 2011).

One mandated safety indicator is the calculated likely frequency of degraded core or core melt accidents. The U.S. Nuclear Regulatory Commission (NRC) specifies that reactor designs must meet a one in ten thousand year core damage frequency, but modern designs go beyond this. U.S. utility requirements are one in one hundred thousand years, the best presently operating plants are about one in one million and those likely to be built in the next decade are almost one in ten million. While this calculated core damage occurrence has been one of the main metrics to evaluate reactor safety, European safety authorities prefer a deterministic approach, focusing on real provision of back-up hardware, though they also take on probabilistic safety investigation for core damage incidence (Safety of nuclear power reactors, 2011).

By regulation, the design of the nuclear reactor must include stipulations for human operator error and equipment failure. Nuclear Plants in the western world use a Defense in Depth idea which is a system with numerous safety components, each with back-up and design to accommodate human error. The components include:

"Control of Radioactivity - This requires being able to control the neutron flux. If the neutron flux is decreased the radioactivity is decreased. The most common way to reduce the neutron flux is include neutron-absorbing control rods. These control rods can be partially inserted into the reactor core to reduce the reactions. The control rods are very important because the reaction could run out of control if fission events are extremely frequent. In modern nuclear power plants, the insertion of all the control rods into the reactor core occurs in a few seconds, thus halting the nuclear reaction as rapidly as possible. In addition, most reactors are designed so that beyond optimal level, as the temperature increases the efficiency of reactions decreases, hence fewer neutrons are able to cause fission and the reactor slows down automatically.

Maintenance of Core Cooling - In any nuclear reactor some sort of cooling is necessary. Generally nuclear reactors use water as a coolant. However some reactors which cannot use water use sodium or sodium salts.

Maintenance of barriers that prevent the release of radiation - There is a series of physical barriers between the radioactive core and the environment. This means that if any radiation were to leak from the reactor it would be sucked into the vacuum building and therefore prevented from being released into the environment" (Safety of nuclear power reactors, 2011).

The design of the reactor also includes numerous back-up components, independent systems meaning two or more systems performing the same task in parallel, watching of instrumentation and the deterrence of a failure of one kind of equipment affecting any other.

Further, regulation necessitates that a core-meltdown occurrence must be restricted only to the plant itself without the need to empty nearby residence. Safety is also significant for the workers of nuclear power plants. Radiation doses are controlled via the following procedures:

The treatment of equipment via secluded in the core of the reactor

Physical shielding

Limit on the time a worker spends in areas with important radiation levels

Monitoring of individual doses and of the work environment (Safety of nuclear power reactors, 2011).

Inside a nuclear power plant, emergency diesel backup generators (EDBG's) are a very important part of plant safety systems. In standard operation, a nuclear plant produces the power needed to operate its coolant circulation system and other safety critical systems. In the occasion that power from the plant itself, or from the electricity grid, should not be accessible. EDBG's spring into action to make sure that coolant circulation is maintained and the reactor can be safely shut down. So vital are EDBG's that every nuclear reactor has at least two of them, ready to start at a moment's notice. As well as being present in replacement to make certain redundancy at all times, nuclear power plant EDBG's are subject to meticulous regulatory control to guarantee their availability and reliability. They must meet strict technical requirements, characteristically being able to reach their rated voltage and occurrence within ten seconds of startup (Maden, 2011).

After setting up, EDBG's must pass recurrent and rigorous tests as prescribed by the relevant national regulator to ensure their availability and reliability. The U.S. Nuclear Regulatory Commission, for instance, requires each EBDG to be started up and loaded at least once every thirty one days, with additional tests necessary at six-monthly intervals, plus further widespread tests at every refueling outage or at least once every two years. Every ten years, when the plant is in outage, the NRC requires all redundant EBDG units to be started at the same time in order to recognize any frequent failure modes that have gone undetected in tests of the single units (Maden, 2011).

Overall the safety of nuclear power is relatively good. Throughout its history there have been three main accidents that have involved unclear power. When comparing this to other energy producing industries this is low. Every year several thousand people die in coal mines to supply this widely used fuel for electricity. There are also important health and environmental effects arising from fossil fuel use. To date, even the Fukushima accident has caused no deaths, and the IAEA reports that to date no health effects have been reported in any person as a result of radiation exposure (Safety of nuclear power reactors, 2011).

The three significant accidents in the fifty year history of civil nuclear power generation are:

Three Mile Island (USA 1979) where the reactor was harshly damaged but radiation was controlled and there were no unfavorable health or environmental penalties

Chernobyl (Ukraine 1986) where the demolition of the reactor by steam explosion and fire killed thirty one people and had important health and environmental consequences. The death toll has since increased to about five

Fukushima (Japan 2011) where three old reactors, together with a fourth, were written off and the effects of loss of cooling due to a huge tsunami were insufficiently contained.

These three significant accidents took place during more than fourteen thousand reactor-years of operation. Of all the accidents and incidents, only the Chernobyl and Fukushima accidents resulted in radiation doses to the public greater than those resulting from the contact with natural sources. The Fukushima accident resulted in some radiation exposure of workers at the plant, but not such as to threaten their health. Other incidents and one accident have been totally confined to the plant. Apart from Chernobyl, no nuclear workers or members of the public have ever died as a result of exposure to radiation due to a commercial nuclear reactor incident. The majority of the serious radiological injuries and deaths that take place each year, two to four deaths and many more exposures above regulatory limits are the result of large unrestrained radiation sources, such as abandoned medical or industrial equipment. There have also been a number of accidents in experimental reactors and in one military plutonium-producing pile, but none of these resulted in loss of life outside the actual plant, or long-term environmental contamination (Safety of nuclear power reactors, 2011).

The primary safety concern has always been the possibility of an unrestrained release of radioactive material, leading to contamination and consequent radiation exposure off-site. Earlier assumptions were that this would be likely in the event of a major loss of cooling accident (LOCA) which resulted in a core melt. The TMI experience suggested otherwise, but at Fukushima this is exactly what happened. In the light of better understanding of the physics and chemistry of material in a reactor core under intense conditions it became evident that even a severe core melt coupled with breach of containment would be improbable to create a major radiological disaster from many Western reactor designs, but the Fukushima accident showed that this did not apply to all. Studies of the post-accident situation at Three Mile Island where there was no breach of containment supported the suggestion, and analysis of Fukushima is pending (Safety of nuclear power reactors, 2011).

Over the years, the price of electricity, gasoline, and heating fuel have been growing at unaffordable rates due to a fear that we will run out of petroleum, coal, and natural gas. Also, atmospheric exhaustion is on the rise due to pollution from the burning of fossil fuels.

A lot of countries throughout the world are now using nuclear energy as a major source of energy, and the United States should as well. By using nuclear power, the United States can help decrease the ozone depletion, lower the cost of energy for the citizens, and have a limitless supply of energy for billions of years to come (Dettmering, n.d.).

In order to understand nuclear energy, a person must first understand what a nuclear reaction is. There are two types; a fusion reaction and a fission reaction. A fusion reaction is when an atom of tritium smashes into a deuterium atom, and combines to form a helium atom and a neutron. This is the most powerful nuclear reaction. The other kind of reaction is a fission reaction. In a fission reaction, a neutron collides into an enriched uranium atom, splitting it, and releasing another uranium atom and two neutrons. When this process continues with the collisions it is called a nuclear chain reaction. This is the present nuclear reaction that takes place within the nuclear power plants around the world. This reaction is only one of the factors that are accountable for the creation of electricity within a nuclear power plant. Once the reaction takes place, a large quantity of heat is given off. This all happens within the reactor core. This heats the water around the core and then the water turns to steam. The steam then travels through pipes and causes the turbine to spin. This spinning of the turbine spins a large generator, creating electricity. However, the process that happens within a nuclear power plant does not stop here. The steam then is cooled by cold water coming from the cooling tower travelling into the condenser below the turbine. This drops the temperature causing it to turn back into water. This water is then pumped back to the reactor to be reheated and continue the process again (Dettmering, n.d.).

Today, nuclear energy is America's second largest source of electric power after coal. More than one hundred and ten nuclear energy plants provide more electricity than oil natural gas or hydropower. Nuclear energy is a cheap effective source of energy. Since this point in time, new technology and research have lowered the cost of nuclear energy even more, where as war and the scare of and oil shortage have driven the price of the other energy sources up considerably. Since 1973, nuclear energy has saved American consumers over forty billion, compared to the other fuels that would have been used to make electricity (Dettmering, n.d.).