An enormous amount of energy exists in the bonds that hold atoms together. This energy can be released through nuclear fission, the splitting of one atom into two or more lighter atoms; or nuclear fusion, the joining of two atoms. At present, only fission can be used to generate electricity.
Energy is released when the nuclei of certain atoms absorb a free neutron, become unstable and split apart, releasing one or more free neutrons. The process is repeated, creating a self-sustained chain reaction. In commercial nuclear power plants, the resulting heat is used to create steam that turns a turbine and generates electricity, without producing greenhouse gas emissions.
Texas has two operating nuclear power facilities, Comanche Peak in Glen Rose and the South Texas Project located near Bay City. Together, the two facilities employ more than 2,000 people with a combined payroll of nearly $200 million annually.
And more facilities are on the horizon. Owners of the South Texas Project have submitted an application to the U.S. Nuclear Regulatory Commission (NRC) to expand their facility. And over the next two years, the NRC expects to receive applications for six more new nuclear reactors in Texas, two more at Comanche Peak and four at two new sites. Once complete, these new reactors will require several thousand employees.
Ancient Greek philosophers first developed the idea that all matter is made of atoms. During the 18th and 19th centuries, scientists conducted experiments to unlock the secrets of the atom. In 1904, British physicist Ernest Rutherford wrote, “If it were ever possible to control at will the rate of disintegration of the radio elements, an enormous amount of energy could be obtained from a small amount of matter.”
One year later, Albert Einstein developed his theory of the relationship between mass and energy. Einstein’s mathematical representation of his theory, E=mc2, related the amount of energy that could be derived from a mass if it were transformed to energy. In 1938, Lise Meitner and Otto Hahn first provided the first experimental evidence of the release of energy from fission.
The world’s first self-sustained nuclear fission chain reaction occurred on December 2, 1942, in a squash court under the University of Chicago’s Stagg Field. Enrico Fermi’s reactor, Chicago Pile 1, was built of six tons of uranium metal, 34 tons of uranium oxide, nearly 400 tons of graphite bricks (to moderate the reaction) and cadmium rods to absorb free neutrons. After World War II, following the success of the Manhattan Project that developed the atomic bomb, the U.S. began to use nuclear energy for non-military purposes.
The first reactor to generate electricity was an experimental breeder reactor run by the U.S. government in Arco, Idaho, beginning on December 20, 1951. Breeder reactors differ from commercial light-water reactors by using a fast neutron process that produces, or breeds, more fuel than it consumes. Civilian commercial nuclear reactors in the U.S. are all light-water reactors, which use ordinary water to cool the reactor cores.
The first civilian nuclear power plant began generating electricity at Santa Susana, California on July 12, 1957. The first large-scale commercial nuclear power plant in the U.S. began operating on December 2, 1957, in Shippingport, Pennsylvania and continued to operate until it was shut down in 1982.
The military uses nuclear energy for explosive warheads and naval propulsion, which was pioneered by the U.S. Navy. The first nuclear-powered submarine, the USS Nautilus, was launched in 1954.
Commercial nuclear energy is used primarily to generate electricity. Today, the U.S. has 104 licensed commercial nuclear reactors that provide approximately 20 percent of the nation’s electricity. In 2006, total generating nameplate capacity for the nation’s nuclear power plants was about 106,000 megawatts (MW), or 9.8 percent of the total nameplate capacity of all electricity generation in the U.S. Nameplate capacity is the maximum rated output of a generator as designated by the manufacturer. It is called such because this capacity is typically written on a nameplate that is physically attached to the generator.
New nuclear power plants obviously will need trained employees – but finding them may be a challenge. The nuclear industry already foresees difficulties with an aging work force; a large percentage of the nation’s nuclear employees will be eligible for retirement in five to ten years. In addition, new “Generation III” and “Generation III+” plant designs feature updated technologies, such as digital instrumentation and control systems, which are not present in the operating plants.
Problems involving the energy industry work force have caught the attention of the nation’s leaders. At an August 2007 meeting of the Southern Governors Association, an “Energy Summit” was convened in conjunction with the U.S. Department of Labor Employment and Training Administration. Assistant Secretary of Labor Emily Stover DeRocco led the conference. Each state was asked to develop a strategy to respond to the challenge of producing the work force needed by the energy industry. Nuclear energy was a major part of this discussion.
The eight new reactors anticipated in Texas will need several thousand workers. Many of these positions will involve technically sophisticated tasks requiring qualified and well-trained individuals.
For operational and technician positions, nuclear utilities provide training lasting up to three years. The curriculum for such training is established by the National Academy for Nuclear Training (NANT) and the Institute of Nuclear Power Operations (INPO).
The utilities with plans to build new plants in Texas have identified additional workers as part of the “critical path” to successful operations. The Texas Workforce Commission is working with these utilities to create the Texas Nuclear Workforce Development Initiative, a grant program to encourage universities, community colleges and the Texas State Technical College to recruit young people into two-year and four-year programs to prepare them for jobs in the new plants. These programs will give students the background in nuclear systems and operations they will need to enter into accelerated training programs upon hiring.
The initiative will offer attractive opportunities for young Texans to find high-paying jobs that allow them to remain in the state and contribute to the growth of the Texas economy.
All U.S. commercial nuclear power plants use enriched uranium fuel pellets in their reactor cores. The three naturally occurring varieties, or isotopes, of uranium are U-234, U-235 and U-238. Uranium-235, which makes up only 0.72 percent of all available uranium, is the only naturally occurring uranium isotope capable of undergoing fission and sustaining a chain reaction under typical civilian power generation conditions.
Uranium Mining and Enrichment
Uranium is found in the earth’s crust and in seawater. All uranium used in the nuclear fuel cycle comes from deposits found on land.
In its natural state, uranium is an ore that must be mined. Once mined, uranium is processed into uranium oxide, sometimes called “yellowcake.” To be enriched for use in a nuclear power plant – that is, to increase its amount of U-235 – uranium oxide must be converted to uranium hexafluoride and then transformed to a gas.
After being enriched to a level of between 3 percent and 5 percent U-235, uranium hexafluoride is converted to uranium dioxide and fabricated into cylindrical fuel pellets. These pellets are loaded into fuel rods that are in turn grouped in fuel assemblies, built to the specifications of each individual reactor. In theory, one pellet weighing only 0.24 ounces can generate as much energy as 1,780 pounds of coal or 19,200 cubic feet of natural gas.
Commercial nuclear reactors have a core composed of fuel assemblies and control rods made of neutron-absorbing materials such as boron or hafnium that can be used to dampen and thus control the nuclear reaction.
Fuel assemblies are transported by truck, rail, air or water to their specific nuclear reactor. Both the U.S. Department of Transportation and the U.S. Nuclear Regulatory Commission (NRC) oversee the security of the transport of nuclear materials.
The number of fuel assemblies in the reactor core depends on the reactor’s size and design. Reactor power output can vary significantly depending on the number of assemblies as well as other factors.
Inside the reactor core, U-235 atoms absorb a neutron and become U-236, which has an unstable nucleus. About 84 percent of the time, the U-236 atoms spontaneously split apart. This fission releases a number of products including gamma rays, beta particles, neutrons, neutrinos and, usually, two fission fragments of the original atom.
These fission fragments carry a large amount of kinetic energy. They collide with the fuel, converting their kinetic energy into increased vibrational energy, or heat. Neutrons released by the fission process are absorbed by other U-235 atoms, turning them into U-236. The process repeats, creating a self-sustaining chain reaction. Control rods are inserted into or withdrawn from the reactor core to regulate the chain reaction by absorbing neutrons and thus preventing them from striking more U-235 atoms.
The heat produced by this self-sustaining chain reaction is used to turn water to steam. The steam then is used to spin a turbine attached to a generator, producing electricity.
In addition to the fission fragments, neutrons that are absorbed by U-235 that do not result in fission or are absorbed in U-238 will produce other radioactive isotopes called actinides or transuranic elements, including plutonium, neptunium, americium and curium.
The two most common types of commercial nuclear reactors used to generate electricity are pressurized water reactors (PWRs) and boiling water reactors (BWRs). Of the 104 commercial reactors in the United States, 69 are PWRs and 35 are BWRs. Both Comanche Peak andSTP use PWRs.
Pressurized water reactors (PWRs) involve three “loops.” The primary loop passes through the reactor core and carries away the heat energy generated in the fuel. The secondary loop absorbs the heat from the first loop in a component called a steam generator, and carries it to the turbine. A third loop rejects the unused heat energy to the atmosphere, either through a cooling tower or into a cooling pond or river. The primary water loop is heated to about 600°F; because the water is under high pressure, it does not boil. Water in the secondary water loop is under lower pressure and heated to 450 to 500°F, which creates steam. The steam hits turbine blades with a pressure of about 1,000 pounds per square inch. The turbine turns a generator that produces electricity .
BWRs have only two loops. Water passes through the reactor core where it boils, creating steam. From the steam generator, a steam line is directed to a turbine that turns a generator used to produce electricity. The steam passes through a condenser where it is turned into water and returned to the reactor core, repeating the process. A secondary coolant loop rejects excess heat energy to the atmosphere. The steam used to turn the turbine comes in contact with the reactor core, making it radioactive.
Depending on variables unique to each reactor, fuel assemblies within the reactor core are replaced about every 18 months to ensure optimum performance.
The U.S. Nuclear Regulatory Commission (NRC) has certified or is reviewing design certification applications for a new generation – “Generation III” – of nuclear reactors in the U.S. Generation III reactors feature design improvements over Generation II reactors, which are currently operating in the U.S.
NRC has certified the design of the Westinghouse AP1000, a 1,000 to 1,200 MW (electric) pressurized water reactor. Six utility companies have selected the AP1000 for 14 reactors to be constructed at seven sites across the U.S.
General Electric has received design certification for its advanced boiling water reactor (ABWR) design, capable of producing 1,350 to 1,600MW. NRG Energy has chosen the ABWR design for two new reactors it plans to build at the South Texas Project in Matagorda County. On September 24, 2007, NRG submitted the first combined Construction and Operating License Application to NRC for the new reactors. NRG expects both units to be operational by 2015.
NRC also has received an application for design certification for General Electric’s Economic Simplified Boiling Water Reactor (ESBWR). The review process for the ESBWR should be completed by fiscal 2012. NRC received design certification applications for the Mitsubishi U.S. Advanced Pressurized Water Reactor (US-APWR) and the Areva Evolutionary Pressurized Water Reactor (EPR) in December 2007.
Other types of reactors include pressurized heavy water reactors, high-temperature, gas-cooled reactors, pebble-bed reactors, sodium-cooled reactors, heavy metal-cooled reactors, supercritical water reactors and molten salt reactors. With the exception of the heavy water reactor, all are considered to be “Generation IV” designs that could be ready for commercial deployment by 2030. So far, none of these types have been submitted to the NRC for use in civilian power plants in the U.S.