Environmental Engineering Reference
In-Depth Information
the greatest portion of uranium becomes a predominantly uranium-238 waste product impoverished
in uranium-235 that cannot be released to the environment and is stored in cylinders as UF
6
.
Fuel Fabrication
The enriched portion of UF
6
is processed into uranium dioxide (UO
2
) pellets, loaded into alloy
tubing, and fabricated into individual fuel assemblies that may be inserted into a power reac-
tor (USEPA 1973a, 2). Systems for conversion of UF
6
to UO
2
are equipped with scrubbers and
high-efficiency particulate air filters for uranium dust removal, which is recycled into the pellet
fabrication process (USEPA 1973a, 17).
Transportation
The principal mode of exposure of a human population to radioactivity in the uranium fuel cycle
is from direct radiation resulting from the passage of hundreds of shipments per year of fuel and
waste products along rail, truck, and barge shipment routes. There are no planned releases of ra-
dioactive materials from transportation activities, so this pathway for radiation exposure is based
entirely on the risk of accidents. Effects are long-term radiation exposure to the skeleton and other
organs of the body, especially the lungs (USEPA 1973a, 9).
Nuclear electric generating plants accounted for about 9.7 percent of summer installed generating
capacity at 104 generating units (USEIA 2011c, Table 1.1.A) and generated about 19.6 percent
of the electricity produced in the United States during 2008 (USEIA 2011d, Table 2.1.A). Like
coal-fired generators, each power plant requires dedication of several hundred to a few thousand
acres of land to a single large industrial use for one or more reactors and generators, unused fuel
handling and storage facilities, spent fuel handling and storage facilities, cooling water storage
and purification, and solid waste, low-level, and high-level radioactive waste handling and storage
facilities, access to which must be severely restricted for safety and security reasons.
Nuclear power plants rely on heat energy generated from nuclear fission to produce steam that
turns a turbine to generate electricity. A nuclear reactor replaces an industrial boiler to produce
steam, but the turbine generator and many auxiliary systems are quite similar to those used to
generate electricity in conventional fossil-fueled generating units. The principal differences are
the nuclear heat source and reactor safety systems.
In the nuclear fission process, the nucleus of a heavy element such as uranium or plutonium
splits when bombarded by neutrons in a nuclear reactor. The fission process for uranium atoms
yields small amounts of radioactive materials and tremendous amounts of energy in the form of
radiation and heat. Because more neutrons are released from uranium fission than are required to
initiate it, the nuclear reaction can become self-sustaining—a chain reaction—under controlled
conditions, thus producing a tremendous amount of energy (USEIA 2011e). The process is es-
sentially identical to that in a nuclear explosion, except in a nuclear reactor it takes place under
controlled conditions at a much slower rate.
In most commercial nuclear power plants, heat energy generated by uranium fuel is transferred
to ordinary water that is carried away from the reactor's core either as steam in boiling-water
reactors (BWRs) or as superheated water in pressurized-water reactors (PWRs). Boiling-water and
pressurized-water reactors are sometimes called light-water reactors (LWRs), because they utilize
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