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General Information
What is nuclear fuel and waste?
Nuclear fuel is made of solid pellets that contain enriched
uranium. These small, ceramic-like pellets create a tremendous
amount of energy when used in a nuclear power plant. For example,
one pellet has an amount of energy equivalent to almost one ton of
coal. The pellets are sealed in tubes of a strong corrosion- and
heat-resistant metal alloy. The tubes containing the uranium pellets
are bundled together to form a nuclear fuel assembly. The assemblies
are put inside a nuclear reactor and used to generate heat to make
electricity. The fuel will be used until it is no longer efficient
in generating heat, or "spent."
Nuclear waste is produced whenever we put nuclear fission to
work. Fission occurs when atoms split and cause a nuclear reaction.
At a nuclear power plant, fission happens under carefully controlled
conditions inside a nuclear reactor. Fission generates energy,
including heat. This heat is used to make steam, which turns
turbines to make electricity.
To understand how nuclear fuel generates electricity, think about
how other power plants work. When electricity is generated at
coal-fired plants, coal is burned to produce heat to make steam. At
nuclear power plants, fission within the fuel pellets creates the
heat used to make steam to turn turbines.
What happens to the spent fuel?
Once a year, approximately one-third of the nuclear fuel inside a
reactor is removed and replaced with fresh fuel. The used fuel is
called spent fuel. It is highly radioactive and is the primary form
of high-level nuclear waste. It must be disposed of carefully in a
repository for thousands of years because, if not properly
protected, its radioactivity can harm people and the environment.
Spent nuclear fuel and high-level radioactive waste are the
by-products of making electricity at commercial nuclear power plants
and from reprocessing spent nuclear fuel, that is, treating it
chemically to separate the uranium and plutonium. When spent fuel is
removed from a reactor, it is put into a pool of water at the
reactor site. The water is a radiation shield and coolant. Storing
the spent fuel in pools is intended only as a temporary measure
until a permanent disposal place is found.
As an alternative to storing in pools, some spent fuel is being
stored above ground at reactor sites in concrete or steel containers
called dry casks. Like storage under water in pools, this approach
also is intended as temporary.
While pool storage is effective for short-term storage, the need
to find safe, permanent disposal is becoming more critical because
at some nuclear power plants, the storage pools are almost full.
What about reprocessing the fuel?
The chemical process by which uranium and plutonium are recovered
from spent fuel is called reprocessing. Several countries with
nuclear power reprocess their spent fuel. Although the United States
reprocessed defense nuclear fuel, private industry in the United
States is not reprocessing fuel now because it costs more than
mining and making new fuel. Besides economic considerations, the
recycling process creates very hazardous radioactive and chemical
wastes. When defense spent fuel was reprocessed, a highly
radioactive and corrosive liquid by-product remained. This will be
turned into a solid, sand-like substance, melted, and poured into a
steel waste package where it will solidify as glass before it is
transported to and placed in a repository.
How long must a repository keep it secure?
A key element of disposal is that the U.S. Department of Energy
(DOE) must be able to demonstrate that a repository can be designed
and built that would protect public health and safety and the
environment for thousands of years. The preliminary repository
design includes a long-lived waste package and takes advantage of
the desert environment and geologic features of Yucca Mountain.
Together the natural and engineered barriers can keep water away
from the waste for thousands of years. Analyses of the preliminary
design using mathematical models, though subject to uncertainties,
indicate that public health and the environment can be protected.
Additionally, for 10,000 years after the repository is closed,
people living near Yucca Mountain are expected to receive little or
no increase in radiation exposure. The maximum radiation exposure
from a repository is expected to occur after about 300,000
years.1 People living approximately 20 kilometers (12
miles) from Yucca Mountain at that time might receive additional
radiation exposures equivalent to present-day background radiation.
How much spent nuclear fuel do we have?
As of September 2000, approximately 42,000 metric tons of spent
fuel are stored in pools and dry casks at power plants across the
country. By the year 2035, that amount could double, if all
currently operating plants complete their initial 40-year license
period. By 2035, the United States will have accumulated
approximately 2,500 metric tons of spent nuclear fuel from reactors
that produce materials for nuclear weapons, from research reactors,
and from reactors on the Navy's nuclear-powered ships and
submarines. The majority of DOE spent nuclear fuel is currently
stored at three major sites in the states of Idaho, South Carolina,
and Washington.
DOE has been studying Yucca Mountain for more than 20 years to
determine whether it is a suitable site for a repository. Even
though the projections for possible radiation exposure from a
repository in the distant future are modest, DOE's scientists and
engineers are continuing to look at ways to improve radiation
protection from a repository. Moreover, scientists will, for at
least 50 years, and as currently planned for up to 300 years, keep
an ongoing check that everything is functioning the way they
predicted it would.
1 The increase in exposure is due
primarily to the following changes occurring. The natural conditions
in the rock remain the same throughout time; however, somewhere
between 1,000 and 10,000 years from now, the climate is anticipated
to begin changing so that there is more rain. Such climate changes
have occurred in the past and will happen again. The likelihood is
that when the climate changes, more water will get into Yucca
Mountain and seep down into the repository, causing radionuclides to
be transported more efficiently by the additional water. These
natural, cyclical changes are modest. Rainfall, on average, doubled
during past wetter climates and will do so in the future when we
again have wetter climates. So the highest possible doses are
thought likely to occur at an extremely distant future - hundreds of
thousands of years from now.
For continuing updates on the site characterization, and
repository engineering and design efforts, call 1-800-225-6972 or
visit our Web site at http://www.ymp.gov/.
See
accompanying graphic
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Update September 2000 | 
