A
nuclear reactor is only part of the life-cycle for nuclear power. The process
starts with mining (see Uranium mining). Uranium mines are
underground, open-pit, or in-situ leach mines. In any case, the uranium ore is
extracted, usually converted into a stable and compact form such as yellowcake,
and then transported to a processing facility. Here, the yellowcake is converted
to uranium hexafluoride, which is then enriched using various techniques. At
this point, the enriched uranium, containing more than the natural 0.7% U-235,
is used to make rods of the proper composition and geometry for the particular
reactor that the fuel is destined for. The fuel rods will spend about 3
operational cycles (typically 6 years total now) inside the reactor, generally
until about 3% of their uranium has been fissioned, then they will be moved to
a spent fuel pool where the short lived isotopes generated by fission can decay
away. After about 5 years in a cooling pond, the spent fuel is radioactively
and thermally cool enough to handle, and it can be moved to dry storage casks
or reprocessed.
Uranium
is a fairly common element in the Earth's crust. Uranium is approximately as
common as tin or germanium in Earth's crust, and is about 35 times more common
than silver. Uranium is a constituent of most rocks, dirt, and of the oceans.
The fact that uranium is so spread out is a problem because mining uranium is
only economically feasible where there is a large concentration. Still, the
world's present measured resources of uranium, economically recoverable at a
price of 130 USD/kg, are enough to last for "at least a century" at
current consumption rates. This represents a higher level of assured resources
than is normal for most minerals. On the basis of analogies with other metallic
minerals, a doubling of price from present levels could be expected to create
about a tenfold increase in measured resources, over time. However, the cost of
nuclear power lies for the most part in the construction of the power station.
Therefore the fuel's contribution to the overall cost of the electricity
produced is relatively small, so even a large fuel price escalation will have
relatively little effect on final price. For instance, typically a doubling of
the uranium market price would increase the fuel cost for a light water reactor
by 26% and the electricity cost about 7%, whereas doubling the price of natural
gas would typically add 70% to the price of electricity from that source. At
high enough prices, eventually extraction from sources such as granite and
seawater become economically feasible.
Current
light water reactors make relatively inefficient use of nuclear fuel,
fissioning only the very rare uranium-235 isotope. Nuclear reprocessing can
make this waste reusable and more efficient reactor designs allow better use of
the available resources.
As
opposed to current light water reactors which use uranium-235 (0.7% of all
natural uranium), fast breeder reactors use uranium-238 (99.3% of all natural
uranium). It has been estimated that there is up to five billion years’ worth
of uranium-238 for use in these power plants.
Breeder
technology has been used in several reactors, but the high cost of reprocessing
fuel safely requires uranium prices of more than 200 USD/kg before becoming
justified economically. As of December 2005, the only breeder reactor producing
power is BN-600 in Beloyarsk, Russia. The electricity output of BN-600 is 600
MW — Russia has planned to build another unit, BN-800, at Beloyarsk nuclear
power plant. Also, Japan's Monju reactor is planned for restart (having been
shut down since 1995), and both China and India intend to build breeder
reactors.
Another
alternative would be to use uranium-233 bred from thorium as fission fuel in
the thorium fuel cycle. Thorium is about 3.5 times as common as uranium in the
Earth's crust, and has different geographic characteristics. This would extend
the total practical fissionable resource base by 450%. Unlike the breeding of
U-238 into plutonium, fast breeder reactors are not necessary — it can be
performed satisfactorily in more conventional plants. India has looked into
this technology, as it has abundant thorium reserves but little uranium.
Fusion
power advocates commonly propose the use of deuterium, or tritium, both
isotopes of hydrogen, as fuel and in many current designs also lithium and
boron. Assuming a fusion energy output equal to the current global output and
that this does not increase in the future, then the known current lithium
reserves would last 3000 years, lithium from sea water would last 60 million
years, and a more complicated fusion process using only deuterium from sea
water would have fuel for 150 billion years. Although this process has yet to
be realized, many experts and civilians alike believe fusion to be a promising
future energy source due to the short lived radioactivity of the produced
waste, its low carbon emissions, and its prospective power output.
The most important waste stream from
nuclear power plants is spent nuclear fuel. It is primarily composed of
unconverted uranium as well as significant quantities of transuranic actinides
(plutonium and curium, mostly). In addition, about 3% of it is fission products
from nuclear reactions. The actinides (uranium, plutonium, and curium) are
responsible for the bulk of the long-term radioactivity, whereas the fission
products are responsible for the bulk of the short-term radioactivity.
After
about 5 percent of a nuclear fuel rod has reacted inside a nuclear reactor that
rod is no longer able to be used as fuel (due to the build-up of fission
products). Today, scientists are experimenting on how to recycle these rods so
as to reduce waste and use the remaining actinides as fuel (large-scale
reprocessing is being used in a number of countries).
A
typical 1000-MWe nuclear reactor produces approximately 20 cubic meters (about
27 tonnes) of spent nuclear fuel each year (but only 3 cubic meters of
vitrified volume if reprocessed). All the spent fuel produced to date by all
commercial nuclear power plants in the US would cover a football field to the
depth of about one meter.
Spent
nuclear fuel is initially very highly radioactive and so must be handled with
great care and forethought. However, it becomes significantly less radioactive
over the course of thousands of years of time. After 40 years, the radiation
flux is 99.9% lower than it was the moment the spent fuel was removed from operation,
although the spent fuel is still dangerously radioactive at that time. After
10,000 years of radioactive decay, according to United States Environmental
Protection Agency standards the spent nuclear fuel will no longer pose a threat
to public health and safety.
When
first extracted, spent fuel rods are stored in shielded basins of water (spent
fuel pools), usually located on-site. The water provides both cooling for the
still-decaying fission products, and shielding from the continuing
radioactivity. After a period of time (generally five years for US plants), the
now cooler, less radioactive fuel is typically moved to a dry-storage facility
or dry cask storage, where the fuel is stored in steel and concrete containers.
Most U.S. waste is currently stored at the nuclear site where it is generated,
while suitable permanent disposal methods are discussed.
As
of 2007, the United States had accumulated more than 50,000 metric tons of
spent nuclear fuel from nuclear reactors. Permanent storage underground in U.S.
had been proposed at the Yucca Mountain nuclear waste repository, but that
project has now been effectively cancelled - the permanent disposal of the
U.S.'s high-level waste is an as-yet unresolved political problem.
The
amount of high-level waste can be reduced in several ways, particularly Nuclear
reprocessing. Even so, the remaining waste will be substantially radioactive
for at least 300 years even if the actinides are removed, and for up to
thousands of years if the actinides are left in. Even with separation of all
actinides, and using fast breeder reactors to destroy by transmutation some of
the longer-lived non-actinides as well, the waste must be segregated from the
environment for one to a few hundred years, and therefore this is properly categorized
as a long-term problem. Subcritical reactors or fusion reactors could also
reduce the time the waste has to be stored.
According
to a 2007 story broadcast on 60 Minutes, nuclear power gives France
the cleanest air of any industrialized country, and the cheapest electricity in
all of Europe. France reprocesses its nuclear waste to reduce its mass and make
more energy. However, the article continues, "Today we stock containers of
waste because currently scientists don't know how to reduce or eliminate the
toxicity. Nuclear waste is an enormously difficult political problem which to
date no country has solved. It is, in a sense, the Achilles heel of the nuclear
industry. If France is unable to solve this issue, says Mandil, then 'I do not
see how we can continue our nuclear program.'" Further, reprocessing
itself has its critics, such as the Union of Concerned Scientists.
The
nuclear industry also produces a huge volume of low-level radioactive waste in
the form of contaminated items like clothing, hand tools, water purifier
resins, and (upon decommissioning) the materials of which the reactor itself is
built. In the United States, the Nuclear Regulatory Commission has repeatedly
attempted to allow low-level materials to be handled as normal waste:
landfilled, recycled into consumer items, et cetera. Most low-level waste
releases very low levels of radioactivity and is only considered radioactive waste
because of its history.
In
countries with nuclear power, radioactive wastes comprise less than 1% of total
industrial toxic wastes, much of which remains hazardous indefinitely. Overall,
nuclear power produces far less waste material by volume than fossil-fuel based
power plants. Coal-burning plants are particularly noted for producing large
amounts of toxic and mildly radioactive ash due to concentrating naturally
occurring metals and mildly radioactive material from the coal. A recent report
from Oak Ridge National Laboratory concludes that coal power actually results
in more radioactivity being released into the environment than nuclear power
operation, and that the population effective dose equivalent from radiation
from coal plants is 100 times as much as from ideal operation of nuclear
plants. Indeed, coal ash is much less radioactive than nuclear waste, but ash
is released directly into the environment, whereas nuclear plants use shielding
to protect the environment from the irradiated reactor vessel, fuel rods, and
any radioactive waste on site.
Reprocessing
can potentially recover up to 95% of the remaining uranium and plutonium in
spent nuclear fuel, putting it into new mixed oxide fuel. This produces a
reduction in long term radioactivity within the remaining waste, since this is
largely short-lived fission products, and reduces its volume by over 90%.
Reprocessing of civilian fuel from power reactors is currently done on large scale
in Britain, France and (formerly) Russia, soon will be done in China and
perhaps India, and is being done on an expanding scale in Japan. The full
potential of reprocessing has not been achieved because it requires breeder
reactors, which are not yet commercially available. France is generally cited
as the most successful reprocessor, but it presently only recycles 28% (by
mass) of the yearly fuel use, 7% within France and another 21% in Russia.
Unlike
other countries, the US stopped civilian reprocessing from 1976 to 1981 as one
part of US non-proliferation policy, since reprocessed material such as
plutonium could be used in nuclear weapons: however, reprocessing is now
allowed in the U.S. Even so, in the U.S. spent nuclear fuel is currently all
treated as waste.
In
February, 2006, a new U.S. initiative, the Global Nuclear Energy Partnership
was announced. It would be an international effort to reprocess fuel in a
manner making nuclear proliferation unfeasible, while making nuclear power
available to developing countries.
Uranium
enrichment produces many tons of depleted uranium (DU) which consists of U-238
with most of the easily fissile U-235 isotope removed. U-238 is a tough metal
with several commercial uses—for example, aircraft production, radiation
shielding, and armor—as it has a higher density than lead. Depleted uranium is
also useful in munitions as DU penetrators (bullets or APFSDS tips) "self
sharpen", due to uranium's tendency to fracture along shear bands.
There are concerns that U-238 may lead to
health problems in groups exposed to this material excessively, such as tank
crews and civilians living in areas where large quantities of DU ammunition
have been used in shielding, bombs, missile warheads, and bullets. In January
2003 the World Health Organization released a report finding that contamination
from DU munitions were localized to a few tens of meters from the impact sites
and contamination of local vegetation and water was 'extremely low'. The report
also states that approximately 70% of ingested DU will leave the body after
twenty four hours and 90% after a few days.