Environmental Engineering Reference
In-Depth Information
which is the time needed for half of the radioactive atoms to “decay.” During this
process, the nuclear waste activity is reduced by 90% in the first year, but 100,000
years are necessary for it to revert to uranium ore levels. Uranium-235 fission gen-
erates radioactive isotopes of xenon and strontium (among others), which undergo
radioactive decays until stable components are formed. Some of these intermedi-
ary products—particularly strontium-90 and cesium-137, with half-lives of about
30 years—are very carcinogenic and persistent in the environment, so much so that
they can settle in people's bones.
Nuclear waste has to be stored for many decades, and maybe centuries, in deep
underground reservoirs, in stable geological formations on solid ground, or on the
sea bed and contained in cement, bitumen, and resins for vitrification. There is still
no final storage capacity for these materials. The United States had plans to build
a permanent large nuclear waste depository, with a 70,000 ton capacity, in Yucca
Mountain by 2019. The estimated cost to build the storage site was between US$10
billion and US$20 billion. However, owing to opposition by environmental groups,
the US administration stopped the project in 2010. Finland is building a smaller
depository to store the nuclear waste from its reactors. France has provisory nucle-
ar waste disposal sites. In the United States the waste produced by the more than
100 reactors in operation is presently being stored in concrete blocks or water-filled
pools at the reactor sites.
The greenhouse gas emissions from nuclear energy production—over a life
cycle—are very low, because nuclear plants do not burn fossil fuels. The main
source of such emissions comes from the energy utilized in the construction of the
nuclear reactor site and the preparation of the nuclear fuel. Reactor operations also
have negligible emissions of sulfur dioxide (SO
2
) and nitrous oxides (NO
x
), the
pollutants emitted by burning fossil fuels. Therefore, from the environmental view-
point nuclear reactors as a source of electricity production are attractive, and the
recent increased concerns with global warming led to strong efforts to revitalize
the nuclear industry.
Uranium reserves are abundant and can cost less than US$40/kgU to extract.
Reserves in 2009 at that cost amounted to 570 thousand tons and production
amounted to 44 thousand tons, so, in principle, they should last for only 13 years.
At higher costs of production (lower than US$80/kgU) reserves jump to 2.5 million
tons.
