The strong nuclear forces that bind the neutrons and
protons together in the nucleus are far greater than the electrical
forces that bind electrons to a nucleus. Energy derived from
chemical processes is small because it involves only electron
movement in the outer reaches of atoms. Energy derived from nuclear
processes is far greater. This is because the binding energy of a
nucleus is a measure of how tightly its neutrons and protons are
held together by the nuclear forces.
The most tightly bound nuclei are found in the middle of the
periodic table. Therefore if two light nuclei coalesce to form a
heavier nucleus, or if a heavy nucleus splits into two lighter ones,
the outcome is a more tightly bound nucleus and energy will be
released.
How
much energy?
Several MeV of energy are released in a fusion reaction and about
200 MeV in a fission reaction. A fission reaction releases about 10
million times as much energy as a chemical reaction.
How is
nuclear energy obtained?
Nuclear power
stations emit few of the gases associated with acid rain and they do
not contribute to the greenhouse effect The use of nuclear power
reduces the need to burn vast amounts of coal. However, nuclear
power is not without its environmental impact. The main issue faced
by the nuclear industry is the disposal of radioactive waste.
Nuclear
Waste
The main environmental issue faced by the nuclear industry is the
safe disposal and storage of radioactive waste. Each year a nuclear
power station produces around 100 cubic meters of solid radioactive
waste. Most of this waste is only slightly radioactive and can be
dealt with easily. High-level nuclear waste is harder to dispose of
and most of it is stored underground. This waste is contained within
multi-layered metal and concrete vessels. Safety standards are
extremely high in regard to the disposal of nuclear waste.
Classification of Waste
Radioactive waste can vary enormously in the amount of radiation
that it is giving out, and so it is categorised into low-level
(84%), intermediate-level (14%), and high-level waste (2%).
High-level waste is concentrated waste that is produced when nuclear
fuel is reprocessed. Even though it represents only about 2% of the
total volume of waste, it contains about 99% of the radioactivity
produced. Most high-level waste is turned into glass blocks. This
makes it easier to store safely. High-level waste is initially in
the form of a liquid, which is hot and very radioactive. In the UK
it is stored initially at Sellafield in stainless steel tanks cooled
by cold water. Then a process called vitrification drives the water
from the waste, and turns it into glass blocks, which will be stored
in deep underground containers.
Intermediate-level waste includes items such as reactor components,
cladding from fuel rods, effluent from treatment plants.
Intermediatelevel waste is potentially dangerous. This waste is then
put inside stainless steel drums. At present much of this sort of
waste is stored at Sellafield (Cumbria, England), but will
eventually be stored in a purpose-built repository cut into hard
rock deep underground.
Low-level waste includes protective clothing and air filters that
might be contaminated with traces of radioactive materials. Most
low-level waste is packed into steel drums and stored in
purpose-built concrete containers.