Environmental Engineering Reference
In-Depth Information
N
UCLEAR
P
OWER VERSUS THE
G
REENHOUSE
E
FFECT
Nuclear fission
Since the use of fossil fuels has to be reduced significantly within the coming
decades, zero-carbon energy sources are required. One option is nuclear power.
Here, we distinguish between nuclear fusion and nuclear fission.
All operational nuclear power stations utilize nuclear fission for electricity
generation. Here, neutrons bombard the uranium isotope
235
U and cause the
fission of the uranium. Among others, krypton
90
Kr and barium
143
Ba are
fission by-products. Furthermore, this fission reaction generates new free
neutrons
1
n that can initiate further fission reactions. The mass of the atomic
particles after the fission is reduced compared to the original uranium atom.
This so-called mass defect is converted to energy
E
in the form of heat. The
following nuclear reaction equation describes the fission process:
∆
235
1
n
0
90
Kr
36
143
Ba
56
1
n
0
+
+
+
+
U
3
∆
E
(1.4)
92
Since nature does not provide uranium in the form that is needed for technical
utilization, it must be extracted from uranium ore. Rock with a uranium oxide
content of more than 0.1 per cent is a workable uranium ore. Uranium mining
produces huge amounts of waste that contains, in addition to some non-toxic
components, a lot of radioactive residues. Uranium oxide from uranium ore
contains only 0.7 per cent uranium-235. The largest portion is uranium-238,
which is not usable for nuclear fission. Therefore, processing plants must
enrich the uranium, i.e. the uranium-235 concentration must be increased to
2-3 per cent. In 2002, worldwide uranium production was about 34,000
metric tonnes.
Altogether, 428 nuclear power stations were in operation at the beginning
of 2003, with an overall capacity of 353,505 MW. The average nuclear power
station power was about 825 MW. Currently, nuclear power's share of the
global primary energy demand is below 10 per cent. Figure 1.8 shows that
nuclear power has a different contribution to electricity supply in different
countries.
Nuclear power dominates the French electricity supply, whereas industrial
nations such as Australia, Austria, Denmark, Norway or Portugal do not
operate any nuclear power stations at all. Italy decided to abort nuclear power
utilization after the Chernobyl disaster; Austria's decision pre-dated it.
However, an electricity industry without nuclear power does not necessarily
mean higher carbon dioxide emissions. For instance, hydro-electricity produces
nearly 100 per cent of Norway's electricity. Iceland's electricity supply is nearly
carbon dioxide free as a result of hydro and geothermal power.
If all fossil energy sources used today were replaced by nuclear power,
about 10,000 new nuclear power stations would have to be built worldwide.
The lifetime of a nuclear reactor is about 30 years, thus all these power stations
