AP3253 Energy, Technology & Environment
Mini-Project
Alternative Sources of Energy ¡V NUCLEAR ENERGY
Introduction
Nuclear energy is cheap and clean. However, some people think that it is very
dangerous. Their main concerns are that during accidents, radiation will leak out of the
reactors, and that the nuclear wastes will contaminate the environment.
Under proper working conditions, the radiation that escapes from nuclear power plants
constitutes less than 0.1% of the background radiation. The fall-out from waste is also
very small because high-level wastes are sealed, shielded and buried in unpopulated
areas where severe earthquakes are unlikely to occur.
The most serious accident that can occur in a nuclear power station is known as
"meltdown". This is when the core melts due to overheating. It could happen if the
cooling system, the warning system and the shut-down mechanism in the reactor all
fail at the same time. Although the engineers who build reactors try hard to minimize
the likelihood of a meltdown, two such accidents have occurred, both due to human
negligence.
Nuclear Accident
The Three Mile Island accident took place in the United States in 1979. The accident
was due to a combination of equipment failure, inadequately designed instrumentation,
and the inability of plant operators to understand the reactor's condition. Water from
the reactor's cooling system passed into the reactor building, but still within the
containment. The resulting heat that built up in the reactor's core melted the metal of
the fuel assemblies and the fuel pellets began to disintegrate. Fortunately, the reactor
was encased in a strong steel-and-concrete dome and only a small amount of
radioactive gas escaped. No one was injured or killed. However, the accident aroused
public concern over the safety of nuclear power plants. On the other hand, the accident
showed that the encased PWR is one of the safest reactor designs because the
accident led to very few environmental or health problems.
The Three Mile Island nuclear power plant in Pennsylvania, USA
The disastrous Chernobyl accident took place in the U.S.S.R in 1986. The plant
employed an outdated and bulky moderating system made of graphite. Such
moderators had long been abandoned by engineers in the West, In this accident, the
shielding was broken by the chemical explosion inside the core. Many fire fighters died
following massive irradiation. People living in a wide surrounding area had to be
evacuated. The ecosystem of the whole region was devastated. Worst of all, a number
of highly radioactive fission products got into the atmosphere and were spread by wind
and rain over most of Europe, where they will contaminate food and water for years to
come.
The Chernobyl nuclear power station.
What is Nuclear Energy?
Nuclear power is the most powerful energy resource at this moment. It was discovered
around 40 years ago. Now, thirty-two countries generated electricity in 437 nuclear
power stations at 250 sites all around the world. Additionally, 36 units are currently
under construction in 14 countries. As nuclear energy produces virtually no global
warming effect, it continues to reduce the load of greenhouse gases on the planet with
437 nuclear plants supplying 17 per cent of the world's electricity. More than 3,000
nuclear facilities of various kinds are operating worldwide to support medical, research,
energy, agriculture and industrial needs.
What is Uranium?
Uranium is a very heavy (dense) metal which can be used as an abundant source of
concentrated energy. Uranium occurs in slightly differing forms known as 'isotopes' as
other elements. The two common uranium isotopes are U-238, accounting for 99.3%
and U-235 about 0.7%.
The isotope U-235 is important because under certain conditions it can readily be split,
yielding a lot of energy. It is therefore said to be 'fissile' and we use the expression
'nuclear fission'.
How does it work?
„Y Uranium Fission
In 1939, scientists Fermi in Italy and Hahn and Strassmann in Germany,
discovered how to split the atom and found that atoms of uranium would split into
two. When the nucleus of a U-235 atom is split in two by a neutron, some energy is
released in the form of heat. The nuclear reaction is called "nuclear fission".
Besides, during fission, two or three additional neutrons are thrown off and thus
mass decrease is appreciable. After that, If enough of these expelled neutrons split
the nuclei of other U-235 atoms, releasing further neutrons, a 'chain reaction' can
be achieved. When this process repeats, a large amount of heat is produced from a
relatively small amount of uranium. The constant heat produced is used to make
steam to produce electricity.
About 85% of the fission energy appears as kinetic energy of the fission fragments,
like barium and krypton nuclei, which fly apart at great speed. The kinetic energy of
the fission neutrons also makes a sight contribution. In addition, one of both of the
large fragments is highly radioactive and a small amount of energy takes the form
of beta and gamma radiation.
Examples of the fission reaction in U-235 may be given of typical reaction products
with, atomic masses distributed around 95 and 135such as:
U-235 + n ===> Ba-144 + Kr-90 + 2n + energy
U-235 + n ===> Ba-141 + Kr-92 + 3n + 170 MeV
U-235 + n ===> Zr-94 + La-139 + 3n + 197 MeV
Both the barium and krypton isotopes subsequently decay with the emission of
several electrons and form more stable isotopes of neodymium and yttrium. It is the
beta decays, with some associated gamma rays, which make the fission products
highly radioactive.
„Y Fusion
As discussed above, we know that atoms produce a large amount of heat to
generating energy when they break up. Not only that, the union of light nuclei into
heavier nuclei can also lead to a transfer of mass and a consequent liberation of
energy. The combining process is called 'fusion'. However, before atoms will fuse
together, they must be heated to almost one hundred million degrees Celsius, as
fusion of the two atoms, likes deuterium nuclei, will only occur if they overcome
their mutual electrostatic repulsion. Very high temperature is necessary to allow
them to collide at very high speed.
Application:
Power Plants
What is a nuclear power reactor?
A nuclear reactor is a device in which a fission chain reaction can be initiated,
maintained, and controlled so that on average only one neutron from each fission
process produces another fission to generate heat. Its essential components are
fissionable fuel, moderator, shielding, control rods, and coolant. A nuclear power
station operates much the same way as any power plant except that the reactor uses
uranium fuel, instead of coal, oil or gas, to produce heat that turns water into steam.
Energy released by the fission heats the water surrounding the uranium rods. The
water itself does not boil because it is under high pressure, which increases its boiling
temperature. The water is pumped to a heat exchanger, where it causes other water to
boil producing steam that turns turbines. The turbines are connected to generators that
produce electrical energy. The only one common characteristic in designing nuclear
reactors used throughout the world is that all nuclear reactors must include a thick
concrete safety shield gives protection from neutrons and highly radioactive gamma
rays.
Inside the reactor
At the center of a nuclear reactor is the core. This looks like a big drum, and contains
'fuel rods'. The uranium fuel is assembled in such a way that a controlled fission chain
reaction can be achieved. Around these flows a 'coolant', that can be gas or water. For
a uranium reactor, the heat created by splitting the U-235 atoms is then used to make
steam which spins a turbine to drive a generator, producing electricity.
The coolant carries heat away from the core, but the heat from the reaction still needs
to be controlled. The chain reaction that takes place in the core of a nuclear reactor is
controlled by the 'moderator', which absorbs neutrons. By, inserting or withdrawing the
moderator, the reactor can be set at the required power level. Water, graphite and
heavy water are used as moderators in different types of reactors. Thick walls of
concrete and steel are surrounded the reactor core of the nuclear reactor. These walls
form a shield against deadly rays. These are given off by the reaction in the fuel rods,
and we call these harmful rays 'radiation'.
Can nuclear reactors produce anything else other than electricity?
When talking about nuclear energy, few people realise that the extend use of
radioisotopes has changed our lives over the last few decades. Nuclear reactors can
produce useful radioisotopes for medicine and industry. Cobalt-60 is used to treat
cancer, as well as to inspect pipe welds. Iodine-131 is used to diagnose and treat
thyroid ailments. Technetium-99m is a medical tracer enabling doctors to 'see' inside
the body using scanning devices. Xenon-133 is used for lung ventilation and blood flow
studies.
The disadvantage and advantages of using nuclear energy
There are already many arguments for the using of nuclear energy.People support the
using of nuclear energy as the fuel of earth is going to running out and has to find a
high efficiency energy to replace the original one.
For those people who are against the using of nuclear energy claim that the resources
of producing nuclear energy is highly radioactive. Once there is and accident during
the processing of nuclear energy will give a big disaster.
Disadvantages of Nuclear Energy
„h Although not much waste is produced, it is very, very dangerous. It must
be sealed up and buried for many years to allow the radioactivity to die
away.
„h Nuclear power is reliable, but a lot of money has to be spent on safety -
if it does go wrong, a nuclear accident can be a major disaster
A) About sixty years ago it was discovered that ionizing radiation such as that
which continually forms part of our environment could induce genetic mutations in
fruit flies. Intensive study since then has shown that radiation can similarly induce
mutations in plants and test animals.
The waste left after the production of nuclear energy is highly radioactive. The body
has defence mechanisms against damage induced by radiation as well as by
chemical carcinogens. However, typically the body has to deal only with a relatively
tiny amount of damage at any one time, as opposed to having to deal with a very
large amount at once, as was the case for the bomb survivors. Therefore the waste
has to be treated carefully.
The highly radioactive wastes are initially stored in pools of water at the power
station site for up to ten years, then moved to above ground, dry storage at the
same site. Long term storage and disposal site has to be built for the management
of wastes. Security and monitoring could be continued if desired, and retrieval
would be possible
B) To produce energy from nuclear reaction, large amount of radioactive
substances has to be stored in the nuclear energy generating plant. There have
been sophisticated statistical studies on reactor safety. Most disaster scenarios
involve primarily a loss of cooling. This may lead to the fuel in the reactor core
overheating and releasing fission products. Hence the provision of emergency
core cooling systems on standby. In case these should fail, a further protective
barrier comes into play: the reactor core is normally enclosed in structures
designed to prevent radioactive releases to the environment. However, all the
costs of decommissioning of nuclear power generation sites, the fuel processing
sites and the uranium mining sites are also contained in the price of electricity paid
by the consumer.
Advantages
„h Nuclear power costs about the same as coal, so it's not expensive to make.
„h Does not produce smoke or carbon dioxide, so it does not contribute to the
greenhouse effect.
„h Produces huge amounts of energy from small amounts of fuel.
„h Produces small amounts of waste.
„h Nuclear power is reliable.
The production of electricity from any form of primary energy has some environment
Comparison of its environmental effects with those of the principal alternative, coal-
fired electricity generational effect has been investigated
Since the production of energy from nuclear power plant doesn't involve the
combustion of fuel, it will not produce as much pollutant as Coal-Fried generation
plant.
Nuclear electricity generation does not produce carbon dioxide or methane, two of the
major contributors to the "Greenhouse Effect". Nuclear electricity generation does not
produce sulphur dioxide, nitrogen oxides or other atmospheric pollutants that cause
acid rain. Nuclear power generators control the wastes produced, in contrast to fossil
fuel electricity generators that disperse wastes into the atmosphere.
Nuclear versus Coal-Fired Electricity Generation
(1,000 MWe plant)
Coal
Nuclear
Fuel (tonnes/year)
2.5 - 3.0 million
125
Waste (tonnes/year)
Ash : 300 - 700 thousand
Used Fuel : 125
C02 : 6 - 7 million
Low and Intermediate
S02 : 40 - 120 thousand
Level Waste : 200 - 600
N0x : 20 - 50 thousand
Nuclear power generation plants emit no greenhouse gases. As the following chart
illustrates, the only technologies for large-scale power generation that emit no
greenhouse gases are nuclear and hydraulic.
This chart also clearly illustrates that while the natural gas fueled co-generation
technology is a considerable improvement over coal and oil fired power plants, there is
still a significant release of carbon dioxide.
The figure below shows the proportion of the world's electricity which is generated by
the various types of fuel. Nuclear power generation supplies approximately 17% of the
power produced. This is almost equivalent to hydroelectric power generation, but the
two are overshadowed by the high dependence on fossil fuels.
The Cost Competitiveness of Nuclear Power Generation
Nuclear power generation is cost competitive against all other forms of current and
future large scale power generation sources. Many cost comparisons have been
conducted to show the relative costs of the primary power generation options.
While the initial investment is higher, this relatively low fuel cost for nuclear generation
results in the long term cost stability and predictability.
The relatively higher investment cost for nuclear power is also a major longer-term
competitive advantage of nuclear power. Technology developments are currently
underway that will reduce the capital cost and construction time for nuclear power
plants. This will lead to a significant reduction of the investment cost of nuclear
electricity generation, thus increasing its competitive advantage even further in some
cases, and converting it to the lowest cost source in others
Despite the commercial nuclear power industry's impressive safety record and the
thorough engineering of reactor structures and systems which make a catastrophic
radioactive release from any Western reactor extremely unlikely, there are those who
simply don't want to run any risk of this. This fear must then be weighed against the
benefits of nuclear power, in the same way that some people's fear of having
aeroplanes crash on top of them must be balanced against the utility of air transport for
the rest of the population. Ultimately, balancing risks and benefits is not simply a
scientific exercise.
Safety
A working nuclear reactor produces both heat and radiation. Although radiation cannot
be seen or touched, it is dangerous. People exposed to radioactive material can
become very ill. It can cause serious diseases such as cancer.
As a result, people who work in a nuclear reactor must be protected. They were special
clothes and are often checked to make sure they are well. They do not touch the
radioactive fuel rods. They work behind walls with thick glass windows, and they
control long 'robot' arms, which handle the radioactive fuel rods.
On the other hand, one of the big concerns of nuclear energy is the waste. Everyone is
concerned if it will affect him or her in any way. We classify the nuclear waste into high
and low levels.
For high level waste, people are concerned if there is any way to safely store these
materials. The most reasonable was to place it deep underground in a very deserted
area. Because it has to stay in that place for a long time, it needs to be kept out of
reach of the public until the radioactive level is low enough to make contact with our
environment today.
For low level waste, it does not mean the nuclear waste itself, but the materials that
have been directly in contact with the fuel and contain radioactivity. There are different
ways to treat the low level waste such as leave it in a safe area to be decayed until it
reaches safe levels, to compact dry wastes into much smaller pieces and store them
and to recycle the object if it is expensive.
Conclusion
National policy decisions have altered the course of nuclear power in various countries
over the last few decades. What the situation will be in 2020 or 2030 will depend on
decisions made in the coming years, which are, today, hard to predict, but on which the
future of the uranium market and thus the economics of plutonium recycling are heavily
dependent.
The engineers who build nuclear power plants try to make them as safe as possible.
But some accidents have happened, and there have been leaks of radiation. There is
also the danger of a 'meltdown'. This could happen if a reactor lost its supply of cooling
gas or water. The core would overheat, melt and break out of its walls. There are good
reasons for using nuclear electricity. It can be produced fairly cleanly, and is an extra
source of power. Some countries, like France and Bulgaria, would like to make nuclear
energy their main source of power. We believe that there will be an increasing demand
in NUCLEAR ENERGY in the future.
The comparison of the electricity generation by nuclear power and by fossil fuel are
given in the following table:
Fossil fuel
Nuclear power
Mineral reserve
Oil will be used up soon.
Coal can still be used for
hundreds of years.
Uranium will be used up in
50 to 100 years.
Mining
Very dangerous
Dangerous
Transportation of fuel
By land or sea, expensive;
risk of oil spills in sea in
case of accident
By land or sea, cheap;
relatively safe even if
accident happens
Escape of radiation
Negligible
Usually very small
Cost
Cheap to build but
expensive to run
Expensive to build but
cheap to run
Pollution
Release SO2, CO2 and
soot; produces
greenhouse effect and acid
rain
Relatively clean in normal
working conditions
Amount of solid waste
(per year)
Millions of tones
Thousands of tones
Reuse of waste
May be used as filling
material for building house
or reclamation areas
Dumped and buried, or
reprocessed to produce
useful radioactive isotopes
such as Iodine 131
World NUCLEAR POWER REACTORS 1999-2000
and Uranium Requirements
COUNTRY
NUCLEAR
ELECTRICITY
GENERATION 1999
REACTORS
OPERATING
31 July 2000
REACTORS
BUILDING
31 July 2000
ON ORDER or
PLANNED
31 July 2000
URANIUM
REQUIRED
2000
%
TWh
No.
MWe
No.
MWe
No.
MWe
tonnes U
Belgium
58
47
7
5680
0
0
0
0
1020
Brazil
1.1
4.0
1
626
1
1245
0
0
292
Canada
12.4
70
18
12058*
0
0
0
0
1326
China
1.2
14.1
3
2079
8
6320
2
1800
418
Egypt
0
0
0
0
0
0
1
600
0
France
75
375
59
63203
0
0
0
0
10513
Germany
31
160
19
21107
0
0
0
0
3707
India
2.7
11.5
12
2144
4
1304
10
4480
312
Indonesia
0
0
0
0
0
0
1
600
0
Iran
0
0
0
0
1
950
3
2850
0
Japan
36
307
53
43505
1
796
14
18288
7334
Korea DPR
(North)
0
0
0
0
0
0
2
1900
0
Korea RO
(South)
43
98
16
12970
4
3800
10
11200
2480
Russia
14.4
111
29
19843
3
2825
9
7450
3213
South Africa
7.1
13.5
2
1842
0
0
0
0
366
Taiwan
25
37
6
4884
2
2600
0
0
971
United
Kingdom
29
91.2
33
12518
0
0
0
0
2578
USA
19.8
728
104
98015
0
0
0
0
17496
WORLD
16
2401
437
351,746
30
24,926
52
49160
61,176
Sources:
Reactor data: ANSTO, based on information to 8 August 2000.
Brazil's second reactor started up in July 2000, but was not connected to the grid by 8 August.
IAEA- for electricity production, 31 May 2000.
Uranium Institute 2000: Global Nuclear Fuel Market (reference scenario) - for U
Operating = Connected to the grid
Planned = Relatively firm plans or Letter of Intent sent
NB: 61,176 tU = 72,145 t U3O8
Belgium, Bulgaria, Finland, France, Germany, Hungary, Japan, South Korea, Lithuania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and Ukraine all get 30% or more of
their electricity from nuclear reactors. The USA has over 100 reactors operating and
supplying 20% of its electricity. The UK gets about a quarter of its electricity from
uranium.
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