Physics

Unit 6: FOSSIL AND NON-FOSSIL FUEL AND POWER PRODUCTION

Topic Area: ENERGY, POWER AND CLIMATE CHANGE

Key unit competence: By the end of this chapter, I should be able to evaluate fossil and non-fossil fuel for power production.

Unit Objectives:

By the end of this unit learners will be able to;

      ◊   explain the concept of fossil and no-fossil fuels and their use in power production properly.  

      ◊   explain the differences between fossil and no-fossil fuels properly.    

      ◊   explain Nuclear fuel and nuclear fission and their use in energy production and associated dangers properly.  

      ◊   explain the environmental problems of fossil fuels and suggest their solution clearly.

6.0 INTRODUCTION

Fossil fuel is a source of conventional or non-renewable energy. There are many examples of fossil fuels which we use in our daily lives. In fact, most of the energy that we consume comes from fossil fuels. Coal, petroleum and natural gas are called fossil fuels. Millions of years ago, during the carboniferous age, due to the change in atmospheric conditions and other changes, the forests were destroyed and they were fossilized. With the action of bacteria and other microorganisms on the surface of the earth, these trees and other vegetation were decayed and disintegrated. Years after these trees were available in solid, liquid and gaseous state. The solid form is coal. It is the most widely used form of fossil fuel for domestic purposes.

6.1 FOSSIL FUELS AND NON-FOSSIL FUELS

6.1.1 Fossil Fuels

Fossil fuels are hydrocarbons, primarily coal, fuel oil or natural gas, formed from the remains of dead plants and animals. In common dialogue, the term ‘fossil fuel’ also includes hydrocarbon-containing natural resources that are not derived from animal or plant sources.

Coal, oil and natural gas are called ‘fossil fuels’ because they have been formed from the fossilized remains of prehistoric plants and animals. Fossil fuels are non-renewable energy source since they take millions of years to form. They ultimately get their energy from the sun.

Types of Fossil Fuels

Coal

Coal is a hard, black coloured rock-like substance formed when dead plants were subjected to extreme heat and pressure for millions of years. It is made up of carbon, hydrogen, oxygen, nitrogen and varying amounts of sulphur. There are two ways to mine coal: surface mining and underground mining.

Natural Gas

Natural gas is formed from the remains of tiny sea animals and plants that died millions of years ago. The gas then became trapped in layers of rocklike water in a wet sponge. Raw natural gas is a mixture of different gases. Its main ingredient is methane. The strange smell of natural gas (like rotten eggs) comes from a chemical added by the companies. It is called mercaptan. This is added to detect the gas leakage.

Oil (Petroleum)

Oil is formed from the remains of animals and plants that died millions of years ago. The organic material was then broken down into hydrogen and carbon atoms and a sponge-like rock was formed, full of oil.

Oil cannot be used as it is when it is drawn from the ground. Oil refineries clean and separate the oil into various fuels and byproducts. The most important of these is gasoline.

Fossil fuels are used to generate electrical energy in a series of energy transformations as shown in Fig.6.2.

6.1.2 Non-fossil fuels

Non-fossil fuels are alternative sources of energy or renewable sources of energy that do not rely on burning up limited supplies of coal, oil or natural gas. Examples of these fuels include: nuclear energy, wind or water generated energy and solar power. These tend to be renewable energy sources, or means of generating power that can be utilized indefinitely.

Non-fossil fuels are considered to be extremely important for power creation. This is because they are usually renewable energy sources that could be tapped for hundreds of years and not run out. In addition, energy production using nonfossil-based fuels usually generates much less pollution than fossil-based energy sources.

6.2  STORAGE AND TRANSPORTATION OF DIFFERENT TYPES OF FOSSIL FUELS

6.2.1 Coal

Types of coal

    • Peat

    • Lignite

    • Semi bituminous

    • Bituminous

    • Anthracite

Means of transporting coal

  • Transportation by rail

   • Transportation by ropeways

   • Transportation by sea or river

   • Road transport

   • Transport by pipeline

Coal storage

Storage of coal is undesirable because it costs more as there is:

    • Risk of spontaneous combustion,

    • Weathering,

    • Possibility of loss and deterioration during storage,

    • Interest on capital cost of coal lying dormant,

    • Cost of protecting the stored coal from deterioration.

Types of coal storage

1. Dead storage:

This storage supplies the coal to places where there is a shortage of coal in plant due to failure of normal supply of coal. This is a long-term storage and comprises 10% of annual consumption, so, it requires protection against weathering and spontaneous combustion.

2. Living storage:

It supplies coal to plant for day-to-day usage. The capacity of live storage is less than that of dead storage. It is usually stored in vertical cylindrical bunkers or coal basins or silos, e.g. coal is transferred to boiler grate. Bunkers are normally diamond-shaped cross-section storage areas made up of steel or reinforced concrete.

Purpose of dead coal storage of coal

    • To prevent shutdown of power plant in case of failure of normal supplies of coal due to coal strike, failure of the transport system, etc.

    • To permit choice of purchase allowing management to take advantage of seasonal market conditions.

Means of coal storage

1. Storage in coal heaps

It is required to:

      • Keep coal at low temperature (>70 oC).

      • Prevention of air circulation from bottom of coal piles.

      • Proper drainage of rainy water to prevent weathering–drainage should not be rapid to prevent washing of coal.

Hence, ground used for stocking should be dry and levelled for proper drainage. It should have concrete floor to prevent flow of air from bottom. Coal is piled up to a height of about 10 to 12 m in layers of 15 to 30 cm.

In dead storage, coal pile is sealed by asphalt, fine coal dust, bituminous or other coating materials.

2. Underwater storage

Possibility of slow oxidation and spontaneous combustion can be completely eliminated by storing coal under water.

Site selection for coal dead storage

   • The storage should be free from standing water

   • If well drainage is not available, artificial drainage should be provided.

   • It should be free from all foreign materials like wood, paper rags, waste oil or materials having low ignition temperature.

   • Handling cost should be minimum.

   • Pile should build up in successive layers and be compact.

   • Pile should be dressed to prevent entry of rainy water.

   • Alternative drying and wetting should be avoided.

   • Stoker size coal should be oil treated to prevent absorption of water and oxygen.

   • Side of pile should not be steep.

   • Air may circulate freely through pile for proper ventilation to keep temperatures low.

   • Hot surfaces or boiler blow down or hot water or steam pipe and tanks should be kept far from coal storage

   • Hot bright days should be avoided.

   • There should be provision for temperature measurement at different points.

   • Conical piling should be avoided.

   • Fire fighting equipment should be easily available.

Coal Transfer

Equipment used in coal transfer are:

A: Belt conveyor

It can transfer large quantities of coal over large distance economically. It has low initial cost and ensures low power consumption.

Advantages:

   • Economical, low power consumption

   • Large capacity

   • Rate of coal transfer rapidly change

   • Low maintenance cost

Disadvantages

   • Not suitable for shorter distance and inclination > 200.

   • Not suitable for dust particles and slurry.

B: Flight conveyor

It is used when coal is discharged at different points in bins situated below the conveyor. All parts are made of steel and iron, so it can handle hot materials. It is totally enclosed, so dust of coal can get transferred. It can transfer coal at high inclination

Advantages

   • It requires small head room.

   • Speed and material transfer rate can easily change.

   • It can handle hot materials also.

Disadvantages

   • High wear and tear, so, it has short life.

   • High maintenance required.

   • Speed is limited up to 300 m/min due to abrasive action of material.

   • High power consumption per unit of material transfer.

C: Screw conveyor

  • It is used for shorter distance.

  • It is totally enclosed from atmosphere.

  • Coal dust can also be transferred easily.

  • It is generally used in metering of coal.

  • Driving mechanism is attached at the end of the shaft.

  • Diameter: 15 cm to 50 cm.

  • Speed: 70 rpm to 120 rpm.

  • Capacity: 125 tones/h (max)

Advantage

  • Cheap initial cost.

  • Simple and compact.

  • Dust tight.

  • It can transfer coal at high inclination also.

  • Most suitable for short distance.

Disadvantages

  • High power consumption.

  • Length is limited up to 30 m.

  • High maintenance due to high wear and tear.

D: Bucket elevator

It is used for vertical lifts. Buckets are fixed on chain which moves on two wheels or sprockets. Buckets are loaded at bottom and discharged at top.

E: Grab bucket elevator

    • It is used for lifting as well as transfer material.

    • It can be used with crane or tower.

    • Initial cost is high but operating cost is less.

    • It is used when another arrangement is not possible.

    • Bucket capacity: 2 to 3 m3

    • Distance: 60 m

    • Capacity: 100 tonnes/h.

6.2.2 Transporting Natural Gas and Crude Oil

Transporting natural gas and crude oil thousands of miles through pipelines is the safest method of transportation. The transportation system for natural gas consists of a complex network of pipelines, designed to transport natural gas from its origin to the areas of high natural gas demand quickly and efficiently. In general, pipelines can be classified in three categories depending on the purpose:

Gathering pipelines

These are smaller interconnected pipelines forming complex networks with the purpose of bringing crude oil or natural gas from several nearby wells to a treatment plant or processing facility. In this group, pipelines are usually short — a couple of hundred metres — and with small diameters. Also subsea pipelines for collecting product from deep water production platforms are considered gathering systems.

Transportation pipelines

These are long pipes with large diameters, moving products (oil, gas, refined products) between cities, countries and even continents. These transportation networks include several compressor stations in gas lines or pump stations for crude and multi-products pipelines.

Distribution pipelines

These are composed of several interconnected pipelines with small diameters, used to take the products to the final consumer. Feeder lines to distribute gas to homes and business downstream, and pipelines at terminals for distributing products to tanks and storage facilities, are included in this group.

6.3 ADVANTAGES AND DISADVANTAGES OF FOSSIL FUELS

6.4 ENERGY PRODUCTION USING FOSSIL FUELS

A fossil-fuel power station is a power station which burns fossil fuels, such as coal, natural gas or petroleum to produce electricity. Central station fossilfuel power plants are designed on a large scale for continuous operation.

There are two main cycles in a power plant; the steam cycle and the gas turbine cycle. The steam cycle relies on the Rankine cycle in which high pressure and high temperature steam raised in a boiler is expanded through a steam turbine that drives an electric generator. The generator then transforms mechanical energy into electrical energy which is distributed for local use.

The steam gives up its heat of condensation to a heat sink, such as water from a river or a lake and the condensate can then be pumped back into the boiler to repeat the cycle. The heat taken up by the cooling water in the condenser is dissipated mostly through cooling towers into the atmosphere.

 6.5 NUCLEAR FUEL AND NUCLEAR FISSION

Nuclear fuel is any material that can be consumed to derive nuclear energy. The nuclear fuel can be made to undergo nuclear fission chain reactions in a nuclear reactor. The most common nuclear fuels are 235U (uranium 235) and 239Pu (plutonium 239). Not all nuclear fuels are used in fission chain reactions.

Nuclear fission is a process, by which a heavy nucleus splits into two or more simpler pieces. This process releases a lot of energy.

When a neutron strikes an atom of uranium, the uranium nucleus splits into two lighter atoms and releases heat simultaneously. Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments.

A chain reaction refers to a process in which neutrons released in fission produce an additional fission in at least one further nucleus. This nucleus in turn produces neutrons, and the process continues. If the process is controlled it is used for nuclear power or if uncontrolled it is used for nuclear weapons. Fig.6.13 illustrates a chain reaction of uranium 235.

The equation of reaction is:

6.6 CONTROLLED FISSION (POWER PRODUCTION)

Of the three neutrons, liberated during a fission reaction, only one triggers a new reaction and the others are simply captured. The system is in equilibrium. One fission reaction leads to one new fission reaction, which leads to one more, and so on. This is known as controlled fission.

In a nuclear power station, the uranium is first formed into pellets and then into long rods. The uranium rods are kept cool by submerging them in water. When they are removed from the water, a nuclear reaction takes place causing heat production. The amount of heat required is controlled by raising and lowering the rods. If more heat is required, the rods are raised further out of the water and if less heat is needed, they are lowered further into it.

6.7 UNCONTROLLED FISSION (NUCLEAR WEAPONS)

A fission reaction which is allowed to proceed without any moderation (by removal of neutrons) is called an uncontrolled fission reaction. Here more and more neutrons are given out and cause more fission reactions, thus, releasing large amounts of energy. An uncontrolled fission reaction is used for nuclear bombs.

Using the energy released from the nuclear fission of uranium-235, an explosive device can be made by simply positioning two masses of U-235 so that they can be forced together quickly enough to form a critical mass and result in a rapid, uncontrolled fission chain reaction.

This is not an easy task to accomplish. First, you must obtain enough uranium which is highly enriched to over 90% U-235, since natural uranium is only 0.7% U-235.This enrichment is an exceptionally difficult task, a fact that has helped control the proliferation of nuclear weapons. Once the required mass is obtained, it must be kept in two or more pieces until the moment of detonation. Then the pieces must be forced together quickly and in such a geometry that the generation time for fission is extremely short. This leads to an almost instantaneous build up of the chain reaction, creating a powerful explosion before the pieces can fly apart. Two hemispheres which are explosively forced into contact, can produce a bomb, such as the one detonated at Hiroshima in 1945.

6.8 IMPACTS OF NUCLEAR WEAPONS

There are five immediate destructive effects from a nuclear explosion:

   1. The initial radiation, mainly gamma rays;

   2. An electromagnetic pulse, which in a high altitude explosion can knock out electrical equipment over a very large area;

   3. A thermal pulse, which consists of bright light (even many miles away) and intense heat equal to that at the centre of the sun);

   4. A blast wave that can flatten buildings; and

   5. Radioactive fallout, mainly in dirt and debris that is sucked up into the mushroom cloud and then falls to earth.

There are three long-term effects of a nuclear explosion:

   1. Delayed radioactive fallout, which gradually fall over months and even years to the ground, ofen in rain;

   2. A change in the climate (possibly by lowering of the earth’s temperature over the whole hemisphere which could ruin agricultural crops and cause widespread famine);

   3. A partial destruction of the ozone layer, which protects the earth from the sun’s ultraviolent rays. If ozone layer is depleted, unprotected Caucasians would get an incapacitating sunburn within 10 minutes, and people would suffer a type of snow blindness from the rays which, if repeated, would lead to permanent blindness. Many animals would suffer the same fate.

6.9  ENERGY TRANSFORMATIONS IN A NUCLEAR POWER STATION

In a nuclear power plant, Nuclear Steam Supply System (NSSS) consists of a nuclear reactor and all of the components necessary to produce high pressure steam, which will be used to turn the turbine for the electrical generator.

The nuclear reactor contains some radioactive isotopes like uranium which undergo fission reaction when bombarded with some neutrons and a large amount of heat energy is evolved. This heat energy converts water into steam, which is piped to the turbine. In the turbine, the steam passes through the blades, which spins the electrical generator, resulting in a flow of electricity. After leaving the turbine, the steam is converted (condensed) back into water in the condenser. The water is then pumped back to the nuclear reactor to be reheated and converted back into steam.

6.10  PROBLEMS ASSOCIATED WITH THE PRODUCTION OF NUCLEAR POWER

•    The problem of radioactive waste is still unsolved. The waste from nuclear energy is extremely dangerous and it has to be carefully looked after for several thousand years (10,000 years according to United States Environmental Protection Agency standards).

•    High risks: Despite a generally high security standard, accidents can still happen. It is technically impossible to build a plant with 100% security. A small probability of failure will always last. The consequences of an accident would be absolutely devastating both for human beings and the nature. The more nuclear power plants (and nuclear waste storage shelters) are built, the higher is the probability of a disastrous failure somewhere in the world.

•    Nuclear power plants as well as nuclear waste could be preferred targets for terrorist attacks. Such a terrorist act would have catastrophic effects for the whole world.

•    During the operation of nuclear power plants, radioactive waste is produced, which, in turn, can be used for the production of nuclear weapons. In addition, the same is used to design nuclear power plants can to a certain extent be used to build nuclear weapons (nuclear proliferation).

•    The energy source for nuclear energy is Uranium. Uranium is a scarce resource; its supply is estimated to last only for the next 30 to 60 years depending on the actual demand.

•    The timeframe needed for formalities, planning and building of a new nuclear power generation plant, is in the range of 20 to 30 years in the western democracies. In other words, it is an illusion to build new nuclear power plants in a short time.       

6.11 ENVIRONMENTAL PROBLEMS OF FOSSIL FUELS

Climate Change/Global Warming and Greenhouse Effect

The earth’s atmosphere allows a lot of sunlight to reach the earth’s surface but reflects much of that light back into space. Some gases trap more sunlight, therefore, less light is reflected back into space. These gases are called Greenhouse Gases, because the effect is like being in a plant glasshouse, or in a car with the windows wound up. The result is a gradual increase in the earth’s temperature or Global Warming. The major greenhouse gases are carbon dioxide, methane, nitrous oxide and chlorofluorocarbons (CFCs).

The main man made causes are thought to be carbon dioxide and methane from factory, power station and car emissions, the waste products of respiration, the mining of fossil fuels and the breakdown of plant matter in swamps. The long-term effects may include melting of glaciers and a rise in sea level and a global change in climate and type of vegetation.

‘Hole’ in the Ozone Layer

Ozone is a gas in the earth’s upper atmosphere whose chemical formula is O3. Ozone acts to block out much of the sun’s ultraviolet radiation which causes skin cancer and contributes to the fluctuations of global climatic conditions that affect the environment. Above Antarctica, there is a thinner layer of ozone caused by the destruction of ozone gas by emissions of chlorofluorocarbons and hydrochlorofluorocarbons which are propellants in pressure-pack spray cans and refrigerants in refrigerators and airconditioning units.

Acid Rain

When gases, such as sulphur dioxide and nitrogen oxides react with water in the atmosphere to form sulphuric acid and nitric acid, they form an acidic ‘rain’ which can destroy vegetation. Some of these gases are from natural sources, such as lightning, decomposing plants and volcanoes. However, much of these gases are the result of emissions from cars, power stations, smelters and factories.

Air Pollution

Air pollution is the release of excessive amounts of harmful gases (e.g. methane, carbon dioxide, sulphur dioxide, nitrogen oxides) as well as particles (e.g. dust of tyre, rubber, lead from car exhausts) into the atmosphere. To reduce emissions, the Australian government has legislated that all new cars should use unleaded petrol and have catalytic converters fitted to the exhausts.

Water Pollution

1. Sewage is the household waste water. Many detergents contain phosphates which act as plant fertilisers. When these phosphates and the sewerage reach rivers, they help water plants to grow in abundance, reducing the dissolved oxygen in the river water. The result is death of aquatic animals due to suffocation by the algal blooms. This harmful effect is called eutrophication. Eutrophication is also caused by excessive use of fertilizers in agricultural fields and subsequent surface run-off.

2. Biodegradable detergents are more environment-friendly because they are readily broken down to harmless substances by decomposing bacteria.

3. Suspended solids in water, such as silt reduce the amount of light that reaches the depths of the water in lakes and rivers. This reduces the ability of aquatic plants to photosynthesise and reduce the plant and animal life. Turbidity is the measure of ‘cloudiness’ or the depth to which light can reach in water.

Introduced Species

They are species of plants or animals that have migrated or been brought to Australia. Many fit into the natural ecosystems and are kept in control by natural predators and parasites. However, some become pests as they are well-adapted to that environment, readily obtain nutrients and lack of natural predators or parasites. Examples include rabbits, foxes, carp and prickly pear cactus plant.

Biological Control

It is an environment-friendly method to control these pests by the introduction of species-specific, living organisms to control their numbers. Successful examples include the myxoma virus and the calici virus for rabbits, and the cactoblastis moth feeding on the prickly pear. Unsuccessful examples include the introduction of the cane toad to reduce the numbers of natural cane beetles.

Soil Salinity

Soil salinity has increased greatly since the widespread logging of trees by farmers. Deep tree roots normally draw water from the underground water table. However, when logging of trees occurs, the water table rises close to the surface bringing with it, salt from rocks. This makes the soil salty so that vegetation cannot grow effectively. The result is loss of vegetation and erosion.

Population Explosion

It is the rapid increase in population in developing countries causing famine, and also in developed countries causing more demand for energy and with that, it increases pollution and destruction of the environment.

6.12  SAFETY ISSUES AND RISKS ASSOCIATED  WITH NUCLEAR POWER

6.12.1 Nuclear Meltdown

A nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating.

A nuclear meltdown occurs when a nuclear power plant system or component fails so the reactor core becomes overheat and melts. Usually, this occurs due to the lack of coolant that decreases the temperature of the reactor. The commonly used coolant is water but sometimes a liquid metal, which is circulated past the reactor core to absorb the heat, is also used. In another case, a sudden power surge that exceeds the coolant’s cooling capabilities causes an extreme increase in temperature which leads to a meltdown. A meltdown releases the core’s highly radioactive and toxic elements into the atmosphere and environment.

The causes of a meltdown occur due to:

A: A loss of pressure control

The loss of pressure control of the confined coolant may be caused by the failure of the pump or having resistance or blockage within the pipes. This causes the coolant to cease flow or insufficient flow rate to the reactor; thus, the heat transfer efficiency decreases.

B: A loss of coolant

A physical loss of coolant, due to leakage or insufficient provision, causes a deficit of coolant to decrease the heat of the reactor. A physical loss of coolant can be caused by leakages. In some cases, the loss of pressure control and the loss of coolant are similar because of the systematic failure of the coolant system.

C: An uncontrolled power excursion

A sudden power surge in the reactor is a sudden increase in reactor reactivity. It is caused by an uncontrolled power excursion due to the failure of the moderator or the control that slows down the neutron during chain reaction. A sudden power surge will create a high and abrupt increase of the reactor’s temperature, and will continue to increase due to system failure. Hence, the uncontrollable increase of the reactor’s temperature will ultimately lead to a meltdown.

6.12.2 Nuclear (Radioactive) Wastes

Nuclear wastes are radioactive materials that are produced after the nuclear reaction. Nuclear reactors produce high-level radioactive (having high levels of radioactivity per mass or volume) and low-level (having low levels of radioactivity) wastes. The wastes must be isolated from human contact for a very long time in order to prevent radiation.

The ‘high-level wastes’ will be converted to a rock-like form and placed in a natural habitat of rocks, deep underground. The ‘low-level wastes’, on the other hand, will be buried in shallow depths (typically 20 feet) in soil.

A number of incidents have occurred when radioactive material was disposed improperly, where the shielding during transport was defective, or when the waste was simply abandoned or even stolen from a waste store.

The principal risks associated with nuclear power arise from health effects of radiation, which can be caused due to contact with nuclear wastes. This radiation consists of sub-atomic particles travelling at or near the velocity of light (186,000 miles per second). They can penetrate deep inside the human body where they can damage biological cells and thereby initiate a cancer. If they strike sex cells, they can cause genetic diseases in progeny.

1. Why should solar energy be harnessed to take care of our electric power needs?

2. How do we confirm that the ‘greenhouse effect’ is real?

3. How does acid rain destroy forests and fish?

4. Is it possible to eliminate the air pollution from coal burning?

5. Radioactivity can harm us by radiating from sources outside our bodies, by being taken in with food or water or by being inhaled into our lungs. But we consider only one of these pathways. Why is it so?

6. Cancers from radiation may take up to 50 years to develop, and genetic effects may not show up for a hundred years or more. How, then, can we say that there will be essentially no health effects from the Three Mile Island accident?

7. Air pollution may kill people now, but radiation induces genetic effects that will damage future generations. How can we justify our enjoying the benefits of nuclear energy while future generations bear the suffering from it?

8. Can the genetic effects of low-level radiation destroy the human race?

9. Isn’t the artificial radioactivity created by the nuclear industry, more dangerous than the natural radiation which has always been present?

10. Can radiation exposure to parents cause children to be born with two heads or other such deformities?

11. Can a reactor explode like a nuclear bomb?

12. If reactors are so safe, why don’t home owners’ insurance policies cover reactor accidents? Does this mean that insurance companies have no confidence in them?

13. How is radioactive waste disposed off?

14. How long will the radioactive waste be hazardous?

15. How will we get rid of reactors when their useful life is over?

Fossil fuels are hydrocarbons, primarily coal, fuel oil or natural gas, formed from the remains of dead plants and animals.

Types of Fossil Fuels

     • Coal

     • Natural Gas

     • Oil (Petroleum)

Types of coal storage

     • Dead storage

     • Living storage

Means of coal storage

     • Storage in coal heaps

     • Underwater storage

Energy production using fossil fuels

A fossil-fuel power station is a power station which burns fossil fuel, such as coal, natural gas or petroleum to produce electricity.

Nuclear fuel and nuclear fission Nuclear fuel is any material that can be consumed to derive nuclear energy.

Controlled fission (power production)

When a fission reaction leads to a new fission reaction, which leads to another one and so on, it is called controlled fission. The amount of heat required is controlled by raising and lowering the rods in the reactor.

Uncontrolled fission (nuclear weapons)

A fission reaction whereby the reaction is allowed to proceed without any moderation (by removal of neutrons) is called an uncontrolled fission reaction. An uncontrolled fission reaction is used for nuclear bombs.

Problems associated with the production of nuclear power

   • problem of radioactive waste.

   • high risks.

   • targets for terrorist attacks.

   • nuclear weapons.

   • uranium is a scarce resource.

   • illusion to build new nuclear power plants.

Environmental problems of fossil fuels

Climate Change / Global Warming and Greenhouse Effect

The earth’s atmosphere allows a lot of sunlight to reach the earth’s surface, but reflects much of that light back into space.

The result is a gradual increase in the earth’s temperature or Global Warming.

‘Hole’ in the Ozone Layer

Ozone acts to block out much of the sun’s ultraviolet radiation which causes skin cancer and contributes to the fluctuations of global climatic conditions that affect the environment.

Acid Rain

When gases, such as sulphur dioxide and nitrogen oxides react with water in the atmosphere to form sulphuric acid and nitric acid, they form an acidic ‘rain’ which can destroy vegetation.

Air Pollution

Air pollution is the release into the atmosphere of excessive amounts of harmful gases  as well as particles.

Other environmental problems of fossil fuels include:

    • Biological Control

    • Biological Magnification

    • Introduced Species

    • Soil Salinity

    • Population Explosion