8. Energy, power and climate change

Nuclear fuel

*Uranium - 235* is the substance undergoing fission! (Only 0.7% of the naturally occuring uranium is U-235. Therefore enrichment is used.) Uranium -238 is also persent byt do not undergo fission by low energy neutrons (not fissile) hence they absorbs neutrons without fissing

Gas-fired power station

More efficient than using coal because of two stages of energy use. The burning gas is blasted through turbine, then heat from burning used to turn turbine (same as for coal etc.)

Oil and gas

Non-renewable fossil fuel. Easier to extract than coal since they are fluid. Burn to release energy --> source of greenhouse gases.

Coal

Non-renewable fossil fuel. Composed of plants that died millions of years ago, the plants used phoyosynthesis (process which requires energy) so originally energy from the sun. Burn to release energy --> emission of carbon dioxide. Has to be dug up from the ground (mining) --> large environmental effect.

Fusion fuel

Not used in commercial production of energy. The fuel is hydrogen. Non-renewable, BUT lot of hydrogen and only little needed to produce a lot of energy.

The sun

"A burning ball of gas" - Made of helium and hydrogen - Thermal energy generated from fusion - Outer temperature: 6 000 K hence fusion takes placce in the much hotter and more dense core - The core is a very dense ball of plasma, estimated temperature: 1,5 million K

Examples of energy transfer

*Light bulb* - converts electrical energy to light + heat *Electric motor* - converts electrical energy to mechanical + heat *Battery* - converts chemical energy to electrical + heat *Car engine* - converts chemical energy to mechanical + heat *Solar cell* - converts light to electrical + heat

Albedo

*The ratio between the reflected radiation to incident radiation.* When electromagnetic radiation is incident on a surface it is either absorbed or reflected. The ratio of reflected to incident radiation is called albedo. The albedo for snow is high since it reflects most of the radiation incident on it, whereas dark forest has a low albedo.

Emmisivity (e)

*The ratio of the energy radiated by a body to the energy radiated by a black body at the same temperature.* A scale from 0 t0 1, where a black body has an emmisivity of 1.

Calculating hydroelectric power

PE=mgh Height is the height difference between the outlet from the lake and the turbine. The average height is used, since not all water in the lake have the same height. Mass = volume ∙ density

World wide consumption of energy

Usage of energy sources: - Oil 38% - Coal 26% - Gas 23% - Hydroelectric 6% - Nuclear 6% - Geothermal, solar, wind, wood 1% Most used renewable enrgy sources: - Solar - Wind - Geothermal - Biofuels

Run-of-the-river power stations

Use water that has been diverted from a fast-flowing river without damming the river. This is a solution for countries without mountain lakes.

Sankey diagrams

Used to visualize the flow of something, for example flow of energy as it changes from one form to another. The widths of the elements are proportional to the amount of energy flowing.

Uncontrolled fission

When there are more than *an average of* one neutron from a split initiating further fission reactions! This would cause the number of fissions to increase constantly (accelerates), hence the reaction would go out of control. (the system could not cool the reaction enough. As an atomic bomb...)

Causes of global warming

- Amount of radiation from the sun (more radiation incident --> increased temperature) -- Solar flares (variation in emmission of radiation) -- Earth's orbit (variation of distance from earth to sun) - Enhanced greenhouse effect (more greenhouse gases --> greater amount of radiation absorbed by the atmosphere --> Earth trying to reach equilibrium)

Advantages of nuclear power

- Extremely high energy density - No emmission of carbon dioxide (CO2) hence do not add to global warming - Reserves of uranium is large compared to oil - The rest product of "used up" uranium, Plotonium, can be used as a fuel (however highly reactive and dangerous...)

Possible causes of ennhanced greenhouse effect and global warming

- Increased burning of fossil fuels (increases greenhouse gases) - Deforistation (reduses the ability of photosynthesis) - Increased pollution upsetting the chemical balance of the atmosphere - Increased energy consumption

Disadvantages of nuclear power

- Risk of devestating meltdown if the reaction goes out of hand - Produces radioactive nuclear waste that is only stored (radioactive for hundereds of years) - Extraction of uranium - Non-renewable - Weapons are made from the waste material (Plotonium)

Factors determening the chance that a fission reaction will occur

1. The number of potential nuclei that are "in the way" for the neutron. 2. The speed (or energy) of the neutrons (the neutrons released in fission generally move too fast, therefor slowed down by the moderator nucleus)

The fusion reaction of hydrogen

1. Two hydrogen atoms fuse together. 2. Beta radiation and a nutrino is radiated, leaving a neutron and a proton 3. An additional hydrogen is attached and gamma radiation is radiated, this leaves two protons and one neutron in the substance (hence a Helium nucleus!) 4. Two helium nuclei fuse and two hydrogen atoms are deattached in the process 5. The lone hydrogen nucleus go on initiating further fusions. This is a pretty long process (and explanation... See page 189 for a more simple PICTURE)

Hydroelectric power

Heat from the Sun turns water into water vapour, forming clouds. The clouds are blown over the land and the water vapour turns back into water as rain falls. Rain water falling on high ground has PE that can be converted into electricity.

Blackbody radiation

A black body absorbs all wavelengths. As it heats up it also emits all wavelengths, called blackbody radiation.

Nuclear reactor

A device that containc, controls and initiates nuclear chain reactions at a steady and sustained rate. With the purpose to convert nuclear energy to thermal energy (and ultimately electrical energy)

Tokamak

A doughnut-shaped (large) ring made of specailly shaped magnets to create a magnetic field in which the plasma is contained.

Fissionable

A material that can undergo nuclear fission

Fissile

A material that can undergo nuclear fission by neutrons with very low KE

Nuclear chain reaction

A nuclear reaction that causes one or more nuclear reactions to take place. A neutron is absorbed by a big nuclei, and so its binding energy increases. The nuclei cannot get rid off this extra energy in any other way than by splitting. When splitting, there will be an additional release of neutrons initiating further reactions.

Fuel

A substance that can release energy by changing its chemical or nuclear structure.

Albedo for Earth

An average of 30 % (DO WE NEED TO KNOW THIS??????) It varies daily since it depends in season, amount of clouds and amount of snow and ice.

Meltdown

An uncontrolled chain reaction releases so much energy that the temperature rises to the point where it overheats the fuel rods, and the rods melt. This makes the fuel impossible to remove --> bursts the pressure vessel --> radioactive material is sent to the environment and atmosphere (this is *not* an explosion!)

Tidal power

At places with big difference between high and low tide, the tidal flow can be used to produce hydroelectric power. The water is held back by a barrage and then released to drive the turbines.

Extraction of uranium

Can be extracted by: 1. Open cast mining --> environmental damage 2. Underground mining --> dangerous working environment 3. Leaching (chemically 'pumping' the uranium out of the ground) --> can damage cause contamination (förorening) of ground water

Efficiency of power stations

Can be up to 59%. If wasted heat is used to heat houses, overall efficiency can be 80%.

Historical and geographical reasons for widespread use of fossil fuels

Coal has been used for 4000 years. Not the same energy needs as now. For them wood was convenien Invention of steam engine made it possible for powered transportation. Industrial revolution was dependent on coal. Refined oil later revolutionzed transportation: higher density, easy to transport. BUT disaster if it leaks! Households used coal and gas until electricity was discovered which is the easiest was to transfer energy from one place to another.

Coal-fired power station

Coal is made into dust and blown into furnace, heat boils water that turns to steam and powers the turbine which turns a generator and produces electricity. Steam out from turbine is cooled and then returned to the boiler. Overall efficiency ~40% due to exhaust gases from orignial heat takes some heat, as heat given out from the steam when it condenses after passing the tubine. Also fricition in the components of turbine and generator.

Photovoltaic cell (solar cell)

Converts solar radiation into electrical energy. The semiconductors in the photvoltaic cell release electrons when photons of light are absorbed. Different types of semiconductors are placed together to create an electrical field that will cause the freed electrons to flow in an external circuit. The potential difference and current produced by a single photovoltaic cell is small, therefore many cells are connected together to produce power commercially.

Factors influencing albedo

Different terrains have a variety of albedos. It depends on its ability to absorb or reflect the radiation from the sun. Some examples: Ocean water: 7%, Snow and ice: 62% to 66%, Desert (36%).

Electrical generator

Electricity can be produced from many different types of energy. All of these methods make use of a generator to convert mechanical energy to electrical energy. (Describe how the generator works)

Nuclear fuel

Energy does not come from the Sun! Non-renewable resource. Does not have to be burnt --> not contributing to greenhouse effect, BUT gives rise to waste materials and radioactive.

Evidence linking global warming to increased levels of greenhouse gases

Ice-core research. Drilling cores of ice to examine atmospheric composition over different times. The Composition is examined through the bubbles of air trapped in the ice and the temperature of the time is determined by the structure.

Storage of high level waste

Ideas: Sending it to the sun, putting it at the bottom of the sea, burying it in the icecap or droppin it to a very deep hole :) Current soutions: - Storing it under water until cooled off, then sealed in steel cylinders - Reprocessing the waste to spare the plutonium remaining fuels of uraium from fission fragments. Results in even higher radioactivity but with much shorter half life.

Trends in emission spectra of black at different temperatures

If we heat a black body to incandescence (glowing) we observe: -The higher the temperature the greater the intensity at all wavelengths. -The higher temperature the smaller the wavelength of the maximum intensity

The second law of thermodynamics

It is impossible to take heat from a hot object and use it all to do work without losing some to the surroundings.

Wood and Biomass

Plants can be used as energy. E.g. wood. Sugarcane used to produce biofuel to run cars. Food waste and cow manure can be used to produce fuel but are not high grade fuels. Burn to release energy --> contribute to global warming, but as plants are growing they absorb CO2 and reduce the overall greenhouse effect.

Wind power

Renewable and do not produce GH gases, derived from the sun. KE in air used to turn a turbine and produce electricity.

Hydroelectric power

Renewable and do not produce GH gases, derived from the sun. The principle of the hydro electric power station: using the PE of the water.

Solar energy

Renewable and do not produce GH gases, derived from the sun. Using mirrors to focus radiation to one point. Sun's radiation directly converted into electricity using a photovoltaic cell. Only possible in countries with a lot of sunlight.

Wave power

Renewable and do not produce GH gases, derived from the sun. Waves and their energy spreads out, this energy can be used to power tubines and produce electricity.

Geothermal energy

Renewable and do not produce GH gases, not derived from the sun. Explosive energy from geysers used to produce electricity.

Tidal power

Renewable and do not produce GH gases, not derived from the sun. Reason for tides is the Moon and and bottom of oceans are different distances, so experience different gravitational force. Movement of water used to drive turbines to produce electricity.

Solar heating panel (Solar Thermal Collectors)

Solar radiation enters the panel through the glass cover. It's absorbed by a black metal plate which get hot and in turn makes the water hot by conduction. Water is continuously circulated, so the hot water flows out and more cold water flows in. Used for central heating or for making hot water for household. Placed on roofs of houses.

Control rods

Substance which absorbs neutrons to alter the chain reactions. Can be removed if the reaction is goint to slow and incerted if the reaction is going to fast. Example: Boron (The U-238 which is already in the reaction also acts to slow the reaction down, but cannot be altered...)

Energy density

The amount of energy that can be extracted per kg of fuel. A fuel with high energy density costs less to transport than one with a low.

Surface heat capacity (Cs)

The amount of heat required to raise the temperature of 1 m^2 of the ground by 1 K.

Solar constant

The energy emitted from the Sun is spread out over a sphere with a radius equal to the Earth's orbital radius. The power per square meter or intensity is 1380 Wm-2.

The molecular mechanism by which greenhouse gases absorb infrared radiation

The energy from the sun is carried in the form of photons. The atmosphere is made up of gases, which are the first layer of matter that the sun's rays interact with. If the frequency of oscillation (when it moves, rotates and oscillates) of the molecule in the atmosphere is the same as the frequency of a photon, it will absorb it. This causes the molecules to move more, hence have a higher temperature. By absorbing a photon, an electron is excited and move to higher energy level, and when it jumps back it releases energy as photons (usually IR radiation). Greenhouse gases usually vibrates/oscillated with the same frequency as infrared radiation, hence it will absorb it.

1 eV

The energy gained by an electron accelerated through a potential difference of 1V

Low level waste

The extraction, enrichment and transfer of heat from fuel rods all leaves traces of radioactive material . Must be disposed away form human contact for 100-500 years. Also old reactors are radioactive

Plasma

The fusion reactor. A *gas* in which the electrons and nuclei are seperate, (ionization on hydrogen atoms) this is also known as "the fourth state of matter". If hot enough, the nuclei collides with other nuclei and with enough speed to overcome their electric repulsion, and ultimately fuse together. This temperature has to be 1oo milion Kelvin...

Pumped storage schemes

The hydroelectric power can be turned off at night when the demand is low. The excess power produced from coal-fired power stations can instead be used to pump water up into a reservoir which can be used to turn the turbines in the daytime. This will in the long run reduce the amount of fossil fuels needed.

Enhanced greenhouse effect

The increase in the greenhouse effect caused by human activities

Describe the greenhouse effect

The infrared radiation radiated from the ground travels upwards through the atmosphere and is absorbed by CO2 and H2O. As a result, these molecules becomes excited, raising the temperature of the atmosphere. They themselves can then radiate IR radiation in all directions, some of which goes back to earth. It is like the atmosphere is trapping the energy. We have seen that the temperature of the Earth is determined by the point at which the radiation leaving the Earth is equal to that arriving. By reducing the amount leaving, the temperature at which this balance will be achieved will be greater.

Stefan-Boltzmann law

The law relates the power per unit area to the temperature of the surface with the equation: Power per unit area= ơ ∙ T^4 ơ= 5,67 ∙ 10 ^-8 (in data booklet)

Main greenhouse gases and their sources

The main gases that are particularly effective in absorbing infrared radiation are: methane (CH4) - There are natural sources, but example human-made sources are leakage from natural gas systems and the raising of livestock. water vapor (H2O) - natural in the environment Carbon dioxide (CO2) - fossil fuel emission of CO2, deforestation, volcanos Nitrous oxide (N2O) - There are natural sources, but ca. 40 % is due to human activities like: agriculture, transportation (fossil fuel), and industry activities. Note that there are both natural and man-made changes.

Critical mass

The minimum mass required for a chain reaction to occur.

Global warming

The natural phenomenon of earch trying to reach equilibrium (????) The term used to describe the trend of Earth's increasing average temperature

Nuclear power

The power associated with energy produced as a result of nuclear reactions.

Fission

The process in which nucleus are forced to split into two smaller nuclei and result in a loss of mass, hence releases energy

Enrichment

The process in which the percentage of the fuel (U-235) is increased by removing U-238. Desired percentage of U-235 is 3% (the extracted U-238 can be used to make nuclear weapons...)

Fusion

The process in which two small nucleus come together to form a larger nucleus. The larger nuclei has lower mass than the sum and the difference is converted to energy.

Degradation of energy

The process of energy transforming into disordered, spread out energy. Thermal energy is the most degraded form of energy, always transferring some of the thermal energy to the cold surroundings when coverted into mechanical energy.

Oil-fired power station

The same as coal-fired set up but oil is burnt to produce energy needed to boil water. Easier to extract than coal using modern technolgy.

High level waste

The spent fuel rods. Must be stored away form human contact for very very very long time (Plotonium is not considered safe until after *240000* years!)

Moderation/Moderators

The substance slowing down the speed of the neutrons to enable further fission reactions. Often regular water.

Intensity of the Sun's radiation incident on a planet

The sun radiates 3,9 ∙ 10^26 joules per second. It spreads out in a sphere. The intensity of it's radiation on a planet can be calculated by: (3,9 ∙ 10^26) /4π ∙ (orbital radius)^2 (Not in data booklet)

Fusion reactor

Theoretical potential source of energy. (Energy source of the sun) - Fuel = hydrogen -- Easily extracted -- Large resource bank - No significant amounts of radioactive waste - Requires plasma...

Global warming (how it works)

There is a fixed *amount *of radiation comin in (reaching earth) However there is a fixed *percentage* of radiation leaving Earth. As times goes, the amount radiated out will equal the amount radiated in, hence Earth reaches equilibrium. Omits the greenhouse effect!

Mechanisms increasing rate of global warming

These effects causes continuous global warming... - Reduced ice/snow cover --> reduces albedo --> increased overall heat absorption - Temperature increase reduces the solubility of CO2 in water --> increased atmospheric concentration of CO2 - Incraesed evaporation and increased atmospheric ability to hold water vapour --> increased amount of greenhouse gases (water is a greenhouse gas) - Deforestation --> release of CO2 AND reduces overall photosynthesis ability

Heat exchanger

Tube of water which is heated by the thermal energy created by the energy released in the reaction. The water evaporates to steam and this steam turns a turbine which generated the electricity. The heat exchanger enables the reaction to take place sealed off from the external environment. Not all the kinetic energy goes to kinetic energy (turning the turbine), the majority is lost to the surroundings

Isotopes

Two or more nuclei with the same nuclear number but different atomic masses (same amount of protons and electrons but different amount of neutrons...)

Nuclear bombs

Uncontrolled chain reaction. Uranium - 235 and the moderator is kept apart until the bomb is dropped. The percentage of U-235 is high, hence fast chain reaction.