Topic 8: Energy, power Topic 8: Energy, power and climate changeand climate change

8.4 Non-fossil Fuel Production8.4 Non-fossil Fuel Production

Non-Fossil fuel productionNon-Fossil fuel production

•Nuclear PowerNuclear Power•Solar PowerSolar Power•Hydroelectric PowerHydroelectric Power•Wind PowerWind Power•Wave PowerWave Power

Chain reactionsChain reactions

Controlled fission

To maintain a sustained controlled nuclear reaction, there To maintain a sustained controlled nuclear reaction, there must be at least one neutron from each fission being must be at least one neutron from each fission being absorbed by another fissionable nucleus. absorbed by another fissionable nucleus.

The reaction can be controlled by using control rods of The reaction can be controlled by using control rods of material which absorbs neutrons. material which absorbs neutrons.

Control rods are commonly made of a strongly neutron-Control rods are commonly made of a strongly neutron-absorbent material such as boron or cadmium.absorbent material such as boron or cadmium.

Uncontrolled fissionUncontrolled fission

A A fissionfission reaction whereby the reaction is allowed to reaction whereby the reaction is allowed to proceed without any moderation or control rods is called proceed without any moderation or control rods is called an an uncontrolled fissionuncontrolled fission reaction . reaction .

If there are too many neutrons, the chain reaction would If there are too many neutrons, the chain reaction would proceed at tremendous pace and result in an explosion.proceed at tremendous pace and result in an explosion.

An example would be in an atomic bomb where the An example would be in an atomic bomb where the reactions are uncontrolled.reactions are uncontrolled.

In a nuclear reactor, if the fission process is not well In a nuclear reactor, if the fission process is not well controlled, the large amounts of energy would cause the controlled, the large amounts of energy would cause the fuel to melt and set fire to the reactor in what is called a fuel to melt and set fire to the reactor in what is called a meltdown. meltdown.

Fuel enrichmentFuel enrichment

• Uranium found in nature consists largely of two Uranium found in nature consists largely of two isotopes, U-235 and U-238. The production of energy in isotopes, U-235 and U-238. The production of energy in nuclear reactors is from the 'fission' or splitting of the U-nuclear reactors is from the 'fission' or splitting of the U-235 atoms, a process which releases energy in the 235 atoms, a process which releases energy in the form of heat. U-235 is the main fissile isotope of form of heat. U-235 is the main fissile isotope of uranium.uranium.

• Natural uranium contains 0.7% of the U-235 isotope. Natural uranium contains 0.7% of the U-235 isotope. The remaining 99.3% is mostly the U-238 isotope which The remaining 99.3% is mostly the U-238 isotope which does not contribute directly to the fission process does not contribute directly to the fission process (though it does so indirectly by the formation of fissile (though it does so indirectly by the formation of fissile isotopes of plutonium).isotopes of plutonium).

Role of control rodsRole of control rods• The control rods, an The control rods, an

important part of the important part of the reactor, regulate or reactor, regulate or control the speed of the control the speed of the nuclear chain reaction, nuclear chain reaction, by sliding up and down by sliding up and down between the fuel rods or between the fuel rods or fuel assemblies in the fuel assemblies in the reactor core. reactor core. 

• The control rods contain material such as cadmium and boron.  Because of their atomic structure cadmium and boron absorb neutrons, but do not fission or split.

Role of moderatorRole of moderator

• In addition to the need to In addition to the need to capturecapture neturons, the neutrons neturons, the neutrons often have too much kinetic energy. often have too much kinetic energy.

• These These fast neutronsfast neutrons are slowed through the use of a are slowed through the use of a moderator such as moderator such as heavy water and ordinary water.heavy water and ordinary water.

• Some reactors use graphite as a moderator, but this Some reactors use graphite as a moderator, but this design has several problems. design has several problems.

• Once the fast neutrons have been slowed, they are more Once the fast neutrons have been slowed, they are more likely to produce further nuclear fissions or be absorbed likely to produce further nuclear fissions or be absorbed by the control rod.by the control rod.

• Java applet nuclear reactionJava applet nuclear reaction• http://library.thinkquest.org/17940/texts/java/Reaction.ht

ml

A nuclear reactorA nuclear reactor

• Inside the "core" where the nuclear reactions take place Inside the "core" where the nuclear reactions take place are the fuel rods and assemblies, the control rods, the are the fuel rods and assemblies, the control rods, the moderator, and the coolant. moderator, and the coolant.

• Outside the core are the turbines, the heat exchanger, Outside the core are the turbines, the heat exchanger, and part of the cooling system. and part of the cooling system.

Heat exchangerHeat exchanger

• A A heat exchangerheat exchanger is a device built for efficient is a device built for efficient heat transfer from one medium to another heat transfer from one medium to another

• The heated water rises up and passes through The heated water rises up and passes through another part of the reactor, the heat exchanger. another part of the reactor, the heat exchanger.

• The moderator/coolant water is radioactive, so it The moderator/coolant water is radioactive, so it can not leave the inner reactor containment. can not leave the inner reactor containment.

• Its heat must be transferred to non-radioactive Its heat must be transferred to non-radioactive water, which can then be sent out of the reactor water, which can then be sent out of the reactor shielding.shielding.

• This is done through the heat exchanger, which This is done through the heat exchanger, which works by moving the radioactive water through a works by moving the radioactive water through a series of pipes that are wrapped around other series of pipes that are wrapped around other pipes. pipes.

• The metallic pipes conduct the heat from the The metallic pipes conduct the heat from the moderator to the normal water. moderator to the normal water.

• Then, the normal water (now in steam form and Then, the normal water (now in steam form and intensely hot) moves to the turbine, where intensely hot) moves to the turbine, where electricity is produced. electricity is produced.

Plutonium-239Plutonium-239

U-238 is not fissile but it is useful because it can be used to U-238 is not fissile but it is useful because it can be used to produced Pu-239, a fissionable isotope. produced Pu-239, a fissionable isotope.

First, U-238 becomes U-239 by neutron capture:First, U-238 becomes U-239 by neutron capture:

Then U-239 goes through beta decay to become Neptunium Then U-239 goes through beta decay to become Neptunium

Then Neptunium beta decays into PlutoniumThen Neptunium beta decays into Plutonium

And Pu-239 is fissionable and large amounts of energy is And Pu-239 is fissionable and large amounts of energy is releasedreleased

Plutonium-239 as a nuclear fuelPlutonium-239 as a nuclear fuel

• U-238 is 140 times more abundant than U-235.U-238 is 140 times more abundant than U-235.• The neutrons given off in a U-235 reaction can be used The neutrons given off in a U-235 reaction can be used

to “breed” more fuel if the non-fissionable U-238 is to “breed” more fuel if the non-fissionable U-238 is placed in a “blanket” around the control rods containing placed in a “blanket” around the control rods containing U-235.U-235.

• On average, 2.4 neutrons are produced in a U-235 On average, 2.4 neutrons are produced in a U-235 reaction with 1 neutron required for the next fission and reaction with 1 neutron required for the next fission and 1.4 left for neutron capture by U-238.1.4 left for neutron capture by U-238.

Safety and risks of nuclear powerSafety and risks of nuclear power

• Problems associated with mining of Problems associated with mining of UraniumUranium

• Problems with disposalProblems with disposal• Risk of thermal meltdownRisk of thermal meltdown• Risk of nuclear programs as means of Risk of nuclear programs as means of

nuclear weapon productionnuclear weapon production

Biggest risk for mining of uranium is the Biggest risk for mining of uranium is the exposure of miners to radon-222 gas and exposure of miners to radon-222 gas and other highly radioactive products, as well other highly radioactive products, as well as water containing radioactive and toxic as water containing radioactive and toxic materialsmaterials

In 1950s, a significant number of american In 1950s, a significant number of american miners developed small cell lung cancer miners developed small cell lung cancer due to radon which was the cancer due to radon which was the cancer causing agent.causing agent.

The biggest concern is Pu-239 which has a half-The biggest concern is Pu-239 which has a half-life of approx 24,000 years.life of approx 24,000 years.

It is also used in nuclear warheadsIt is also used in nuclear warheads

Presently the disposal methods include deep Presently the disposal methods include deep storage underground.storage underground.

If these methods fail, there would be catastrophic If these methods fail, there would be catastrophic consequencesconsequences

Radioactive waste would find its way into the food Radioactive waste would find its way into the food chain and underground water would become chain and underground water would become contaminated.contaminated.

Nuclear power using nuclear fusion Nuclear power using nuclear fusion

The most probable way is to fuse deuterium The most probable way is to fuse deuterium and tritium.and tritium.

Deuterium atoms can be extracted from Deuterium atoms can be extracted from seawater and tritium can be bred from seawater and tritium can be bred from lithium. lithium.

Nuclear power using nuclear Nuclear power using nuclear fusion?fusion?

The basic problems in attaining useful nuclear The basic problems in attaining useful nuclear fusion conditions are fusion conditions are

(1)(1) to heat the gas to these very high temperatures to heat the gas to these very high temperatures and and

(2)(2) to confine a sufficient quantity of the reacting to confine a sufficient quantity of the reacting nuclei for a long enough time to permit the nuclei for a long enough time to permit the release of more energy than is needed to heat release of more energy than is needed to heat and confine the gas. and confine the gas.

(3)(3) the capture of this energy and its conversion to the capture of this energy and its conversion to electricity. electricity.

If fusion energy does become practical, it offers If fusion energy does become practical, it offers the following advantages: the following advantages:

(1)(1)a limitless source of fuel, deuterium from the a limitless source of fuel, deuterium from the ocean; ocean;

(2)(2)no possibility of a reactor accident, as the no possibility of a reactor accident, as the amount of fuel in the system is very small; and amount of fuel in the system is very small; and

(3)(3)waste products much less radioactive and waste products much less radioactive and simpler to handle than those from fission simpler to handle than those from fission systems. systems.

Photovoltaic cellsPhotovoltaic cells

• Photovoltaic devices make use of the Photovoltaic devices make use of the photoelectric effect. photoelectric effect.

• Solar photovoltaic modules use solar cells to Solar photovoltaic modules use solar cells to convert light from the sun into electricity. convert light from the sun into electricity.

Solar heating panelsSolar heating panels

Solar thermal panels contain liquid that circulates Solar thermal panels contain liquid that circulates through special panels and is heated by through special panels and is heated by sunlight, this then passes through a coil in the sunlight, this then passes through a coil in the water tank which in turn heats the water stored water tank which in turn heats the water stored in the tank in the tank

What are the factors that would What are the factors that would affect the amount of solar affect the amount of solar

radiation that a place gets?radiation that a place gets?

The main factors are:The main factors are:

• Geographic location Geographic location • Time of day (altitude of the sun from the Time of day (altitude of the sun from the

sky)sky)• Season Season • Local landscape Local landscape • Local weather Local weather • The distance of earth from the sunThe distance of earth from the sun

Because the Earth is round, the sun strikes the Because the Earth is round, the sun strikes the surface at different angles ranging from 0º (just surface at different angles ranging from 0º (just above the horizon) to 90º (directly overhead). above the horizon) to 90º (directly overhead).

When the sun's rays are vertical, the Earth's When the sun's rays are vertical, the Earth's surface gets all the energy possible. surface gets all the energy possible.

The more slanted the sun's rays are, the longer The more slanted the sun's rays are, the longer they travel through the atmosphere, becoming they travel through the atmosphere, becoming more scattered and diffuse. more scattered and diffuse.

Because the Earth is round, the frigid polar regions Because the Earth is round, the frigid polar regions never get a high sun, and because of the tilted never get a high sun, and because of the tilted axis of rotation, these areas receive no sun at all axis of rotation, these areas receive no sun at all during part of the year during part of the year

Countries like the United States, which lie in Countries like the United States, which lie in the middle latitudes, receive more solar the middle latitudes, receive more solar energy in the summer not only because energy in the summer not only because days are longer, days are longer,

but also because the sun is nearly overhead. but also because the sun is nearly overhead.

The sun's rays are far more slanted during The sun's rays are far more slanted during the shorter days of the winter months. the shorter days of the winter months. Cities like Denver, Colorado, (near 40º Cities like Denver, Colorado, (near 40º latitude) receive nearly three times more latitude) receive nearly three times more solar energy in June than they do in solar energy in June than they do in December December

3 main schemes3 main schemes

• Water storage in lakesWater storage in lakes• Tidal water storageTidal water storage• Pump storagePump storage

Water storage in lakesWater storage in lakes

Water storage in lakesWater storage in lakes

The Three Gorges Dam on the Yangtze River will be the The Three Gorges Dam on the Yangtze River will be the largest hydroelectric dam in the world when it is largest hydroelectric dam in the world when it is complete in 2009.complete in 2009.

It will generate 18200MWIt will generate 18200MW

The dam is more than 2 km wide and has a height of 185m.The dam is more than 2 km wide and has a height of 185m.

Its reservoir will stretch over 600km upstream and force the Its reservoir will stretch over 600km upstream and force the displacement of more than 1.3million people.displacement of more than 1.3million people.

Tidal water storageTidal water storageA dam is built to catch the high tide.A dam is built to catch the high tide.

A sluice gate is opened to let the high tide water inA sluice gate is opened to let the high tide water in

The water is released at low tide, and the gravitational The water is released at low tide, and the gravitational potential energy is used to drive turbines which produce potential energy is used to drive turbines which produce electrical energyelectrical energy

Pumped storage Pumped storage

Used in off-peak electricity demand periodUsed in off-peak electricity demand periodWater is pumped from low reservoir to high Water is pumped from low reservoir to high

reservoirreservoir

Generating Mode Pumping Mode

Energy transformationsEnergy transformationsWater trapped in reservoirs have gravitational potential energyWater trapped in reservoirs have gravitational potential energy

Water falls through a series of pipes where its potential energy Water falls through a series of pipes where its potential energy gets converted to rotational kinetic energy that drives a gets converted to rotational kinetic energy that drives a series of turbinesseries of turbines

The rotating turbines drive generators that convert the kinetic The rotating turbines drive generators that convert the kinetic energy into electrical energy by electromagnetic induction.energy into electrical energy by electromagnetic induction.

Basic featuresBasic features

1)1) FoundationFoundation

2)2) TowerTower

3)3) NacelleNacelle

4)4) Rotor bladesRotor blades

5)5) HubHub

6)6) Transformer (not part of Transformer (not part of wind turbine)wind turbine)

1) Foundation and 2) Tower 1) Foundation and 2) Tower Guarantee the stability of a wind turbine a pile or Guarantee the stability of a wind turbine a pile or

flat foundation is used, depending on the flat foundation is used, depending on the consistency of the underlying ground. consistency of the underlying ground.

The The towertower carry the weight of the nacelle and the carry the weight of the nacelle and the rotor blades, AND must also absorb the huge rotor blades, AND must also absorb the huge static loads caused by the varying power of the static loads caused by the varying power of the wind. wind.

Generally, a tubular construction of concrete or Generally, a tubular construction of concrete or steel is used. An alternative to this is the lattice steel is used. An alternative to this is the lattice tower form.tower form.

3) Nacelle and 5) Hub3) Nacelle and 5) HubThe nacelle holds all the turbine machinery. The nacelle holds all the turbine machinery.

Because it must be able to rotate to follow the wind Because it must be able to rotate to follow the wind direction, it is connected to the tower via bearings. direction, it is connected to the tower via bearings.

The build-up of the nacelle shows how the manufacturer The build-up of the nacelle shows how the manufacturer has decided to position the drive train components (rotor has decided to position the drive train components (rotor shaft with bearings, transmission, generator, coupling shaft with bearings, transmission, generator, coupling and brake) above this machine bearing. and brake) above this machine bearing.

4) Rotor and rotor blades4) Rotor and rotor blades

The The rotorrotor is the component which, with the help of the rotor is the component which, with the help of the rotor blades, converts the energy in the wind into rotary blades, converts the energy in the wind into rotary mechanical movement.mechanical movement.

Currently, the three-blade, horizontal axis rotor dominates. Currently, the three-blade, horizontal axis rotor dominates. The The rotor bladesrotor blades are mainly made of glass-fibre or are mainly made of glass-fibre or carbon-fibre reinforced plastics (GRP, CFRP). carbon-fibre reinforced plastics (GRP, CFRP).

The blade profile is similar to that of an aeroplane wing. The blade profile is similar to that of an aeroplane wing. They use the same principle of lift: on the lower side of They use the same principle of lift: on the lower side of the wing the passing air generates higher pressure, the wing the passing air generates higher pressure, while the upper side generates a pull. while the upper side generates a pull.

These forces cause the rotor to move to rotate.These forces cause the rotor to move to rotate.

Power calculationPower calculation

The power in the wind is proportional to:The power in the wind is proportional to:• the area of windmill being swept by the the area of windmill being swept by the

wind wind • the cube of the wind speed the cube of the wind speed • the air density - which varies with altitude the air density - which varies with altitude

FormulaFormula

P = 0.5P = 0.5ρρAv³Av³

WhereWhere

P: is power in watts (W) P: is power in watts (W)

ρ: is the air density in kilograms per cubic metre (kg/m3), ρ: is the air density in kilograms per cubic metre (kg/m3), (about 1.225 kg/m3 at sea level, less higher up) (about 1.225 kg/m3 at sea level, less higher up)

A: is the swept rotor area in square metres (m2) A: is the swept rotor area in square metres (m2)

V: is the windspeed in metres per second (m/s). V: is the windspeed in metres per second (m/s).

The actual power that we can extract from the wind is The actual power that we can extract from the wind is significantly less than what the previous formula significantly less than what the previous formula suggests. The actual power will depend on several suggests. The actual power will depend on several factors, such as factors, such as – the type of machine and rotor used, the type of machine and rotor used, – the sophistication of blade design, the sophistication of blade design, – friction losses, and friction losses, and – the losses in the pump or other equipment the losses in the pump or other equipment

connected to the wind machine. connected to the wind machine.

Wave PowerWave Power

DescribeDescribe the principle of operation of an oscillating water the principle of operation of an oscillating water column (OWC) ocean-wave energy convertercolumn (OWC) ocean-wave energy converter

DetermineDetermine the power per unit length of a wavefront, the power per unit length of a wavefront, assuming a rectangular profile for the wave.assuming a rectangular profile for the wave.

SolveSolve problems involving wave power. problems involving wave power.

Simple animation of OWC:Simple animation of OWC:

http://www.daedalus.gr/DAEI/PRODUCTS/RET/General/OWC/OWCsimulation2.htm

Offshore OWCOffshore OWC Onshore OWCOnshore OWC

As the wave enters a capture chamber, the air As the wave enters a capture chamber, the air inside the chamber is compressed inside the chamber is compressed

and the high velocity air provides the kinetic and the high velocity air provides the kinetic energy needed to drive a turbine connected to a energy needed to drive a turbine connected to a generator. generator.

As the captured water level drops, there is a rapid As the captured water level drops, there is a rapid decompression of the air in the chamber which decompression of the air in the chamber which

again turns the turbine that has been specially again turns the turbine that has been specially designed with a special valve system which designed with a special valve system which turns in the same direction regardless of the turns in the same direction regardless of the direction of the air flowing across the turbine direction of the air flowing across the turbine blades. blades.

http://www.darvill.clara.net/altenerg/wave.htm

http://www.alternative-energy-news.info/technology/hydro/wave-power/

Power Per Unit LengthPower Per Unit Length

Power per metre of the wave assuming the wavefront has a Power per metre of the wave assuming the wavefront has a rectangular profilerectangular profile

(on the data booklet)(on the data booklet)

Power per metre = 0.5ρgAPower per metre = 0.5ρgA22vv