Energy and Power Ib2

8/10/2019 Energy and Power Ib2

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IB 12

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Power Generation in a typical electrical power plant

) Some fuel is used (coal, natural gas, oil, uranium) torelease thermal energy which is used to boil water to

make steam.

) Generator (Dynamo)- Steam turns turbines attached tocoils of wire which turn in a magnetic field inducing an

alternating otential difference.

) !otential difference is steed u by transformers in

order to reduce I2" loss of ower in transmission lines

then steed down for consumer use.

Energy and Power

#hat are the energy transformations that take lace$

%egraded energy&


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'*& In most instances, the rime energy source for world energy is . . .

ankey diagrams (energy flow diagrams)& used to kee track ofnergy transfers and transformations

1) hickness of arrow is roortional to amount of energy.

2) %egraded energy oints away from main flow of energy.

+) otal energy in total energy out.

his histogram shows the relatieroortions of world use of the different

tyes of energy sources, though it will ary

from country to country.

ossil fuels&

rigins of fossil fuels&

'on-renewable fuels&

"enewable fuels&

uel&

/ow does a fuel work$ 0 fuel releases energy by changing its chemical (or nuclear) structure. hemical (or nuclear)bonds are broken reducing the fuels internal otential energy but increasing the kinetic energy of the substances articles

which is seen macroscoically as an increase in the temerature of the substance. It is this thermal energy that is used to heat

the water that will change to steam to turn the generators turbines.

Fuels

*3cetions&


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IB 12

+

Fossil Fuel Power Production

istorical and geograhical reasons for the widesread use of fossil fuels&

1. industriali4ation led to a higher rate of energy usage (Industrial "eolution)

2. industries deeloed near large deosits of fossil fuels (coal towns)

ransortation and storage considerations&

Use of fossil fuels for generating electricity

Advantages Disadvantages

1. high energy density

2. relatiely easy to transort

+. chea comared to other sources

5. ower stations can be built anywhere

6. can be used in the home

1. combustion roduces ollution, esecially S2(acid rain)

2. combustion roduces greenhouse gases (2)

+. e3traction (mining, drilling) damages enironment

5. nonrenewable

6. coal-fired lants need large amounts of fuel

+. !ower stations using coal and steel mills are usually located near coal mines.

Advantages minimi4es shiing costs

Disadvantages enironmental imact (stri mining), mine cae-ins

2. 7any oil refineries are located near the sea close to large cities. il is

transorted ia shis, trucks, and ielines.

Advantages workforce and infrastructure in lace, easy access to shiing

Disadvantages oil sills and leakage, hurricanes, terrorist actiities

1. 'atural gas is usually transorted and stored in ielines.

Advantages cost effectie

Disadvantagesunsightly, suscetible to leaks, e3losions, terrorist actiities,

olitical instability (withholding use of ielines or terminals forolitical reasons)


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IB 12

5

Energy density of a fuel

8nits&

8se&

/ow is choice of fuel influenced by energy density$

Fuel Energy Density

(!"#kg)usion fuel +99,999,999

8ranium-2+6 :9,999,999

'atural gas 6+.;

.9

#ood 1>.9

ow dung 16.6

/ousehold waste 19

ormula&

1. 0n oil-fired ower station roduces 1999 7# of ower.

b) *stimate how much oil the ower station needs each day.

a) /ow much energy will the ower station roduce in one day$


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IB 12

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2. 0 269 7# coal-fired ower lant burns coal with an energy density of +6 7?@kg. #ater enters the

cooling tower at a temerature of +69 A and leaes at a temerature of 2:+ A and the water flows

through the cooling tower at a rate of 5299 kg@s.

a) alculate the thermal energy remoed from the water in the cooling towers each second.

b) 0ssuming the only significant loss of energy is this thermal energy of the water, calculate the

energy roduced by the combustion of coal each second.

c) alculate the mass of coal burned each second.


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IB 12

;

$uclear Energy

7ost common source&

2+6 1 151 :2 1

:2 9 6; +; 9+U n Ba Kr n+ + +

!rocess&

a) unstable uranium nucleus is bombarded with a

neutron and slits into two smaller nuclei and some

neutrons

#hy use neutrons$

b) rest mass of roducts is less than reactants so some

matter is conerted into energy

orm of energy&

c) released neutrons strike other uranium nuclei

causing further fissions

1) 0 articular nuclear reactor uses uranium-2+6 as its fuel source. #hen a nucleus of uranium-2+6

absorbs a neutron, the following reaction can take lace&

2+6 1 155 :9 1

:2 9 65 += 9U n Xe Sr x n+ + +

a) /ow many neutrons are roduced in the reaction$

b) 8se the information to show that the energy released in the reaction is aro3imately 1=9 7e.

2+6 6 2

:2

1 2

9

155 6 2

65

:9 6 2

+=

rest mas of 2.1=:6 3 19 7eB c

rest mas of :+:.6; 7eB c

rest mas of 1.+59= 3 19 7eB c

rest mas of =.+>5: 3 19 7eB c

U

n

Xe

Sr

=

=

=

=


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2. he energy released by one atom of carbon-12 during combustion is aro3imately 5 e. heenergy released by one atom of uranium-2+6 during fission is aro3imately 1=9 7e.

a) Based on this information, determine the ratio of the energy density of uranium-2+6 to that of

carbon-12. (hen, check your answer with the gien table of energy densities.)

b) Based on your answer aboe, suggest one adantage of uranium-2+6 comared

with fossil fuels.


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'aturally ccurring Isotoes of 8ranium&

1) Uranium%&'most abundant (::.+C) but not used for fuel since it has a ery small robability of

fissioning when it catures a neutron.

2) Uranium%&'rare (9.+C) but used for fuel since it has a much greater robability of fissioning

when catures a neutron but must be a low-energy neutron (thermal neutron).

Fuel Enric*ment

Advantage 7ore uranium is aailable for fission and a chain

reaction can be sustained in a reactor to roduce nuclear energy.

Disadvantage If the fuel is enriched to a high leel (:9C weaons grade) it can be used in the core of a nuclear weaon.

!ossession of nuclear weaons is seen by many to be a threat to

world eace.

$uclear Fuel and +eactors

,*ermal $eutron

1) formation of gaseous uranium (uranium he3afluoride) from

uranium ores

2) searated in gas centrifuges by sinning D heaier 8-2+=

moes to outside

+) increases roortion of 8-2+6 to about +-6C of total (low

enrichment)

5) his low enriched he3 is comressed and turned into solid

uranium-o3ide fuel ellets which are acked into tubes called

fuel rodswhich will be used in the core of a nuclear reactor.


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IB 12

:

Fuel +ods enriched solid uranium

#hen neutrons are emitted from a fission reaction in the fuel rods, they haea ery high kinetic energy and will ass right out of the fuel rod without

colliding with another uranium nucleus to cause more fission. /igh energyneutrons cannot sustain a chain reaction. herefore, a material is needed toslow them down. yically, a material like water or grahite (called a

EmoderatorF) is used to slow down these high-energy neutrons down to

Ethermal leelsF (thermal neutrons G 1 e) for use in further fission

reactions to sustain the chain reaction. he high-energy neutrons slow downwhen they collide with the atoms in the moderator.

o control the rate at which the thermal energy is roduced, and

therefore to control the temerature of the reactor core, control

rodsare used to seed u or slow down the chain reaction. hese

are rods made of a neutron-absorbing substance, like cadmium or

boron. hey are inserted in between the fuel rods and raised orlowered as needed. If the reaction is roceeding too fast (too hot)

the rods are lowered and enough thermal neutrons are absorbed to

slow down the reaction to the desired leel. onersely, if thereaction is too slow, the control rods are raised allowing more

thermal neutrons to collide with uranium nuclei.

*ain +eaction .neutrons released from one fission reaction go on to

nitiate further reactions

8ncontrolled hain "eaction

ontrolled hain "eaction

ncontrolled nuclear fission&

ontrolled nuclear fission&

1) Some material (control rod) absorbs e3cess neutrons before theystrike another nucleus.

2) his leaes only one neutron from each reaction to roduce

another reaction.

+) If the total mass of uranium used is too small, too many neutrons

will escae without causing further fissions so the reactioncannot be sustained.

-ritical !ass

,*e $uclear +eactor -ore


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IB 12

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/ow is the thermal energy released in the fission reactions used to generate electricity$

he coolant(which is often the same as the moderator) is fluid circulating around the fuel rods in the

reactor core and is heated u by the thermal energy released in the fission chain reaction.his coolant in a closed loo (rimary loo) flows through ies in a tank of water known as the E*eat

e/c*anger0F /ere the thermal energy of the hot coolant is transferred to cooler water in a secondary loo

which turns it to steam. his steam e3ands against fan blades of turbines and turns a magnet is a coil ofwire to generate electricity.

2. Sketch a Sankey diagram

for a tyical nuclearower lant.

. State the energy transformations in using nuclear fuels to generate electrical energy&


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IB 12

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+. Suose the aerage ower consumtion for a household is 699 # er day. *stimate the amount ofuranium-2+6 that would hae to undergo fission to suly the household with electrical energy for a

year. State some assumtions made in your calculation.


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IB 12

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5. 0 fission reaction taking lace in a nuclear ower station might be&

2+6 1 151 :2 1

:2 9 6; +; 9+U n Ba Kr n+ + +

*stimate the initial amount of uranium-2+6 needed to oerate a ;99 7# reactor for oneyear assuming 59C efficiency and 299 7e released for each fission reaction.


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IB 12

1+

2+:

:5

1

9

159

6;

:;

+=

rest mass of 2+:.96216>

rest mass of 1.99=;;6

rest mass of 1+:.:196=1

rest mass of :6.:21>69

Pu u

n u

Ba u

Sr u

=

=

=

=

Plutonium and $uclear +eactors

!lutonium-2+: is another nuclide used as nuclear fuel because of the energy it releases when it undergoes

fission. /oweer, it is not as naturally abundant as uranium and so it tyically must be artificially roducedas a by-roduct of uranium fission. In a uranium-fueled reactor, as the 8-2+6 deletes oer time, the

amount of !u-2+: increases. his lutonium is then e3tracted (by rerocessing of the uranium fuel rods) for

use in a lutonium reactor or in a nuclear warhead.

2+: 1 159 :;

:5 9 6; +=Pu n Ba Sr+ + +

2+= 1 2+: 2+:

:2 9 :2 :+U n U Np+ +

2+: 2+:

:+ :5Np Pu +

/ow is lutonium-2+: roduced in a uranium reactor$ It actually is roduced from the non-fissionable

isotoe uranium-2+= that occurs in large amounts in fuel rods. 8ranium-2+= doesnt undergo nuclearfission but is considered EfertileF since it roduces lutonium-2+: by the following rocess.

ome uranium reactors are een secially designed to roduce (or EbreedF) large amounts

f lutonium and are known as 1reeder reactors. hey are designed so that the fuel rodsre surrounded by a blanket of 8-2+= so that neutrons escaing from the 8-2+6 fissions

ill induce the conersion of this 8-2+= to !u-2+:.

1. omlete the nuclear reactions listed aboe.

+. %etermine the amount of energy released in

the fissioning of lutonium-2+:.

2. onstruct a nuclear energy leel diagram for the

series of nuclear reactions listed aboe.


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IB 12

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Safety 2ssues and +isks in t*e Production of $uclear Power

*ermal !eltdown

erheating and melting of fuel rods may be caused by a malfunction in the cooling system

r the ressure essel. his oerheating may cause the ressure essel to burst sendingadioactie material and steam into atmoshere (as in hernobyl, 8kraine 1:=;). /ot

material may melt through floor (as in hree 7ile Island, !ennsylania 1:>:), a scenario

ubbed the Ehina syndrome.F he damage from these ossible accidents is often limited bycontainment essel and a containment building.

ranium !ining

open%cast miningenironmental damage, radioactie waste rock (tailings)

underground miningrelease of radon gas (mines need entilation), radioactie rock is dangerous

for workers, radioactie waste rock (tailings)

leac*ingSolents are umed underground to dissole the uranium and then umed back out.

his leads to contamination of groundwater.

uclear 3aste

4ow%level waste"adioactie material from mining, enrichment and oeration of a lant mustbe disosed of. Its often left encased in concrete.

5ig*%level wastea maHor roblem is the disosal of sent fuel rods. Some isotoes hae

lies of thousands of years. !lutoniums is 259,999 years.

1) Some are stored under water at the reactor site for seeral years to cool off then sealed in

steel cylinders and buried underground.

2) Some are rerocessed to remoe any lutonium and useful uranium. he remaining

isotoes hae shorter lies and the long-term storage need is reduced.

uclear 3eapons !anufacture

*nrichment technology could be used to make weaons grade uranium (=6C) rather than fuel

grade (+C)

!lutonium is most used isotoe in nuclear weaons and can be gotten from rerocessing

sent fuel rods

-omparing $uclear Fuel to Fossil Fuel

Advantages

'o global warming effect D no 2emissions

#aste Juantity is small comared with fossils fuels

/igher energy density

Karger reseres of uranium than oil

Disadvantages

1. Storage of radioactie wastes

2. Increased cost oer fossil fuel lants

+.


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IB 12

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$uclear Fusion

uclear Fusion wo light nuclei combine to form a more massie nucleus with the release of energy.

aturally occurring fusion&

1 1 2 9

1 1 1 1

1 2 +

1 1 2

H H H e

H H He

+ + +

+ +

+ + 5 1 1

2 2 2 1 1He He He H H+ + +

0 robable mechanism for the Suns fusion is called theproton-proton chain.

his chain is sometimessimlified to

5H He energy +

1. If the total mass of four hydrogen nuclei is ;.;:+ 3 19-2>kg and the mass of a helium nucleus is

;.;56 3 19-2>kg, determine the energy released in this simlified fusion reaction.

2. he Sun has a radiusRof >.9 3 19=m and emits energy at a rate of +.: 3 192;#.

he nuclear reactions take lace in the sherical core of the Sun of radius 9.26R.

%etermine the number of nuclear reactions occurring er cubic meter er secondin the core of the Sun.


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1;

Plasma he fuel for a fusion reactor is known as lasma. his is a high energy ioni4ed gas in which

the electrons and nuclei are searate. If the energy is high enough (that is, the lasma is hot enough),nuclei can collide fast enough to oercome oulomb reulsion and fuse together. /eating the lasma

to the reJuired temeratures (19 million A) is challenging. he nuclei, since they are charged, areaccelerated by means of magnetic fields and forces to high kinetic energies (high temeratures).

!agnetic confinement hese charged articles are contained ia magnetic fields and trael ina circle in a doughnut shaed ring called a EtokamakF which an acronym of the "ussian hrase

for Etoroidal chamber with magnetic coilsF (toroidal'naya kamera s magnitnymi katushkami).

Pro1lems wit* current fusion tec*nology

7aintaining and confining these ery high-density and high-temerature lasmas for anylength of time is ery difficult to do.

*3erimental reactors that currently can achiee fusion use more energy inut than

outut which makes them not commercially efficient.

Nuclear fission Nuclear FusionSplitting of a heavy nucleus into two or more light nuclei Combination of two light nuclei

to form a heavy nucleus Takes place at room temperature Requires a very high temperature equal to 4 X 10

LC Comparatively less amount of energy is release! "normous amount of energy is release! #ission reaction can be

controlle! an! the energy release! can be use! to generate electricity #usion reaction cannot be controlle! an! hence the

energy release! cannot be use! to generate electricity $t is a chain reaction $t is not a chain reaction $t leaves behin!

ra!ioactive wastes $t !oes not leave behin! any ra!io active wastes

omarison of 'uclear ission and 'uclear usion

Artificially induced fusion

ttemts hae been underway since the 1:69s to build fusion reactors. *3erimental reactors

ae come ery close to roducing more energy than the amount of energy ut in, but a

ommercial fusion reactor has yet to be built.


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IB 12

1>

Solar Power

olar *eating panel (active solar *eater)onerts light energy from Sun into thermal

nergy in water run through it

P*otovoltaic cell (solar cell) conerts lightenergy from Sun into electrical energy

se&8se&

e amount (intensity) of sunlight aries with&

a) time of day

b) season (angle of incidence of sunlight D altitude of Sun in sky D *arths distance from Sun)

c) length of day

d) latitude (thickness of atmoshere)

ich way should a solar anel or cell be facing in the 'orthern hemishere$ #hy$

Advantages

1. "enewable source of energy

2. Source of energy is free

+. 'o global warming effect D no 2emissions

5. 'o harmful waste roducts

Disadvantages

1. Karge area needed to collect energy

2. nly roides energy during daylight

+. 0mount of energy aries with season,location and time of day

5. /igh initial costs to construct@install

antages of solar heating anel oer solar cell&


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IB 12

1=

0n actie solar heater whose efficiency is +2C is used to heat 1599 kg of water from 299 to 699. he aerage ower receied

from the Sun in that location is 9.:9 k# er m2.

a) /ow much energy will the solar heater need to roide to heat the water$

b) /ow much energy will be needed from the Sun to heat the water$

c) alculate the area of the solar heater necessary to heat the water in 2.9 hours.

0 hotooltaic cell with an area of 9.59 m2is laced in a osition where the intensity of the Sun is 1.9 k#@m2.

a) If the cell is 16C efficient, how much ower does it roduce$

b) If the otential difference across the cell is 6.9 m, how much current does it roduce$

c) omare lacing 19 of these solar cells in series and in arallel.


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IB 12

1:

3ind Power

asic features of a hori4ontal a3is wind turbine&

) ower to suort rotating blades.

) Blades that can be rotated to face into the wind.

)


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IB 12

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0 wind turbine has a rotor diameter of 59 m and the seed of the wind is 26 m@s on a day when the air density is 1.+ kg@m+.

alculate the ower that could be roduced if the turbine is +9C efficient.

0 wind generator is being used to ower a solar heater um. If the ower of the solar heater um is 9.69 k#, theaerage local wind seed is =.9 m@s and the aerage density f air is 1.1 kg@m+, deduce whether it would be ossible to

ower the um using the wind generator.

Advantages





Disadvantages

1. Karge land area needed to collect energy since

many turbines are needed

2. 8nreliable since outut deends on wind

seed

+. Site is noisy and may be considered unsightly

5. *3ensie to construct


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IB 12

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3ave Power

ergy can be e3tracted from water waes in many ways. ne

h scheme is shown here.

cillating 3ater -olumn (63-)ocean wae energy

erter&

1. #ae cature chamber is set into rock face on land

where waes hit the shore.

2. idal ower forces water into a artially filled chamber

that has air at the to.

+. his air is alternately comressed and decomressed by

the Eoscillating water column.F

5. hese rushes of air drie a turbine which generates

electrical energy.

*nergy transformations&

%etermining the energy in each waelength of the wae and the ower er unit length of a waefront

ow would this ower estimate change if the waes were

modeled as sine waes instead of sJuare waes$


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Advantages





Disadvantages

1. an only be utili4ed in articular areas

2. /igh maintenance due to ounding of waes

+. /igh initial construction costs

2. #aes that are ;.9 meters high with a 199 meter waelength roll onto a beach at a rate of onewae eery 6.9 seconds. *stimate the ower of each meter of the waefront.

1. #aes of amlitude 1.6 meter roll onto a beach with a seed of 19 m@s. alculate&

a) how much ower they carry er meter of shoreline

b) the ower along a 2 km stretch of beach.


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IB 12

2+

5ydroelectric Power

hird scheme is calledpumped storage0 #ater is umed to a high reseroir during the night when the

mand, and rice, for electricity is low. %uring hours of eak demand, when the rice of electricity is high,stored water is released to roduce electric ower. 0 umed storage hydroelectric ower lant is a net

sumer of energy but decreases the rice of electricity.

econd scheme, called tidal water storage, takes adantage of bigferences between high and low tide leels in bodies of eater such as

ers. 0 barrage can be built across a rier and gates, called sluices, aren to let the high-tide water in and then closed. he water is released

ow tide and, as always, the graitational otential energy is used to

e turbines to roduce electrical energy.

ere are many schemes for using water to generate

ctrical energy. But all hydroelectric ower schemese a few things in common. /ydroelectric energy is

duced by the force of falling water. he graitational

ential energy of the water is transformed into

chanical energy when the water rushes down the sluicestrikes the rotary blades of turbine. he turbineMs

ation sins electromagnets which generate current inionary coils of wire. inally, the current is ut throughansformer where the oltage is increased for long

ance transmission oer ower lines.

far, the most common scheme for harnessing the

ginal graitational otential energy is by means of

ring water in lakes, either natural or artificial, behind

am, as illustrated in the to icture at right.

ergy transformations&

Advantages





Disadvantages

1. an only be utili4ed in articular areas

2. onstruction of dam may inole land being

buried under water

+. *3ensie to construct


24/24

IB 12 0 barrage is laced across the mouth of a rier at a tidal

ower station. If the barrage height is 16 meters and water

flows through 6 turbines at a rate of 199 kg@s in each

turbine, calculate the ower that could be roduced if theower lant is >9C efficient.

0 reseroir that is 1.9 km wide and 2.9 km long is held

behind a dam. he to of this artificial lake is 199 metersaboe the rier where the water is let out at the base of

the dam. he to of the intake is 26 meters below thelakes surface. 0ssume the density of water is 1999

kg@m+.

a) alculate the energy stored in the reseroir.

b) alculate the ower generated by the water if it flows at a rate of 1.9 m+er second through the turbine.

Documents

Energy and Power Ib2