nuclear fission

19
23.4 Nuclear energy P.221 P.221 nuclear energy nuclear energy

Upload: stooty-s

Post on 20-May-2015

1.462 views

Category:

Education


1 download

TRANSCRIPT

Page 1: Nuclear Fission

23.4 Nuclear energy

P.221P.221nuclear energynuclear energy

Page 2: Nuclear Fission

23.4 Nuclear energy

Nuclear fissionNuclear fission Nuclear fission: heavy nuclei split into two heavy nuclei split into two

smaller partssmaller parts in order to become more stable

proton

neutron

U-235 nucleus

Kr-90 nucleus

Ba-144 nucleus

energy

Page 3: Nuclear Fission

23.4 Nuclear energy

Nuclear chain reactionNuclear chain reaction

Neutrons released in fissionNeutrons released in fission trigger the fissions of other nuclei

proton

neutron

U-235 nucleus

Page 4: Nuclear Fission

23.4 Nuclear energy

The chain reaction is not slowed down

a huge amount of energy is released very quickly

the rate of fission increases rapidly

Nuclear bombNuclear bomb

Uncontrolled nuclear reactionUncontrolled nuclear reaction

Page 5: Nuclear Fission

23.4 Nuclear energy

Nuclear reactorsNuclear reactors

Nuclear power plant: rate of fission is controlled by artificial means to generate electricity

the Daya Bay Nuclear Power Station

Simulation: Nuclear power plant

Page 6: Nuclear Fission

23.4 Nuclear energy

Schematic diagram of a nuclear plant

control rods

fuel rods

reactor pressure vessel

water (cool)

water (hot)

water (high pressure)

water (low pressure)

coolant out

coolant insteam condenser

steam (low pressure)

turbine

electric power

steam generator

steam (high pressure)

pump

primary loop secondary loop

generatorreactor

core

pump

Page 7: Nuclear Fission

23.4 Nuclear energy

control rods

reactor pressure vessel

water (cool)

water (hot)

water (high pressure)

water (low pressure)

coolant out

coolant insteam condenser

steam (low pressure)

turbine

electric power

steam generator

steam (high pressure)

pump

primary loop secondary loop

fuel rods They contain the nuclear fuel: uranium (U-235)

They are surrounded by a moderator (water or graphite)moderator (water or graphite) to slow down the neutrons slow down the neutrons released.released.

Page 8: Nuclear Fission

23.4 Nuclear energy

control rods

reactor pressure vessel

water (cool)

water (hot)

water (high pressure)

water (low pressure)

coolant out

coolant insteam condenser

steam (low pressure)

turbine

electric power

steam generator

steam (high pressure)

pump

primary loop secondary loop

fuel rods

They control the rate of reaction by moving in and out of the reactor.

Move in: rate of reaction Move out: rate of reaction All are moved in: the reactor is

shut down

They are made of boron 硼 or cadmium 鎘 that can absorb absorb neutrons.neutrons.

Page 9: Nuclear Fission

23.4 Nuclear energy

control rods

reactor pressure vessel water

(high pressure)

water (low pressure)

coolant out

coolant insteam condenser

steam (low pressure)

turbine

electric power

pump

primary loop secondary loop

fuel rods

The energy released in fissions heats up the water around the reactor.

The water in the The water in the secondary loop secondary loop is boiled to is boiled to steamsteam.

water (hot)

water (cool)

steam generator

steam (high pressure)

Page 10: Nuclear Fission

23.4 Nuclear energy

steam generator

control rods

reactor pressure vessel water

(high pressure)

water (low pressure)

coolant out

coolant insteam condenser

steam (high pressure)

pump

primary loop secondary loop

fuel rods

The steam drives a turbine, The steam drives a turbine, which turns the generator.which turns the generator.

Electricity is produced by the generator.

water (hot)

water (cool)

steam (low pressure)turbine

electric power

generator

Page 11: Nuclear Fission

23.4 Nuclear energy

control rods

fuel rods

reactor pressure vessel

water (cool)

water (hot)

water (high pressure)

water (low pressure)

coolant out

coolant insteam condenser

steam (low pressure)

turbine

electric power

steam generator

steam (high pressure)

pump

primary loop secondary loop

Two separate water systemsTwo separate water systems are used to avoid radioactive substances to reach the turbine.

Page 12: Nuclear Fission

23.4 Nuclear energy

Nuclear waste Nuclear waste 核廢料核廢料

They are highly radioactive Many of them have very long half-lives.

Radioactive wasteRadioactive waste must must be stored carefully.be stored carefully.

Page 13: Nuclear Fission

23.4 Nuclear energy

Low level radioactive wasteLow level radioactive waste

cooling water pipes, radiation suitscooling water pipes, radiation suits, etc., etc. stored in storage facilitiesstored in storage facilities radioactivity will fall to a safe level after radioactivity will fall to a safe level after

10 to 50 years10 to 50 years..

Page 14: Nuclear Fission

23.4 Nuclear energy

used nuclear fuelused nuclear fuel highly radioactivehighly radioactive embedded in concrete and embedded in concrete and

stored stored deep undergrounddeep underground for for several thousand yearsseveral thousand years

High level radioactive waste 高危險性核廢料

Page 15: Nuclear Fission

23.4 Nuclear energy

Nuclear fusionNuclear fusion

Nuclear fusion: light nuclei fuse together to form a heavier nucleus

proton

neutron

helium nucleus

neutron

energy

deuterium nucleus

tritium nucleus

H-2 + H-3 He-4 + n + energy

Page 16: Nuclear Fission

23.4 Nuclear energy

They must have They must have enough kinetic energy to enough kinetic energy to overcome the electrical repulsionovercome the electrical repulsion..

Very high temperature Very high temperature (about 10(about 107 7 K)K) isis required required to start a nuclear fusion.to start a nuclear fusion.

Atomic nuclei are Atomic nuclei are positively positively chargedcharged and repelled each other. and repelled each other.

How can two nuclei fuse togetherHow can two nuclei fuse together??

Page 17: Nuclear Fission

23.4 Nuclear energy

The temperatures The temperatures inside inside the Sunthe Sun and the stars reach and the stars reach such such high temperaturehigh temperature..

Inside the Sun, Inside the Sun, 657 million 657 million tons of hydrogen undergo tons of hydrogen undergo fusion to form helium each fusion to form helium each second.second.

Page 18: Nuclear Fission

23.4 Nuclear energy

Man-made uncontrolled Man-made uncontrolled fusionfusion was first achieved was first achieved in 1952, during the in 1952, during the explosion of the first explosion of the first hydrogen bomb.hydrogen bomb.

Controlled fusion is still under investigated by scientists.

No one has succeeded in yielding a net surplus of energy from fusion reactors.

Page 19: Nuclear Fission

23.4 Nuclear energy

Unlimited supply of fuelUnlimited supply of fuel for fusion reactors. for fusion reactors. We can get We can get hydrogen from waterhydrogen from water..

Little problem on disposal of radioactive wasteLittle problem on disposal of radioactive waste.. The The end products of fusion are generally end products of fusion are generally

stable and not radioactive.stable and not radioactive.

What are the advantages of fusion What are the advantages of fusion power?power?