23.4 Nuclear energy

NUCLEAR

POWER

Millstone Station

23.4 Nuclear energy

U.S. Nuclear Power Plant Locations

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 Releases a huge amount of energy

proton

neutron

U-235 nucleus

Kr-90 nucleus

Ba-144 nucleus

energy

23.4 Nuclear energy

Nuclear chain reaction-Nuclear chain reaction-a reaction sustained by its productsa reaction sustained by its products

Neutrons released in fissionNeutrons released in fission act as reactants to split more nuclei

proton

neutron

U-235 nucleus

23.4 Nuclear energy

Critical Mass- minimum amount of fissionable material needed to maintain a chain reaction

Sub-critical mass Sub-critical mass

Above critical mass, chain reaction!

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

23.4 Nuclear energy

Nuclear reactorsNuclear reactors

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

Only 3% of fuel rod uranium is fissionable Enough for chain reaction; not enough to explode

Millstone Nuclear Power Station located in Waterford, CT

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

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.

23.4 Nuclear energy

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.

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)

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

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.

23.4 Nuclear energy

Nuclear wastesNuclear wastes

highly radioactive have very long half-lives (thousands of years)

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

Radioactive Decay- spontaneous process of an atom changing into another atom by emitting a particle and/or energyHalf Life- time needed for one-half of a sample to decay

23.4 Nuclear energy

Bismuth has a half-life of 5 days

What % of bismuth is present after 5 days? 20 days?How many grams are present after 5 days? 10 days?

With each half-life,what happens to the amount of radioactivematerial remaining?

Decreases by ½

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 radioactivity will fall to a safe levelsafe level after after

10 to 50 years10 to 50 years..

23.4 Nuclear energy

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

stored deep underground stored deep underground for several thousand yearsfor several thousand years

Proposed storage sites in Proposed storage sites in Yucca Mountain, NevadaYucca Mountain, Nevada

High level radioactive waste:

23.4 Nuclear energy

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

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??

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.

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.

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?