1COURSE CODE (CC 88-167)ENERGY AND ENVIRONMENT

Part II: Energy and Essential ResourcesChapter 5: Nuclear Power

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1. Working principle2. Nuclear reactors3. Detection and safety issues4. Radioactive wastes treatment 5. Comparison to other powers6. Possible alternatives

Outlines

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All of the following are possible sources of radiation excepta. background radiation from the Earths

crust.b. nuclear waste.c. medical & dental X-rays.d. distilled water.

Do you know?

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Mass number (A) = No. of __________ + No. of __________ in the nucleus of

an atom

Atomic number (Z) = No. of _____________ in the nucleus of an atom No. of _____________ in the neutral atom

Mass & Atomic Numbers

A

Z Symbol

X 12

6 Carbon-12

C 13

6 Carbon-13

C 14

6 Carbon-14

C

Isotopes

5 Contain different no. of __________ but the same no.of __________ & __________

Behave the same chemically but other characteristics may differ profoundly

Isotopes

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Natural radioactive materials1. __ Rays ( He/ )

Made up of particles (Helium nucleus minus 2e), +22. __ Rays ( / e)

Made up of particles (Electron), negligible mass3. __ Rays ( )

Similar to X-rays, No mass, high-energy _____________ _________________ with very short wavelength

Not emitted simultaneously Have sufficient energy to break chemical bonds, thus

disrupt living organisms

Types of Radiation42

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0-1

0-1

00

7 8

EM Spectrum Properties

9 Nuclear energy Different from burning fuels/other chemical reactions Involves changes at the atomic level Released from either

1. Fission (A large atom of 1 element is _________________ 2 atoms of different elements)

2. Fusion (2 small atoms _________________ a larger atom of a different element)

1. From Mass to Energy

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Nuclear Fission & Fusion

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Uranium occurs naturally in the Earths crust Exists in 2 isotopes mainly, 238U & 235U

All nuclear plants use 235U as fuel

235U readily undergoes fission, but not 238U

Fuel Element (235U)

235

92 U 238

92 U

2 Isotopes

Uranium-238(146 neutrons)

Uranium-235(143 neutrons)

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A neutron hits the nucleus of 235U Some atoms of 235U undergo radioactive decay &

release neutrons These neutrons can hit other 235U atoms, producing

highly unstable 236U

236U undergoes fission into lighter atoms (fission products)

More neutrons are given off, releasing lots of energy This domino effect causes a chain reaction

Fission of 235U

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Fission Reactions

1. n + 235U Kr + Ba + ___ n + Energyor

2. n + 235U Kr + Ba + ___ n + Energy

Low energy (slow) neutrons

Barium (Ba)

Krypton (Kr)

92

92

36

36

56

5614

Amplification

Leads to nuclear explosion!

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Control

Extra neutrons are absorbed in control rods: No amplification!

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Fuel rods Radioactive spent-fuel rods are replaced with new

ones

Control rods Neutron-absorbing materials slow down the rate of

fission & heat production Inside a water-holding vessel (the moderator &

coolant)

2. Reactor Core

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Long metal tubes

(Uranium pellets)

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Type of Nuclear Reactors A device allows us to extract energy from

nuclear fission1. Pressurized-water reactor (2/3 of US power

station) Employ double loop isolating the pressurized water

from the steam-generating loop that drives the turbogenerator

2. Boiling-water reactor Boil the water by circulating it via the reactor

3. Breeder reactor (More advanced)

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Also named as fast-neutron reactor U.S. used for military purposes France, Russia, Japan have commercial ones

Uranium (235U) is not highly abundant Use the extra 2 neutrons created during fission of

235U to convert non-fissionable 238U to plutonium (239Pu)

Nuclear fuel reserves more than 100 times

Breeder Reactors

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23892 10n U +

23992 U

23992 0

-1U 23993 Np +

23993

0-1Np

23994 Pu +

(_____________) (________)

(__________)

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Safety & security precautions are greater Large amounts of 239Pu could cause serious meltdowns The half-life of 239Pu is 24,000 years

239Pu can be made into nuclear weapons more easily More expensive to build & operate

But they extract more energy from recycled nuclear fuel They produce much less high-level waste than

conventional power plants

Pros & Cons

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Geiger counter The most common instrument for detecting &

measuring radioactivity Is essentially a modified cathode-ray tube Cathode: A metal cylinder contains Argon (Ar) gas Anode: A wire runs down the axis of the tube

3. Detection of Radiation

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DetectionRadioactive substances cause ionization of the Ar(g) which generates pulses of electric current flow between the electrodes 26

The degree of damage caused by ionization1. Type & penetrating power of radiation2. Location of the source of the radiation

e.g. Inside/Outside the body

3. Type of tissue exposed4. Amount & frequency of exposure

Exposure to Radiation

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e.g. > 1 Sieverts (Sv) Radiation can prevent cell division,

replacement/repair of blood, skin, other tissues(Radiation sickness)

Can lead to death in days/months

Exposure to High Doses

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e.g. ~ 100 to 500 mSv Can damage DNA, eggs/sperm can cause birth

defects The risk of developing cancer (e.g.

Tumors/leukemia) Other effects such as weakened immune system,

mental retardation & cataracts Effects of exposure may go unseen for 1040

years

Exposure to Low Doses

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Health effects are directly related to the level of exposure

The National Research Council (NRC) found no safe level of radiation

Federal agencies Assume a relationship between exposure & cancer Set maximum permitted exposure at 1.7 mSv/yr

(excluding medical X-rays)

Exposure Level

30 Catastrophic, the former Soviet Union (1986)

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The consequences of the Chernobyl accident?a. 135,000 people were evacuated & relocated.b. Soil was contaminated & remains so to this day.c. Hundreds of thousands of cancer deaths were

predicted to have occurred.d. All of the above

Do you know?

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Genetic Mutations

Chernobyl Victims

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International Nuclear and Radiological Event Scale (Introduced in 1990) by the International Atomic Energy Agency (IAEA)

In case of nuclear accidents Enables prompt communication of safety-significant

information

INES (Level 0 to 7)

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Both direct & indirect products of fission are radioactive

1. High-level wastes: ________ products of fission Highly radioactive

2. Low-level wastes: ________ products of fission Much less radioactive Materials in & around the reactor can become

radioactive by absorbing neutrons

4. Radioactive Wastes

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Radioactive Emissions

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Unstable isotopes become stable by ejecting particles & radiation

Half-life The time for half of the amount of a radioactive

isotope to decay Ranges from a fraction of a second to thousands

of years It is always the same for the isotope

Radioactive Decay

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Spent fuel elements Stored under water in storage pools at the reactor

site to let the short half-live radioactive wastes decay first, then treated via geologic formation/

total elimination.

Wastes Treatment

Multi-barrier approach is used to store the wastes to prevent leakage of radiation

42Geologic formations & total elimination are the 2 possibleways to dispose high level radioactive wastes.

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Generated from nuclear power plants, industries/hospitals Buried in shallow trenches in the ground at a number of

privately owned sites

Low-Level Radioactive Wastes

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A 1,000 MW nuclear plant Uses 30 tons of uranium coming from 75,000 tons of ore Energy from fission of 1 lb of uranium > 50 tons of coal

5. Nuclear vs. Coal Power

Equivalent fuel requirements for same electrical output.

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Pros No mining is needed

Strip mining causes environmental damage, acid leaching Deep mining causes deaths & harm to health

No production of CO2, ash & acid-forming pollutants(SO2)/particulates, Low levels of waste gas, thermal pollution onlyCons Radioactive wastes require storage & disposal Accidents can range from minor to catastrophic

Nuclear vs. Coal Power

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Coal generates the most GHGs & pollution Oil (vital for transportation) & natural gas are

limited Hydroelectric technology is already heavily

developed Wind & solar power provide only a small

amount of electricity

Other Sources of Electricity

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439 operating worldwide 42 more under construction Provides 14% of electrical generation &

growing at 3.2%/yr China & India have made large investments

(building 6 more units each) France produces 77% of its electricity (willto

80%)

Nuclear Power Plants

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Generation IV Plants Now being designed to restore publics

confidence in nuclear energy, will be built within 20 years

Small, cheap reactors will be built in a factory & then shipped to the plant location

Pebble-bed modular reactor (PBMR) Will feed uranium pebbles into the reactor Cooled with fluidized helium (Gas-cooled)

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Pebble

Pebble-Bed Modular Reactor

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6. Long-Term Options1. Fusion

1 g of deuterium (obtained from 8 gallons of water) Energy released = Burning 2,400 gallons of gasoline

The extraction of deuterium from water is not very difficult/expensive.

No long-lived radioactive wastes, end products are unused deuterium, helium & neutrons

No global warming52

The most current work is focusing on D-T reaction which has the lowest ignition temperature (~ 50 million C)

Fusion Reaction

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Fusion Conditions Obstacle to nuclear fusion

Is the electrical force of repulsion between the +venuclei

Very high temperature (50 to 100 million C) to overcome the electric repulsion

So far, the energy output obtained from demonstration reactors is less than the total energy input

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1. Ionized hydrogen trapped in a magnetic fieldis heated

2. Pellet of frozen hydrogen is hit with laser beams

3. X-rays produced from short powerful pulses of current is used for fusion initiation

3 Techniques Being Tested