Reading Qs

1. List the different reasons why these nuclear accidents occurred.

2. Select the one that interests you the most and explain why.

Starter Q (1/13)

1. What is the difference between an atom, element, molecule, atomic number, isotope and ion?

Nuclear Weapons Atom Bomb (fission) Hydrogen Bomb (fission-fusion)

Which releases more energy?

• Nuclear fission of U 235 molecule or the explosion of one molecule of dynamite?

• “The energy released by the fission of one uranium-235 nucleus is enormous—about seven million times the energy released by the explosion of one TNT molecule.”

Paul Hewitt—from Conceptual Physical Science Explorations (2003)

Release of nuclear potential energy vs. chemical potential energy

Which is more powerful?

• Nuclear energy provides more energy per unit time than does burning an equivalent amount of a source of chemical PE.

Chemical Reactions vs. Nuclear Reactions

• Chemical reactions do not change the nucleus, they just release the chemical PE stored in the molecular bonds. There is no conversion of mass into energy, just energy to energy transformations.

– In chemical reactions, mass is conserved and the elements do not change.

• Nuclear reactions change the nucleus, releasing the nuclear PE stored in the nucleus and changing the element (transmutation).

– A small amount of mass is converted into energy during this process (mass loss = energy gain)

– The sun loses 2 to 3 x 10-14 solar masses per year due to fusion.

Two types of nuclear reactions

• Releasing the energy stored in the nucleus causes a small amount of matter to be converted into energy.– Fission (splitting of a heavy nucleus)

• U235 and Pu239 absorbs 1 neutron and splits!

– Fusion (fusing together of light nuclei)• Hydrogen nuclei fuse to form Helium

http://www.ida.liu.se/~her/npp/demo.html

Fission vs. Fusion

• Prime examples of fission reactions– Nuclear power plants– Atomic bombs

• Prime example of fusion reaction– Fusing hydrogen nuclei into helium nuclear at

the core of every star (including the Sun)

http://www.visionlearning.com/library/flash_viewer.php?oid=2747http://www.visionlearning.com/

library/flash_viewer.php?oid=3602

What is radioactive decay?

• Process by which an unstable nucleus emits one or more particles or energy in the form of electromagnetic radiation.

Radioactive Decay

• Loss of Mass– Alpha decay (emits a helium nucleus)– Beta decay (emits an electron)

• Loss of Energy– Gamma decay (emits a gamma ray)

Common Radioactive Elements and Half-Lives

•      Beryllium...................2,700,000 years      Calcium.....................100,000 years      Cesium-137................half life - 30 years      Cesium-135................2,000,000 years      Rubidium...................47,000,000,000 years      Palladium...................7,000,000 years      iodine-129..................17,200,000 years      plutonium-239............half life -  24,390 years      strontium-89...............53 days      strontium-90...............28 years      tin-126.......................100,000 years      uranium-235........................713,000,000 years      uranium-238...............4,510,000,000 years

Nuclear power plant

To Power lines

_________ potential energy is released by ________ of the isotope _____ , producing __________ energy. This energy causes the water in the steam generator to change state and __________, increasing the pressure in the steam generator. The steam then applies a __________ to the turbine causing it to turn a certain distance. This represents ______ done by the steam, which represents a transfer of ___ - ________ energy to ____________ energy. The movement of the turbine represents __________ energy. As the turbine turns, a coil of copper wire turns inside a magnetic field, generating _____________. So the ___________ of the turbine is transferred to ____________, which is conducted to homes and businesses via high voltage power lines.

What is the basic fuel for nuclear power?

• Uranium 235 (a heavy radioactive metal) or Plutonium 239

• The earth contains U238 (99%) and U235 (0.7%).• U-235 is one of the few materials that can

undergo induced fission. • U 235 must be enriched to 3-5 % to be used in

nuclear reactors.• Weapons-grade U235 needs to be 95%.

What happens during fission of Uranium 235?

1. The nucleus will split into two lighter nuclei (Krypton and Xenon or Strontium and Barium, for example)

2. A large amount of thermal energy is released.

3. Gamma rays are released.

4. Two additional neutrons are released.

Uranium Fuel

Nuclear Fuel Rods

                                                                                                       

Nuclear Reactor Core and Control Rods

Radioactive Wastes

• The fission process produces highly-radioactive products, including plutonium.

• Generation (new fuel needed every 16-18 months)

• Holding (at the power plant)• Transportation (DOE approved routes)• Disposal/Burial Vault (in theory)• http://www.nrc.gov/waste/hlw-disposal/

design.html

How do we get electricity from nuclear energy?

• Nuclear fission releases thermal energy, which heats a fluid (water), which boils producing high pressure steam. Work can be done by the steam, which turns a turbine connected to a generator, which transfers mechanical energy to electrical energy.

• http://www.nei.org/scienceclub/nuclearworld.html

Nuclear Power Plants in the United States

There are over 100 nuclear power plants in the USA.

Can a nuclear power plant explode like a nuclear bomb?

• No.

• Nuclear fuel contains a small percentage of uranium 235 (3-5%). Weapons grade is over 90% uranium 235.

• A meltdown of the core can occur, which can lead to a steam explosion, not a nuclear blast. Like Chernobyl.

Question

1. What is the difference between an atom bomb and an nuclear bomb?

2. Atom bombs use U235 or Pu239, which release stored nuclear energy by fission

3. Nuclear bombs require an initial atomic bomb explosion to initiate hydrogen fusion.

The sun gets its energy from nuclear fusion reactions at its core.

Sunlight is mostly yellow-green visible light

Blue star

Sun

Red star