NUCLEAR ENERGYFISSION AND FUSION

NUCLEAR ENERGY

• The nucleus of an atom is the source of nuclear energy.

NUCLEAR ENERGY

• Fission - when the nucleus splits & nuclear energy is released. (Heat and Light energy)

• Fusion - when 2 or more nuclei join together to make 1 nucleus & energy is released

• The atomic Bombs used in WWII were fission bombs.

• Radioactive Uranium–235 is used to form chain reaction.

• A chain reaction is started by colliding a neutron into the Uranium – 235.

• http://www.youtube.com/watch?v=-Qliifidcuw&safety_mode=true&persist_safety_mode=1

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• http://www.youtube.com/watch?v=kHXMiYsFSrU&feature=related&safety_mode=true&persist_safety_mode=1

FISSION – ATOMIC BOMBS

NUCLEAR ENERGY

• Nuclear energy is the most concentrated form of energy.

• Fission reactions occur in nuclear power plants.

• The reaction produces large amounts of heat energy which turns water to steam.

• This moves the turbines and produces energy.

FISSION – POWER PLANTS

http://www.youtube.com/watch?NR=1&feature=endscreen&v=VrhzkoNU84g http://www.youtube.com/watch?v=igf96TS3Els&safety_mode=true&persist_safety_mode=1

• Very harmful to humans, plants, and animals.

• Can cause cancer, mutations, and death.

• The waste has a very long half-life and takes years to decay – which means it never really goes away.

NUCLEAR WASTE

BASIC DIAGRAM OF A PWR

http://www.nrc.gov/

Advantages

• Nuclear power costs about the same as coal, so it's not expensive to make

• Does not produce smoke or carbon dioxide, so it does not contribute to the greenhouse effect.

• Produces huge amounts of energy from small amounts of fuel.• Produces small amounts of waste.• Nuclear power is reliable

DISADVANTAGES• Although not much waste is produced, it is very, very

dangerous. It must be sealed up and buried for many thousands of years to allow the radioactivity to die away.

• For all that time it must be kept safe from earthquakes, flooding, terrorists and everything else. This is difficult.

• Nuclear power is reliable, but a lot of money has to be spent on safety - if it does go wrong, a nuclear accident can be a major disaster.

• People are increasingly concerned about this - in the 1990's nuclear power was the fastest-growing source of power in much of the world. In 2005 it was the second slowest-growing.

Fusion on the Sun

• The sun’s energy is produced from a nuclear fusion reaction

• 2 hydrogen nuclei fuse to form 1 helium nucleus, a neutron, & ENERGY

3 2 4

1 H + 1 H 2 He + n0 + ENERGY

ADVANTAGES OF FUSION• Abundant Fuel Supply

– Deuterium - inexhaustible supply from sea water (1 part/ 6,500 H20)

– Tritium - produced from Lithium, thousands of years supply

• • No Risk of Nuclear Accident

– No meltdown possible

– Large uncontrolled release of energy impossible

• • No Air Pollution of Greenhouse Gases

– Reaction product is Helium

• • Minimal or No High Level Nuclear Waste

– Careful material selection should minimize waste caused by neutron activation

DIFFICULTY USING FUSION

• Like Charged Particles Repel Each Other and requires extreme amounts of heat and pressure.

VERY HIGH TEMPERATURE IS REQUIRED

A PWR IN PRACTICE

http://www.nukeworker.com/

VVER – RUSSIAN PWR (WATER-COOLED, WATER-MODERATED, ENERGY REACTOR)

http://www.nucleartourist.com/

Fission is the release of energy by splitting heavy nuclei such as Uranium-235 and Plutonium-239

Fusion is the release of energy by combining two light nuclei such as deuterium and tritium

How does a nuclear plant work?• Each fission releases 2 or 3

neutrons• These neutrons are slowed down

with a moderator to initiate more fission events

• Control rods absorb neutrons to keep the chain reaction in check

• The goal of fusion research is to confine fusion ions at high enough temperatures and pressures, and for a long enough time to fuse

• This graph shows the exponential rate of progress over the decades

Controlled Fission Chain ReactionConfinement Progress

• Magnetic Confinement uses strong magnetic fields to confine the plasma

• This is a cross-section of the proposed International Thermo-nuclear Experimental Reactor (ITER)

• Inertial Confinement uses powerful lasers or ion beams to compress a pellet of fusion fuel to the right temperatures and pressures

• This is a schematic of the National Ignition Facility (NIF) being built at Lawrence Livermore National Lab

Nuclear Power Plant

There are two main confinement approaches:

The energy from the reaction drives a steam cycle to produce electricity

Nuclear Power produces no greenhouse gas emissions; each year U.S. nuclear plants prevent atmospheric emissions totaling:•5.1 million tons of sulfur dioxide•2.4 million tons of nitrogen oxide•164 million tons of carbon

Nuclear power in 1999 was the cheapest source of electricity costing 1.83 c/kWh compared to 2.04 c/kWh from coal

D

T

D-T Fusion4He3.52 MeV

Neutron14.1 MeV

http://www.youtube.com/watch?v=PKNbwcIaGng&safety_mode=true&persist_safety_mode=1

http://www.youtube.com/watch?NR=1&v=2Vua6uuJO_c&feature=endscreen

http://www.youtube.com/watch?v=esdA_TFzxpw&safety_mode=true&persist_safety_mode=1

http://www.youtube.com/watch?v=VJfIbBDR3e8&safety_mode=true&persist_safety_mode=1

Natural (radioactive) decay (fission)

Neutron-induced fission

• Many heavy elements (eg. Uranium) decay (slowly) into lighter elements (natural decay)

• However, this fission can also be induced by an incoming neutron.

• Fission reaction release a lot of energy.

• Fission often creates new neutrons!!

Conditions for a chain reaction to occur (nuclear bomb):

1. Need a source of neutrons to trigger chain reaction.

2. Bomb material needs to be fissionable (splits when hit by a neutron.

3. Each fission has to produce more neutrons.

4. Each fission needs to induce more than one subsequent fission ((super-)critical mass = 60 kg; 7 inch sphere for 235U).

235U (Uranium isotope with 92 protons and 143 neutrons) works!! Releases 2.5 neutrons when fissioning.

238U (Uranium isotope with 92 protons and 146 neutrons), which naturally occurs more abundantly (99.28%) does not work.

For bomb: Need to enrich 235U (very difficult, fortunately).

Assembly of supercritical mass

(to initiate 235U bomb)

Hiroshima, Aug. 6, 1945“Little boy”

Two-thirds of Hiroshima was destroyed. Within three miles of the explosion, 60,000 of the 90,000 buildings were demolished. Clay roof tiles had melted together. Shadows had imprinted on buildings and other hard surfaces. Metal and stone had melted. Hiroshima's population has been estimated at 350,000; approximately 70,000 died immediately from the explosion and another 70,000 died from radiation within five years.

At the time this photo was made, smoke billowed 20,000 feet above Hiroshima while smoke from the burst of the first atomic bomb had spread over 10,000 feet on the target at the base of the rising column.

239Pu (Plutonium) bomb

Supercritical mass (density) of Plutonium core is achieved when explosion crushes 239Pu core.

Nagasaki, Aug. 9, 1945“Fat man”

A dense column of smoke rises more than 60,000 feet into the air over the Japanese port of Nagasaki, the result of an atomic bomb, the second ever used in warfare, dropped on the industrial center August 8, 1945, from a U.S. B-29 Superfortress.

Approximately 40 percent of Nagasaki was destroyed. Though this atomic bomb was considered much stronger than the one exploded over Hiroshima, the terrain of Nagasaki prevented the bomb to do as much damage. Yet the decimation was still enormous. With a population of 270,000, approximately 70,000 people died by the end of the year.