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Page 1: Nuclear Reactors

Nuclear Reactors

Page 2: Nuclear Reactors

What is fission again?• Nuclear reactors take advantage of the

process of nuclear fission which splits an atom and releases a great deal of energy

• FP = Fission Product

Page 3: Nuclear Reactors

Quick Review of Nuclear Plants

Nuclear Fission

Generates Heat

Water intoSteam

Drives Turbine

Generates Electricity

Page 4: Nuclear Reactors

Different Types of Power Plants

• In the US:– Pressurized Water Reactor– Boiling Water Reactor

• In general, most reactors are “Generation II,” such as the Fukushima Dai-ichi reactors

• Modern reactors are “Generation III” which are dramatically improved and more efficient– So-called “passive” safety measures which rely

solely on natural laws such as gravity

Page 5: Nuclear Reactors

Cut-Away of “Peach Bottom”

Page 6: Nuclear Reactors

How is Radiation Contained?• The nuclear core is contained within a

“3.9 to 7.9 ft thick pre-stressed, steel-reinforced, air-tight concrete dome” to prevent escape

Page 7: Nuclear Reactors

How is Waste Material Secured?

• Fuel can be replaced every 12-18 months• Two types of waste:– Low-Grade: Refers to materials in contact with the fuel

rods, directly or indirectly– High-Grade: Refers to the spent nuclear material and

byproduct• Secured in underground pools and depots for several

years in the plants or nearby• Geologists study naturally occurring fission

processes to better understand how to dispose of waste material

Page 8: Nuclear Reactors

What could go wrong?

• Damage to the core due to loss of cooling– Due to loss of pressure– Due to loss of coolant– Due to uncontrolled power excursion

• Nuclear Meltdown– Not a technical term, but refers to the melting of

nuclear material and a breach in the containment vessel

Page 9: Nuclear Reactors

Worst-case• When:

– “A limiting fault … that leads to the failure of heat removal within the core ”

– The Emergency Core Cooling System (ECCS) fails

Then the core would heat beyond it’s melting point and turn into corium causing a containment breach

Page 10: Nuclear Reactors

Radiation in the Environment

• Iodine 129 and 131 are radioactive and can be absorbed by the body causing thyroid cancer

• Acute radiation syndrome• Stunted growth and death in local wildlife• Increase in mutations in humans and other

animals• Groundwater absorbs radionuclides

Page 11: Nuclear Reactors

Naturally Occurring Fission• First found in Oklo in

Gabon, Africa by physicist Francis Perrin

• These reactions occurred about 2 billion years ago, and were self-sustained for some hundred thousand years

• Scientists are studying this process to better learn how radioactive material travels through the Earth’s crust and how to contain radioactive inert gases release

1. Nuclear reactor zones2. Sandstone3. Uranium ore layer4. Granite