Transcript Nuclear Energy

Nuclear Energy
Fusion vs. Fission
 Fusion: involves fusing two smaller
atoms together to produce one larger
one and a tremendous amount of
energy
 Experimental
stages
 Fission:
involves splitting a larger
atom to produce two smaller ones
and a tremendous amount of energy
 Used
extensively in US
Uranium
 Fuel
for nuclear Fission
 Naturally
U238 with 0.7%
U235,
 reactors
need 3%U235,
bombs need 80% U235
 enrichment:
process by
which percentage of U235
is increased from its
natural state
The Fission Process

Nucleus of any atom can be split if hit hard
enough with neutrons

U235 is split more easily (235 is the atomic
weight)

Results of the Fission are
 Massive
amounts of energy
 Small
amounts of Barium
 Small
amounts of Krypton
 Two
additional Neutrons
U235 Fission
Half-Life

The time required for ½ of the atoms
present to decay into a new, more stable
element.
Reactor Terminology

“Light Water” reactors-like all American
reactors use regular water

“Heavy Water” reactors- use water made
up of oxygen and Deuterium (Heavy
isotope of Hydrogen)

Boiling Water Reactor (BWR)

Pressurized Water Reactors (PWR)
Boiling Water Reactors

Water surround the nuclear fuel core

Control rods sit between fuel rods-they
absorb stray neutrons

When fission begins water turns to steam

Expanding steam spins turbine to create
electricity

Steam is condensed back into liquid and
returned to reactor for heating
Boiling Water Reactor
Pressure Water Reactors

Similar but uses a “Steam Generator”

Can operate at higher temperatures

Primary loop contains water that contacts
the reactor core

Secondary loop contains water that is
turned to steam to drive turbine

Steam (secondary loop) is cooled in
condensing tower and reused.
Pressure Water Reactor
Supply & Demand

Today 100 plants supply 20% of all
electricity produced in US

In 2004-439 nuclear reactors were in
operation globally

Lithuania gets 80% of power from Nuclear

France gets 78% from Nuclear

Slovakia gets 58% from Nuclear
US Nuclear Reactors
Nuclear Reactor
Nuclear Reactor
Nuclear Reactor
Nuclear Reactor
 uses
 no
uranium to boil water!
gas exhaust
 moderator:
chemical mixed with the fuel to
slow down the neutrons w/o absorbing
them (H2O or D2O)
 “control
 fast
rods” - graphite rod moderator
neutrons bounce off the moderator
and become thermal (slow) neutrons
Can a reactor turn into
a bomb?

NO - reactors depend on slow neutrons,
bombs need fast neutrons

when reactor “blows”, it releases energy of
about TNT (million times smaller than a
bomb)
Energy Equivalent

In terms of BTUs no other energy source
comes close to uranium

One uranium pellet (the size of your
fingertip)
Nuclear Waste

radioactive fission fragments left over from
reaction - same particles as radioactive
fallout

half-lives range form few seconds to years

Strontium-90: ff= 5%, hl= 28 yrs
Nuclear Waste
China Syndrome

term (created by someone with a sense of humor) used to
describe worst possible scenario of a power plant melt
down.

1. coolant would leak (no water to boil)

2. reaction would stop!

3. “waste heat” from fission fragments
China Syndrome

4. melts through container

5. melts through steel vessel

6. keeps getting hotter and melts all the way “to China”

*actually it wouldn’t get too far because it spreads out and
that allows it to cool
What should we do with
the waste?

•
•
1. bury it:
•
what if it gets into the ground water?
•
must find a place very geologically stable => Navada
How can you balance the real risks vs. the perceived
risks?
*coal plants bury waste in the ground. ashes that are very
high in carcinogens.

enough radioactivity in a reactor to kill 50
million people (if they ate it)

Chernobyl is about 24,000
Impacts on the Environment

Nuclear waste: Stored in pools on site

Originally waste was to be separated into
Plutonium and unused Uranium.
 Jimmy
Carter banned the process in 1977
because the Uranium can be used for
weapons
 Now
the pools are filling up and if stored too
close together a reaction begins
 Now
stored in above ground Casks
Storage of Nuclear Waste

Yucca Mountain (Nevada): porous rock
that serves as a barrier to radiation

Waste will be permanently stored 1000’
below surface

Opening in 1989, 1998, 2003, 2010
because of delays

9/11 has caused
further delay
Transporting Nuclear Waste

Sent in Shipping
Casks

Tested by…

Dropping from
airplanes

Running into them with
diesel locomotives

Burning them in jet fuel
Recycling Nuclear Waste

Can render the waste harmless by
processing

Less expensive to bury it then reprocess it

What would you do?
Nuclear Reactor Safety - US

In the US reactors are housed in
“environmental containment shields”
designed to withstand any explosion or
plane crashes

After TMI safety systems that cannot be
overridden were installed

We do not rely on human intervention to
prevent meltdowns
Chernobyl

1986 – Chernobyl
accident in Kiev.

Poorly designed - no
containment building

24,000 people were killed

Radiation spread through
Europe and was detectable
in USA a few days later
Nuclear Reactors Elsewhere

No containment
shields

Often built in
commercial buildings

Chernobyl-demolished
reactor and building
releasing radiation
Breeder Reactors (Pros)

Process that can extend the life of our
proven uranium reserves by hundreds or
thousands of years

99% of uranium mined is U238 (Nonfissionable)

Breeder reactors create reactions that
release heat and Plutonium 239
(fissionable)
Breeder Reactors (Cons)

this can be used for weapons too

Half life is 24000 years
 Needs
to be processed or stored for
24000 years

Proliferation is a concern: the illegal
acquisition of nuclear fuel for potentially
harmful purposes
Breeder Reactor
Nuclear Fusion - Ultimate
Energy Source

Combining light (weight) atoms

Fuel source for fusion is found in WATER

The potential contained in Deuterium found in
10gallon of water is = to 2400 gallons of
Gasoline

It is considered limitless

No chance of runaway reactions

Very efficient
Nuclear Fusion .......But

Researched since the 1940s

No successful fusion reactor yet because
of difficulty containing plasma

Temperatures of over 50,000,000-Celcius

Magnetic reactors are possibility but not
yet

Research and experimentation continues
Nuclear Weapons

Nuclear weapon- use energy of radioactivity to
make explosion

Radiological weapon- use of radioactivity as
weapon
Radiation

rem: rontegen equivalent for man = 2 billion
gamma/ cm3

sievert: 100 rem = measurement of damage
caused to cell

1 sievert= clear damage to cell

3 sieverts= “LD 50” (lethal dose 50%)

“whole body dose”= 3 sieverts to every body
cell

25 sieverts = 1 cancer
Uranium Bomb
Nuclear Weapons

Nuclear weapon- use energy of radioactivity to
make explosion

Radiological weapon- use of radioactivity as
weapon