2. Nuclear Reactions
Uranium is a fairly common element on
Earth and was incorporated into the
planet during the planet's formation
U-238 makes up 99 percent of the
uranium on the planet
Uranium-235 makes up about 0.7
percent of the remaining uranium found
naturally
Uranium-235 has an interesting
property
3. Nuclear Reactions
U-235 decays naturally, just as U-238
does, by alpha radiation
U-235 also undergoes spontaneous
fission a small percentage of the time
Fission is defined as “the splitting of an
atom”
Also, U-235 is one of the few materials
that can undergo induced fission
4. Nuclear Reactions
If a free neutron runs into a U-235
nucleus, the nucleus will absorb the
neutron without hesitation, become
unstable and split immediately
The probability of a U-235 atom
capturing a neutron as it passes by is
fairly high
In a reaction two or three neutrons are
ejected from each fission causing other
fissions to occur
5.
6. Nuclear Reactions
Theprocess of capturing the neutron
and splitting happens very quickly
(1 x 10-12 seconds) picoseconds
An incredible amount of energy is
released, in the form of heat and
gamma radiation, when a single atom
splits
The energy is released because the
products and the neutrons, together,
weigh less than the original U-235 atom
7. Nuclear Reactions
The difference in weight is converted
directly to energy at a rate governed by
the equation E = mc2
a pound of highly enriched uranium
used to power a nuclear submarine or
nuclear aircraft carrier is equal to about
a million gallons of gasoline
a pound of uranium is smaller than a
baseball and a million gallons of
gasoline would fill a five-story building
8. Nuclear Reactions
In order for a reactor to work, a sample
of uranium must be enriched , so that it
contains two to three percent or more of
uranium-235
Weapons-grade uranium is composed
of 90 percent
9. Nuclear Power
uranium is formed into pellets with
approximately the same diameter as a
dime and an inch long
These pellets are then placed in rods
that are “super critical” meaning they
would over heat and melt if left alone
To prevent this, control rods made of a
material that absorbs neutrons are
inserted
10. Nuclear Power
The depth the rods are inserted into the
uranium, determines the amount of
fission taking place
All the way in… the reactions stop
All the way out….the reactions increase
until meltdown occurs
The uranium bundle acts as an
extremely high-energy source of heat. It
heats the water and turns it to steam
11.
12. Nuclear Power
The steam drives a steam turbine,
which spins a generator to produce
power
In some plants the steam contacts other
water and turns it to steam… this way,
the radioactive water never touches the
turbine
there is little difference between a
nuclear plant and a coal or oil-fired plant
except for the source of the heat used
13. Nuclear Power
The reactor's pressure vessel is
typically housed inside a concrete liner
that acts as a radiation shield
the containment vessel is protected by
an outer concrete building that is strong
enough to survive such things as
crashing jet airliners
14.
15. Nuclear Power
Uranium-235 is not the only possible
fuel for a power plant. Another
fissionable material is plutonium-239
16. Nuclear Power
Plutonium-239 can be created by U-238
fission, therefore some reactors are
used to make weapons grade plutonium
If fact, the first reactors every produced
were used for this purpose…. Atomic
bombs
Research reactors work on the same
principals as power reactors, however
are used for other purposes
17. Nuclear Power
They can be used to expose materials
to high levels of radiation
To bombard elements with neutrons to
create new isotopes
And can be used to work on new
energy possibilities
How safe are they? Do they hurt the
environment?
18. Nuclear Safety
Compared with a coal-fired power plant,
nuclear power plants are a dream come
true from an environmental standpoint
coal-fired power plant actually releases
more radioactivity into the atmosphere
than a properly-functioning nuclear
power plant
Fossils fuel plants (oil/coal) release
huge amounts of carbon into the
atmosphere, C-14 is radioactive
19. Nuclear Safety
There are also drawbacks with nuclear
power…
Mining and purifying uranium has not,
historically, been a very clean process
Improperly-functioning nuclear power
plants can create big problems i.e. The
Chernobyl
Spent fuel from nuclear power plants is
toxic for centuries and there is no safe
permanent storage facility for it, yet
20. Nuclear Safety
Transporting nuclear fuel to and from
plants also poses some risk
Unfortunately, there are less new
nuclear power plants being constructed
due to these risks
At some point however, there will be no
more fossil fuel and we will have no
choice but to build more nuclear power
plants
21. Reactor Types
There are a couple different types of
reactors, all use the same principle of
nuclear fission
The four types are …
Graphite Moderated Reactor
Fast Breeder Reactor (FBR)
Liquid Metal (LMFBR) (most common
type of breeder)
22. Reactor Types
LightWater Reactor (LWR)
Heavy Water Reactor (HWR)
There are two types of light water
reactors
Boilingwater reactor
Pressurized water reactor
Boiling water reactor
CoolantType - water
Moderator Type – water
23. Reactor Types
Fuel - uranium-dioxide (UO2)
Comments - steam generated inside the
reactor goes directly to the turbine
24.
25. Reactor Types
Pressurized water reactor
Coolant Type - water
Moderator Type – water
Fuel - uranium-dioxide (UO2)
Comments - steam is generated outside
the reactor in a secondary heat transfer
loop
26.
27. Reactor Types
Heavy Water reactors work just like light
water reactors, however, instead of
using water H2O…. Normal hydrogen is
replaced with deuterium H2
28. Reactor Types
There
are two types of Graphite
moderated reactors…
Gas Cooled
Water Cooled
Gas Cooled
Coolant Type - gas (carbon dioxide or
helium)
Moderator Type – graphite
Fuel -- uranium
30. Reactor Types
Water Cooled Reactors
Coolant Type – water
Moderator Type – graphite
Fuel -- uranium
Comments - used in USA & former
Soviet Union, e.g. Chernobyl
31. Reactor Types
Fast Breeder Reactor (FBR)
Coolant Type – molten liquid sodium
Moderator Type – none required
Fuel - plutonium dioxide and uranium
dioxide in various arrangements
Comments - breeder reactors are
designed to produce more fissile
material than they consume