1. Radiation
Nuclear Reactors

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

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

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

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

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

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

29. Reactor Types
 Comments - used in Britain, and France

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