Fundamentals of Nuclear Power

1
Fundamentals of Nuclear Power
2
The Nucleus
Protons 1.672 10?27 kg
Neutrons 1.675 10?27 kg
isotopes
3
Strong Nuclear Force

• Holds the protons and neutrons together.
• Third Fundamental Force (after gravity and the
  electromagnetic forces)
• operates on distances like 10?15 m
• the more protons you have, the more neutrons
  needed for stability

4
Binding Energy

• What does it take to break a nucleus into its
  constituents?

binding energy (mass defect)c2
5
Example Helium Nucleus

• two protons two neutrons
• mass of intact helium nucleus
• difference is converted to binding energy

6
Curve of Binding Energy
Nuclei with the largest binding energyper
nucleon are the most stable.---------------------
----------The largest binding energy per
nucleon is 8.7 MeV, for mass number A 56
(Fe).Beyond bismuth, A 209, nucleiare
unstable.
7
Nuclear Fission

• We convert mass into energy by breaking large
  atoms (usually Uranium) into smaller atoms. Note
  the increases in binding energy per nucleon.

8
(No Transcript)
9
A slow moving neutron induces fission in Uranium
235
10
Fission products

• The fission products shown are just examples,
  there are a lot of different possibilities with
  varying probabilities

11
Expanding Chain Reaction

• The fission reaction produces more neutrons which
  can then induce fission in other Uranium atoms.

12
(No Transcript)
13
Linear Chain Reaction

• Obviously, an expanding chain reaction cannot be
  sustained for long (bomb). For controlled
  nuclear power, once we reach our desired power
  level we want each fission to produce exactly one
  additional fission

14
Tricks of the trade

• Slow moving (thermal) neutrons are more effective
  at inducing fission, but, fissions produce fast
  moving electron. We need to slow neutrons down.
• Fissions typically produce several neutrons, but
  a linear chain reaction only needs one. We need
  to get rid of a good fraction of our neutrons.

15
Moderator

• Neutrons are slowed down by having them collide
  with light atoms (Water in US reactors).
• Highest level of energy transfer occurs when the
  masses of the colliding particles are equal (ex
  neutron and hydrogen)

16
Control Rods

• Control rods are made of a material that absorbs
  excess neutrons (usually Boron or Cadmium).
• By controlling the number of neutrons, we can
  control the rate of fissions

17
Basic Ideas

• The Uranium is both the fuel and the source of
  neutrons.
• The neutrons induce the fissions
• The Water acts as both the moderator and a heat
  transfer medium.
• Control rods regulate the energy output by
  sucking up excess neutrons

18
Practicalities

• Processing of Uranium
• Each ton of Uranium ore produces 3-5 lbs of
  Uranium compounds
• Uranium ore is processed near the mine to produce
  yellow cake, a material rich in U3O8.
• Only 0.7 of U in yellow cake is 235U. Most of
  the rest is 238U which does not work for fission
  power.

19
US Uranium Deposits
20
World Distribution of Uranium
21
Enrichment

• To be used in US reactors, fuel must be 3-5
  235U.
• Yellow cake is converted into UF6 and this
  compound is enriched using gaseous diffusion
  and/or centrifuges.
• There are some reactor designs that run on pure
  yellow cake.

22

• NOTE A nuclear bomb requires nearly 100 pure
  235U or 239Pu. The 3 found in reactor grade
  Uranium CANNOT create a nuclear explosion!

23
Fuel Pellets

• The enriched UF6 is converted into UO2 which is
  then made into fuel pellets.
• The fuel pellets are collected into long tubes.
  (12ft).
• The fuel rods are collected into bundles (200
  rods per bundle
• 175 bundles in the core

24
Cladding

• The material that the fuel rods are made out of
  is called cladding.
• It must be permeable to neutrons and be able to
  withstand high temperatures.
• Typically cladding is made of stainless steel or
  zircaloy.

25
Controlling the chain reaction depends on

• Arrangement of the fuel/control rods
• Quality of the moderator
• Quality of the Uranium fuel
• Neutron energy required for high probability of
  fission

26
(No Transcript)
27
Other Options

• Other countries use different reactor designs.
• Some use heavy water (D2O) as a moderator. Some
  use Graphite as a moderator.
• Some are designed to use pure yellow cake without
  further enrichment
• Liquid metal such as sodium or gasses such as
  Helium are possibilities to use for coolants

28
Nuclear Power in the US

• We currently generate approximately 21 of our
  electricity using nuclear power.
• No new nuclear power plants have been ordered
  since the late 1970s. The last one to come
  online was in 1996 in Tennessee.
• Even the newest plants are nearing 30 years old
  and will start to need replacing.

29
US Nuclear Power Plants
30
World Nuclear Power
31
Jan 2011
32
(No Transcript)