Transcript Topic 8: Power production 8.3 & 8.4

TOPIC 8: POWER PRODUCTION
8.3 & 8.4 (A)
FOSSIL FUELS & NUCLEAR ENERGY
Allen High School
IB Physics SL
Source: Chris Hamper Physics
THE HISTORY
As technology has advanced, it has become easier
to extract fossil fuels like coal.
 This is a difficult and dangerous job; however coal
produces more heat and energy than wood.
 The invention of James Watt’s steam engine
changed the world in 1769 and still today.
 Steam engines turned a wheel and were powered
by coal (twice the energy density than wood).
 This invention kicked off the Industrial Revolution
and the ability to transport goods around the
world. Coal cities boomed.

COAL TO OIL (PETROLEUM)
Oil technology allows us to drill and pump crude oil
(thick sticky substance). Oil has a higher energy
density than coal, but before 1852, it was more
difficult to utilize than coal.
 In 1852, Ignacy Lukasiewicz invented a method to
refine crude oil to make kerosene (cleaner fuel
with even higher energy density). It became
possible to inject the fuel inside a piston of an
engine (internal combustion), which revolutionized
transport.
 Easy to transport, but hard to clean up oil spills.

GENERATION OF ELECTRICITY
In 1831, Michael Faraday discovered that
moving a wire in a magnetic field created
current. But in 1866, Werner Siemens
invented the dynamo, which brought electricity
generation to the big scale.
 In 1884, Sir Charles Pearson invented the
steam turbine, which was the final puzzle
piece.
 Electricity was now the easiest way to transfer
energy from one place to another.

FOSSIL FUEL POWER STATIONS
Coal-fired stations burns the coal, which boils
the water, then produces steam and powers the
turbine, which turns a generator and produces
electricity. The steam leaving the turbine is
cooled, causing it to condense and is returned
to the boiler.
 Overall efficiency of coal-fired stations are 40%.
Degraded energy is exhaust gas, waste heat,
and also friction in the components of the
turbine and generator.

COAL-FIRED POWER STATION
FOSSIL FUEL POWER STATIONS
Oil-fired stations are the same as coal, but oil is
cleaner and easier to transport.
 Gas-fired stations are more efficient because
there are two stages of energy use.

 Burning
gas is blasted through a turbine
 Heat produced can boil water & power turbine.
 Gas-fired can be 59% efficient, but if the “wasted”
heat is utilized, it could be as high as 80%.
What
can be more
efficient and
cleaner??
NUCLEAR POWER
Fission: Big nucleus (U-236) splits into two
smaller nuclei, resulting in a loss of mass (defect)
and hence a release of energy.
 23692U  14256Ba + 9236Kr + 10n
 The energy released from the ∆m is given to the
fission fragments as KE.
 If one mole of Uranium split, then the energy
released would be 16.5 x 10 12 J, which is a lot
more energy than coal.
 The neutron released in the above reaction is an
essential part of nuclear reactions.

NUCLEAR REACTIONS
A neutron is added a U-235 nucleus to produce
U-236, which then splits in two. As a result there
are too many neutrons and some are released.
 These neutrons can be captured by more U atoms
and so on, leading to a chain reaction.
 The chain reaction depends on slow moving
neutrons. Neutrons are slowed down by
introducing some other nuclei between U atoms.
Colliding with the other nuclei slow down the
neutrons.

CHAIN REACTION
NUCLEAR REACTIONS
A minimum amount of U is needed in order for
these chain reactions to take place. This is called
Critical Mass.
 Once U is extracted from the ground (as uranium
ore) and processed, only U-235 (only 0.7%) is used
as nuclear fuel. Uranium must be enriched
(increasing the U-235 percentage).
 The fuel is then made into fuel rods (cylinders
stacked together); the rods are then bundled
together and many are placed in the reactor.

NUCLEAR REACTIONS

Is this an atomic bomb?
 NO,
not all nuclear energy results in a bomb.
 An atomic bomb is an out-of-control reaction takes
place. The total mass is above the critical mass. It
depends on the initial mass. A nuclear weapon
begins with 85% U-235, where normal nuclear
reactions are less than 20%.

How do we prevent an out-of-control reaction?
 Control
the number of neutrons produced and the
speed of the neutrons (we want them slowed
down).
NUCLEAR POWER STATIONS
A nuclear reactor produces the heat and contains
the fuel rods surrounded by the moderator.
 The control rods are raised/lowered to control the
rate of reaction (they absorb the neutrons not
needed).
 There is a pressured vessel, which has a gas
circulating to pick up heat from fuel rods and
transfer it to the heat exchanger. The water then
turns to steam and turns a turbine and generates
electricity. See picture on next slide.

NUCLEAR REACTOR
PLUTONIUM
When U-238 absorbs a neutron, it turns into
U-239, which then decays to produce beta
radiation and Np-239, which then decays again
by beta radiation to Pu-239, Plutonium.
 Plutonium also undergoes fission and can be
used as a fuel or in the manufacture of nuclear
weapons.
 The production of Pu from U can be extracted
and used for subsequent energy production (or
bombs).

WHY DOES GOOD NUCLEAR ENERGY
STILL GET A BAD RAP?
Chernobyl; Three-Mile Island; emphasis on
“nuclear” as a weapon.
 As with all energy sources, there are
cons/problems with nuclear.

 Radioactive
waste from U extraction (“short-term”)
& spent fuel rods (the latter leads to long-term
storage).
 Nuclear meltdown: when reactions are not
controlled and fuel rods melt together. Pressure
vessel bursts, thus releasing radioactive material
into the atmosphere. (Chernobyl, Ukraine, 1986).
FISSION VS. FUSION
Fusion is the opposite of fission. Fusion involves
fusing light nuclei to form a larger nuclei. Once
again, the mass defect is converted to energy.
Fusion happens on the Sun.
 There is less known and less experience with
Fusion as compared to Fission.
 The difficulty with Fusion is maintaining and
confining a high-temperature, high-density
plasma necessary for a fusion reaction.

FISSION VS. FUSION

Going back to the Energy Density chart.
Fuel
Energy Density (MJ/kg)
 Fusion fuel
300,000,000
 Uranium-235
90,000,000


Think of the power efficiency if we were able to
use Fusion more often!