2 important postulates of Einstein
All laws of nature are the same in all
uniformly moving frames of reference.
The speed of light in free space has the
same measured value for all observers,
regardless of the motion of the source or
the motion of the observer; that is,
the speed of light is a constant
Simultaneity
- Two events that are simultaneous in one frame of
reference need not be simultaneous in a frame moving
relative to the first frame.
Space Time
- Spacetime is the four-dimensional
continuum in which all events take place
and all things exist: three dimensions are
the coordinates of space and time is the
fourth.
Relativity Principle
If two frames of reference move with constant
velocity relative to each other, then the laws of
physics will be the same in both frames of
reference.
Speed of Light Principle
The speed of light in space is the same for any
observer no matter what the velocity of the
observer or the source.
-Space and time change depending
on the situation.
Time Dilation
what is t
what is t0
what is v
- the stretching of time by a moving object
- A clock that is moving will run slow.
Length Contraction
what is L
what is L0
what is v
- The length of an object is measured to be
shorter when it is moving than when at rest.
Relativity and Mass
what is m
what is m0
what is v
The mass of a body is not the same for all observers,
but depends on the object’s velocity with respect to
each observer who measures its mass.
Nuclear Reactions
what are.. nuclear reactions? isotopes? moderators? chain reaction? critical mass?
- A nuclear reaction involves whole atoms, with some rearranging of electrons in the process. Nuclear
reactions involve changes in the atomic nucleus. - Isotopes are different forms of the same element that have different numbers of neutrons. Isotopes exist
for every chemical element though some are more stable than others. - A moderator is a material that slows the speed of neutrons. Moderators are used in nuclear reactors to
slow the neutrons enough to increase the likelihood of interaction with another nucleus to initiate fission. - A chain reaction is a self-sustaining reaction in which the products of one reaction event simulate
further reaction events. - Critical mass is the minimum mass of fissionable material in a reactor or nuclear bomb that will sustain
a chain reaction.
Nuclear Fission
- is the splitting of the nucleus of a heavy atom, such as uranium-235, into two main
parts, accompanied by the release of much energy. - A nuclear fission reactor generates energy through a controlled nuclear fission reaction. These reactors
are nuclear furnaces, which boil water to produce steam for a turbine.
-A nuclear fission power plant converts nuclear energy to electrical energy. - Fission is source of energy for all nuclear power generation used today. About 15% of Canada’s
electricity is produced by nuclear fission. - A reactor contains 3 main components: nuclear fuel combined with a moderator, control rods, and water.
-A major drawback to fission power is the generation of radioactive waste products of fission. When
uranium fissions into two smaller elements, the ratio of neutrons to protons in the product is too great to
be stable. These fission products are radioactive. Safely disposing of these waste products requires
special storage casks and procedures, and is subject to a developing technology. - Some factors are:
Control – Keeping the nuclear reaction from dying out or exploding.
Safety – If something goes wrong it can be contained.
Refueling – Adding more nuclear fuel without stopping the reactor.
Waste production – The by products of the reaction must be manageable.
Reactors
– a device to initiate and control a sustained nuclear chain reaction. There are many types of reactors.
- The 3 most common type of reactors are boiling water reactor (BWR), pressurized water
reactor (PWR) and pressurized heavy water reactor (CANDU).
Breeder Reactors
- A breeder reactor is a nuclear fission reactor that produces more nuclear fuel than it consumes. It converts a non-fissionable uranium isotope into a fissionable plutonium isotope.
-A breeder reactor is a much more efficient version of a fission reactor because it “breeds” new fuel while
consuming the old fuel. This is possible because the fission reactions release lots of neutrons that can be
used to transform certain non-useful isotopes into useful isotopes or elements - in particular Plutonium is generally a product of breeder reactors.
-However, plutonium is rather hazardous and dangerous for reasons associated with proliferation of
nuclear weapons, so breeder reactors have not been very popular in some countries.
-Germany, France and UK have closed Breeder Reactors. Russia, Japan, China and India are using them.
CANDU
- (CANada Deuterium Uranium) is a heavy water reactor that was developed in Canada and make up
11% of all reactors used in the world. - Heavy water (containing Deuterium) is used as a coolant in the reactor, and also used as a moderator.
- In most reactors, the moderator is regular water but CANDU reactors use heavy water, or deuterium
oxide. This slows down absorption of neutrons and makes the chain reaction more stable - CANDUs make more efficient use of mined uranium than enriched fuel reactors. The disadvantages are
that heavy water is expensive to make, representing about 20% of the capital cost of each reactor, and
the reactor core size is larger. - One of the unique features of a CANDU reactor is that it allows on-line fuelling. The fuel bundles are
placed in horizontal tubes (called pressure tubes). These tubes can be loaded remotely from either end
while the reactor is running (on-line). This avoids scheduled shutdowns to replace the fuel. The CANDU
design requires significantly more “plumbing” than a PWR reactor, as each pressure tube has high
pressure heavy water passing through it. - The typical lifespan of a fuel bundle in the reactor is one to two years. As a fuel bundle is loaded in one
end of the pressure tube, a spent fuel bundle is pushed out of the other end. The picture to the right taken
during a shutdown shows the machine that loads the fuel bundles.
Nuclear Fusion
Nuclear Fusion is the combination of the nuclei of light atoms to form heavier nuclei, with the release of much energy.
- After fusion, the total mass of the light nuclei formed in the fusion process is less than the total mass of
the nuclei that fused.
-For fusion to occur, they must collide at very high speeds to overcome electrical repulsion.
-Fusion is the source of the sun’s energy.
- Fusion has already been achieved in several devices, but instabilities in the plasma have prevented a sustained reaction.
-A big problem is devising a field system that will hold the plasma in a stable and sustained position
while a number of nuclei fuse.
- Fusion power is nearly ideal.
- There is no air pollution because the only product of the thermonuclear combustion is helium.
- Disposal of radioactive waste is not a major problem.
-The development of fusion power has been slow and difficult, already extending over 50 years.
- Have not been able to find a safe and efficient way to control the method
- With modern day technology, the only atoms we can consider fusing are deuterium and tritium.
-The heavier an atom, the more energy required to fuse it with another.
- Hydrogen bombs can potentially 1000 times stronger than an atomic bomb.
Pros of Nuclear Energy
- efficient
- clean - no drastically contributing to climate change
- cheap to run (operating costs)
cons of nuclear energy
- pricey to construct
- there are better alternatives
- waste dispossal
- disasters/ human mistake
- health concerns
