Nuclear Energy - Eastside Physics

Download Report

Transcript Nuclear Energy - Eastside Physics

Nuclear Energy
• Nuclear fission is when a heavy nucleus splits into
two smaller nuclei. The total mass of the products
is less than the original mass. The mass difference
results in an energy gain, about 200MeV for each
fission event.
• 01n + 92235U----->56141Ba + 3692Kr + 301n
• The intermediate stage, 92236U, which is very
unstable is when the nucleus elongates and
compresses until finally splitting. The three
neutrons are available to bombard other nuclei.
Nuclear Reactors
• When a nucleus undergoes neutron
bombardment and fission occurs, the
neutrons released bombard other nuclei and if
not controlled result in a chain reaction
releasing a large amount of energy in a chain
reaction, an explosion.
• A nuclear reactor is a system designed to
maintain a self sustained chain reaction
releasing controlled energy.
• The average number of neutrons produced per
fission event is 2.5, defined as the reproduction
constant K. In reality K is less than 2.5. Self
sustain chain reaction occurs when K = 1, then
the reactor is said to be critical. When K is less
than 1 it is subcritical and the reaction dies out. If
it is greater than 1 it is super critical and the
reaction is runaway.
• When neutrons are released they have high kinetic
energy and need to be slowed down to be absorbed
by 235 U. This is done by the use of a Moderator,
originally Carbon later heavy water. The moderator
absorbs the kinetic energy of the neutrons allowing
it to be captured by the nucleus causing fission.
• Not all neutrons are captured some leak out of the
core before capture. A large surface area to volume
ratio in the reactor will reduce the leakage. To
much leakage and the reaction will stop.
Control of Power Level
• If nuclear bombardment is not controlled the
reactor becomes too hot and will melt and/or the
chain reaction is too fast and an explosion may
occur. Temperature if often controlled by
cooling water that removes excess heat from the
core. In addition it is necessary to use control
rods that absorb excess neutrons before being
captured by the fission process. These rods
made of either graphite, boron or cadmium are
inserted between the fuel rods and adjusted to
control the amount of neutron absorption.
• The heat from a nuclear reactor is used to
produce steam that is used to run a turbine
that in turn powers a generator.
• Power production whether by nuclear
reactors, burning fossil fuel or some other
means from the point of turning a turbine to
powering a generator are virtually all the
Nuclear Fusion
• Fusion is the opposite to fission in that two
smaller nuclei are combined to form a heavy
nucleus which also results in the release of
energy from the conversion of matter. The
sun provides heat due to nuclear fusion of
protons (hydrogen ions) to deuterium, then a
hydrogen ion and deuterium to 3He and
finally either hydrogen and 3He to 4He or
two 3He to 4He and two hydrogen ions
First 11H + 11H--->12D + e+ + v
then 11H + 12D --->23He + 
then either 11H + 23He ---> 24He + e+ + v
or 23He + 23He ---> 24He + 2(11H)
The energy liberated is carried by the gamma
rays, positrons and neutrinos. The gamma rays
are absorbed increasing the temperature, the
positrons combine with electrons forming gamma
rays and are absorbed, the neutrinos escape the
star taking with them energy.
A Star Formation
• A star is formed by a shock wave from a
supernova collapsing a cosmic dust cloud
upon itself. As the particles collapse they
accelerate and generate huge gravitation force
and heat. As protons collide they repel and
gravity continues to attract. The heat
generated is in the order of 107K. As fusion
occurs the energy liberated prevents the star
from collapsing under its own gravity and the
cycle continues.
Fusion Power
• A large amount of energy is released in a
thermonuclear reaction (fusion) and
comparatively few radioactive by-products are
formed. However proton-proton reaction are
unrealistic due to the need of extremely high
temperatures and pressures. The sun functions
because of the extreme density of protons at its
core. Reaction of deuterium with tritium seems
promising but for the confinement of plasma at
temperatures 108K and the time required.
Magnetic Field Confinement
• It is the combination of two magnetic fields
either helical or spiral in design used to
confine plasma in a chamber and prevent it
from touching the vessel walls. Temperatures
30 times hotter than the sun are produced by
introduction of high kinetic energy neutral
particles into the plasma or by the addition of
energy from intense lasers
Elementary Particles
• Atom from ‘atomos’ indivisible remained
until the early 20th century, the proton
neutron and electron until 1937 and then
collision of high energy particles discovered
new particles. From 1960 on except for the
electron, photon and a few others subatomic
particles matter is made of quarks.
Forces of Nature
range of
• Strong
short 1fm
• electro
long 1/r2
• Weak
short 10-3 fm
• Gravitational 10-43 long 1/r2
field particle
• For virtually every particle there is an
antiparticle, having the same mass but
opposite charge.
• Electron-positron, proton-antiproton,
• Exceptions are the photon and neutral pion
which are their own antiparticles
• Two mesons of slightly different mass, the
muon () has weak and electromagnetic
interaction and plays no role in strong nuclear
forces. Its life time around 2.2x10-6s decays to
an electron, a neutrino and an antineutrino.
The other, pi meson, pion () comes in three
varieties - + o and decays into muon and an
antineutrino in 2.6x10-8s. The pion is involved
in transferring energy between nucleons
Particle Classification
• All particles except the photon can be
classified into two group.1) Hadrons which
include mesons and baryons are distinguished
by mass and spin. All mesons decay to
electrons, positrons neutrinos and photons.
Baryons have masses equal to or larger than a
proton and except for the proton all decay
and produce a proton. Protons are composed
of quarks.
• 2) Leptons (meaning light), include electrons,
muons and a tau and all have neutrinos
associated with them. They have weak
interaction and are considered truly elementary.
• Hadrons are composed of two or three
fundamental constituents called quarks, (u,d,s).
Quarks have fractional electronic charge and
each have an antiquark of opposite charge.
Colored Quarks
• The three quarks are colored red blue and green.
The antquarks are anti-red anti-blue and antigreen. Baryons consist of the three different
colored quarks and mesons consist of one color
and an anti quark of the anti-color. Both baryons
and meson are colorless. The strong force between
quarks is called color force and is carried by
massless particles called gluons.
• Different colored quarks attract each other as
opposites oppose. When gluon are absorbed or