Energy From Nuclear Power

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Energy From Nuclear Power

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Title: Energy From Nuclear Power

1
Energy From Nuclear Power

APES CH 13

Nuclear Energy in Perspective
We are currently in the midst of an energy
crunch.
Fossil fuels will not last forever.
Nuclear power does not contribute to global
warming.
31 nations now have nuclear power plants in place
or under construction
Some of these countries rely on nuclear power for
most of their electricity
The history of Nuclear power goes back to the
years right after WW II, it was an effort to use
the technology developed for war as a means of
producing energy for peace time.

GE and Westinghouse built power plants paid for
by utility companies
They received assurances from the federal
government that they would not be liable for
legal liabilities.
Department of Energy set safety standards for
operations and maintenance.
In 1970, there were 53 plants operating in the
US, producing 9 of the electricity. There were
another 170 plants either planned or being built.
Since 1975, utilities stopped ordering nuclear
plants, numerous existing orders were canceled.

The Shorham Plant on Long Island was built,
licensed at a cost of 5.5 billion and dismantled
after generating electricity for only 32 hours.
The state determined that there was no way to
evacuate the people in the event of an accident.
Rancho Seco Plant near Sacramento was also shut
down.
28 separate reactors have been shut down to date.
At the end of 2003, 104 nuclear power plants were
operating in the US.
Nuclear Power Plants are not forever, as plants
are decommissioned, estimates are that 27 will
be out of commission by 2020.

The world ha a total of 441 operating nuclear
plants with 32 under construction.
This generates about 17 of the worlds
electricity.
France generates 78 of its electricity with
Nuclear power and plans to go to more than 80.
Japan has few resources, and generates
electricity with 55 nuclear reactors. 35 of
their electricity needs.
How does Nuclear Power Work?
Nuclear energy involves changes at the atomic
level.
In fission, a large atom of one element is split
to produce 2 smaller atoms of different elements.
In fusion, 2 small atoms combine to form a larger
atom of a different element

In fusion and fission,
The mass of the product is lass than the mass of
the starting material.
The lost mass is converted to energy in
accordance with the equation Emc2.
Fuel for Nuclear Power Plants
All current power plants use U-235 as a fuel.
U occurs naturally in two forms (isotopes)
Uranium 238
Uranium 235
These differ by the number of neutrons in the
nucleus of the atom. The number of protons and
electrons remain the same.
The difference is that U-235 will readily undergo
fission, U-238 will not.

So what causes fission to occur?
A neutron hitting the nucleus at just the right
speed causes an atom of U-235 to undergo fission.
The neutron creates U-236 which is highly
unstable and will spontaneously decay into two
lighter elements.
The fission reaction gives off more neutrons and
releases a great deal of energy.
More neutrons and more energy is released. This
is called a chain reaction, like a domino effect.

8
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9

Nuclear Fuel
U is mined and purified into uranium dioxide
(UO2).
U must be enriched. This involves separating
U-235 from U-238. This is done with a special
centrifuge. This technology is what keeps less
developed countries from advancing their nuclear
capabilities.
Nuclear Bomb
When U-235 is highly enriched, a small amount of
U-235 can generate a chain reaction
spontaneously.
In a bomb, 2 small amounts of almost U-235 are
forced together so that a critical mass is
reached. This allows all the mass to undergo
fission in a fraction of a second, releasing all
the energy in one huge explosion

The Nuclear Reactor
This is designed to sustain a chain reaction but
not allow it to amplify into a nuclear explosion.
In the reactor, there is only 4 U-235 and 96
U-238.
In the process of enrichment, some U -238 absorbs
neutrons converting them into Pu-239. This also
undergoes fission when hit by another neutron.
Actually, about 1/3 of the energy from a reactor
comes from Pu fission.

The moderator
A chain reaction can be achieved only if a
sufficient mass of enriched uranium is arranged
in a suitable geometric pattern and is surrounded
by a material known as a moderator.
The moderator slows down neutrons so that they
travel at the right speed to induce fission
In the process, the moderator gains heat.
In the US, the moderator is nearly pure water.
Other reactors use graphite or heavy water
(deuterium oxide).
Fuel Rods
To achieve the geometric pattern the uranium fuel
is made into pellets which are then loaded into
long metal tubes.
The long tubes are called fuel rods
Many fuel rods are placed close together inside a
reactor vessel which holds the water.
The water acts as a moderator and a heat exchange
fluid.

12
Nuclear Reactor Components
Fuel rod assembly
13

Fuel rod assembly including control rods
Diagram of a nuclear fuel assembly revealing the
complexity of the system to be considered over
the long term. Approximately 4 m long and 9.5 mm
in section, each of the 264 rods is secured in a
space apart by grids to make up an assembly the
rod is made up of Zircaloy (alloy based on metal
zirconium) cladding 580 mm thick into which 265
pellets of uranium dioxide UO2 are loaded.

14
The control rod assembly
The control rod moves inside the fuel element to
control nuclear fission. During operation it is
lifted to compensate the burn-up of the nuclear
fuel.
15

Over time, the daughter products accumulate in
the fuel rods and slow down the fission rate.
This is now spent fuel and is removed
Control Rods
These consist of neutron absorbing material and
are inserted between the fuel elements.
The chain reaction is started and controlled by
inserting and withdrawing the control rods.
As the control rods are removed and a chain
reaction begins, the fuel rods and the moderator
become intensely hot,

The Nuclear Power Plant
Heat from the reactor is used to boil water to
provide steam to drive a conventional turbine.
In the US, the moderator water is heated to 600
C. It is circulated through the reactor but does
not boil as it is under very high pressure.
This superheated water is circulated through a
heat exchanger, boiling other unpressurized water
that flows past the heat exchanger tubes this
produces the steam that drives the turbines.

LOCA
This stands for loss of coolant accident.
The US systems are what is called a double loop
design. It has the drawback in that this design
is subject to LOCA.
This can result in the cores overheating. This
could cause fission to cease since the moderator
would no longer be present.
It would still cause the fuel core to overheat.
This would release the materials in the core -
meltdown.
then the molten material falling into the
remaining water could cause a steam explosion.

To prevent this, there are backup cooling systems
to keep the reactor immersed in water. Also, the
entire assembly is housed in a thick concrete
containment building.
Comparing Nuclear Power with Coal Power.
Right now, no more nuclear plants are being
built. We have no choice but to replace nuclear
plants with coal burning plants.
Even though there are concerns about nuclear
power, there are some good environmental reasons
to pursue nuclear power.

In one year..at a 1000 megawatt nuclear power
plant compared with a 1000 megawatt coal plant
Fuel -
coal plant
consumes 2-3 million tons of coal
this is obtained by strip mining, which causes
environmental destruction and acid leaching
also a cost in the form of accidental deaths and
health concerns
7 tons of CO2
Nuclear power plant
requires 30 tons of U obtained from mining 75,000
tons of ore
less harm to humans and the environment
the fission of 1 lb of U releases the energy
equivalent of 50 tons of coal.
60 tons of U is sufficient to run the nuclear
plant for 2 years
no CO2

Radioactivity
a coal plant releases 100 times more
radioactivity than a nuclear power plant
the coal plant produces 600,000 tons of ash
requiring land disposal
wastes
the nuclear plant produces 250 tons of highly
radioactive wastes requiring safe storage and
ultimate safe disposal. (unsolved problem).
Accidents -
worst case accident could cause death to workers
and fire
accidents in a nuclear plant could be as small as
a small emission of radioactive gases or a
catastrophic release of radioactive material with
many dead, long-lasting environmental damage and
cancers to humans and animals

13.3 The Hazards and Costs of Nuclear Power
Facilities
radioactive emissions
direct products of the fission reaction are
unstable. These are called radioisotopes
they become stable by radioactive decay
this process emits alpha particles, beta
particle, neutron and high energy radiation.
Radioactivity is measured in curies. One gram of
pure radium-226 gives off 1 curie per second
the particles and radiation are collectively
referred to as radioactive emissions and are the
wastes of nuclear power

biological effects
radioactive emissions can penetrate tissue.
Their ability to do damage is measured in units
called sieverts
the emissions leave no mark, nor are they felt.
They can dislodge electrons from molecules or
atoms that they strike. This produces an ion.
These emissions are therefore called ionizing
radiation.
The process of ionization can create molecules
that are no longer able to function in their
normal capacity.
In high doses (over 1 sievert is considered high)
radiation can cause enough damage to prevent cell
division.
This can cause radiation sickness, preventing
normal repair of blood, skin and other tissues.
Death can occur in a few days or months.

Low dose
radiation might damage DNA. Cells with damaged
DNA may then begin growing out of control.
(malignant tumor or leukemia).
If the damaged DNA is in an egg or a sperm, the
result might be birth defects
the redults might be unseen until many years
after the event.
Exposure
health effects are directly related to the level
of exposure
between 100 and 500 millisieverts results in an
increase in the risk of developing cancer.
Many scientists believe that no dose is without
some harm.
Some believe that there is a mechanism to repair
some damaged DNA.

Federal standards are set at 1.7 mSv/year as the
maximum exposure permitted for the general
population except for medical X-rays.
Sources of radiation -
People are exposed to radiation naturally from U
and Rn in Earths crust. We are also exposed to
cosmic rays from outer space.
Medical and ental X-rays are the largest source
of human induced exposure.
The average person in the Us receives about 3.6
mSv/year.
So, the question is, is radiation from nuclear
power likely to significantly raise radiation
levels and elevate the risk of developing cancer?
During normal operation, the fission products
remain within the fuel elements. No routine
discharges of radioactive materials occur.
The real problems arise from the storage and
disposal of radioactive wastes and the potential
for accidents.

Radioactive Wastes
radioactive decay occurs over a time period known
as a half life
the half life is the time it takes for half of
the starting amount of a given isotope to decay.
During the next half life, half as much will
again decay.
Each radioactive isotope has a characteristic
half life.
This can be as long as a fraction of a second to
many thousands of years.
The main culprit is U-239, which has a half life
of 24,000 years.
In France and Great Britain, P-239 is recovered
and recycled as nuclear fuel in an operation
called reprocessing.

Disposal of Radioactive Wastes
In 10 years most radioactive waste lose more than
97 of their radioactivity.
Short term containment - waste is stored in tanks
and casks in deep swimming pools. The water in
the tanks absorbs waste heat. The waste storage
capacity reached 50 in 2004 and will be at 100
by 2015.
After this, the waste can be stored in a dry
storage facility and air cooled for interim
storage until long term storage becomes
available.
The waste is accumulating at a rate of 10,000
tons per year and is all stored on site at
nuclear reactors.

Military radioactive wastes
some of the worst failures in handling wastes
have occurred at ,military facilities in the S
and in the Soviet Union.
Some of these releases have been deliberate.
For at least 20 years nuclear wastes were
discharged into the Techa River and then into
Lake Karachay.
At least 1000 cases of leukemia have been kinked
to this radiation contamination.
Today, standing on the hore of Lake Karachay for
one hour ill cause radiation posioning and death
within a week.
In 1967 the lake dried up and the winds blew the
radioactive sediments all over.
This lake is considered the most polluted spot on
Earth.

Yucca Mountain
the US has decided that the best plan to deal
with high level nuclear waste is to bury it.
No rock formation can be guarantied to remain
stable and dry for tens of thousands of years.
If earthquake activity or even groundwater
leaching occurs, the radioactive wastes could
escape into the environment and contaminate
water, soil, or air.
Yucca mountain has been selected to be the
nations civilian nuclear waste disposal site.
Nevadans have fought this selection
there is a NIMBY attitude everywhere.

George W Bush voided a veto by Nevada Governor
Kenny Guinn, w3ho was attempting to block further
development on the YM site.
The site could be ready to accept wastes by
2010.in the meantime, there is an underground
storage facility in New Mexico from nuclear
weapons facilities since 1999.

Nuclear Power Accidents
Three Mile Island
partial meltdown as a result of s series of human
and equipment failures and a flawed design
steam generator shut down automatically because
of a lack of power in its feedwater pumps
a valve on top of the generator opened in
response to the buildup of pressure.
The valve remained stuck in the open position and
drained coolant water from the reactor vessel.
There were no sensors to indicate that this valve
was opened.Operators shut down the emergency
cooling system at one point and shut down the
pumps in the reactor vessel (compounded the
problem).
The core was uncovered for a time and suffered a
partial meltdown.

10 million curies of radioactive gas were
released into the atmosphere.
The reactor damage was bad. The cleanup I
proving to be as costly as building a new power
plant.
The company has never admitted any radiation
caused illnesses

Chernobyl April 26, 1986
A test for standby diesel generators.
Engineers disabled the power plants safety
systems withdrew the control rods, shut off the
flow of steam to the generators and decreased the
flow of coolant water in the reactor.
They did not allow for the radioactive heat
energy generated by the fuel core, and , lacking
coolant, the reactor began to heat up.
The steam that was produced could not escape and
boosted the energy production of the reaction
the engineers inserted the control rods.
The control rods acted as moderators
the neutrons were still speedy enough to trigger
more fission
steam explosions blew off the top of the reactor
and the reactor melted down.

50 tons of dust and debris bearing 100-200
million curies were spread over thousands of
square miles
this was 100 times the radiation fallout from the
bombs dropped on Hiroshima and Nagasaki.
135,000 people were evacuated
the reactor was eventually sealed in steel and
concrete.
There is a 1000 square mile exclusion zone around
the reactor site.
2 engineers were directly killed
29 emergency personnel died within a few months.
There has been a great increase in thyroid cancer
due to the short lived I-131 being released.
The authorities waited a week to distribute I
pills to those effected.
More than 4000 Ukrainians who participated in the
cleanup died, 70,000 have become disabled

It is expected that between 140,000 - 475,000
cancers will be attributed to the accident world
wide
Can it happen here?
The US designed power plants use water as a
moderator, not graphite.
LWRs (light water reactors) are incapable of
developing a power surge more than twice their
normal power
LWRs have better back up systems to prevent the
core from overheating
the reactors are housed in containment buildings
designed to withstand explosions. (Chernobyl had
no containment building)
An LWE could totally lose coolant, although this
has never happened, Three Mile Island was a close
call.

New Generations of Reactors -
more safety features
likely to be built within the next 20 years
smaller reactors
cheaper to build
Terrorism
this is a problem
Economic problems-
life of a nuclear plant shorter than previously
thought
due to embrittlement - metals become brittle and
more subject to stress

Corosion - hot pressurized water cause cracks to
develop over time
Decommissioning - closing down a reactor is
costly. The materials are now radioactive.
Old sites need to be turned into something.
Breeder reactors
a breeder reactor converts U-238 to P-239 which
can be used a a nuclear fuel.. The breeder may
actually produce more fuel than it consumes.
Most of the U in the reactor is U-238 an is not
fissionable so this increases nuclear fuel
reserves more than 100-fold.
These reactors still have all the problems and
hazards of the old style reactors.

Fusion
This is what happens on the Sun
two H atoms fuse to produce a He atom, releasing
energy.
Source of H would be water.
He is an inert, nonpollution, nonradioactive gas.
At the present state, fusion I still an energy
user rather than a producer due to the high
temperatures required to get H atoms to fuse.
The joke is that fusion is the energy source of
the future and always will be.

In nuclear fusion, you get energy when two atoms
join together to form one. In a fusion reactor,
hydrogen atoms come together to form helium
atoms, neutrons and vast amounts of energy. It's
the same type of reaction that powers hydrogen
bombs and the sun. This would be a cleaner,
safer, more efficient and more abundant source of
power than nuclear fission.
There are several types of fusion reactions. Most
involve the isotopes of hydrogen called deuterium
and tritium

Proton-proton chain - This sequence is the
predominant fusion reaction scheme used by stars
such as the sun.
Two pairs of protons form to make two deuterium
atoms.
Each deuterium atom combines with a proton to
form a helium-3 atom.
Two helium-3 atoms combine to form beryllium-6,
which is unstable.
Beryllium-6 decays into two helium-4 atoms. These
reactions produce high energy particles (protons,
electrons, neutrinos, positrons) and radiation
(light, gamma rays)

Deuterium-deuterium reactions - Two deuterium
atoms combine to form a helium-3 atom and a
neutron.
Deuterium-tritium reactions - One atom of
deuterium and one atom of tritium combine to form
a helium-4 atom and a neutron. Most of the energy
released is in the form of the high-energy
neutron.
Conceptually, harnessing nuclear fusion in a
reactor is a no-brainer. But it has been
extremely difficult for scientists to come up
with a controllable, non-destructive way of doing
it. To understand why, we need to look at the
necessary conditions for nuclear fusion.

Conditions for Nuclear Fusion
When hydrogen atoms fuse, the nuclei must come
together. However, the protons in each nucleus
will tend to repel each other because they have
the same charge (positive). If you've ever tried
to place two magnets together and felt them push
apart from each other, you've experienced this
principle first-hand. To achieve fusion, you need
to create special conditions to overcome this
tendency. Here are the conditions that make
fusion possible
High temperature - The high temperature gives the
hydrogen atoms enough energy to overcome the
electrical repulsion between the protons.
Fusion requires temperatures about 100 million
Kelvin (approximately six times hotter than the
sun's core).
At these temperatures, hydrogen is a plasma, not
a gas. Plasma is a high-energy state of matter in
which all the electrons are stripped from atoms
and move freely about.
The sun achieves these temperatures by its large
mass and the force of gravity compressing this
mass in the core. We must use energy from
microwaves, lasers and ion particles to achieve
these temperatures.

High pressure - Pressure squeezes the hydrogen
atoms together. They must be within 1x10-15
meters of each other to fuse.
The sun uses its mass and the force of gravity to
squeeze hydrogen atoms together in its core.
We must squeeze hydrogen atoms together by using
intense magnetic fields, powerful lasers or ion
beams.
With current technology, we can only achieve the
temperatures and pressures necessary to make
deuterium-tritium fusion possible.
Deuterium-deuterium fusion requires higher
temperatures that may be possible in the future.
Ultimately, deuterium-deuterium fusion will be
better because it is easier to extract deuterium
from seawater than to make tritium from lithium.
Also, deuterium is not radioactive, and
deuterium-deuterium reactions will yield more
energy.

Fusion Reactors Magnetic Confinement
Tokamak
"Tokamak" is a Russian acronym for "toroidal
chamber with axial magnetic field."There are two
ways to achieve the temperatures and pressures
necessary for hydrogen fusion to take place
Magnetic confinement uses magnetic and electric
fields to heat and squeeze the hydrogen plasma.
The ITER project in France is using this method.
Inertial confinement uses laser beams or ion
beams to squeeze and heat the hydrogen plasma.
Scientists are studying this experimental
approach at the National Ignition Facility of
Lawrence Livermore Laboratory in the United
States.
Let's look at magnetic confinement first. Here's
how it would work

Microwaves, electricity and neutral particle
beams from accelerators heat a stream of hydrogen
gas. This heating turns the gas into plasma. This
plasma gets squeezed by super-conducting magnets,
thereby allowing fusion to occur. The most
efficient shape for the magnetically confined
plasma is a donut shape (toroid).

A reactor of this shape is called a tokamak. The
ITER tokamak will be a self-contained reactor
whose parts are in various cassettes. These
cassettes can be easily inserted and removed
without having to tear down the entire reactor
for maintenance. The tokamak will have a plasma
toroid with a 2-meter inner radius and a
6.2-meter outer radius.
Let's take a closer look at the ITER fusion
reactor to see how magnetic confinement works.

Vacuum vessel - holds the plasma and keeps the
reaction chamber in a vacuum
Neutral beam injector (ion cyclotron system) -
injects particle beams from the accelerator into
the plasma to help heat the plasma to critical
temperature
Magnetic field coils (poloidal, toroidal) -
super-conducting magnets that confine, shape and
contain the plasma using magnetic fields
Transformers/Central solenoid - supply
electricity to the magnetic field coils
Cooling equipment (crostat, cryopump) - cool the
magnets
Blanket modules - made of lithium absorb heat
and high-energy neutrons from the fusion reaction
Divertors - exhaust the helium products of the
fusion reaction

The fusion reactor will heat a stream of
deuterium and tritium fuel to form
high-temperature plasma. It will squeeze the
plasma so that fusion can take place.
The power needed to start the fusion reaction
will be about 70 megawatts, but the power yield
from the reaction will be about 500 megawatts.
The fusion reaction will last from 300 to 500
seconds. (Eventually, there will be a sustained
fusion reaction.)
The lithium blankets outside the plasma reaction
chamber will absorb high-energy neutrons from the
fusion reaction to make more tritium fuel. The
blankets will also get heated by the neutrons.
The heat will be transferred by a water-cooling
loop to a heat exchanger to make steam.
The steam will drive electrical turbines to
produce electricity.
The steam will be condensed back into water to
absorb more heat from the reactor in the heat
exchanger.
Initially, the ITER tokamak will test the
feasibility of a sustained fusion reactor and
eventually will become a test fusion power plant.

Fusion Reactors Inertial Confinement
The National Ignition Facility (NIF) at Lawrence
Livermore Laboratory is experimenting with using
laser beams to induce fusion. In the NIF device,
192 laser beams will focus on single point in a
10-meter-diameter target chamber called a
hohlraum. A hohlraum is "a cavity whose walls are
in radiative equilibrium with the radiant energy
within the cavity"

At the focal point inside the target chamber,
there will be a pea-sized pellet of
deuterium-tritium encased in a small, plastic
cylinder. The power from the lasers (1.8 million
joules) will heat the cylinder and generate
X-rays.
The heat and radiation will convert the pellet
into plasma and compress it until fusion occurs.
The fusion reaction will be short-lived, about
one-millionth of a second, but will yield 50 to
100 times more energy than is needed to initiate
the fusion reaction.
A reactor of this type would have multiple
targets that would be ignited in succession to
generate sustained heat production.
Scientists estimate that each target can be made
for as little as 0.25, making the fusion power
plant cost efficient.
Like the magnetic-confinement fusion reactor, the
heat from inertial-confinement fusion will be
passed to a heat exchanger to make steam for
producing electricity.

All information from How Stuff Works.
50

Applications of Fusion
The main application for fusion is in making
electricity. Nuclear fusion can provide a safe,
clean energy source for future generations with
several advantages over current fission reactors
Abundant fuel supply - Deuterium can be readily
extracted from seawater, and excess tritium can
be made in the fusion reactor itself from
lithium, which is readily available in the
Earth's crust. Uranium for fission is rare, and
it must be mined and then enriched for use in
reactors.
Safe - The amounts of fuel used for fusion are
small compared to fission reactors. This is so
that uncontrolled releases of energy do not
occur. Most fusion reactors make less radiation
than the natural background radiation we live
with in our daily lives.
Clean - No combustion occurs in nuclear power
(fission or fusion), so there is no air
pollution.
Less nuclear waste - Fusion reactors will not
produce high-level nuclear wastes like their
fission counterparts, so disposal will be less of
a problem. In addition, the wastes will not be of
weapons-grade nuclear materials as is the case in
fission reactors.
NASA is currently looking into developing
small-scale fusion reactors for powering
deep-space rockets. Fusion propulsion would boast
an unlimited fuel supply (hydrogen), would be
more efficient and would ultimately lead to
faster rockets.

Cold Fusion
In 1989, researchers in the United States and
Great Britain claimed to have made a fusion
reactor at room temperature without confining
high-temperature plasmas. They made an electrode
of palladium, placed it in a thermos of heavy
water (deuterium oxide) and passed an electrical
current through the water. They claimed that the
palladium catalyzed fusion by allowing deuterium
atoms to get close enough for fusion to occur.
However, several scientists in many countries
failed to get the same result. But in April 2005,
cold fusion got a major boost. Scientists at UCLA
initiated fusion using a pyroelectric crystal.
They put the crystal into a small container
filled with hydrogen, warmed the crystal to
produce an electric field and inserted a metal
wire into the container to focus the charge. The
focused electric field powerfully repelled the
positively charged hydrogen nuclei, and in the
rush away from the wire, the nuclei smashed into
each other with enough force to fuse. The
reaction took place at room temperature.