adapted to HTML from lecture notes of Prof. Stephen A. Nelson Tulane
Ionizing Radiation is radiation that ionizes (or removes electrons from)
material that it passes through.
Examples of Ionizing Radiation include:
Neutrons - Have high enough energy to be able to knock electrons off
of nearby atoms.
Alpha particles - Helium atoms with no electrons.
Beta Particles - Electrons
Gamma rays - Very high energy radiation.
X-Rays - Another high-energy radiation, the main source of which is
Cosmic rays - Photons and alpha particles. The earth is being
constantly bombarded with this type of radiation; the average person
is hit by around a hundred cosmic rays a second
Radioactivity is natural; we have been bombarded by ionizing radiation
from Uranium (U), Potassium (K), and Thorium(Th) as well as by cosmic rays
all our lives.
Billions of years ago when life first started there was much more natural
radiation than at present. Life has evolved with natural ionizing
radiation. Some maintain that without the natural radiation which causes
genetic mutations, evolution would not be possible.
Average Relative Radiation Exposure of Humans
Relative Exposure (%)
Misc. nuclear plants, waste
1,000 to 2,000
Vomiting, fatigue, increased rate of abortion
within first 2 months, temporary sterility in males
Maximum allowed for nuclear employees per year
Dosages are based on relative effects of different types of ionizing
radiation on living tissue.
Effect on life more damaging to tissues that regenerate rapidly such
as bone marrow, spleen, lymph nodes, skin, embryos, etc.
Extremely high dose
burns and damage to brains, die within 48 hours
Diarrhea, bleeding and hair loss
Increased susceptibility to infection
Lowest (Natural) Dose
Genetic mutation (some argue that this is necessary for
There is no question that radiation is extremely dangerous at high
levels but we are not sure of its effect at lower levels.
Studies on the subject do not always agree; some studies suggest
that slightly increased dosages actually result in a decrease in the
chance of cancer. (Example: Nuclear power plant employees).
Examples of Radiation Risk
Normal background is 1 - 2.5 mSv.
Japanese atomic bomb survivors have lower incidence of cancer then
In the western U.S., people receive 1 mSv per year more radiation
(due to elevation), but they have a 15% lower cancer rate than do
people in the eastern U.S.
In China two groups of 70,000 people with a dosage difference of 2
mSv were studied. The group with higher doses of radiation had 1/2 of
In the U.S. 28,000 nuclear workers were compared to 33,000
non-nuclear workers. The nuclear workers had a lower cancer rate and a
total mortality rate that was 24% less then the non-nuclear workers.
Nuclear Energy Fission
A nuclear reaction derives energy from:
Fission of uranium or plutonium
Fusion of hydrogen to make helium.
Uranium has two isotopes:
U-238 - about 99% of natural occurring uranium is in this state.
U-235 - only 1% or naturally occuring uranium.
In a reactor U-235 or Pu-239 undergoes fission.
For this reaction to occur, U-235 or Pu-239 need only be enriched
slightly. U-235 with a half life of about 700 million years is found
in nature. Pu-239 with a half-life of 24,000 years is made in a
reactor. ( U-238 -> P-239)
A breeder reactor is designed to increase the amount of Uranium-238
that is transformed to Plutonium-239.
The Pu-239 produced can be used for fuel in a nuclear reactor or in
an atomic bomb. It is relatively easy to separate Pu-239 from the
How does a reactor work?
We first start off with fuel rods which are made up of U-235
pellets which have been enriched to about 3% (from original 1%).
These rods are interdispersed vertically into a water bath (in
U.S. reactors) with control rods which contain neutron absorbing
The control rods are raised to allow the fuel rods to react with
each other. The water bath itself helps control the rate of
Once the reaction starts the rods are lowered until the proper
rate of reaction is achieved.
Another enclosed water system constantly brings new cool water
into the system and takes the heated water out to a heat exchanger
This unit takes this heated water and pushes it towards a turbine.
A cold water system is run around this heated water causing a huge
heat differential which allows the turbine to move creating
This entire system is enclosed in a containment building for further
protection in case of a accident.
Comparison of coal and nuclear power plants:
As can be seen, the two types of plants are basically the same...the only
real difference is in the method of heat generation. In Australia there is
one nuclear facility which produces medical isotopes. In the U.S., as of
1988 there were 110 operable nuclear power plants, 1 in construction and
10 for which construction permits had been granted. None of the new plants
were completed and put into energy production.
Nuclear power plants are only good for about 30 years... after that
time, they need to be torn down and disposed of.
A fuel assembly needs to be replaced every 2.5 years or so to
At this time the fuel assembly produces 10,000 watts of energy.
After 100 years it produces 100 watts of energy.
Spent fuel rods are placed in cooling pools for a few years, and
then sealed and stored in yards near the reactors.
Environmental impacts and concerns of Fission:
Weapons proliferation from breeder reactors
Fusion of Hydrogen to make
In this reaction a tritium nucleus (hydrogen 3) is combined with a
deuterium nucleus (hydrogen 2) (fused) to create a helium 4 nucleus. This
reaction releases energy and neutrons.
Environmental Effects of Various Energy Sources - Comparison
Environmental Effects of Various Energy Sources
Acid Mine Drainage
Disposal of Nuclear Waste
Some Radioactive Gasses (Contained)
Nitrogen Oxides & Acid Rain
Environmental Effects of Various Energy Sources Coal Oil Natural Gas
Uranium Disturbed Land
Acid Mine Drainage
Brine Pipeline Construction Disposal of Nuclear Waste Pipeline
Construction Oil Spills Carbon Dioxide Some Radioactive Gasses (Contained)
Nitrogen Oxides & Acid Rain Carbon Dioxide Radioactive Gasses
Accidental Deaths per Billion Watt Power Plant
Processing and Transport
April 26, 1986 - the worst nuclear accident in the history of nuclear
power generation occurred here. Operators of the plant were testing the
emergency core cooling system. Power in the system rose rapidly. A steam
explosion occurred followed by a hydrogen explosion. The graphite
moderator began to burn. The outside containment structure, although
substantial, was not adequate enough to hold the accident. Some 30 workers
who were trying to prevent further probems received lethal dosages
of radiation. The local people as well as the world were not informed of
the accident until several days later. The wind was blowing toward the
northwest. Sweden was alerted to the problem when it found unusually high
radiation counts in its atmosphere. Eventually some 400,000 people were
evacuated from the area.
I131 has a half-life of 8 days. Many people recieved substantial doses
of I131 as word about the accident was not released for several days.
Thyroid cancer in children that were living in this area has increased
dramatically. Iodine is concentrated in the thyroid gland in humans.
Other cancers have not yet shown an increase, but it can sometimes take up
to 20 or 30 years for an increase in certain cancer rates to show up.
The psychological stresses related to this accident seem to be having the
worst health effects on the people.
Radioactive Waste Repositories
(examples from U.S.A.)
There is a need for repositories for two types of waste:
Each state is supposed to have a repository where the material will
be isolated for 500 years.
High Level Waste
Spent fuel rods
Plutonium, Uranium, Thorium
Nuclear weapons waste, liquid and solid.
High Level Waste Repositories
By the year 2,000 there will be 178,000 canisters ready for
waste to be in stable form (not liquid)
Spent fuel rods
Should result in only 1,000 deaths in 10,000 years.
Waste package should stay stable for 1,000 years.
Isolated from groundwater as long as possible.
Waste package designed to provide least possible exchange with
groundwater after contact.
Waste will not reach biosphere for at least 1,000 years.
What will a high level nuclear waste repository look like?
The site will probably be the size of a typical underground mine.
It will have tunnels leading to vertical containment areas.
Spent fuel rods will be placed into these containment shafts.
These shafts will probably be kept open for the first few years to
allow heat to escape, after which they will be sealed off with
The government considered three possible sites for such a repository:
Basalt in Hanford, Washington
Salt basin in New Mexico
Welded volcanic tuff in Yucca mountain, Nevada
Congress has decried that only Yucca Mountain should be considered for
non-defense waste. Yucca mountain has some advantages choice for this
Arid climate - there is no ground saturation by rain.
Rocks are made up of welded volcanic tuff, which is nearly
The water table is 500 meters below the site.
The welded tuff contains zeolite and zeolite should be able to trap
radioactive ions released from the site, and keep them out of the
A problem with Yucca Mountain is that the site area is in an area of
active faults (earthquakes). If an earthquake occurred on a fault crossing
the repository it could pump water into the repository and hasten
migration of the high level waste.
Agencies involved in high level waste site selection: