Radiation
FAQ
What is radiation?
It’s an energetic particle
or packet on energy that is released from the nucleus of an atom in order so
that atom can become more stable. There can several forms of this radiation
Alpha particle, beta particles, gamma rays, etc (see
definitions)
Where is radiation?
EVERYWHERE…
We get radiation from just about everywhere you can think of. There is
radiation from outer space, dirt, rocks, water, air, food you eat, consumer
products, and even your own body has radioactive elements in it.
What is radiation therapy?
Radiation can
come from special machines or from radioactive substances. When radiation is
used at high doses (many times those used for x-ray exams); it can be used to
treat cancer and other illnesses. Special equipment is used to aim the
radiation at tumors or areas of the body where there is disease. The radiation
causes more of the cancer cells to die than the normal cells because cancer
cells are more radiosensitive than normal cells. The use of high energy rays or
particles to treat disease is called radiation therapy. Sometimes it's called
radiotherapy, x-ray therapy, cobalt therapy, electron beam therapy, or
irradiation.
How much extra radiation do we receive from
flying?
Radiation
exposure, from natural cosmic sources, increases with altitude, with peak dose
at about 45,000 feet. Dose from cosmic radiation also varies with latitude; it
is lowest near the equator and highest near the poles. Therefore, the extra
radiation dose from flying depends on (a) the particular route, (b) the
duration of the flight, and (c) the fraction of the trip spent below the
flight's maximum altitude. A good reference flight would be from California to
New York and back, is an extra dose of about 0.003 rem (3 milli-rems).
Whole-body dose from all natural radiation combined---which is about 200-350
milli-rems per year of whole-body exposure in the USA.
How much extra radiation dose do I get from a
smoke detector?
Very,
very little.
If you have the much more common "ionization" type, there is a
radionuclide in it -- usually 1 micro-curie of Americium-241. A micro-curie is
one-millionth of one curie. Americium-241 emits alpha particles, which are kept
inside the case. It also emits some gamma radiation which can penetrate the
case. The dose rate at 3 feet away from the smoke detector was well lost within
the background radiation of the area and could not tell if it was there or not.
If you have a photoelectric smoke detector, there is no radioactive substance
in it. Remember the benefit received from the smoke detector, would it be worth
its safety precaution even if there were more radiation coming out of the smoke
detector.
What methods are used to detect radiation?
Because
ionizing radiation does just that, ionizes, it is easy to see that using a
medium like a gas, and a voltage, you can measure the amount of charge
liberated in that medium. That is the most common method of measuring
radiation. The infamous Geiger Counter is in reality a
small volume of gas, with a voltage applied across it. As the radiation enters
the gas, it causes electrons to be formed, which are collected and measured to
determine the amount of initial radiation present. The processes used with
radiation detection is called scintillation. Scintillation is the giving off of
visible light after interaction with radiation. The light can be collected then
and used as another measure of the radiation intensity and energy. But, there
are many different ways of measuring radiation, using semiconductors, liquids,
superheated bubbles, crystals and plastics.
How much electricity do we get from nuclear power?
In the U.S.
we get about 20% of all the electricity from nuclear power. Other countries
vary but can go as high as 75% for France.
How much radiation do I get from nuclear power
plants?
Very
little.
From all sources, a person in the U.S. receives an average exposure to
radiation of about 360 millirems per year. Most of this comes from the natural
radiation in soil, water, rocks, building materials, and food. For example,
potassium is a common, naturally occurring radioactive element found in many
foods. Radiation exposure from all commercial nuclear energy power plants has
averaged 0.01 millirem per person annually. Those who live near a nuclear power
plant receive less than 5 millirems per year. The federal limit for people who
work in nuclear power plants is a maximum of 5,000 millirems per year.
Utilities themselves normally have set their own limits even lower than that.
How Does a Reactor Work?
Neutrons
striking uranium atoms cause these atoms to fission. In the process of fissioning they produce heat in a chain reaction in a
nuclear reactor. This heat is used to turn water into steam and then the steam
turns turbines, which turn generators that produce electricity.
Most
commercial nuclear reactors use water to remove the heat created by the fission
process. We call these light water reactors. The greater the nuclear reaction,
the more heat is produced. The increasing heat turns more water to steam, which
slows down the nuclear reaction. So the water works like a brake. It prevents
the nuclear reaction from running out of control. If the water is cut off, the
fission process stops.
Water flowing
in a closed, pressurized loop removes heat in a pressurized water reactor. The
heat passes to a second water loop through a heat exchanger. The second loop
stays at a lower pressure, allowing the water to boil and create steam. The
steam turns the turbine generator and produces electricity. Afterward, the
steam is condensed into water and returned to the heat exchanger.
In a boiling
water reactor, water boils inside the reactor itself. Steam from the water goes
directly to the turbine generator to produce electricity. Here, too, steam is
condensed and reused.
Can a nuclear power plant explode like a bomb?
No. It's impossible for a nuclear plant to explode like an
atomic bomb because of the low concentration of U-235—fissionable uranium—in
the fuel. There is only about 3-5 percent of U-235—the type of uranium whose
atoms can be split to release large amounts of heat—in commercial nuclear fuel.
In contrast, there is 20-90 percent of U-235 in a nuclear bomb.
Is it safe to live near a nuclear power plant?
Yes. That's
because the companies that run nuclear power plants—and the Nuclear Regulatory
Commission, which regulates the use of radioactive materials—make sure the
plants operate safely.
To protect the
public from a release of radiation, the plant design takes advantage of natural
processes and incorporates backup safety systems—safety in depth. Because plant
designers assume that equipment will fail and that operators will make errors,
nuclear power plants have multiple backup systems to cope with equipment
failure and human error. The systems work automatically and immediately. The
plants also use a series of physical barriers to prevent the escape of
radioactive material.
How many power plants are there in the U.S. and in
the world?
In 1997,
there were 437 nuclear power plants—105 of them in the U.S.—operating around the
world. But since then several plants in the U.S. have closed down and the
number is around 96. No new power plants have been built in the U.S. for many
years (since about 1986), but many plants are being built in other countries.
What are the emissions from a nuclear power plant
vs. a coal plant?
Water Vapor
is emitted from the cooling towers at a power plant. Nuclear energy supplies us
with enough emission-free electricity each year to serve 60 million homes.
Fossil-fueled plants emit carbon dioxide (the primary greenhouse gas), nitrogen
oxide (the source of our ozone problems), and sulfur dioxide (the precursor to
acid rain) and yes even radioactive particulates that were contained in
the coal.
Here are the
annual "savings" to our atmosphere from U.S. nuclear power plants:
147 million
metric tons of carbon
2.5 million
tons of nitrogen oxide
5.3 million
tons of sulfur dioxide
What happened at Three Mile Island?
Short Answer
On March 28,
1979 near Harrisburg, Pa., the worst accident in the history of nuclear power
in the United States occurred at the Three Mile Island unit 2 reactor. The
accident was caused by a combination of equipment failure and an inability of
plant operators to properly assess and understand the condition of the reactor.
Equipment failure caused a gradual loss of cooling water to the reactor's
heat-producing core, which resulted in the partial melting of the fuel rod
cladding and the uranium fuel, and the release of a small amount of radioactive
material. There were no injuries or deaths attributed to the accident. Experts
officially stated that the amount of radiation released into the atmosphere was
too small to impair the health of the population in the vicinity of the plant.
In response to the accident, the Institute of Nuclear Power Operations was
established to promote excellence in operator training, plant management and
operation. Also the industry formed a center to study the accident.
Long Answer
The accident
started at approximately 4:00AM, March 28, 1979 when the main feedwater pump
stops due to a resin buildup. The temperature and pressure of the reactor
increased as a result of the lack of coolant flow. A safety relief valve opened
as the pressure raised and the reactor automatically shut down. The reactor
core began losing pressure as steam escaped through the open safety relief
valve. At this point, the incident should be a mild failure unworthy of news
attention. However, the safety relief valve failed to shut properly, so the
pressure continued to drop and too much cooling water was lost. This excessive
loss of coolant caused the temperature of the reactor core to increase above
its normal operating temperatures.
The reactor
operators improperly assessed the problem at this point-- they incorrectly
assumed that the safety valve had closed. The lost coolant was not replaced and
the water eventually turned into steam as the pressure continued to drop. The
operators still erroneously thought that the reactor was overpressurized
so they shut down the emergency and standby feedwater pumps.
The pressure
continued to drop which caused large steam bubbles to form and impede the
effectiveness of the remaining coolant. The temperatures in the reactor core
eventually rose above the melting point of the uranium fuel and fuel cladding.
All the fuel was damaged or destroyed and approximately 700,000 gallons of
radioactive cooling water were spilled onto the floor of the reactor building.
To control the excessive quantity of water that spilled out of the reactor,
400,000 gallons of radioactive water were released into the Susquehanna River.
In addition, some of the radioactive gasses that flowed through the open valve
were emitted into the atmosphere and some radioactive materials managed to pass
through the four-foot thick walls of the plant. The estimates of the actual
levels of radiation leaked vary, but the state insists that they were too low
to adversely affect the health of people that lived in the vicinity of the
reactor. To ensure the safety of the people most susceptible to radiation, on
March 30, 1979 the governor did recommend the evacuation of all pregnant women
and preschool aged children. Schools were closed in the area and the governor
ordered people to stay indoors. The decision to evacuate was controversial as
many experts insisted that there was no threat to the public health and such
evacuation orders would cause public panic.
What happened at Chernobyl?
As is usually
the case in any accident, a number of things combined
to cause this one at Chernobyl. Unlike power reactors operating in the U.S. and
other nations, the Chernobyl RBMK reactor (which is a graphite rather than a
light water system) has a built-in instability that occurs at low power, which
is how the reactor was operating at the time of the accident. If some of the
cooling water in this reactor converts to steam, the RBMK increases in power.
This in turn causes more steam to form, which causes another increase in power.
The power increase feature of the RBMK caused a rupture in the cooling system
and a large steam explosion occurred. This caused the cooling system to fail
and the outer covering (or cladding) of the fuel elements to increase in
temperature. The cladding was hot enough to react with the steam, causing
hydrogen to form. The hydrogen then caused a second explosion. The release of
this energy set the graphite core on fire.
A second
factor in the Chernobyl accident involved a safety experiment being conducted.
It required that the reactor be run in a very unusual manner. Because of a
series of operational problems, the operators found themselves running the
reactor far outside its safety limits. In their efforts to finish the
experiment anyway, the operators --in spite of running the reactor under
unfamiliar conditions-- turned off seven of the safety systems in the reactor
and its control systems. Any one of these seven automatic controls could have
prevented the accident had it been on.
How are U.S. reactors different from the reactor
at Chernobyl?
There are
many differences, which include not only physical differences but philosophical
ones as well. The key differences have already been noted in the previous
answer. These physical differences were made worse by the totally different
attitude toward safety between the two countries. The U.S. is cautious to the
extreme by comparison. It took seven years to restart Three Mile Island Unit 1
following the accident in the Three Mile Island Unit 2 reactor in 1979, the
results of, which were much less severe than in the Soviet Union. The Soviets
restarted their other reactors (of the identical design) at Chernobyl in a
matter of a few weeks.
How much nuclear waste is there?
Since the
first commercial nuclear power plant began producing electricity in 1957, the
total amount of accumulated spent fuel (classified as high-level waste) is 9000
tons. For comparison, the Environmental Protection Agency reported that in
1982, 46 million tons of poisonous waste (that is, not nuclear) were disposed
of. In comparison the amount of nuclear waste is very small.
Nuclear wastes
are, for the same power output, some 3.5 million times smaller in volume than
the wastes from coal plants. High-level nuclear wastes can be disposed of by
diluting them with twice their own volume of neutral materials as they are
changed into glass or ceramic form. The reprocessed waste volume form a
1,000-megawatt nuclear power plant would fit easily under a typical dining room
table. A coal plant of the same capacity (1,000 megawatts) produces some 10
tons of waste per minute
After
changing it to stable form, the volume of all nuclear waste produced until the
year 2000 (including low-level waste from the entire U.S nuclear power
industry) would fit into a cube 250 feet on each side. The high-level waste
portion would fit into a cube 50 feet on each side within the 250-foot block.
What is food irradiation?
This is the
use of high levels of radiation exposure to kill all of
the bacteria, fungus, and insect larva and eggs that cause food to get eaten or
spoil and go bad. This would prevent the food poisonings that come from
improperly handled or processed meat, seafood or chicken. Tens of thousands of
people get sick each year and several hundred die due to food poisoning. This
would also prevent the losses of food being transported to a far designation.
Without the bacteria to make the food go bad the shelf life of truck life of
foods, especially fruits and vegetables are greatly increased.
Does irradiation adversely affect the nutritional
value of food?
Extensive
research has shown that macronutrients, such as protein, carbohydrates, and
fat, are relatively stable to radiation doses of up to 10 kilogray.
Micronutrients, especially vitamins, may be sensitive to any food processing
method, including irradiation. Different types of vitamins have varied sensitivity
to irradiation and to some other food processing methods. For example, vitamins
C and B-l (thiamine) are sensitive to irradiation as well as to heat
processing. The Joint Expert Committee of the Food and Agriculture Organization
(FAO), World Health Organization (WHO), and International Atomic Energy Agency
(IAEA), which examined these and other issues, stated in its conclusions in
1980 that irradiation does not induce special nutritional problems in food.
The change in
nutritional value caused by irradiation depends on a number of factors. They
include the radiation dose to which the food has been exposed, the type of
food, packaging, and processing conditions, such as temperature during
irradiation and storage time. Most of these factors are also true for other
food preservation technologies. For example, measurement of vitamin C content
in three varieties of apples kept in cold storage for up to 1 year showed
decreases of between 40% to 70%, depending on the variety of apple. Yet it has
never been suggested that cold storage is an inappropriate technology for
apples and should not be used.
Just as
vitamins vary in their sensitivity to heat, so do they vary in their
sensitivity to radiation. This sensitivity depends upon the conditions under
which food is irradiated. Vitamins A,E,C,K and B-1
(thiamine) in foods are relatively sensitive to radiation, while some other B
vitamins such as riboflavin, niacin, and vitamin D are much more stable. Losses
are generally less if oxygen is excluded and if the temperature during
irradiation is low. Under optimal conditions, vitamin losses in foods
irradiated at doses up to 1 kilogray are considered
to be insignificant. At higher doses the effect of irradiation will depend on
the specific vitamin, temperature, dose, food, and packaging. All of the food that the astronauts eat have been
irradiated.
Does it make the food radioactive?
NO! The food
that is irradiated does not become radioactive. Its just
like using your microwave oven the food does not become radioactive.
What are some other uses for radioactive material
other than nuclear power?
LOTS
!!!
Well there is
food irradiation (see earlier question). There is sterilization of medical and
dental equipment, radiation is used to sterilize baby powder, bandages, contact
lens solution and many cosmetics, including false eyelashes and mascara.
Industry uses it to measure density and level of materials in pipes and tanks
as well as a thickness indicator.
They also use
radiation to check the integrity of welds on bridges and other large
structures. It is used to treat cancer (see earlier question). Not to mention
all the medical applications; x-rays, cat scans, Pet scans, flouroscopies.
About 50-66% of all people who enter a hospital has some sort of procedure that
involves radiation. Smoke detectors (see earlier question) save thousands of
lives each year. It is used to identify metals, enhance rubber tires, make
frying pans ect.