is not a modern creation. Most radiation comes from natural
sources - the air, rocks, earth, sun, building materials and
even the food we eat.
term radiation is very broad and includes such things as light
and radio waves. But it is most often used to mean ionizing
radiation, which is radiation that can produce charged particles
(ions) in the materials it strikes.
sources of ionizing radiation include cosmic rays from the
sun and outer space, and radioactive elements that occur naturally
in the soil, rocks and building materials, such as concrete.
Nuclear radiation is particles or rays given off by unstable
atoms. Radiation is produced inside a nuclear reactor when
the uranium atoms split or "fission". This also
produces heat which is used to generate electricity.
three basic types of ionizing radiation produced by radioactive
atoms are alpha particles, beta particles, and gamma rays.
Alpha particles and beta particles have low penetrating power.
Alpha particles can be blocked by a piece of paper. Beta particles
can be blocked by a thick piece of cardboard or by a piece
of aluminum foil. Gamma rays are electromagnetic energy, similar
to visible light and X-rays, but they have a higher penetrating
power. Heavy shielding of lead or concrete, such as a nuclear
power plant's containment structure, will stop gamma rays.
unit most commonly used to measure human exposure to radiation
is the rem. Because most normal exposures involve only a fraction
of a rem, the most commonly used unit is the millirem, one
thousandth of a rem.
amount of natural radiation to which people are exposed depends
upon where they live and the concentration of radioactive
materials in the ground. The table on this page gives you
an idea of sources of radiation that people are exposed to.
The effects of human exposure to radiation depend upon how
much is received, the length of exposure and the person's
general health and age. The risk from radiation exposure can
be reduced by shortening the time of exposure, getting farther
away from the source, and shielding or blocking the source.
It is known that whole-body radiation doses of more than 10,000
millirem over a short period of time can cause a slight increase
in a person's risk of developing some types of cancer years
after exposure. The risk that radiation-induced cancer will
develop during the person's lifetime is estimated by the National
Academy of Sciences to be about 1/20 of one percent for every
1,000 millirem of short-term exposure greater than 10,000
millirem. In other words, if you were to receive a short term
exposure of 11,000 millirem (11 rem), your estimated risk
of developing some type of cancer would increase by 0.05 percent.
the federal government and the State of California have established
radiation dose limits for the public from a nuclear power
plant at 100 millirem/year. For doses expected to be greater
than 1,000 millirem, protective actions such as evacuations
or sheltering would be required.
The purpose of these actions would be to keep people away
from the radioactive materials that might be released during
a severe accident.
Canyon's design makes a large release of radioactive materials
extremely unlikely. The safety systems at the plant are designed
to control and contain the release of radioactive materials
under accident conditions. The federal and state limits on
radiation exposure established for the public, guide the emergency
planning for public protective actions. The emergency plans
for the Diablo Canyon Power Plant are designed to minimize
the exposure to the public by using the protective actions
of sheltering and evacuation.
Annual Radiation in millirem/year
Living in a House Made of:
Trip Cross-Country Air Flight
at the Diablo Canyon Boundary for One Year