Radiation has been part of our natural environment since the Earth was formed. The planet receives cosmic radiation from outer space, and radioactive materials naturally present in the soil, rocks, air and seawater also emit this type of energy. From the very beginnings of human civilization, radiation has been part of everyday life.

The amount of radiation exposure given off in the normal operation of a nuclear power plant is very small. For example, the exposure from a coast-to-coast airplane trip is approximately 5 millirem, while the exposure living within 1 mile of a nuclear power plant is approximately 0.6 millirem per year.

Some familiar sources of radiation are shown in the following table. Although radiation is invisible, it can be measured. Radiation is measured in units called rems and millirems. The rem is a unit of measure that takes into account the effect different types of radiation have on the body. A millirem is 1/1000th of a rem.

NOTE: International information sources may reference exposure in SI units of Sieverts or millisieverts. For ease of US to SI unit correlation, 1 millisievert = 100 millirem.
Amounts of Radiation from Common Sources Millirems

Average annual radiation exposure from all sources


Natural background radiation


Medical procedures


Consumer products (air travel, smoking, building materials, etc.)


Remainder (including living near a nuclear power station)

Less than 1