All nuclear plants have radiation safety programs intended to minimize worker and public exposure to radiation. Title 10 Code of Federal Regulations Part 20 (10CFR20) is the NRC regulation governing radiation protection at a nuclear power plant. This regulation imposes requirements on such important items as annual allowed radiation exposure, radiation protection methods, radioactive releases, and records.
Radiation can be viewed as the energy given off by a radioactive material when it decays. Contamination can be viewed, like dust or dirt, as radioactive materials being where they do not belong. Radiation Safety training courses and materials are available on the internet. In some cases, there may be a charge; however, there are a lot of quality free materials available.
|Four types of radiation may be found at a nuclear plant - alpha, beta, gamma, and neutrons. Gammas and neutrons are the more highly penetrating as illustrated by the figure to the left. Neutrons are typically only found near the reactor during operation. Alpha is found near new or exposed fuel. Betas and Gammas are found when systems are opened.|
|Courtesy Dr. Eric Hall and Uranium Information Centre|
At the nuclear plant, radiation protection specialists (or health physicists) use meters to determine radiation levels. Radiation levels are normally (in the US) measured in Roentgens/hour (R/hr). The Roentgen is a unit of radiation exposure. The Rem (Roentgen Equivalent Man) is the unit of Dose (actually absorbed taking biological effects into account).The Rad (Roentgen Absorbed Dose) is simply the actual amount of radiation absorbed. The two are related by the relationship:
Rem = Rads x Quality Factor (QF)
where the Quality Factor depends on the type of radiation. Heavy particles as alphas have a QF of 20, neutrons have a QF of 3-10 depending on the energy of the neutrons. Betas and gammas have a QF of 1.
In other countries, the SI unit for dose (Sieverts) is used (1 Rem = .01 Sieverts).
Contamination is measured by taking "swipe" or "smear" surveys. A small piece of absorbent paper is rubbed over a 100 square centimeter area in a S-shaped pattern. The paper is then counted under a radiation detector. The counter expresses the observed radioactivity in terms of disintegrations per minute (dpm). At some plants, a level above 100 dpm/100 square centimeters is considered to be contaminated. At others the level could be 500 dpm/100 square centimeters.
All persons who work at nuclear plants are directed to keep their radiation exposure as low as reasonably achievable (ALARA). Adult workers may receive a whole body dose 5 Rem per year; minors are restricted to 0.5 Rem per year; pregnant women are restricted to 0.5 Rem during the term of the pregnancy (for protection of the embryo). For comparison, actual physical effects (minor blood changes) from radiation exposure are not expected until a person receives 25 Rem in a short period of time. Higher eye and extremity doses are allowed because these have less effect than on that part of the body containing blood-forming organs.
Radiation Protection Areas at a Nuclear Plant
At a nuclear plant, areas containing radioactive materials may be classified according to radiation level, contamination level, and airborne radioactivity level. Unrestricted areas are those where a person could expect to receive less than 500 millirem in a year. Persons working in radiation, contamination, or airborne radioactivity areas must be monitored for radiation exposure. Depending on the type of plant, the following areas are usually controlled with respect to radiation safety:
Other areas at the plant are considered unrestricted unless indicated otherwise.
High radiation areas are those where a person could receive more than 100 millirem in an hour. Additional controls are imposed for these areas.
If one must work in a contaminated area at a plant, special clothing requirements may exist depending on the level of contamination. From least to most contaminated areas, clothing requirements vary from lab coat and rubbers to anti-contamination suits (anti-Cs) to double anti-Cs or plastic covering over normal anti-Cs.
When a worker enters a controlled area, they are expected to wear appropriate clothing and dosimetry depending on the requirements specified on the Radiation Work Permit for the area. When the worker leaves a controlled area, they are expected to monitor themselves for contamination and to turn in their dosimetry that indicates how much radiation dose they may have received. For additional information, go to the NEI search page and type in either "radiation safety" or "radiation protection practices at nuclear plants.".
Key Methods of Reducing Radiation Exposure
Three methods are used - Time, Distance, Shielding. If you reduce the time you are exposed to a radiation source, maximize the distance from the radiation source, and place some object or other form of shielding between you and the radiation source, you can reduce your radiation exposure. Masks are sometimes used reduce the amount of radioactive materials inhaled.
All nuclear plants have special safety and training requirements for working in areas containing radioactive materials or hazards. Examples of some of the radiation safety requirements are provided in the manuals identified in the radiation protection requirements search results.
Effect of Nuclear Plants on the Public
Nuclear plants are licensed on the basis that there will be no undue hazard or significant effect on the public health and safety. According to the NRC regulations, any individual member of the public should not receive more than 100 millirem per year In actuality, the effect on the public is usually less than 1 millirem per year. For comparison, a worker is allowed to receive up to 5000 millirem per year.
Background radiation levels are typically around 300 millirem per year. In some areas of the world, background levels can reach as high as 15,000 millirem.
How Much Radiation Exposure is harmful?
At the present time, reasonable introductory sources are Dr. John McCarthy of Stanford, and Uranium Information Centre's presentation of Dr. Eric Hall's perspective on Radiation and Life.
Copyright © 1996-2006. The Virtual Nuclear Tourist. All rights reserved. Revised: January 3, 2006.