What does the word “ALARA” stand for?
“ALARA” is an acronym for “As Low As Reasonably Achievable”.
How is ALARA used in the practice of radiation protection?
ALARA is a basic radiation protection concept or philosophy. It is an application of the “Linear No Threshold Hypothesis,” which assumes that there is no “safe” dose of radiation. Under this assumption, the probability for harmful biological effects increases with increased radiation dose, no matter how small. Therefore, it is important to keep radiation doses to affected populations (for example, radiation workers, minors, visitors, students, members of the general public, etc.) as low as is reasonably achievable.
Is the “no safe dose” assumption valid?
This assumption is currently being hotly debated in the scientific community. Although the “jury is still out” on this issue, it appears that there is more evidence than not that there is, indeed, a safe dose level. It is conceivable that if our knowledge of radiation effects expands to the point that a “safe” dose is defined, the ALARA philosophy, as we know it today, would be eliminated.
Why should I be interested in the ALARA philosophy?
Even if you are not a radiation worker or have ever visited a nuclear facility, you should be aware that the philosophy to keep radiation exposures as low as reasonably achievable is an integral component of radiation protection programs throughout this country and the world. While one of its primary aims is to reduce the dose incurred by an occupational worker, another equally important ALARA goal is to minimize radiation/radioactivity releases to the environment – your environment! When ALARA goals are realized at the nuclear facility in your “neighborhood”, everyone benefits.
How did this philosophy develop and become a required component of radiation safety or health physics programs?
Reducing radiation exposures to levels that are “as low as reasonably achievable” has long been a goal of radiation safety programs. The concern over possible genetic effects (effects that can be passed from adults to their children) in the 1960s led the Atomic Energy Commission (AEC), the predecessor to the Nuclear Regulatory Commission (NRC) and the Department of Energy (DOE), – two federal regulatory authorities in the United States – to require that human exposures be kept “as low as practicable” (the “ALAP” philosophy). Although ALARA was recognized during this time frame, emphasis was placed on controlling exposures in the workplace within the dose limits, rather than lowering the exposures to levels below the limits.
Then what happened?
Emphasis on the ALARA philosophy heightened in the 1970s when scientists studying Japanese survivors of the atomic bomb blasts noticed an increased incidence of solid tumors (i.e., tumors other than leukemia). Similar increases were also observed in patients undergoing medical treatments. These increases were associated with very large radiation doses. Unfortunately, the scientists were not able to say whether the same results occur at small doses.
Can you explain further?
An analogy that might help to explain this problem deals with exposure to the Sun. We all know that prolonged exposure to intense sunlight will cause not only sunburns but also increase the likelihood of contracting skin diseases (e.g., cancer) in the future. Scientists can’t say whether less intense exposure will also cause long-term skin problems. Therefore, they recommend using sun screen and avoiding exposure to intense sunlight, even for brief periods.
In a similar manner, the observations of increased cancer led the International Commission on Radiological Protection (ICRP), a body of recognized radiation experts which offer recommendations to regulatory agencies around the world, to state that, “As any exposure may involve some degree of risk, the Commission recommends that all unnecessary exposures be avoided, and that all justifiable exposures be kept as low as is reasonably achievable, economic, and social considerations being taken into account.” Because of this and other findings, both the DOE and NRC, for a number of years, have required an ALARA program at nuclear facilities.
Why does the ALARA concept include social, technical, and economic considerations?
If we had an infinite amount of money, we could think of all sorts of techniques to reduce radiation dose. Some of these techniques may not be technically feasible (e.g., snuffing out the Sun, since it releases so much radiation). Some techniques would be so expensive that, even though they might be technically feasible, they couldn’t be justified (e.g., requiring that every home be equipped with a radon interception system without considering whether radon was a problem or not). Some techniques simply wouldn’t be acceptable to society (e.g., forbidding homes to be built in Denver since its background is higher than areas with lower elevations).
Most scientists and all standard-setting bodies feel that the radiation limits currently in force are safe. They feel that it is prudent, however, to reduce radiation doses below these limits when it makes sense. This concept is captured in the ALARA philosophy by incorporating the word “reasonable” into its definition. Of course, we must determine what constitutes a “reasonable” approach. Certainly, this could well be subject to widely different interpretations!
What kind of interpretations?
For example, suppose your entire community supported the construction of a lead-lined dome over your homes to reduce the natural background dose received from cosmic radiation each and every day. While this is certainly possible from a technical standpoint (i.e., such a dome could conceivably be built), and from a social perspective (since it has been found to be acceptable to the community), is it nonetheless “reasonable” to build it if the cost for such a dome is several billion dollars? Probably not, in this instance, since it would afford very little reduction in the natural background radiation dose . . . certainly nothing observable. Therefore, several factors are, by design, involved in the implementation of ALARA and must be examined on a case-by-case basis.
Is the ALARA concept affiliated with a particular dose limit?
No. ALARA is not a dose limit, but rather a goal. It exemplifies a mind set to achieve radiation exposures which are as far below the applicable limits as is reasonably achievable.
Where are ALARA principles utilized?
ALARA principles can be utilized in an infinite number of situations. For example, the proper design of a nuclear facility depends on ALARA considerations (e.g., can the addition of more shielding to an area be justified in terms of the lower doses it will achieve?). In addition, designing an x-ray facility for medical applications requires consideration of the amount of shielding needed to ensure that individuals located near the facility (e.g., on the other side of the wall from the x-ray unit) do not receive any more dose than is really necessary during operation of the x-ray device.
Why is emphasis regarding ALARA implementation placed first on physical design features at a nuclear facility rather than on procedures, administration, or personal practices?
The design of a nuclear facility is very important in the eventual success of an effective ALARA program. If designed satisfactorily, worker doses and releases of radioactivity to the environment can not only be controlled but reduced. An improperly designed facility, on the other hand, may require subsequent modifications, often at considerable expense to reach the desired dose rates and with a corresponding impact on existing operations. While procedures, etc. are important as well, they represent a secondary, rather than primary, layer of support.
What are the essential components in an ALARA program?
Generally speaking, a successful ALARA program requires an appreciation, understanding, and acceptance from each individual involved in work with radioactivity and radiation-producing machines. More specifically, an ALARA program must have some (preferably all) of the following: a strong commitment from facility management at all levels and throughout the entire organization, dedicated staff, an ALARA program manual or approved program procedures, education and training programs, a well-defined ALARA organization with established responsibilities, a Radiological Safety Committee which reports to upper management on ALARA issues, and routine internal and external audits of the effectiveness of the dose reduction program.
Are there fundamental principles which can be used to reduce radiation doses and the release and spread of radioactive materials?
Yes! Implementing the ALARA concept involves six basic principles. These are: eliminating or reducing the source of radiation; containing the source; minimizing the time spent in a radiation field; maximizing the distance from a radiation source; using radiation shielding; and optimization analyses.
How can the source of radiation be eliminated? (ALARA Principle #1)
Eliminating the source of radiation can be accomplished by substituting other appropriate technologies or materials. For example, using an ultrasound exam (sonogram) in prenatal examinations, rather than an x-ray exam, is a much preferred practice due to the type of radiation received by the fetus.
What do we mean by “source reduction”? (Continuation of ALARA Principle #1)
Source reduction is a reduction in the dose rate (the time over which the dose is delivered). Several methods are available. These include installing filtration and processing equipment to capture radioactive sources before they can reach populated areas, removal of non-essential radioactive materials or equipment from the vicinity of personnel, selection of appropriate materials to minimize radioactivity depositing on surfaces, draining/flushing fluid systems to remove radioactive liquids, and ventilation of airborne radioactive areas.
The control of contamination on building surfaces, equipment, etc. is an important ALARA consideration in source reduction. Removing/reducing the source of contamination will in turn eliminate (or at least reduce) the likelihood of worker contamination and dose.
Is there an example showing an ALARA consideration in equipment decontamination?
Yes. In this case, the method chosen to reduce the dose (internal and external) to the worker during the decontamination must be given some thought, while at the same time, reducing the volume of radwaste produced and the cost of the decontamination. In many radiological situations, not every method selected is appropriate for a particular radionuclide or surface.
Can I accomplish source reduction in any other way?
Yes. If practical, allow the radionuclide source(s) to decay for several half-lives. This is a passive (rather than active) approach relying on the nuclide’s radioactive properties. It is feasible in those situations where the half-life is short enough (e.g., minutes, days) to produce acceptable results in a short period of time.
By what means can radioactivity be controlled and contained? (ALARA Principle #2)
This ALARA principle can be considered a subset of the first principle and involves containment, ventilation, and filtration.
What is containment?
Containment involves using leak-tight or controlled-opening enclosures to prevent radioactive materials from migrating to areas where we don’t want them. Containment may be used temporarily and then removed after the job is complete, or be a permanent component (as, for example, from a structural standpoint).
What is the principle behind ventilation?
Ventilation is the flow of air and other gases in a certain direction and rate such that radioactive airborne particles and gases are captured and directed to collection filters, followed by release to the atmosphere once appropriate release limits have been met. A well-designed ventilation system will go a long way in limiting the potential for intakes of radioactive material. For example, designing the flow of air containing radioactive materials so that it moves away from people will help to ensure that they don’t receive unnecessary exposure.
What is filtration?
Filtration (“filtering”) is the capture of airborne particles on a medium (like a vacuum cleaner bag), which can then be disposed of in an acceptable manner.
What protective designs are used in containment and confinement?
To meet ALARA objectives in a radiation protection program, it may be necessary to use some or all of the following items: ventilated fume hoods, gloveboxes (used to handle radioactive materials), exhaust systems, water filtration and processing systems, ventilation cleanup systems, and double-walled pipes and tanks, leak-tight valves, etc.
What is the importance of time and its relationship to ALARA? (ALARA Principle #3)
Simply put, the less time spent in a radiation field, the lower the dose. To meet ALARA goals, no more time should be spent in a radiation field than is necessary to perform the required tasks. There are several design factors which can be utilized in a nuclear facility to promote this principle. For example, personnel who have to work in the vicinity of radioactive sources often conduct rehearsals in low dose areas to ensure that they keep their time in the area to a minimum, that they have all the tools they need, etc. (The concept of exposure time is discussed in further detail in the webpage chapter entitled “External Exposure Control”.)
How is distance incorporated into ALARA planning? (ALARA Principle #4)
In the case of distance, the further away from a radiation source you are, the lower the dose. This is especially true for “point” sources of radiation which follow the inverse-square law. As with time, several design factors are available to aid in maximizing the distance from radioactive sources. (The concept of distance is also discussed in further detail in the chapter on “External Exposure Control”.)
Explain the concept of shielding (ALARA Principle #5)
Shielding involves the use of different materials placed between the worker and the source to absorb the radiation. The choice of shielding depends on the type of radiation and may either be temporary or permanent. As with time and distance, several design factors are available to reduce worker dose. (Once again, be sure to review the webpage chapter on “External Exposure Control” for more information about shielding.)
What do we mean by “Optimization”? (ALARA Principle #6)
Optimization sounds impressive and maybe a little intimidating when you first hear it, but the concept (not necessarily the application!) is pretty straightforward. In an ALARA design, cost-benefit analyses are performed to balance economic considerations with the expected benefits. Optimization is used to demonstrate that any expenses involved – in terms of money, time spent by personnel, dose received, etc. – is justified in terms of the benefit received. In so doing, reducing radiation exposures can be weighed against competing conflicts (technical considerations, social, operational, and economic).
In general, what three phases in the ALARA process are examined in performing work activities in a radiological area?
Working in an area containing radiation and/or radioactive materials requires pre-job planning (the extent of which depends on the complexity of the job), implementation of pre-established ALARA controls and tracking of worker doses, and a post-job review to evaluate the “lessons learned”. These steps allow the application of ALARA principles before the job is started, ensure that the principles are being applied correctly, and assist in improving performance on future jobs.
Where can I obtain more information about the ALARA concept?
There are a number of excellent references that discuss ALARA, its basis and its implementation in great detail. Quite a few of them are listed in the “Bibliography” that is located in this web page’s “Tool Box”. If you don’t find the information you need there, please don’t hesitate to “Ask a CHP”.