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 potential affected populations as low as is reasonably (or possible) achievable.
The "no safe dose" assumption is still an assumption. Nevertheless, it appears that there is more evidence than not that there is, indeed, a safe dose level.
The philosophy to keep radiation exposures as low as reasonably achievable is an integral component of radiation protection programs in many countries where "hazardous materials" are manipulated. While one of its primary goals is to reduce the dose incurred by an occupational worker, another equally important Alara aim is to minimize radiation/radioactivity releases to the environment.
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, which means that can be passed from adults to their children, in the years sixty (1960) 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 of America, 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.
Emphasis on the Alara philosophy heightened in the 1970's 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.
A possible analogy is the exposure to the sun's radiations. Everyone agrees that prolonged exposure to intense sunlight may increase the risk of contracting skin diseases (e.g., cancer). Scientists can't say whether less intense exposure will also cause long-term skin problems, but they they recommend to use sun screens and to avoid exposure to intense sunlight.
In the same way, the studies around 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." This is no less than the so-called Alara Principle.
The Alara concept includes beside the protection of workers, social, technical, and economic because even considerable amounts of money, some possible techniques to reduce the exposure may not be technically feasible.
On the opposite, some techniques even if technically feasible would be so expensive that they couldn't be justified. Moreover, some techniques wouldn't be acceptable to society.
Therefore, more than one feels that it is prudent to reduce radiation doses below certain limits when it makes sense; consequently, the word "reasonable" into the defintion of Alara, even if what constitutes a "reasonable" approach has to be determined.
The Alara approach is most used where hazardous materials may on one hand lead to critical consequences on the human health, for an individual as well as for the (a) community. By the way, the principle itself can be utilized in an infinite number of situations.
There exist Alara programs which are the effective application of the principle itself; they would normally have to be used from the beginning, from the study-phase up to the exploitation time, let's say also until the removal of any kind of hazard.
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 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.
Implementing the Alara concept involves six basic principles which 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.
Alara Principle n°1 :
eliminating the source of radiation can be accomplished by substituting other appropriate technologies or materials.
"Source reduction" means reduction in the dose rate (the time over which the dose is delivered). Several methods are available, for exampke 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, ... is also an important Alara consideration in source reduction. Removing/reducing the source of contamination will in turn at least reduce the likelihood of worker contamination and dose.
Alara Principle n°2 :
radioactivity may be controlled and/or contained by means of containment of areas, ventilation, and filtration.
Containment involves using leak-tight or controlled-opening enclosures to prevent radioactive materials from migrating to areas where they have to be avoided. Containment may be used temporarily and then removed after the job is complete, or be a permanent component.
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.
Filtration is the capture of airborne particles on a medium, which can then be disposed of in an acceptable manner. Most of filtration systems are solid ones like filters (like in your vacuum cleaner) but of very high efficiency (HEPA type).
To meet the objectives of an Alara approach or program in terms of radiation protection (radioprotection), 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,
- double-walled pipes and tanks,
- leak-tight valves,
Alara Principle n°3 :
the time-exposure is one of the major factor to be taken into account in the application of an Alara program.
It seems clear for everyone that the less time spent in a radiation field, the lower the dose is. 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.
Alara Principle n°4 :
on another hand but with more or less the same importance of significance, the distance plays a role : the further away from a radiation source one stays, the lower the dose he gets. This is especially true for "ponctual sources" of radiation which follow the inverse-square law.
Alara Principle n°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.
Alara Principle n°6 :
optimization is a concept 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 economic terms (=money), time spent by personnel, dose received, etc...- could be justified in terms of the benefit received.
While doing so, reducing radiation exposures can be weighed against competing conflicts (technical considerations, social, operational, and economic).
In general, three of these six principles are held in an Alara program : justification, optimization and (acceptable) limits.
Working in an area containing radiation and/or radioactive materials requires pre-studies, including planification of the works, as good as possible knowledge of the handled materials (physical, chemical AND radiological datas), availability of adapted protection means for the workers, implementation of pre-established Alara controls and tracking of worker doses, and surely not the less important, evaluation of the "lessons learned", the so-called return of experience.