This section presents the principles of radiation safety and how they are applied in the protection of the health and safety of human beings.
6.1. INTERNATIONAL ARRANGEMENTS
Approaches to protection against ionizing radiation are remarkably consistent throughout the world. This is due largely to the existence of a well established and internationally recognized framework.
The International Commission on Radiological Protection (ICRP) is a non-governmental scientific organization founded in 1928, which has regularly published recommendations for protection against ionizing radiation. Its authority derives from the scientific standing of its members and the merit of its recommendations. It bases its estimates of the probability of fatal cancer mainly on studies of populations that have been exposed to relatively high levels of radiation, particularly the survivors of the atomic bombs that were dropped on Japan in 1945, and on the work of UNSCEAR.
The IAEA has a statutory function to establish safety standards where appropriate in collaboration with other relevant international organizations. In doing this, it relies heavily on the work of UNSCEAR and the ICRP. It also has a responsibility for providing for the application of those standards at the request of a State and it does this through various mechanisms, including the provision of services and training.
The most relevant safety standards are:
— International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (BSS)[31], sponsored by the IAEA and five other international organizations;
— Preparedness and Response for a Nuclear or Radiological Emergency [39], sponsored by the IAEA and six other international organizations;
— Legal and Governmental Infrastructure for Nuclear, Radiation, Radioactive Waste and Transport Safety [32].
The first two specify technical, scientific and administrative requirements for the safe use of radiation. The third specifies the basic infrastructure require-ments in order to implement the requirerequire-ments given in the other two.
6.2. GENERAL PRINCIPLES
For all human actions or practices that add to the radiation exposure that individuals receive from natural sources, the ICRP recommends a system of protection based on three central requirements:
(1) Justification of a practice. No practice involving exposure to radiation should be adopted unless it produces at least sufficient benefit to the exposed individuals or to society to offset the radiation detriment that it causes.
(2) Optimization of protection. In relation to any particular source of radiation within a practice, the dose to any individual from that source should be below an appropriate dose constraint, and all reasonable steps should be taken to adjust the protection so that exposures are ‘as reasonably achievable’, economic and social factors being taken into account.
(3) Application of individual dose limits. A limit should be applied to the dose received by any individual as the result of all the practices (other than medical diagnosis or treatment) to which the individual is exposed.
In some cases, such as after an event that causes a release of radioactive material to the environment, it may be necessary to intervene to reduce the exposure of people. Under such circumstances, the ICRP recommends a system of radiological protection for intervention based on two principles — justification for the intervention taking account of the reduction in dose and costs of achieving that reduction, and optimization of the level of protection.
They differ from the set for practices in that they omit limits for individuals, because limits might require measures to be taken that would be out of all proportion to the likely benefit of the reduction in dose.
6.3. LIMITATION OF DOSES
The third requirement for practices — application of individual dose limits — is an obligation not to expose individuals and their descendants to an unacceptable degree of risk. The ICRP [40] has proposed dose limits for those who are occupationally exposed to radiation and for the general population and these are given in the BSS:
— For workers, 20 mSv in a year (averaged over five years), with no more than 50 mSv in any one year;
— For members of the public, 1 mSv in a year.
There are also separate limits for exposure of the skin, extremities and the lens of the eye.
There are two common misconceptions about dose limits. The first is that they mark a line between absolute safety and what is unsafe. This is not in fact the case. All radiation exposure is prudently assumed to have the potential to cause harm so these limits reflect a judgement regarding the level of risk that is considered acceptable. The second is that all that is necessary in protection is to keep doses below the limits. Again, this is not so. The overriding requirement is optimization of protection.
6.4. PROTECTION AGAINST EXTERNAL EXPOSURE
The first way in which external exposure to radiation can be reduced is to increase the distance from the source of the radiation. The dose rate for gamma and X ray radiation generally varies with the inverse square of the distance from a ‘point’ source. For example, doubling the distance from a radiation source will reduce the dose rate by a quarter. Remote handling devices, such as forceps or tongs, should therefore be used to minimize direct contact with radioactive sources and their containers.
The second method to reduce the dose is to minimize the time of exposure.
The third method is to shield the radiation source. The most suitable shielding material varies according to the type of radiation, as follows:
— Beta radiation: Plastic material of a few centimetres in thickness.
Handlers of beta emitting radionuclides should always wear protective goggles to shield their eyes.
— Gamma and X radiation: Lead of between 1 and 10 cm thickness, or 30–60 cm of concrete, depending on the gamma energy.
— Neutron radiation: Hydrogen based material of between 10 and 50 cm thickness, such as water, paraffin or plastic, depending on the neutron energy.
6.5. PROTECTION AGAINST INTERNAL EXPOSURE
There are three ways radioactive material can be incorporated into the body and cause internal exposure: inhalation, ingestion and absorption through a break in the skin. If there is the risk of inhaling radioactive particles, it is necessary to use respiratory protection such as a filter mask. Also, persons close to radioactive material should not smoke. To avoid the ingestion of radioactive particles, it is a fundamental safety procedure not to introduce any food or drink into a location where there are radioactive substances. Persons working with radioactive material should ensure that they do not have any undressed wound, cuts or abrasions and should guard against puncture wounds from such packaging items as nails, wire or splinters. They should be particu-larly careful to avoid lacerations from glass breakage or other sharp material that might be present in a damaged container.