Radiation safety and radioactive waste (RAW)

Safety is the prime consideration during management of RAW on account of the potential that exists for exposure of people to radiation. Such expo­sure can be to workers involved in the handling and management of RAW or to members of the public, due to any radioactive material associated with the waste being released into the publicly accessible environment. Similarly, environments contaminated with radioactive materials can cause exposure of persons to radiation. Both the management of RAW and contaminated environments can also lead to plant and animal species being exposed to radiation. Exposure can arise at the present time and can also occur in the future, and its magnitude can vary from insignificant to very high depending on the nature of the RAW and the circumstances of exposure. Exposure can also arise during normal anticipated circumstances associated with waste management and contaminated environments and from accidents or disruptive events.

The same philosophical basis for radiation safety has been adopted for all facilities and activities that can give rise to radiation exposure. However,

the manner in which this philosophical basis has been developed and applied to waste management and contaminated environments is influ­enced by the often long timescales involved and the desire to dispose of the waste, i. e. to no longer have to exercise active control and management over the materials. There is also need to differentiate those materials containing radioactive material but at such low levels that the material does not need to be managed as radioactive waste.

The effects of exposure to radiation have been studied throughout the twentieth century and a sound knowledge base has been developed [ 1]. Studies continue to refine and update this knowledge base, but in general the effects are known. Lower levels of radiation dose cause an increase in the incidence of cancer in the exposed populations and at higher levels of radiation dose in excess of a threshold in the region of 1 Gy, deterministic health impacts start to occur. The latter effects range from chromosomal aberrations to organ damage and skin burns to death at doses beyond a few Gy. The rate of cancer incidence increases with increasing radiation dose in a stochastic manner; in the lower range of doses, no increase in the natural incidence of cancers is detectable, at higher levels of dose in larger popula­tions, an excess incidence is discernible. The basic approach to radiation safety is both to prevent short-term deterministic health effects and to ensure that the longer-term risk of cancer induction is not significant.

Exposure to radiation can arise from radioactive material emitting pen­etrating radiation located outside the body of a person or other species, which due to proximity impinges on the body. Alternatively, exposure can arise from radioactive material being incorporated into the body, generally by inhalation or ingestion. Other diffusive transfer mechanisms generally apply to incorporation into plants.

All these factors have to be considered in developing and applying a safety regime for the management of RAW and contaminated environments. The fundamental approach is to reduce the volume of waste to the extent reason­ably possible, to solidify it into an immobile form, and to provide measures to contain and isolate the waste from the accessible environment. The con­tainment is intended to keep the radionuclides within the containment boundary by chemical or physical fixation within the waste matrix and by physical containing barriers, and to provide shielding for any penetrating radiation emitted from the radionuclides within the waste [2]. The isolation function aims to keep the radionuclides away from people and the environ­ment and also to protect the waste and its protective features from disturbing and degrading influences such as fire, water, physical disruption, etc. The timeframes required for such containment and isolation are influenced by the radioactive half-lives of the radionuclides contained in the waste.

Many activities involving radioactive material processing, handling and use also give rise to contaminated effluents. Treatment of the fluids generally involves cleaning by filtration, solvent extraction, ion exchange or by evaporation. The aim of these cleaning processes is to reduce the radio­activity levels in the effluent to the extent that they can be safely discharged into the environment.

This chapter outlines the general international principles of radiation, waste and transport safety. Examples of their application in various coun­tries are given in Part II.

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