Isolation of radioactive waste

Isolation of radioactive wastes for long periods to allow adequate decay is sought by the use of multiple barriers. These include the waste form itself, the primary containers made of resistant materials, overpacks as secondary layers, buffer materials, concrete vaults, and finally the host rock or sod. Barriers limit water access to the waste and minimize contamination of water suppHes. The length of time wastes must remain secure is dependent on the regulatory limit of the maximum radiation exposure of individuals in the vicinity of the disposal site. 

The work presented here enables us to get a clearer picture of the problems involved in permanent isolation of radioactive wastes from the environment. 

The Department of Energy Program for Long-Term Isolation of Radioactive Waste... 

Over the last year or so, several papers have been published which have been concerned with the adequacy of the technology for providing for permanent isolation of radioactive wastes. In all cases the concerns that have been raised have focused on the second set of issues, rather than the first, so that the apparent dispute between those who say that there are no technical problems and those who say that there are still some to be solved is perhaps more a dispute as to what particular set of problems are being described. 

The objective of geologic isolation of radioactive wastes is to preclude their reaching the biosphere until after they have decayed to the extent that they no longer constitute a health hazard. Concern over radioactive wastes from military, industrial and research uses has elicited many lines of commentary and deep concern from many individuals. In California, the concern about waste disposal was the focal point in establishing a moratorium on the construction of new reactors until a satisfactory waste disposal technology could be demonstrated. 

One of the more important factors affecting the isolation of radioactive waste is the rate of release of the radioactivity from the solid waste form to the environment. The most probable mechanism for release and transport of radioactivity from a solid waste form is by leaching of radioactive isotopes with groundwater. The objective of leach-testing various waste forms is to evaluate the rate at which specific hazardous radionuclides migrate from waste if and when the waste form comes in contact with groundwater. In this paper, measurement of leach rates of radioactive waste by a method which incorporates neutron activation is described. 

McCarthy, G. J., Quartz Matrix Isolation of Radioactive Wastes, /. Ma-... 

Kiihn, K., and J. Hamstra Geologic Isolation of Radioactive Wastes in the Federal Republic of Germany and the Respective Program of the Netherlands, Proceedings of the International Symposium on the Management of Wastes from the LWR Fuel Cycle, Denver, 1976, Report CONF-76-0701, p. 580. 

Provisions for the isolation of radioactive waste from site personnel and the public, with access control. For example, this might be accomplished by zoning the facility in accordance with the potential for radioactive contamination and radiation exposure ... 

D Alessandro, M. Gera, F. 1986. Geological isolation of radioactive waste in clay formations fractures and faults as possible pathways for radionuclide migration. Radioactive Waste Management and the Nuclear Fuel Cycle, 7(4), 381-406. 

The reactors at Oklo and Bangombe provide great confidence in the feasibility of radioactive waste isolation. The reactors operated for 800 000 years and after two billion years, most of the radionuclides (except for iodine that has migrated away completely) and/or their decay products have migrated only a few metres. 

Much interest in the past few years has been generated in connection with problems of radioactive waste isolation in a growing nuclear economy. Many studies have been irfitiated to find the most suitable sites for waste repositories, and the environmental impact if breaches occur in such repositories. 

Figure 16.11 Water dilution volume for radionuclides in PWR spent fuel. (From National Research Council, A Study of the Isolation System for Geologic Disposal of Radioactive Waste, NAS, Washington, 1983.)...

In general terms, the goal of long-term waste storage is to isolate the radioactive waste from humans and the environment. The prevailing design strategy for waste repositories is that of multiple barriers (Fig. 16.12). 

The waste streams may be disposed safely if they do not contain contaminants that are harmful to living beings. Several waste streams, however, contain harmful chemicals that enter the human body through the food chain via soil or water or the air that we breathe. These contaminants may be toxic chemicals or radioactive. The former is referred to as hazardous , and the latter as radioactive . Both need treatment to isolate the contaminants from the groundwater, air, and soil prior to disposal. Treatment of hazardous waste streams is the subject of this chapter, while treatment of radioactive wastes, or those containing both hazardous and radioactive contaminants ( mixed wastes), is discussed in Chapter 17. 

Waste management is a field that involves tlie reduction, stabilization, and ultimate disposal of waste. Waste reduction is tlie practice of minimizing tJie amount of material tliat requires disposal. Some of the common ways in which waste reduction is accomplished are incineration, compaction, and dewatering. The object of waste disposal is to isolate tlie material from tlie biosphere, and in the case of radioactive waste, allow it time to decay to sufficiently safe levels. 

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