Safety_Series_015_1965 - gnssn - International Atomic Energy ...

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This publication is not longer validPlease see http://www-ns.iaea.org/standards/reasonable assurance may be secured on the magnitude of any potentialhazard.The main concerns of planned large-scale ground disposals arethe possible long-term effects. The half-lives of certain radionuclidesnormally present in waste are long when viewed against the processesthat cause migration through the ground. The half-lives may be similarin time to the duration of processes that change hydrologicalpatterns, and thus pollution could conceivably reappear in a populatedenvironment at some distant time if geological disturbances alteredthe pattern of river or ground water flow.(2) LiquidIn densely populated areas the discharge of medium or highlyactive liquid wastes into the ground cannot be recommended. However,low -level liquid radioactive wastes are discharged into theground at several establishments where conditions are favourable,and waste products are retained substantially in the sub-soil withintheir boundaries. Where large volumes of slightly radioactive effluentsare to be discharged it may often be preferable to introducethem into the ground even when it is clearly evident that they willultimately reach a surface water body. The soil offers additionaldelay and therefore time for further decay before discharge to surfacewaters. The various processes in the ground even out hightransient releases to a more uniform seepage concentration.The capacity of the ground to accept liquid wastes safely may berealized fully if the liquids are pre-conditioned to be fully compatiblewith the natural minerals in the soil. If this is achieved the soil willafford the maximum attenuation to contaminants and their eventualrelease into surface waters will be diminished. Pre-conditioningmay be by filtration, by pH adjustment or by simple segregation.A more positive form of treatment, in which less emphasis islaid upon the sorptive properties of the soil, is to remove specificlong-lived nuclides from the wastes before disposal. This greatlyreduces the time needed for the radioactivity to diminish sufficientlybefore the seepage may enter surface drainage waters. One pretreatmentmethod under development uses beds of highly selectivesorbantsfor strontium-90, caesium-137, radium-226 and plutonium-239.Another treatment method is to convert the solutions into solidsof low leachability such as glass or ceramics or alternatively to concentratethe solutions and enclose the concentrates or sludges in an54
This publication is not longer validPlease see http://www-ns.iaea.org/standards/insoluble material such as bitumen. The resultant solids may thenbe stored or disposed of in the less exacting environment requiredfor solids.(3) SolidSolid radioactive wastes buried in the ground normally presenta much lower potential hazard than liquid radioactive wastes, so therestrictions on disposal procedures may be less exacting. The priorinspection and monitoring of material destined for disposal ensuresthat the more highly radioactive waste is segregated and disposedinto containers appropriate in size and shape for the level of radioactivity.The large bulk of low -level or potentially contaminatedmaterial discharged into the aerated zone in the soil enters an environmentwhere nuclides are anticipated to remain stationary unlessleached by water. In general, the minimal packaging afforded to lowlevelsolid waste makes it the most susceptible to leaching, but theensuing contamination is likely to be low. For waste of higher activityit is generally arranged that the higher the potential hazardof the waste, the more protective is its container. Thus the containerfor a potentially hazardous disposal will have a built-in monitoringdevice to detect the first signs of leaching and provide warningof the need for repair or replacement. It is unlikely that hazardousquantities could be inadvertently released but if the situation did arisethe offending material could be removed and handled separately.The economics of a ground disposal scheme will certainly takeinto account the initial capital investment commensurate with thepredicted activity levels in the water supplies of population centresand their development, but the cost of maintaining the site and ofmonitoring and surveillance could well be ultimately more expensive.When the choice of disposal site depends on the type of soil andthe hydrodynamics of the ground water system, great responsibilityis thrown on the correct interpretation of sub-surface investigations.Owing to the present shortcomings in measurement or sampling techniquesin certain types of ground the choice of site may well be limitedto those from which the maximum information can currentlybe extracted and so provide the basis for the most accurate prediction.(4) StorageWhere a particular plant site is not suitable for ground disposal,or where the radioactivities are so high that direct ground disposal55
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