Safety_Series_015_1965 - gnssn - International Atomic Energy ...

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