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Is cl-36 from weapons' test fallout still cycling in the atmosphere?.

出版	Atomic Energy Of Canada Limited, 1997
URL	http://books.google.com.hk/books?id=cPhn0AEACAAJ&hl=&source=gbs_api

註釋Aecl has submitted an environmental impact statement (eis) to evaluate the concept of nuclear fuel disposal at depth in crystalline rock of the canadian shield. in this disposal concept used fuel would be emplaced in corrosion-resistant containers which would be surrounded by clay-based buffer and backfill materials. once groundwater is able to penetrate the buffer and corrosion-resistant container, radionuclides could be transported from the waste form to the surrounding geosphere, and eventually to the biosphere. the release of radionuclides from the waste form and their subsequent transport would be determined by the geochemistry of the disposal vault and surrounding geosphere. organic substances affect the geochemistry of radionuclides through complexation reactions that increase solubility and alter mobility, be affecting the redox of certain radionuclides and be providing food for microbes. the purpose of this study was to determine whether the buffer and backfill materials proposed for use in a disposal vault contain organics that could be leached by groundwarer in large enough quantities to complex with radionuclides and affect their mobility within the disposal vault and surrounding geosphere. buffer material, made from a mixture of 50 wt.% avonlea sodium bentonite and 50 wt.% silica sand, was extracted with deionized water to determine the release of dissolved organic carbon, humic acid and fulvic acid. the effect of radiation and heat from the used fuel was simulated by treating samples of buffer before leaching to various amounts of heat (60 degrees c and 90 degrees c) for periods of 2,4 and 6 weeks, and to ionizing radiation with doses of 25 kgy and 50 kgy. humic substances were isolated from the leachates to determine the concentrations of humic and fulvic acids and to determine their functional group content by acid-base titrations. the results showed that groundwater could leach significant amounts of organics that would complex with radionuclides such as the actinides, affecting their solubility and transport within the disposal vault and possible the surrounding geosphere. heating and radiation affect the amount and nature of leachable organics. however, one of the key parameters that needs to be addressed is the mobility of organic molecules through an intact buffer and backfill.