Carbon-14 in the biosphere: Modeling and supporting research for the Canadian Nuclear Fuel Waste Management program

Carbon-14 stands apart from most of the radionuclides present in nuclear fuel waste for several reasons. It has a relatively long radiological half-life and low retardation by granitic geological media so that 14C is superceded only by 36Cl and 129I in potential release to the biosphere from unprocessed used fuel. In the biosphere, its importance continues because it is readily incorporated into the carbon compounds of life. Much of the behavior of 14C in the biosphere can be conceptualized as isotopic exchange, where the 14C mixes with 12C from the biosphere. However, because of lack of data, the authors model the behavior of 14C only partly as isotopic exchange, with most of the calculations relying on compartment transfer models. The authors experimental work has shown that soil-to-plant transfer may be dominated by the soil-atmosphere-plant pathway. Gaseous loss of 14C from soils and lakes is significant. However, recalcitrant forms may persist in soils and sediments for long time periods. The impact of these forms is expected to be relatively low because their bioavailability is correspondingly low. Future research should be directed to support full modeling of 14C as a series of isotopic exchange processes