THE TRANSPORT OF RADIONUCLIDES DISCHARGED FROM A GEOLOGIC WASTE REPOSITORY

A 3-D conservative solution to the convection-dispersion-retardation e quation describing the migration of radionuclides from a geologic nucl ear waste disposal site is derived using a Green's function approach u nder conditions in which the contaminant inventory is preferentially d ischarged to the steady groundwater flow. The numerical implementation of the upper estimate to the transported inventory, as embodied in th e CANUKEO(C) code, is described; its applicability is demonstrated by calculating the groundwater concentration of the neptunium series nucl ides released from used CANDU(TM) fuel emplaced in an hypothetical rep ository; and its general usage is discussed. The ability to handle act inide chains of arbitrary length, whatever their initial inventories, yields both less conservative and physically more realistic estimates of transported inventories than schemes which begin with a contracted chain of longer-lived nuclides whose progeny are assumed to accompany them in their migration, irrespective of their relative mobilities.