Abstract: MIGRATION STUDIES ON FISSION PKODUCTS NUCLIDES IN ROCKS Ⅲ.DETERMINATION OF THE LONGITUDINAL DISPERSION COEFFICIENT AND A MODEL EQUATION OF MIGRATION OF~(129)Ⅰ IN GRANITEWEN RUIYUAN；ANG XIANGYUN；AO HONGCHENG（Department of Technical Physics ，Peking University，Beijing，100871）ABSTRACT The adsorption kinetics of ~(129)Ⅰ in granite is studied with ~(125)Ⅰcomcentration in the effluxsorption is found to be negligibly small．The time dependence of ~(125)Ⅰcomcentration in the effluxfrom a granite layer is deduced from the measured penetration and flow curves by materialbalance calculation.Using the property of the distribution function,the longitudinal dispersioncoefficient，the interstitial flow velocity nd the effective interstice fraction are obtained．Adiffer-ential equation describing the migration of ~(129)Ⅰin granite is suggested，and both analytical andnumerical solutions to the eguation are given.Key words~(129)ⅠDispersion coefficient Interstitial flow velocity