Field study of the migration of 90Sr, 237Np, 238Pu and 241Am in unsaturated Chinese loess under artificial rainfall condition

Abstract

Summary The migration of 90Sr, 237Np, 238Pu and 241Am in unsaturated Chinese loess under artificial rainfall condition was investigated at the CIRP´s field test site. Quartz containing 90Sr, 237Np, 238Pu and 241Am was introduced into an experimental pit and the pit was backfilled. Artificial rainfall of 10-15 mm/d was applied to the experimental pit for 1078 days. HTO was used for obtaining the migration rate of moisture water in the pit. Vertical core soil samples were taken twice a year and cut into 0.5cm long section soil samples. The section soil samples were weighed and wind dried. Radioactivity of 237Np and 241Am in the section soil samples was measured with a low energy photon detector (HPGe); 90Sr and 238Pu were determined with a low background α & β detector after chemical separation. During the experiment, moisture water at different depths was taken on a daily basis and 3H in the moisture water samples was determined with liquid scintillation technique. Experimental result indicates that the downward migration rate of moisture water was 2.27 cm/d and the retardation factors of 90Sr, 237Np, 238Pu and 241Am in the loess unsaturated zone were 9.9 × 102, 3.2 × 103, 3.2 × 103 and 4.5 × 103, respectively. This result suggests that 90Sr, 237Np, 238Pu and 241Am could be effectively retarded by the loess unsaturated zone.