Field study of the migration of⁹⁰Sr,²³⁷Np,²³⁸Pu and²⁴¹Am in unsaturated Chinese loess under artificial rainfall condition

Abstract

The migration of 90 Sr, 237 Np, 238 Pu and 241 Am in unsaturated Chinese loess under artificial rainfall condition was investigated at the CIRP's field test site. Quartz containing 90 Sr, 237 Np, 238 Pu and 241 Am 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 0.5 cm long section soil samples. The section soil samples were weighed and wind dried. Radioactivity of 237 Np and 241 Am in the section soil samples was measured with a low energy photon detector (HPGe); 90 Sr and 238 Pu 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 3 H 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 90 Sr, 237 Np, 238 Pu and 241 Am in the loess unsaturated zone were 9.9 × 10 2 , 3.2 × 10 3 , 3.2 × 10 3 and 4.5 × 10 3 , respectively. This result suggests that 90 Sr, 237 Np, 238 Pu and 241 Am could be effectively retarded by the loess unsaturated zone.