The migration of radionuclides ²³⁷Np, ²³⁸Pu and ²⁴¹Am in a weak loess aquifer: A field column experiment

The migration of radionuclides ²³⁷Np, ²³⁸Pu and ²⁴¹Am in a weak loess aquifer were investigated in-situ with a bisectional experimental column. The experimental column was constructed by connecting 2 undisturbed aquifer medium columns together and inserted into the aquifer horizontally through holes pre-prepared in the wall of a vertical experimental shaft in an Underground Research Facility at the CIRP´s field test site. Quartz containing radionuclides ³H, ²³⁷Np, ²³⁸Pu and ²⁴¹Am was introduced as a point source at the center of the experimental column. Outflow water of the experimental column was collected and ³H in the outflow was determined for calculating the water flow velocity through the experimental column. The experimental column was cut into slices of 0.3 cm long and the radioactivity of ²³⁷Np, ²³⁸Pu and ²⁴¹Am in the sliced soil samples was analyzed when the experiment was completed.

The water flow velocity in the experimental column was calculated as 1.15±0.05 cm/d. The activity distribution of ²³⁷Np, ²³⁸Pu and ²⁴¹Am in the experimental column indicate that each radionuclide has a very strong activity distribution region adjacent to the source introduction point and decreases abruptly as the distance increases. In addition there are other secondary activity distribution regions with different strength and widths. The calculated apparent distribution coefficients of the main specie of these radionuclides is (8.90±1.51)×10² ml/g for ²³⁷Np, (9.48±1.61)×10² ml/g for ²³⁸Pu and (9.79±1.66)×10² ml/g for ²⁴¹Am.