Accelerated physical modelling of radioactive waste migration in soil

Abstract

A 100 g-tonne geotechnical centrifuge was used to study the long-term migration of a contaminant and radioactive tracer through a saturated soil medium. The use of the centrifuge simulates the acceleration of traveltime in the prototype, which is N times larger than the model, by N2, where N is the desired g level. For a 5 h run at 60 g, the test modelled a migration time of about 2 years for a prototype 60 times larger than the small-scale model tested. Iodine 131 (I-131), used as the tracer, was injected onto the surface of the soil, and was allowed to migrate with a constant head of water through the saturated soil. End window Geiger–Mueller (G–M) tubes were used to measure the count rate of the radioactive tracer flowing through the soil. The time from the peak response of one G–M tube to the other denotes the traveltime between the two points in the flow domain. The results obtained using the radioactive tracer are in good agreement with the test performed on the same model setup using potassium permanganate as a tracer and with numerical flow net modelling. Radioactive tracers can be useful in the study of nonradioactive contaminants as well, offering a nonintrusive (nondestructive) method of measuring contaminant migration. Key words : contaminant transport, centrifuge modelling, radioactive waste, nondestructive measurement, waste disposal.