A Simulation Study on the Mitigation Capability of Bentonite Backfill to Gaseous Radionuclides

The properties of bentonitewere characterized byuse ofDTA, XRD and SEManalyses. Moreover, the chemical components and the specific surface area of bentonite were analyzed. Sulfur hexafluoride is an ideal non-radioactive gaseous tracerwith low ambient concentration (about 10-13mL/mL). It is analyzed expediently by gas chromatograph with an electron capture detector. Its analysis sensitivity is very high (about 10-13mL/mL). SF6tracer is used to simulate gaseous radionuclides to studytheir adsorption and diffusion in bentonite. The diffusion coefficientof SF6in bentonite backfill with different apparent densities was determined experimentally. The results show that bentonite backfill has a good gas mitigation capability. When the apparent densityof bentonite backfill is close to 1.8 g/m3, the diffusion coefficient of SF6is lowerthan 10-9m2/s. As the engineering characteristic improving agentof backfill, quartzwill reduce the mitigation ability of bentonite backfill togaseous radionuclides. Active carbon is effective to improve the obstruction capability of bentonite backfill. Consideringsuch contrary aspects comprehensively, if 5% quartz is added in bentonite togain the favorable engineering characteristic of backfill, 5% active carbon should be mixed in it to maintain or to improve the obstruction capability of backfill to gaseous radionuclides.