Backfill as an engineered barrier for nuclear waste management

The swelling, plastic flow, and relative impermeability of bentonite and hectorite were observed and measured after wetting with concentrated brines. Measurements of stable values of pH > 6.5 for the interstitial brines in wetted bentonite and hectorite confirmed conditions favorable for precipitation and sorption of transuranics. Values of K/sub d/ > 2000 ml/g were measured for Pu and Am. Calculated estimates of the effectiveness of a one-foot-thick backfill barrier are presented. They show that the breakthrough of Pu and other transuranics (K/sub d/ = 2000 ml/g) can be delayed for 104 to 105 years. The breakthrough of most fission products (K/sub d/ = 200 ml/g) can be delayed for 103 to 104 years, sufficient time for them to decay to very low concentrations. A backfill barrier can contribute significantly to a radioactive waste isolation system