The long-term durability of WAXFIX, a paraffin-based grout, was evaluated for in situ grouting of activated beryllium wastes in the subsurface disposal area (SDA), a radioactive landfill at the Radioactive Waste Management Complex, part of the Idaho National Laboratory (INL). The evaluation considered radiological and biological mechanisms that could degrade the grout using data from an extensive literature search and previous tests of in situ grouting at the INL. Conservative radioactive doses for WAXFIX were calculated from the "hottest" (i.e., highest-activity) Advanced Test Reactor beryllium block in the SDA. These results indicate that WAXFIX would not experience extensive radiation damage for many hundreds of years. Calculation of radiation-induced hydrogen generation in WAXFIX indicated that grout physical performance should not be reduced beyond the effects of radiation dose on the molecular structure. Degradation of a paraffin-based grout by microorganisms in the SDA is possible and perhaps likely, but the rate of degradation will be at a slower rate than found in the literature reviewed. The calculations showed the outer 0.46-m (18-in.) layer of each monolith, which represents the minimum expected distance to the beryllium block, was calculated to require 1000 to 3600 yr to be consumed. The existing data and estimations of biodegradation and radiolysis rates for WAXFIX/paraffin do not indicate any immediate problems with the use of WAXFIX for grouting beryllium or other wastes in the SDA.