Leaching Behavior of Polyethylene Encapsulated Nitrate Waste

The leaching behavior of sodium nitrate salts (simulating wastes from the Hanford single-shell tanks) encapsulated in polyethylene was investigated. These wastes are sufficiently radioactive that they may be self-heating. Laboratory scale waste forms prepared for leach tests were mixtures of NaNO³ and low-density polyethylene, with nominal salt loadings of 50, 60 and 70 wt%. In this study we determined: (1) leach rates of NaNO₃/polyethylene waste forms at several waste loadings (2) leach rates at temperatures as high as 70°C which is the maximum projected temperature of this self-heating waste (3) leaching mechanism of NaNO₃/polyethylene waste forms and predicted releases.

The Accelerated Leach Test (ALT) used for this study was recently developed at Brookhaven National Laboratory (BNL). It is particularly well suited for this application since it was designed to be run at elevated temperatures.