Results from a one-year leach test: long-term use of MCC-1

This paper presents results from the long-term use of the MCC-1P Static Leach Test Method which has already been used for short-term testing and for comparing waste forms. Data were obtained on the leaching behavior of PNL 76-68 glass over a 1-year period. The results of this test led to the following conclusions. The MCC-1P Static Leach Test Method has been demonstrated to be useful for studies up to 1 year at temperatures up to 900C. Accurate measurements of leachant volume at the start and the end of the test are important. PNL 76-68 glass appears to continue to alter, albeit at a significantly reduced rate, even though the solution concentrations of many elements are saturated or supersaturated with respect to alteration phases. The original surface of the glass was still present after 1 year, evidence that the gel layer will slowly get thicker but dissolution will not occur, or will occur at extremely slow rates. At 400C, more than 1 year is required to reach saturation of some important elements. Even at 900C, testing beyond 1 year is needed to define alteration rates and details of the leaching mechanisms