The Leaching Behavior of Non-Pertechnetate Species in Cementitious Waste Forms

Uncertainty has been identified around the release behavior of nonpertechnetate species from cementitious waste forms disposed at locations with a pathway to potable water. Nonpertechnetate species have been identified in the legacy nuclear wastes stored at the Hanford Site, yet little is known regarding the retention behavior of nonpertechnetate species from cementitious waste forms. This work presents an evaluation of the nonpertechnetate species immobilized as cementitious waste forms using real Hanford tank waste. The tank waste samples were stripped of pertechnetate leaving a nonpertechnetate inventory dominated by either Tc(VI) or Tc(I). Semidynamic leach testing of the resulting waste form samples was combined with a resin contact of the leachates to show a significant oxidation of the nonpertechnetate to pertechnetate (>80% conversion). The rate of oxidation and release of the nonpertechnetate compound was slower in the presence of reducing blast furnace slag in the waste form suggesting that reducing conditions can slow the oxidation process. These results mature the understandings around the behavior of nonpertechnetate within cementitious waste forms and around long-term waste form modeling for how to handle the release from a nonpertechnetate inventory in the parent waste stream.