DEVELOPMENT OF A CAST STONE FORMULATION FOR HANFORD TANK WASTES

The U.S. Department of Energy (DOE) Hanford Site, the location of plutonium production for the U.S. nuclear weapons program, is the focal point of a broad range of waste remediation efforts. This presentation will describe a test program to develop a “cast stone” formulation for the stabilization of certain Hanford tank wastes (Lockrem 2005). The program consisted of (1) a short series of tests with nonradioactive simulant to select preferred dry reagent formulations (DRF) and determine allowable liquid addition levels, (2) waste form performance testing on cast stone made from the DRF formulations using low-activity waste (LAW) simulant, (3) waste form performance testing on cast stone made from the preferred DRF using LAW, (4) waste form validation testing on a selected nominal cast stone formulation using the preferred DRF and LAW simulant, and (5) technetium “getter” testing with cast stone made with LAW simulant and with LAW. In addition, nitrate leaching observations were drawn from nitrate leachability data obtained in the course of waste form performance testing. The nitrate leachability index results are presented along with data on other performance criteria. The results of this study led to the selection of a specific DRF. The key attributes of the DRF/waste loading combination considered were presence of “bleed” (or free) water, volume change on curing, compressive strength, maximum curing temperature, toxicity characteristic leaching testing, ANSI/ANS-16.1 (Measurement of the Leachability of Solidified LowLevel Radioactive Wastes by a Short-Term Test Procedure) leachability, and hydraulic conductivity. Important considerations included that the monoliths could be produced using readily available, low-cost reagents. The key results from each of these testing and evaluation activity categories will be summarized.