Stabilization of Rocky Flats Pu-contaminated ash within chemically bonded phosphate ceramics

A feasibility study was conducted on the use of chemically bonded phosphate ceramics for stabilization of combustion residue of high transuranic (TRU) wastes. Using a matrix of magnesium potassium phosphate formed by the room -temperature reaction of MgO and KH2PO4 solution, we made waste forms that contained 5 wt% Pu to satisfy the requirements of the Waste Isolation Pilot Plant, The waste forms were ceramics whose compression strength was twice that of conventional cement grout and whose connected porosity was approxim ate to 50% that of cement grout. Both surrogate and actual waste forms disp layed high leaching resistance for both hazardous metals and Pu. Hydrogen g eneration resulting from the radiolytic decomposition of water and organic compounds present in the waste form did not appear to be a significant issu e. Pu was present as PuO2 that was physically microencapsulated in the matr ix. In the process, pyrophoricity was removed and leaching resistance was e nhanced. The high leaching resistance was due to the very low solubility of PuO2 coupled with superior microencapsulation. As a result, the waste form s satisfied the current Safeguard Termination Limit requirement for storage of TRU combustion residues. (C) 1999 Elsevier Science B.V. All rights rese rved.