In-tank processes for destruction of organic complexants and removal of selected radionuclides

Abstract

This report establishes the need and technical feasibility for using in-tank pretreatment processes for destruction of organic complexants and removal of {sup 90}Sr, transuranic (TRU) elements, and {sup 99}Tc from double-shell tank (DST) liquid wastes. Neither {sup 90}Sr nor {sup 99}{Tc} have to be removed from any DST solution to obtain vitrified product containing less than the Nuclear Regulatory Commission (NRC) criteria for Class C commercial low-level waste (LLW). To meet the NRC criterion for Class C LLW, TRU elements must be removed from liquid wastes in three (possibly five) DSTs. No {sup 90}Sr will have to be removed from any solution for the total vitrified waste from both DSTs and single-shell tanks to meet a goal of <7 MCi of radionuclides and a NRC ruling for Hanford Site Incidental Waste. Guidance from ALARA principles and the TWRS Environmental Impact Statement may dictate additional removal of radionuclides from DST supernatant liquids. Scavenging processes involving precipitation of strontium phosphate and/or hydrated iron oxide effectively remove {sup 90}Sr and/or TRU elements from actual DST wastes including complexant concentrate (CC) wastes. Destruction of organic complexants is not required for these scavenging processes to reduce the {sup 90}Sr and/or TRU element concentrations of DST waste solutions to or below the NRC criteria for Class C commercial LLW. However, substantially smaller amounts of scavenging agents would be required for removal of {sup 90}Sr and TRU elements from CC waste if organic complexants were destroyed. Low concentrations of added Sr(NO{sub 3}){sub 2} and Fe(NO{sub 3}){sub 3} are desirable to minimize the volume of HLW glass.