PNNL

Abstract

Radioactive wastes from nuclear fuel processing are stored in large underground storage tanks at the Hanford Nuclear Reservation near Richland, Washington. Treatment and remediation requires that waste feed from the storage tanks be delivered to the Hanford Tank Waste Treatment and Immobilization Plant (WTP) in a manner that ensures continuous WTP operations over the life cycle of the treatment mission. The complex physical and chemical processes required for this mission, the significant scale, and the hazardous nature of the waste necessitate the use of simulants in lab- and pilot-scale process testing. Hanford simulants were initially developed by attempting to mimic the chemical composition of the waste. This was typically done by characterizing the chemical analytes of a tank waste sample, then matching the chemical composition either with precipitated metal hydroxides or by adding metal oxides. However, this approach can have significant drawbacks wherein the simulants that did not reproduce properties of the tank waste significant to treatment process performance, such as particle size or rheological properties. Because of these limitations, a new class of simulants, “performance-based simulants,” was developed to match physical properties salient to waste processing step performance. This approach targets the performance of the simulant relative to actual waste performance data, which has been developed into an ASTM standard for simulant development. This paper summarizes the development and testing results of three specific Hanford waste performance-based simulants addressing the waste feed delivery (WFD) system and leaching and cross-flow filtration performance in the WTP. Simulants developed using specific Hanford waste performance characteristics have been used to successfully demonstrate and understand these aspects of process performance.