Results of Deposition Scoping Tests

Hu, M.Z.

Oak Ridge National Laboratory

关键词: Evaporators;    Aluminium;    12 Management Of Radioactive Wastes, And Non-Radioactive Wastes From Nuclear Facilities;    Thermodynamic Model;    Storage Facilities;   

DOI  :  10.2172/885831
RP-ID  :  ORNL/TM-2003/5
RP-ID  :  DE-AC05-00OR22725
RP-ID  :  885831

美国|英语

来源: UNT Digital Library

【 摘 要 】

The processes of crystallization and solid deposit formation that led to the shutdown of the 2H evaporator operation at the Savannah River Site (SRS) and that could possibly cause similar problems in the future or in other evaporators need to be better understood. Through experimentation, thermodynamic modeling, and correlation of scaling to historical tank farm operations, progress has been made in developing guidelines as to the concentrations of silicon and aluminum that can be processed by evaporators while avoiding unacceptable levels of scale formation. However, because of limitations of the thermodynamic model and an insufficient amount of operational data at slightly supersaturated concentration levels, uncertainty still exists regarding acceptable feed concentrations. The objective of this effort is to provide information that can be used in defining acceptable levels of silicon and aluminum in evaporator feed solutions. Data collected previously showed that particle formation reactions can be rapid at evaporator temperatures for elevated silicon and aluminum concentrations. However, insufficient data exists to estimate the silicon and aluminum concentrations above which solids will form in the time frame of evaporator processing. The work described in this report was designed to determine the induction period for solutions of decreasing aluminum and silicon concentration such that the supersaturation level corresponding to a 4-h induction time for particle nucleation/growth in bulk solution can be estimated. In addition, experiments were conducted to explore the supersaturation levels that can result in deposition of solids on metal surfaces at varying aluminum-to-silicon concentration ratios. Laboratory studies of particle growth in solution were conducted at relatively low supersaturation levels. Dynamic-light-scattering (DLS) studies and deposition tests, similar to those performed in FY 2001, were conducted with solutions at relatively low supersaturation levels and at elevated temperatures to explore the formation of solids under conditions similar to those encountered in evaporator processing. The deposition of solids on stainless steel samples placed in the solutions during the experiments was simultaneously investigated. In addition, the deposition of solids on stainless steel surfaces was investigated in laboratory-scale batch evaporation experiments. Completion of this effort will aid the development of operating strategies to mitigate or avoid solid scale formation on surfaces in evaporator systems. The results are expected to benefit plant operations by helping to determine acceptable silicon and aluminum feed concentrations.