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Geochemical Testing and Model Development - Residual Tank Waste

Geochemical testingClick for larger version.

The goal of this project is to provide source-term release models for contaminants of concern present in residual waste that will remain in tanks after waste retrieval. The contaminant release models are components of the long-term performance assessments being conducted as part of the Tank Farm Operations Contractor’s Tank Closure Project.

Challenge

Develop quantitative, scientifically-defensible models of contaminant release from tank residuals to inform tank closure risk assessments.

Approach

Characterize complex residual tank waste solids, measure contaminant release rates as a function of chemical environment, and build mechanistic release models.

Outcomes

Develop the scientific basis for risk-informed tank closure, which allows for leaving a greater volume of waste in the tanks post-retrieval, while increasing protectiveness to human health and the environment.

Characterization Testing and Analyses

Following retrieval to remove as much material as possible from the tanks, a sample of the residual waste is collected for testing and development of contaminant release models. Testing includes the following:

  • Flow through leach testing
  • X-ray diffraction analysis
  • Scanning electron microscopy/energy dispersive spectroscopic analysis
  • Selective extractions to identify the rate of release of contaminants from the sludge and the likely solid phases containing the contaminants.
  • X-ray Absorption Fine Structure Spectroscopy (EXAFS), X-ray Absorption Near Edge Structure (XANES) analysis
  • Mossbauer spectroscopy

Results of this work provide a detailed characterization of the chemical and mineralogical properties of the tank residual waste and the necessary data for developing mechanistic contaminant release models for use in the Tank Closure Project performance assessments.

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