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Applied Geology and Geochemistry

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Waste Form Development, Characterization and Performance Testing

Pacific Northwest National Laboratory has initiated a Waste Form Testing Program (WFTP) to support the long-term durability evaluation of waste forms for treatment of low activity and secondary wastes generated from the treatment and immobilization of Hanford radioactive tank wastes. The purpose of the work is to identify candidate stabilization technologies and getters that have the potential to successfully remove contaminants and/or radionuclides from low activity waste (LAW) and secondary waste stream liquid effluents, mainly from off-gas scrubbers and spent solids produced by the Hanford Tank Waste Treatment and Immobilization Plant (WTP).


PUF – Pressurized Unsaturated Flow Apparatus. Click for larger version.

Solidification technologies for liquid waste streams include cement/grout, ceramicrete, geopolymers, hydroceramics, L-TEM, and fluidized-bed steam reforming (FBSR). A cementitious waste form known as Cast Stone has been selected as the preferred waste form for solidification of the Hanford Tank Waste Treatment and Immobilization Plant (WTP) secondary liquid effluents from process condensates. The Caste Stone waste form is also being considered as an immobilization technology for the LAW melter off-gas caustic scrubber effluents and supplemental treatment of LAW.

Challenge

Develop waste forms that can effectively incorporate problematic contaminants, such 99Tc and 129I, in LAW and secondary waste effluents within their matrix and limit their leachability to rates that are sufficiently low as to be protective of human health and the environment.

Approach

Once a waste formulation is selected for testing, standard regulatory test methods are used to measure contaminant leachability, waste form physical strength, and provide an overview of factors that must be considered for further long-term performance testing and model development. State-of-the-art characterization tools are used to provide data needed to technically defend predictive modeling simulations of long-term material behavior. The long-term waste form testing and solid and leachate characterization must be robust enough to effectively predict material performance in the Integrated Disposal Facility (IDF) over the 10,000-year period of performance for the engineered system.

Characterization Testing and Analyses

A variety of leachability and durability testing of the waste forms are employed. These include regulatory agency mandated testing, such as the durability test by ANSI/ANS 16.1, compressive strength testing, and the leachability index test. Other more specialized leach testing methodologies are also employed, including the PNNL-patented pressurized unsaturated flow (PUF) apparatus and stop flow hydraulically-saturated column leaching experiments. Typical characterization instruments and applications used for analysis of secondary waste forms include the following.

Characterization instruments and applications used for analysis of secondary waste forms.

Characterization instruments and applications used for analysis of secondary waste forms.

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