Initial Investigation of Waste Feed Delivery Tank Mixing and Sampling Issues

The Hanford tank farms contractor will deliver waste to the Waste Treatment Plant (WTP) from a staging double-shell tank. The WTP broadly classifies waste it receives in terms of 'Envelopes,' each with different limiting properties and composition ranges. Envelope A, B, and C wastes are liquids that can include up to 4% entrained solids that can be pumped directly from the staging DST without mixing. Envelope D waste contains insoluble solids and must be mixed before transfer. The mixing and sampling issues lie within Envelope D solid-liquid slurries. The question is how effectively these slurries are mixed and how representative the grab samples are that are taken immediately after mixing. This report summarizes the current state of knowledge concerning jet mixing of wastes in underground storage tanks. Waste feed sampling requirements are listed, and their apparent assumption of uniformity by lack of a requirement for sample representativeness is cited as a significant issue. The case is made that there is not an adequate technical basis to provide such a sampling regimen because not enough is known about what can be achieved in mixing and distribution of solids by use of the baseline submersible mixing pump system. A combined mixing-sampling test program is recommended to fill this gap. Historical Pacific Northwest National Laboratory project and tank farms contractor documents are used to make this case. A substantial investment and progress are being made to understand mixing issues at the WTP. A summary of the key WTP activities relevant to this project is presented in this report. The relevant aspects of the WTP mixing work, together with a previously developed scaled test strategy for determining solids suspension with submerged mixer pumps (discussed in Section 3) provide a solid foundation for developing a path forward