Waste Mixing Issues in Hanford’s Waste Treatment Plant

By Suzanne Dahl, Tank Waste Treatment Manager, Nuclear Waste Program

The M3 mixing issue at Hanford’s Waste Treatment Plant (WTP) has been in the news lately, and I want to explain the issue and our position. Many of the vessels in WTP use pulse jet mixers (PJMs), air-driven devices with no moving parts that will be used to suspend solids in the liquid waste. This waste is from the 177 underground storage tanks at Hanford. The concern surrounding the PJMs is that they will not produce enough energy to keep the waste properly mixed.

As early as 2006, we were aware of the mixing challenges. Since then, the project has received many reviews. Project managers and engineers at our office have been closely monitoring the WTP’s design and construction and studying the mixing concerns. In addition, the External Flowsheet Review Team (EFRT), composed of 50 independent experts, reviewed this project’s flowsheet — a description of the sequence of operations in the WTP — and provided a list of concerns. We also attended these EFRT briefings.

Due to the EFRT concerns, an extensive, ongoing testing program was launched to determine the adequacy of the mixing components in WTP vessels. That program included building a scaled-down test platform with a small open-top vessel, evaluating different PJM configurations, and analyzing the mixing capabilities. The United States Department of Energy (USDOE) provided test results and initial analyses to Ecology from late June through August 2010. Those results revealed a need to change the way many vessels perform, vessel configuration, mixing velocity, and the number of PJMs needed for each vessel. Results also showed that sediment could potentially accumulate in the bottoms of some vessels.

Ecology, the Defense Nuclear Facilities Safety Board (DNFSB), Bechtel, USDOE, and stakeholder groups are aware of these technical challenges. We expect the problems to be resolved in a way that ensures WTP construction and operation will proceed safely and efficiently, resulting in a fully capable WTP. To this end, we review permit submissions for the scope of changes and must approve those changes before construction can continue in the WTP.

If you are interested in this issue, DNFSB has a public hearing scheduled for October 8, 2010.

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