SRS Laboratory, Contractor Collaborate on Innovative Leaching Test

AIKEN, S.C. – A Savannah River Site (SRS) laboratory and contractor are developing an innovative process to better understand how radionuclides leach out of the low-level radioactive waste form called saltstone over long periods of time.

   The Savannah River Ecology Laboratory (SREL), an independent research unit of the University of Georgia, and Savannah River Remediation (SRR), the SRS liquid waste contractor, are creating a new test, called Dynamic Leaching Method (DLM.) It simulates groundwater passing through intact saltstone over extended periods. Other leaching tests conducted on crushed material may overestimate the leaching of contaminants from cementitious waste forms.

   The DLM test uses pressure to force the water to move through the intact monolith material more quickly than would happen naturally. This tactic accelerates the time scale for testing to investigate changes in pore water chemistry and contaminant releases that would occur over long time periods in the actual disposal system.

   SREL Associate Director for Research Dr. John Seaman said the DLM is a novel way to test the effectiveness of the saltstone in the long run.

   “The Dynamic Leaching Method efficiently tests the long-term effectiveness of the saltstone in immobilizing radioactive contaminants for time periods that are difficult to evaluate using existing methods,” he said.

   The initial use of this method focuses on two radionuclides, iodine-129 (I-129) and technetium-99 (Tc-99), and how quickly they leach from an actual core sample of saltstone from Saltstone Disposal Unit (SDU) 2A at SRS. SDU 2A is a permanent disposal unit that contains decontaminated salt solution mixed with cement materials to form saltstone. I-129 and Tc-99 are key radionuclides to analyze because both are extremely mobile in the environment and have long half-lives.

   The test results will be used as inputs into the modeling of the movement of radionuclides thousands of years into the future in the performance assessment supporting the Saltstone Disposal Facility. The DLM testing also supports the performance assessment maintenance program, a federally required process to reduce uncertainty in modeling activities.

   Three sample types are used in the testing process: cold samples (non-radiological simulated saltstone samples), simulated radiological samples (saltstone created in the laboratory, but with Tc-99 or I-129 added), and actual radiological saltstone samples from SDU 2A.

   SRR Waste Disposal Authority Manager Steve Thomas said SRR and SREL are observing the initial results of the new technique to determine what tweaks are required before fully executing the tests in fiscal year 2017.

   “This new method of leach testing has a lot of promise,” Thomas said. “The interface with SREL has been awesome. Dr. John Seaman is really good to work with, very creative and accommodating.”