1997 Technical Reports
Sensitivity Tests of the Waste-Form-Alone Design for the Low-Activity-Waste Disposal System
M.J. Fayer, M.D. White, C.T. Kincaid
Pacific Northwest National Laboratory, Richland, Washington
PNNL-11717 (UC-702), Pacific Northwest National Laboratory, Richland, Wa., 1997.
Summary
Computer simulations were performed in FY 1995 and 1997 by the Pacific Northwest National Laboratory (PNNL) to assess the performance of the waste-form-alone (WFA) design for the low activity-waste (LAW) disposal system for the U.S. Department of Energy (DOE). Most of the work was conducted in 1995 and used to support the development of the LAW product acceptance specification. The results of the 1995 work are attached as an appendix to this report.
In FY 1997, PNNL performed additional simulations for Lockheed Martin Hanford Company (LMHC) to address specific questions about the disposal. LMHC manages the Glass Performance Assessment Project for DOE. The objectives of the additional simulations were to demonstrate the impact of grid resolution, diffusion, fracture flow within the waste form, and consumption of water by the waste form. It was assumed that the waste form would be the only part of the engineered disposal system that inhibits radionuclide release, referred to as WFA assumption. All calculations were performed with the latest version of the STOMP (Subsurface Transport Over Multiple Phases) simulator.
Multiple simulations of the WFA disposal were performed to identify parameter and conceptual model sensitivities. The corrosion rate, recharge rate, well interception factor, hydraulic properties, and hydraulic and retardation models were shown to be important. The grid resolution could be important if the diffusion coefficient in the disposal facility is sufficiently small. Diffusion was shown to be important for the gravel model of glass but not the soil model. The impact of temperature changes was discussed and determined to be negligible. Water consumption during corrosion was evaluated and found to have a minimal effect on the dose calculations. Fracture flow within the glass was evaluated and found to have only a minimal effect on the dose calculations.
The steady-state simulations of the WFA disposal have been useful as a guide for understanding the disposal and highlighting some important features and parameters. However, this type of analysis should not be relied on to provide a complete analysis of disposal sensitivities. The concern is that the importance of some parameters and processes depends on the actual facility design, materials, and waste form. To supplement and complement this type of study, additional detailed simulations ought to be conducted using the actual facility design, measured hydraulic and chemical properties, and reasonable estimates of the disposal waste form corrosion rate, formation of secondary minerals, and resulting changes in properties.
Developing a Model for Moisture in Saltcake Waste Tanks: Progress Report
C.S. Simmons, N. Aimo, M.J. Fayer, M.D. White
Pacific Northwest National Laboratory, Richland, Washington
PNNL-11595 (UC-2030), Pacific Northwest National Laboratory, Richland, Wa., 1997.
Summary
This report describes a modeling effort to provide a computer simulation capability for estimating the distribution and movement of moisture in the saltcake-type waste contained in Hanford's single-shell radioactive waste storage tanks. This moisture model goes beyond an earlier version because it describes water vapor movement as well as the interstitial liquid held in a saltcake waste. The work was performed by Pacific Northwest National Laboratory to assist Duke Engineering and Services Hanford(DESH) with the Tank Waste Safety Program.
Gas Release During Salt-Well Pumping: Model Predictions and Laboratory Validation Studies for Soluble and Insoluble Gases
L.M. Peurrung, S.M. Caley, P.A. Gauglitz
Pacific Northwest National Laboratory, Richland, Washington
PNNL-11621 (UC-2030), Pacific Northwest National Laboratory, Richland, Wa., 1997.
Summary
The Hanford Site has 149 single-shell tanks (SSTs) containing radioactive wastes that are complex mixes of radioactive and chemical products. Of these, 67 are known or suspected to have leaked liquid from the tanks into the surrounding soil, while 82 are considered sound (Hanlon 1996). To minimize the amount of material that could potentially leak into the surrounding soil, all of the SSTs are scheduled to have drainable liquid removed and to be designated as interim stabilized. Of the SSTs, 117 have been declared stabilized while only 32 require further processing (Hanlon 1996). The Tri-Party Agreement (Ecology 1996) has set a series of milestones for completing interim stabilization, with completion set for September 2000. While process equipment exists for removing drainable liquid, and its operation is well known from previous pumping campaigns, a number of safety issues associated with the release and potential ignition of flammable gases within the tanks is interrupting progress on completing the removal of drainable liquid.
A Comprehensive Analysis of Contaminant Transport in the Vadose Zone Beneath Tank SX-109
A. L. Ward, G. W. Gee, M. D. White
Pacific Northwest National Laboratory, Richland, Washington
PNNL-11463 (UC-702), Pacific Northwest National Laboratory, Richland, Wa., 1997.
Summary
The Vadose Zone Characterization Project is currently investigating the subsurface distribution of gamma-emitting radionuclides in S and SX Waste Management Area (WMA-S-SX) located in the 200 West Area of the U.S. Department of Energy's Hanford Site in southeastern Washington State. Spectral-gamma logging of boreholes has detected elevated 137Cs concentrations as deep as 38 m, a depth considered excessive based on the assumed geochemistry of 137Cs in Hanford sediments. Routine groundwater sampling under the Resource Conservation and Recovery Act (RCRA) have also detected elevated levels of site specific contaminants downgradient of WMA-S-SX. The objective of this report is to explore the processes controlling the migration of 137Cs, 99Tc, and NO3- through the vadose zone of WMA-S-SX, particularly beneath tank SX-109.