2004 Initial Assessments of Closure for the S-SX Tank Farm: Numerical Simulations
In support of CH2M HILL Hanford Group, Inc.'s (CHG) preparation of a Field Investigative Report (FIR) for the closure of the Hanford Site Single-Shell Tank (SST) Waste Management Area (WMA) tank farms, a set of numerical simulations of flow and solute transport was executed to investigate different potential contaminant source scenarios that may pose long-term risks to groundwater from the closure of the S-SX Tank Farm. This report documents the simulation of 7 cases (plus two verification) involving two-dimensional cross sections through the S Tank Farm (Tanks S-101, S102, and S-103) and the simulation of one case involving three-dimensional domain of the S Tank Farm. Using a unit release scenario at Tank S-103, three different types of leaks were simulated. These simulations assessed the effect of leaks during retrieval as well as residual wastes and ancillary equipment after closure. Two transported solutes were considered: uranium-238 (U-238) and technetium-99 (Tc 99). To evaluate the effect of sorption on contaminant transport, six different sorption coefficients were simulated for U 238. Overall, simulations results for the S Tank Farm showed that only a small fraction (< 0.4%) of the U-238 with sorption coefficients 0.6 mL/g migrated from the vadose zone in all of the cases. For the conservative solute, Tc-99, results showed that the simulations investigating leaks during retrieval demonstrated the highest peak concentrations and the earliest arrival times due to the high infiltration rate before water was added and surface barriers installed. Residual leaks were investigated with different release rate models, including uniform release, advection-dominated, diffusion-dominated, and saltcake (solubility-controlled) release models. Of the four models, peak concentrations were lowest and arrival times later for the uniform release model due to the lower release rate of the residual tank waste solids; similar high peak concentrations occurred for the advection-dominated and the salt cake models due to the higher release rate. For the tank ancillary equipment leak case, the diffusion-dominated release rate model yielded peak concentrations and arrival times that were similar to the majority of the past leak cases for residual tank wastes. Comparison between the results of the two-dimensional and those of the three-dimensional simulations show that the two-dimensional simulation significantly overestimated the peak concentrations of the contaminants by a factor of about 41 for Tc-99 and 37 for U-238 with sorption coefficient of 0.03 mL/g.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 860080
- Report Number(s):
- PNNL-14604; 830403000; TRN: US0504867
- Country of Publication:
- United States
- Language:
- English
Similar Records
2005 Closure Assessments for WMA-C Tank Farms: Numerical Simulations
Contaminant Release from Residual Waste in Single Shell Tanks at the Hanford Site, Washington, USA - 9276
Related Subjects
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
STORAGE FACILITIES
TECHNETIUM 99
URANIUM 238
HANFORD RESERVATION
DECOMMISSIONING
GROUND WATER
FLOW MODELS
RADIONUCLIDE MIGRATION
LEAKS
SORPTION
S-SX Tank Farm
Numerical Simulation
STOMP
Vadose Zone
Transport