[en] Mathematical simulation of radionuclide transport was conducted by applying the finite element sediment and contaminant transport model, SERATRA, to the Columbia River between the Priest Rapids and McNary Dams near the ERDA Hanford Reservation. Model computations were performed to solve time-dependent, longitudinal and vertical distributions of sediments and radionuclides by taking into account sediment-radionuclide interaction. Sediment transport was modeled for three sediment size fractions (i.e., sand, silt, and clay), and radionuclide transport was simulated for dissolved and particulate nuclides. Particulate radionuclides were analyzed for those adsorbed by sediment in each sediment size fraction. Five cases were simulated in this study to identify the effects of river sediments on radionuclide migration: continuous release of ⁶⁵Zn without adsorption mechanics; continuous release of ⁶⁵Zn with adsorption; instantaneous release of ⁶⁵Zn without adsorption; instantaneous release of ⁶⁵Zn with adsorption; and radionuclide resuspension. Sediment and radionuclide results indicate very good agreement with measured data

[en] Radionuclide migration in rivers was simulated in this study to advance the state-of-the-art of computer modeling on radionuclide transport by including the effects of sediment-radionuclide interaction. Specifically, the finite element sediment and contaminant transport model, SERATRA, was modified and applied to the Clinch River in Tennessee to solve time-dependent, longitudinal and vertical distributions of sediments and radionuclides. Sediment transport was modeled for each sediment size fraction (i.e., sand, silt and clay), and radionuclide transport was modeled for dissolved and particulate nuclides. Furthermore, particulate radionuclides were solved for those adsorbed by each sediment size fraction. Three radionuclides, cesium-137, strontium-90 and gold-198, were selected as sources of continuous and instantaneous releases because of their adsorption characteristics and field data availability. Agreement of predicted results and field data for continuous release cases was very good, while for instantaneous releases agreement was poor. It was revealed that approximately 93 percent of the cesium-137 is in a particulate form, and only about 7 percent is dissolved. The model predicted that approximately 50 percent of the cesium 137 introduced in the Clinch River will be deposited on the river bed before it reaches the river mouth as a result of contaminated sediment deposition in slow moving areas of the river. Results on strontium-90 indicated the opposite trend, i.e., approximately 97 percent is in the dissolved form and only 3 percent was associated with the sediment; hence, the majority of strontium-90 moves with the water through the river system. Gold-198 was used for instantaneous release simulation, but since agreement between simulated results and data was not good no conclusions can be drawn for this case

[en] The purpose of this study was to confirm the adequacy of a single mixer pump to fully mix the wastes that will be stored in Tanks 241-AP-102 and -104. These Hanford double-shell tanks (DSTs) will be used as staging tanks to receive low-activity wastes from other Hanford storage tanks and, in turn, will supply the wastes to private waste vitrification facilities for eventual solidification. The TEMPEST computer code was applied to Tanks AP-102 and -104 to simulate waste mixing generated by the 60-ft/s rotating jets and to determine the effectiveness of the single rotating pump to mix the waste. TEMPEST simulates flow and mass/heat transport and chemical reactions (equilibrium and kinetic reactions) coupled together. Section 2 describes the pump jet mixing conditions the authors evaluated, the modeling cases, and their parameters. Section 3 reports model applications and assessment results. The summary and conclusions are presented in Section 4, and cited references are listed in Section 5

[en] A field sampling program was conducted on Cattaraugus and Buttermilk Creeks, New York during November and December 1977 to investigate the transport of radionuclides in surface waters as part of a continuing program to provide data for application and verification of Pacific Northwest Laboratory's (PNL) sediment and radionuclide transport model, SERATRA. Suspended sediment, bed sediment, and water samples were collected during mean flow conditions over a 45 mile reach of stream channel. Radiological analysis of these samples included primarily gamma ray emitters; however, some plutonium, strontium, curium, and tritium analyses were also included. The principal gamma emitter found during the sampling program was ¹³⁷Cs where, in some cases, levels associated with the sand and clay size fractions of bed sediment exceeded 100 pCi/g. Elevated levels of ¹³⁷Cs and ⁹⁰Sr were found downstream of the Nuclear Fuel Services Center, an inactive plutonium reprocessing plant and low level nuclear waste disposal site. Based on radionuclide levels in upstream control stations, ¹³⁷Cs was the only radionuclide whose levels in the creeks downstream of the site could confidently be attributed to the site during this sampling program. This field sampling effort is the first of a three phase program to collect data during low, medium and high flow conditions

[en] The finite element model, FETRA, is an unsteady, two-dimensional (longitudinal and lateral) model for simulating the transport of sediment and contaminants (e.g., radionuclides, heavy metals, pesticides) in coastal waters. FETRA includes major transport and fate mechanisms explicitly, including sediment/contaminant interactions. The purpose of the study was to test FETRA model with available field data and was not intended to assess the potential impact of the Windscale Nuclear Fuel Reprocessing Plant on the Irish Sea. The model was tested by applying it to the Irish Sea to simulate wind-generated waves and the migration of sediment and ¹³⁷Cs. The model predicted distributions of suspended sand; suspended silt; suspended clay; ¹³⁷Cs sorbed by each of the three sizes of suspended sediments; dissolved ¹³⁷Cs; bed sediment size fractions; and ¹³⁷Cs sorbed by bed sand, bed silt, and bed clay over a two-month period in 1974. FETRA generally predicted reasonable migration patterns for the sediments and ¹³⁷Cs. The prediction of ¹³⁷Cs distributions can be further improved by using a finer grid near the radionuclide release point. The study results indicate that FETRA can simulate the complex phenomena involved in sediment and contaminant transport in coastal waters. However, we recommend that FETRA be tested further at other field sites where the necessary field data are available to validate the model. 47 references, 64 figures, 4 tables

[en] In the U.S. Department of Energy (DOE) complex, 100 million gallons of radioactive and chemical wastes from plutonium production are stored in 281 underground storage tanks. Retrieval of the wastes from the tanks is the first step in its ultimate treatment and disposal. Because billions of dollars are being spent on this effort, waste retrieval demands a strong scientific basis for its successful completion. As will be discussed in Section 4.2, complex interactions among waste chemical reactions, rheology, and mixing of solid and liquid tank waste (and possibly with a solvent) will occur in DSTs during the waste retrieval (mixer pump) operations. The ultimate goal of this study was to develop the ability to simulate the complex chemical and rheological changes that occur in the waste during processing for retrieval. This capability would serve as a scientific assessment tool allowing a priori evaluation of the consequences of proposed waste retrieval operations. Hanford tan k waste is a multiphase, multicomponent, high-ionic strength, and highly basic mixture of liquids and solids. Wastes stored in the 4,000-m3 DSTs will be mixed by 300-hp mixer pumps that inject high-speed (18.3 m/s) jets to stir up the sludge and supernatant liquid for retrieval. During waste retrieval operations, complex interactions occur among waste mixing, chemical reactions, and associated rheology. Thus, to determine safe and cost-effective operational parameters for waste retrieval, decisions must rely on new scientific knowledge to account for physical mixing of multiphase flows, chemical reactions, and waste rheology. To satisfy this need, we integrated a computational fluid dynamics code with state-of-the-art equilibrium and kinetic chemical models and non-Newtonian rheology (Onishi (and others) 1999). This development is unique and holds great promise for addressing the complex phenomena of tank waste retrieval. The current model is, however, applicable only to idealized tank waste conditions-solids are crystals, not hydrates; kinetic rates are fast; the slurry has simple rheology; and the water mass is constant. Thus, this idealized reactive transport model, ARIEL could provide a basis for addressing potentially crippling waste retrieval issues associated with hydrated mineral formation by systematically expanding its modeling capabilities

[en] The TEMPEST computer code has been used to address many waste retrieval operational and safety questions regarding waste mobilization, mixing, and gas retention. Because the amount of sludge retrieved from the tank is directly related to the sludge yield strength and the shear stress acting upon it, it is important to incorporate the sludge yield strength into simulations of erosion-resisting tank waste retrieval operations. This report describes current efforts to modify the TEMPEST code to simulate pump jet mixing of erosion-resisting tank wastes and the models used to test for erosion of waste sludge with yield strength. Test results for solid deposition and diluent/slurry jet injection into sludge layers in simplified tank conditions show that the modified TEMPEST code has a basic ability to simulate both the mobility and immobility of the sludges with yield strength. Further testing, modification, calibration, and verification of the sludge mobilization/immobilization model are planned using erosion data as they apply to waste tank sludges

[en] One mechanism affecting the dispersal of radioactive materials in water bodies is radionuclide adsorption by sediment. Consequently, sediment transport is a major factor to consider when evaluating radionuclide migration. As a part of a study on sediment and radionuclide transport in rivers, Pacific Northwest Laboratory (PNL) is investigating the effect of sediment on the transport of radionuclides in Cattaraugus and Buttermilk Creeks, New York, during different flow conditions. Sources of radioactivity in these creeks were a low-level waste disposal site and a nuclear fuel reprocessing plant. Reprocessing operations were terminated in 1972 and waste disposal was discontinued in 1975. Other sources of radioactivity include fallout from worldwide weapons testing and natural background radioactivity. The major objective of the PNL Field Sampling Program is to provide data on sediment and radionuclide characteristics in Cattaraugus and Buttermilk Creeks to verify the use of the Sediment and Radionuclide Transport model, SERATRA, for nontidal rivers. The program is divided into three phases: Phase 1, medium-flow condition; Phase 2, low-flow condition; and Phase 3, high-flow condition. To date, results have been obtained primarily for the Phase 1 portion. For the Phase 1 sampling, 10 transects were established to collect data on flow and channel, water, sediment, and radionuclide characteristics. Some radiological analyses were made on samples of water, suspended sediment, and bed sediment

[en] The three-dimensional, finite difference model, FLESCOT simulates time-varying movements of flow, turbulent kinetic energy, salinity, water temperature, sediment, and contaminants in estuarine, coastal, and ocean waters. The model was applied to a 106-km (66-mi) reach of the Hudson River estuary in New York between Chelsea and the mouth of the river. It predicted the time-varying, three-dimensional distributions of tidal flow, salinity, three separate groups of sediments (i.e., sand, silt, and clay), and a radionuclide (¹³⁷Cs) in both dissolved and particulate (those sorbed by sediments) forms for over 40 days. The model also calculated riverbed elevation changes caused by sediment deposition and bed erosion, bed sediment size distribution and armoring, and distributions of the particulate ¹³⁷Cs sorbed by sand, silt, and clay in the bed

[en] The finite-element model FETRA is an unsteady, verically averaged two-dimensional model to simulate the transport of sediment and contaminants (radionuclides, heavy metals, pesticides, etc.) in coastal and estuarine water. The model, together with the hydrodynamic model CAFE-I, was applied to the Irish Sea to predict the migration and accumulation of sediment (both cohesive and noncohesive) and of a radionuclide (dissolved and sediment-sorbed) in a tide- and wind-driven system. The study demonstrated that FETRA is a useful tool for assessing sediment and toxic contaminant transport in a marine environment