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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Thermal Analysis Of Saltstone Disposal Units

SRR requested that SRNL develop a two-dimensional computer simulation model to be capable of predicting grout temperatures attained in Saltstone Disposal Units (SDUs) during the transient addition of saltstone grout and its subsequent storage period. A simulation model was developed to calculate the transient grout temperatures of the SDU facility by taking an axisymmetric and two-dimensional Computational Fluid Dynamics (CFD) approach. The final performance calculations were based on the conduction and radiation model without a convection cooling mechanism for conservative estimate of the grout temperatures and computational efficiency. While convection within the SDU is disabled in the current calculations, the simulation model has the capability of turning convection back on if desired by the user. Hence, the thermal model in its current configuration is best characterized as a finite-volume heat transfer model. However, given that the model can account for convection if desired by the user, it will be referred to as a CFD model. The grout material contains a transient heat source due to the exothermic hydration reactions of the cementitious material mixed with salt solution. The model can predict the transient temperatures at point locations within the poured grout and the overlying vapor space, and at the interior and exterior surfaces of the structure. The thermal model has been developed for two SDUs at the Savannah River Site (SRS); namely, SDU 2A and SDU 6. SDU 2A is a cylindrical unit measuring 150 feet (ft) in diameter, 22 ft tall, and holds approximately three million gallons of grout. SDU 6 is 375 ft in diameter and 43 ft high with a capacity of over thirty million gallons. Prior to performing the thermal calculations for the SDU 6 facility, the benchmarking test for the smaller SDU 2A unit was performed to establish the solution method and to verify the computational results using existing thermocouple data. Based on the Lagrangian discrete method and boundary conditions established by the SDU 2A benchmarking test, the CFD calculations were performed to predict the transient temperatures at local positions of the poured grout and air spaces within the SDU 6 structure.

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DOE OSTI2019

Mercury Speciation and Stabilization in Saltstone - 19103

Mercury is a contaminant of concern in Savannah River Site (SRS) high level waste (HLW). For five decades elemental mercury was used in the catalytic dissolution of aluminum cladding from the enriched-alloy uranium recovery process. Over 60,000 kg of mercury are now distributed in the SRS HLW tanks. The mercury speciation in the liquid waste streams resulting from conditioning HLW sludge for vitrification and in the decontaminated low activity sodium salt solution removed from the tanks was initially thought to be primarily ionic with a minor amount of elemental mercury. Recent sampling detected organic mercury, primarily methylmercury, HgCH{sub 3}{sup +} (MeHg{sup +}), and a trace amount of ethylmercury (EtHg) in these streams in addition to the ionic and elemental forms of mercury. The objective of this work was to identify the fate of the organic mercury in saltstone, a waste form containing portland cement, slag cement, and Class F fly ash. This information is needed to evaluate total mercury and organic mercury limits for the saltstone Waste Acceptance Criteria to assure regulatory compliance with mixed waste disposal requirements and to evaluate opportunities to enhance the waste form performance. Results to date indicate that the MeHg{sup +} reacts with sulfide in the cementitious reagents, slag in particular, to form nanoparticles of β-HgS, meta cinnabar, which is very insoluble and has a solubility product in water, pK{sub sp}, at 25 deg. C of 53. (authors)

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DOE OSTI2019

Saltstone Facility Operating Experience with Mega-Vault Disposal Units - 19497

The Saltstone Production Facility (SPF) has been treating low-level waste aqueous salt solution at the Savannah River Site (SRS) since 1990. Salt solutions are transferred from a large-volume, underground storage tank via underground waste transfer line into the SPF. The waste is received into one of two receipt tanks and then transferred to a twin-shaft mixer where dry feeds are introduced to create a fresh grout slurry. The grout exits the mixer into a hold tank, which has a residence time of approximately two minutes. The slurry is then pumped via peristaltic pump through a grout transfer line to one of several disposal units in the Saltstone Disposal Facility (SDF). The transfer line length varies from 0.4 km to 0.8 km depending on disposal location. With the salt disposal mission at SRS accelerating via the operation of the Modular Caustic Side Solvent Extraction (MCU) facility and the anticipated startup of the Salt Waste Processing Facility (SWPF), it is important that the SPF and SDF operate with minimal outage time and maximum facility availability. To this end, the design of the newest disposal units has incorporated the benefits of commercially available cylindrical concrete tank design on a very large scale to maximize economies of scale. This new design has been placed into radioactive service and the initial operational data will be compared with previous disposal operations along with an overview of how disposal unit design has significantly evolved since the initial construction in the early 1990's. Additionally, several processing facility modifications have either been implemented or developed in recent years to improve operating reliability and ensure facility availability once the SWPF becomes the primary waste generator providing feed for the SPF. These modifications, the issues driving their development, and an assessment of their effectiveness will also be discussed. (author)

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DOE OSTI2014

Sensitivity Analysis for Saltstone Disposal Unit Column Degradation Analyses

PORFLOW related analyses supporting a Sensitivity Analysis for Saltstone Disposal Unit (SDU) column degradation were performed. Previous analyses, Flach and Taylor 2014, used a model in which the SDU columns degraded in a piecewise manner from the top and bottom simultaneously. The current analyses employs a model in which all pieces of the column degrade at the same time. Information was extracted from the analyses which may be useful in determining the distribution of Tc-99 in the various SDUs throughout time and in determining flow balances for the SDUs.

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DOE OSTI2019

Conceptual Design for Replaceable Paddle for the Saltstone Production Facility (SPF) Mixer

The primary objective of this task was to provide a recommendation for a replaceable paddle that could be incorporated into the Saltstone Production Facility (SPF) process. The replaceable paddle concept was proposed given the time it took to replace the existing paddle designs was approximately a week of downtime. Two different types of replaceable paddles were considered, a split paddle and a replaceable tip paddle. The split paddle design was developed; however, a review of the drawings by maintenance personnel determined that changeout of the new design would take about the same time/effort as replacing the existing paddles. Five different replaceable tip designs were considered: side attachment, V neck, straight notch, angled notch, and dovetail. The recommended replaceable tip design was the angled notch, which includes a central hub with two angled notches, where the replaceable tips are secured to the hub using two ½” – 13 Unified National Coarse Threads (UNC) socket head cap screws (SHCS). Design drawing for both the flat and helical paddle blades are complete and are included in Appendix A. A structural calculation (M-CLC-Z-00137) was performed on this design which determined the design is structurally adequate for normal or extreme loads that would be encountered in the SPF READCOTM mixer. This calculation is included in Appendix C. Based on the calculation, mechanical failure will not limit the life of the tip or tip attachment. The quantity of erosion will be the primary driver dictating tip replacement schedules.

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DOE OSTI2020

Methane generation rates from Tank 50 simulant with methylmercury containing saltstone grout solids

This report documents the tests performed to address the requirements listed in the Technical Assistance Request, which resulted in a Test Plan to obtain the required information. To that end the results are documented herein to determine the capacity, and reaction time, for methylmercury (MeHg) contained within Tank 50 salt solution simulant (T50SS) to produce methane when mixed with saltstone dry feed ingredients, as individual components (cement, slag cement, and fly ash) or a combination of those components.

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DOE OSTI2021

Replaceable Paddle Tip Fabrication and Testing for Saltstone Production Facility (SPF) Mixer (FY2020 Update)

Details of the operations and issues related to the paddles used in the Saltstone Production Facility (SPF) employing the 10-inch READCO ™ -Kurimoto co-rotating dual shaft continuous mixer are provided in SRNL-ST1-2019-00142, Based on a recent effort performed by the Savannah River National Laboratory (SRNL) and funded by Savannah River Remediation (SRR), eight different replaceable paddle designs were proposed and the angled notched design was selected for this study. This design was selected over the other designs due to its simplicity and its ability to meet the fitness of duty requirements. There are two types of angled notched replaceable tip designs, one being flat and the other helical. Either of these designs can be used for blending the premix with the salt solution. Stress calculations performed on this design (the use of the bolts and connections) are documented in M-CLC-Z-00137 showing it was suitable for use.

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DOE OSTI2015

Reactive amendment saltstone (RAS). A novel approach for improved sorption/retention of radionuclides such as technetium and iodine

This study examined the use of reactive amendments (hydroxyapatite, activated carbon, and two types of organoclays) that prior research suggests may improve retention of 99 Tc and 129 I. Tests were conducted using surrogates for 99 Tc (NaReO 4 ) and 129 I (NaI). Results showed that adding up to 10% of organoclay improved the retention of Re without adversely impacting hydraulic properties. To a lesser extent, iodine retention was also improved by adding up to 10% organoclay. Numerical modeling showed that using organoclay as a reactive barrier may significantly retard 99 Tc release from saltstone disposal units.

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DOE OSTI2015

PORFLOW Simulations Supporting Saltstone Disposal Unit Design Optimization

SRNL was requested by SRR to perform PORFLOW simulations to support potential cost-saving design modifications to future Saltstone Disposal Units in Z-Area (SRR-CWDA-2015-00120). The design sensitivity cases are defined in a modeling input specification document SRR-CWDA-2015-00133 Rev. 1. A high-level description of PORFLOW modeling and interpretation of results are provided in SRR-CWDA-2015-00169. The present report focuses on underlying technical issues and details of PORFLOW modeling not addressed by the input specification and results interpretation documents. Design checking of PORFLOW modeling is documented in SRNL-L3200-2015-00146.

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DOE OSTI2018

PORFLOW Simulations Supporting the Saltstone Performance Assessment Revision

The most recent Performance Assessment (PA) of the Z-Area Saltstone Disposal Facility (SDF) was performed in 2009, and three Special Analyses were subsequently conducted. Currently the SDF PA analysis is being revised by the Savannah River Remediation (SRR) Waste Disposal Authority group to reflect updated input information and assumptions, and improved understanding of disposal system performance. In support of the PA revision, Savannah River National Laboratory has developed revised methods for simulating the transport of I-129 and Tc-99 through porous media in a shrinking core model using the PORFLOW code. The revised methods are based on updated reduction capacity, I-129 distribution coefficient, and Tc-99 solubility values from SRR. PORFLOW simulations of aquifer transport have been revised to reflect a recent update to the General Separations Area groundwater flow model and improved treatment of plume dispersion. Hydraulic properties for some soils / sediments have been revised based on E-Area PA maintenance work. Example simulation results are provided to illustrate the behavior of the new I-129 and Tc-99 shrinking core models.

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DOE OSTI2023

July 2022 Semiannual Saltstone Toxicity Characteristic Leaching Procedure (TCLP) Results

The aqueous waste from Tank 50 (salt solution) is sampled semiannually for transfers to the Saltstone Production Facility (SPF). Salt solution is treated at SPF and disposed of in the Salstone Disposal Facility (SDF). Per request of customer, X-TTR-Z-00025, Revision 0, two SDF waste form (salstone) samples were prepared in the Savannah River National Laboratory (SRNL) from the Tank 50 Waste Acceptance Criteria (WAC) sample and Z-Area premix material for the July 2022 Semiannual Toxicity Characteristic Leaching Procedure (TCLP) samples. One sample contained a Full Premix which included 10:45:45 (by weight) of cement, slag and fly ash. The second sample contained 60:40 (by weight) of slag and fly ash only referred to as the "Cement-Free grout sample." Results from this technical report support Task 2: 'Grout Leaching Analyses' of the Task Technical Request (TTR) prepared by Savannah River Mission Completion (SRMC). After at least 28 days cured, a sample of each of the SDF waste forms was collected and shipped to a certified laboratory for analysis using Toxicity Characteristic Leaching Procedure (TCLP). The July 2022 semiannual salstone (Full Premix) and the Cement-Free grout samples met the South Carolina (SC) Code of Regulations for Hazardous Waste Management Regulations (HWMR) 61-79.261.24 and 61-79-268.48 requirements for the non-hazardous waste form with respect to Resource Conservation and Recovery Act (RCRA) metals and Underlying Hazardous Constituents (UHCs), and also met the SPF WAC that was in effect at the time of the tank sampling.

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DOE OSTI2019

Implementation of a Risk-Informed Monitoring Program for the Saltstone Disposal Facility - 19374

Section 3116(b) of the Ronald W. Reagan National Defense Authorization Act for Fiscal Year 2005 (NDAA) requires the US NRC, in coordination with the appropriate State agency, to monitor certain disposal actions of the US DOE to assess compliance with the performance objectives in Subpart C of Part 61 of Title 10 of the Code of Federal Regulations (CFR). Under Section 3116(b), the US NRC monitors the US DOE disposal of salt waste at the Saltstone Disposal Facility (SDF) at the Savannah River Site (SRS) in South Carolina. Since the first US NRC monitoring plan for the SDF was issued in 2007, the US NRC staff has made the risk-significant areas of interest more specific. Following the US DOE issuance of the 2009 performance assessment for the SDF and the US NRC review of that document, the US NRC issued its second monitoring plan for the SDF in 2013. The 2013 US NRC monitoring plan included 11 monitoring areas, which were broken down into 40 specific monitoring factors. The US NRC prioritized those monitoring factors (i.e., low, medium, high) based on the sensitivity of model results to the assumptions or processes covered by the monitoring factor and the uncertainty in those assumptions or processes. Those monitoring factors can be opened, closed, revised, and re-prioritized based on new information or changes in the US DOE activities and plans. For example, the list of US NRC high-priority monitoring factors has changed in response to changing information. The flexibility of this approach allows the US NRC to remain focused on risk-significant areas of interest. The US NRC staff has made changes to the NDAA monitoring program at the SDF since the issuance of the 2007 monitoring plan. First, the development of more specific monitoring factors and the prioritization of those monitoring factors has been successful in focusing the US NRC and the US DOE resources on risk-significant issues and providing transparency to stakeholders. Second, the US NRC reviews have become more focused on addressing specific monitoring factors, which has made the process for updating the monitoring plan more transparent. Finally, periodic management meetings and monthly telephone calls maintain open communications between the US NRC, US DOE, South Carolina Department of Health and Environmental Control (SCDHEC), and US EPA. (authors)

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DOE OSTI2019

Thermal Analysis for SRS Saltstone Disposal Unit Facility

Saltstone Disposal Units (SDU) are long term disposal units for low activity grout produced from the solidification of decontaminated non-hazardous salt waste at SRS. The unit is a cylindrical disposal vault of 150 ft. in diameter and 23 ft. in height. The total volume the SDU can hold is 3 million gallons of grout. The hydration process of the grout material produces heat from an exothermic chemical reaction. If the grout reaches temperatures higher than the maximum safety temperature of 95 deg. C, cracks can start forming leading to contamination of the environment. The purpose of this study is to develop the optimal baseline domain boundary conditions and to perform a sensitivity analysis with respect to the baseline modeling conditions. The following assumptions were made for the modeling calculations: - The system geometry is axisymmetric; - The system was at steady state; - Ambient temperature was set to 100 deg. F; - Air was assumed to be an incompressible ideal gas; - Radiation was neglected for a conservative estimation; - Natural convection for the SDU vapor space is assumed to be turbulent because Rayleigh number based on typical operating conditions is higher than 10{sup 8}; - Water tables were not taken into consideration. The following sensitivity analyses were performed to find the optimal domain boundary: - Mesh size sensitivity; - Soil depth sensitivity - Soil depth varied from 30 ft to 250 ft with a soil thickness of 90 ft; - Soil thickness sensitivity - Soil thickness varied from 30 ft to 270 ft with a soil depth of 180 ft; - Soil conductivity sensitivity - Soil thermal conductivity varied from 0.25 W/m-K to 1 W/m-K; - Ambient Temperature Sensitivity - Ambient temperature varied from 70 deg. F to 110 deg. F. For the thermal calculations, the temperature of the bottom of the soil was set to 17.4 deg. C. The heat flux on the roof of the building and surface of the earth is 163.2 W/m{sup 2}. The soil sides are set to be adiabatic. The sensitivity analysis shows that the mesh size has no effect on the numerical results. This is mainly due to a small convection zone and large conduction zones in the modeling domain. The optimal domain boundary was found to be a soil thickness of 90 ft and a soil depth of 150 ft. The different sensitivity analysis performed here shows the optimal boundary domain to be used for thermal calculations is a soil depth of 150 ft beneath the SDU and a soil thickness of 90 ft. Anything larger would produce similar solutions but at a longer computational time to solve. The maximum temperature was more sensitive to soil properties as shown here. While the ambient temperature affected the max temperature linearly. Most of the heat transfer takes place downward vertically between the SDU and the soil beneath it. Using the optimal domain boundary determined by the sensitivity analyses, the maximum thermal loading to keep the maximum grout temperature below 95 deg. C is 1.646 W/m{sup 3}.

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DOE OSTI2021

Methylmercury Retention Evaluation to Support Tank 50 and Saltstone Waste Acceptance Criteria: Parts 2 and 3

The objective of this work was to provide a technical basis for the organic mercury waste acceptance criterion (WAC) for Tank 50 salt solution. The current mercury WAC for Tank 50 solution is 325 mg/L as Hg regardless of the form of mercury, which is about three times higher than any total Hg concentrations measured to date in Tank 50 solution. To date, the highest total Hg and MeHg + concentrations in the Tank 50 solution were 105 and 62 mg/L, respectively.

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DOE OSTI2018

Hydrogen Generation Rates for Tank 50 and Saltstone Related Samples using a Sealed Reactor System

This report documents the results of sealed reactor tests to measure the hydrogen generation rate (HGR) from Tank 50 waste, which may be on the order of 10 -10 (ft 3 /h)/gal. Because the estimated HGR limit of detection (LOD) for an open, continuous flow system is approximately 10 -7 (ft 3 /h)/gal a more sensitive method was needed. By accumulating generated gasses in a sealed system without a continuous purge gas, the resulting concentrations can increase the sensitivity of measurement, which is based on time of heating.

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