Results 1 - 10 of 2352
Results 1 - 10 of 2352. Search took: 0.03 seconds
|Sort by: date | relevance|
[en] The Nuclear Nonproliferation Programs Design Authority is in the design stage of the Waste Solidification Building (WSB) for the treatment and solidification of the radioactive liquid waste streams generated by the Pit Disassembly and Conversion Facility (PDCF) and Mixed Oxide (MOX) Fuel Fabrication Facility (MFFF). The waste streams will be mixed with a cementitious dry mix in a 55-gallon waste container. Savannah River National Laboratory (SRNL) has been performing the testing and evaluations to support technical decisions for the WSB. Engineering Modeling and Simulation Group was requested to evaluate the thermal performance of the 55-gallon drum containing hydration heat source associated with the current baseline cement waste form. A transient axi-symmetric heat transfer model for the drum partially filled with waste form cement has been developed and heat transfer calculations performed for the baseline design configurations. For this case, 65 percent of the drum volume was assumed to be filled with the waste form, which has transient hydration heat source, as one of the baseline conditions. A series of modeling calculations has been performed using a computational heat transfer approach. The baseline modeling results show that the time to reach the maximum temperature of the 65 percent filled drum is about 32 hours when a 43 C initial cement temperature is assumed to be cooled by natural convection with 27 C external air. In addition, the results computed by the present model were compared with analytical solutions. The modeling results will be benchmarked against the prototypic test results. The verified model will be used for the evaluation of the thermal performance for the WSB drum
[en] Thin-film technology using polycrystalline semiconductors has been widely applied to active-matrix-addressed liquid crystal displays (AMLCDs) where thin-film transistors act as digital pixel switches. Research and development is in progress to integrate the driver circuits around the peripheral of the display, resulting in significant cost reduction of connections between rows and columns and the peripheral circuitry. For this latter application, where for instance it is important to control the greyscale voltage level delivered to the pixel, an understanding of device behaviour is required so that models can be developed for analogue circuit simulation. For this purpose, various analytical models have been developed based on that of Seto who considered the effect of monoenergetic trap states and grain boundaries in polycrystalline materials but not the contribution of the grains to the electrical properties. The principal aim of this thesis is to describe the use of a numerical device simulator (ATLAS) as a tool to investigate the physics of the trapping process involved in the device operation, which additionally takes into account the effect of multienergetic trapping levels and the contribution of the grain into the modelling. A study of the conventional analytical models is presented, and an alternative approach is introduced which takes into account the grain regions to enhance the accuracy of the analytical modelling. A physically-based discrete-grain-boundary model and characterisation method are introduced to study the effects of the multienergetic trap states on the electrical characteristics of poly-TFTs using CdSe devices as the experimental example, and the electrical parameters such as the density distribution of the trapping states are extracted. The results show excellent agreement between the simulation and experimental data. The limitations of this proposed physical model are also studied and discussed. (author)
[en] Recent probabilistic risk assessment studies indicate that potential accidents initiated by large earthquakes are among the major contributors to public risk from nuclear power plants. During a severe earthquake, the symptoms presented to operators may be unreliable and may endanger the validity of actions in emergency response guidelines (ERGs). The objective of the present study is to improve the operator capability of responding to seismic damage through the use of ERGS. The methods used are to deterministically identify the possible weakness of ERGs, given a severe earthquake, and to probabilistically evaluate those identified weaknesses. Several cases are postulated. Each of them contains system failures with or without indicator failures and leads the core to meltdown conditions if the operator follows the ERGs strictly without any deviation. The likelihood of each case is estimated. A LISP program is developed to estimate the plant seismic risk with which the relative risk contribution of each postulated case is estimated. As a result, ten cases are postulated and possible remedies for each case are discussed. The likelihood of each case is estimated to be not negligible. The identified indicator failures should be considered in future refinement of the ERGS. The development of an expert system to provide remedial procedures should be considered after a more thorough study in which many more cases are postulated
[en] The process of recovering the waste in storage tanks at the Savannah River Site (SRS) typically requires mixing the contents of the tank to ensure uniformity of the discharge stream. Mixing is accomplished with one to four slurry pumps located within the tank liquid. The slurry pump may be fixed in position or they may rotate depending on the specific mixing requirements. The high-level waste in Tank 48 contains insoluble solids in the form of potassium tetraphenyl borate compounds (KTPB), monosodium titanate (MST), and sludge. Tank 48 is equipped with 4 slurry pumps, which are intended to suspend the insoluble solids prior to transfer of the waste to the Fluidized Bed Steam Reformer (FBSR) process. The FBSR process is being designed for a normal feed of 3.05 wt% insoluble solids. A chemical characterization study has shown the insoluble solids concentration is approximately 3.05 wt% when well-mixed. The project is requesting a Computational Fluid Dynamics (CFD) mixing study from SRNL to determine the solids behavior with 2, 3, and 4 slurry pumps in operation and an estimate of the insoluble solids concentration at the suction of the transfer pump to the FBSR process. The impact of cooling coils is not considered in the current work. The work consists of two principal objectives by taking a CFD approach: (1) To estimate insoluble solids concentration transferred from Tank 48 to the Waste Feed Tank in the FBSR process and (2) To assess the impact of different combinations of four slurry pumps on insoluble solids suspension and mixing in Tank 48. For this work, several different combinations of a maximum of four pumps are considered to determine the resulting flow patterns and local flow velocities which are thought to be associated with sludge particle mixing. Two different elevations of pump nozzles are used for an assessment of the flow patterns on the tank mixing. Pump design and operating parameters used for the analysis are summarized in Table 1. The baseline pump orientations are chosen by the previous work (Lee et. al, 2008) and the initial engineering judgement for the conservative flow estimate since the modeling results for the other pump orientations are compared with the baseline results. As shown in Table 1, the present study assumes that each slurry pump has 900 gpm flowrate for the tank mixing analysis, although the Standard Operating Procedure for Tank 48 currently limits the actual pump speed and flowrate to a value less than 900 gpm for a 29 inch liquid level. Table 2 shows material properties and weight distributions for the solids to be modeled for the mixing analysis in Tank 48.
[en] Proton pulsed NMR on three complementary one-dimensional systems, Cu(pc), Ni(pc)I, and Cu(pc)I is reported. Each of these exhibits different electronic behavior: localized electrons (spin 12) of Cu(pc), free electrons in the case of Ni(Pc)I, and a coexisting system of localized electrons and free electrons in Cu(pc)I. The spin-spin relaxation times for these materials are well explained at high temperature by the second moment of the proton dipole-dipole interaction, 20 μS, and at low temperature a demagnetization effect. Measurements of the proton spin-lattice relaxation rate, T1-1, reveal that the organic insulator Cu(pc) is a highly one-dimensional spin- 12 Heisenberg system with absolute value JK/sub B/ = 0.29 K and absolute value JJ' > 6 x 103, where J and J' are the intrachain and interchain exchange interactions. The energy band structure of the highly one-dimensional conductor Ni(pc)I appears to change at 60 K. NMR spin-lattice relaxation-rate measurements reveal that the conduction electron density is low at the positions of protons attached to the outside carbons of the pc ring. NMR and EPR data suggest that in Cu(pc)I the indirect exchange interaction mediated by conduction electrons, 6 K, is an order of magnitude stronger than that of the direct exchange interaction between Cu+2 local moments, 0.34 K
[en] Nuclear waste at Savannah River Site (SRS) waste tanks consists of three different types of waste forms. They are the lighter salt solutions referred to as supernate, the precipitated salts as salt cake, and heavier fine solids as sludge. The sludge is settled on the tank floor. About half of the residual waste radioactivity is contained in the sludge, which is only about 8 percentage of the total waste volume. Mixing study to be evaluated here for the Salt Disposition Integration (SDI) project focuses on supernate preparations in waste tanks prior to transfer to the Salt Waste Processing Facility (SWPF) feed tank. The methods to mix and blend the contents of the SRS blend tanks were evalutaed to ensure that the contents are properly blended before they are transferred from the blend tank such as Tank 50H to the SWPF feed tank. The work consists of two principal objectives to investigate two different pumps. One objective is to identify a suitable pumping arrangement that will adequately blend/mix two miscible liquids to obtain a uniform composition in the tank with a minimum level of sludge solid particulate in suspension. The other is to estimate the elevation in the tank at which the transfer pump inlet should be located where the solid concentration of the entrained fluid remains below the acceptance criterion (0.09 wt% or 1200 mg/liter) during transfer operation to the SWPF. Tank 50H is a Waste Tank that will be used to prepare batches of salt feed for SWPF. The salt feed must be a homogeneous solution satisfying the acceptance criterion of the solids entrainment during transfer operation. The work described here consists of two modeling areas. They are the mixing modeling analysis during miscible liquid blending operation, and the flow pattern analysis during transfer operation of the blended liquid. The modeling results will provide quantitative design and operation information during the mixing/blending process and the transfer operation of the blended liquid in the Salt Disposition Integration (SDI) facility. The results will also help validate the anticipated performance of the pump vendor's design.
[en] Savannah River National Laboratory (SRNL) evaluated methods to mix and blend the contents of the blend tanks to ensure the contents are properly blended before they are transferred from the blend tank such as Tank 21 and Tank 24 to the Salt Waste Processing Facility (SWPF) feed tank. The tank contents consist of three forms: dissolved salt solution, other waste salt solutions, and sludge containing settled solids. This paper focuses on developing the computational model and estimating the operation time of submersible slurry pump when the tank contents are adequately blended prior to their transfer to the SWPF facility. A three-dimensional computational fluid dynamics approach was taken by using the full scale configuration of SRS Type-IV tank, Tank 21H. Major solid obstructions such as the tank wall boundary, the transfer pump column, and three slurry pump housings including one active and two inactive pumps were included in the mixing performance model. Basic flow pattern results predicted by the computational model were benchmarked against the SRNL test results and literature data. Tank 21 is a waste tank that is used to prepare batches of salt feed for SWPF. The salt feed must be a homogeneous solution satisfying the acceptance criterion of the solids entrainment during transfer operation. The work scope described here consists of two modeling areas. They are the steady state flow pattern calculations before the addition of acid solution for tank blending operation and the transient mixing analysis during miscible liquid blending operation. The transient blending calculations were performed by using the 95% homogeneity criterion for the entire liquid domain of the tank. The initial conditions for the entire modeling domain were based on the steady-state flow pattern results with zero second phase concentration. The performance model was also benchmarked against the SRNL test results and literature data.
[en] Before 1994, Core Laboratories Canada Ltd. adopted local country benefit plans as stipulated by the government of the day. This approach meant that the company had many different benefit plans in place or in some situations no benefit plans at all, if the law of the land allowed such an approach. The company at this time viewed the lack of or minimal benefit plans as a cost saving venture. The parent company did not take onto account the effect on morale, employee retention and loyalty that these limited plans provided. A change in ownership in 1994 presented the opportunity for Core to re-assess its benefits package and introduce an incentive plan for its worldwide employees. The introduction of a pension with profits plan proved to be satisfying to employees, and the manager's incentive plan enabled the company to retain, with the exception of people who retired from the business, its entire management staff over a four year period. The stock option plan led to the retention of essential employees and reduced the turnover in this area. Discretionary bonuses succeeded in promoting recognition amongst employees as well as providing monetary reward, and the combination of benefits, incentive and stock option plans enabled the company to retain the vast majority of key employees and to entice selected individuals to the company from other organizations. 3 refs