198 research outputs found
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Factors affecting performance of engineered barriers
For the Yucca Mountain Viability Assessment (VA), a reference design was tentatively selected` In September 1997, and a series of model abstractions are being prepared for the performance assessment (PA) of that design. To determine the sensitivity of peak dose rate at the accessible environment to engineered components, several design options were subjected to the PA models available late in FY97
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Major repository design issues
The Yucca Mountain Project is focused on producing a four-part viability assessment in late FY98. Its four components (design, performance assessment, cost estimate, and licensing development plan) must be consistent. As a tool to clarify design issues and compare design and performance assessment options, a series of repository sketches were developed for the sequential time phases of a repository. The boundaries of the time phases correspond to evolution In the engineered barrier system (EBS)
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Pulse Star inertial confinement fusion reactor
Pulse Star is a pool-type ICF reactor that emphasizes low cost and high safety levels. The reactor consists of a vacuum chamber (belljar) submerged in a compact liquid metal (Li/sub 17/Pb/sub 83/ or lithium) pool which also contains the heat exchangers and liquid metal pumps. The shielding efficiency of the liquid metal pool is high enough to allow hands-on maintenance of (removed) pumps and heat exchangers. Liquid metal is allowed to spray through the 5.5 m radius belljar at a controlled rate, but is prohibited from the target region by a 4 m radius mesh first wall. The wetted first wall absorbs the fusion x-rays and debris while the spray region absorbs the fusion neutrons. The mesh allows vaporized liquid metal to blow through to the spray region where it can quickly cool and condense. Preliminary calculations show that a 2 m thick first wall could handle the mechanical (support, buckling, and x-ray-induced hoop) loads. Wetting and gas flow issues are in an initial investigation stage
Investigations on Repository Near-Field Thermal Modeling - Repository Science/Thermal Load Management & Design Concepts (M41UF033302) Rev.1
The various layers of material from the waste package (such as components of the engineered barrier system and the host rock surface) to a given distance within the rock wall at a given distance can be described as concentric circles with varying thermal properties (see Figure 5.1-1). The selected model approach examines the contributions of the waste package, axial waste package neighbors and lateral neighboring emplacement drifts (see Section 5.2.1 and Appendix H, Section 2). In clay and deep borehole media, the peak temperature is driven by the central waste package whereas, in granite and salt, the contribution to the temperature rise by adjacent (lateral) waste packages in drift or emplacement borehole lines is dominant at the time of the peak temperature. Mathematical models generated using Mathcad software provide insight into the effects of changing waste package spacing for six waste forms, namely UOX, MOX, co-extraction, new extraction, E-Chem ceramic and E-Chem metal in four different geologic media (granite, clay, salt and deep borehole). Each scenario includes thermal conductivity and diffusivity for each layer between the waste package and the host rock, dimensions of representative repository designs (such as waste package spacing, drift or emplacement borehole spacing, waste package dimensions and layer thickness), and decay heat curves generated from knowledge of the contents of a given waste form after 10, 50, 100 and 200 years of surface storage. Key results generated for each scenario include rock temperature at a given time calculated at a given radius from the central waste package (Section 5.2.1 and Appendix H, Section 3), the corresponding temperature at the interface of the waste package and EBS material, and at each EBS layer in between (Section 5.2.2 and Appendix H, Section 4). This information is vital to understand the implications of repository design (waste package capacity, surface storage time, waste package spacing, and emplacement drift or borehole spacing) by comparing the peak temperature to the thermal limits of the concentric layers surrounding the waste package; specifically 100 C for the bentonite buffer in granite and clay repositories, 100 C for rock wall in a clay repository and 200 C at the rock wall for a salt repository. These thermal limits are both preliminary and approximate, and serve as a means to evaluate design options rather than determining compliance for licensing situations. The thermal behavior of a salt repository is more difficult to model because it is not a concentric geometry and because the crushed salt backfill initially has a much higher thermal resistance than intact salt. Three models were investigated, namely a waste package in complete contact with crushed salt, secondly a waste package in contact with intact salt, and thirdly a waste package in contact with 75% intact and 25% crushed salt. The latter model best depicts emplacement of a waste package in the corner of an intact salt alcove and subsequently covered with crushed salt backfill to the angle of repose. The most conservative model (crushed salt) had temperatures much higher than the other models and although bounding, is too conservative to use. The most realistic model (75/25) had only a small temperature difference from the simplest (non-conservative, intact salt) model, and is the one chosen in this report (see Section 5.2.3). A trade-study investigating three key variables (surface storage time, waste package capacity and waste package spacing) is important to understand and design a repository. Waste package heat can be reduced by storing for longer periods prior to emplacement, or by reducing the number of assemblies or canisters within that waste package. Waste package spacing can be altered to optimize the thermal load without exceeding the thermal limits of the host rock or EBS components. By examining each of these variables, repository footprint (and therefore cost) can be optimized. For this report, the layout was fixed for each geologic medium based on prior published designs in the international community, but it will be varied in future work. Section 5.2.4 summarizes the conclusions based on varying two of the three parameters (storage time and waste package capacity), and the results are shown in Appendix H, Sections 5 and 6
Investigations on Repository Near-Field Thermal Modeling - Repository Science/Thermal Load Management & Design Concepts (M41UF033302)
The various layers of material from the waste package (such as components of the engineered barrier system and the host rock surface) to a given distance within the rock wall at a given distance can be described as concentric circles with varying thermal properties (see Figure 5.1-1). The selected model approach examines the contributions of the waste package, axial waste package neighbors and lateral neighboring emplacement drifts (see Section 5.2.1 and Appendix H, Section 2). In clay and deep borehole media, the peak temperature is driven by the central waste package whereas, in granite and salt, the contribution to the temperature rise by adjacent (lateral) waste packages in drift or emplacement borehole lines is dominant at the time of the peak temperature. Mathematical models generated using Mathcad software provide insight into the effects of changing waste package spacing for six waste forms, namely UOX, MOX, co-extraction, new extraction, E-Chem ceramic and E-Chem metal in four different geologic media (granite, clay, salt and deep borehole). Each scenario includes thermal conductivity and diffusivity for each layer between the waste package and the host rock, dimensions of representative repository designs (such as waste package spacing, drift or emplacement borehole spacing, waste package dimensions and layer thickness), and decay heat curves generated from knowledge of the contents of a given waste form after 10, 50, 100 and 200 years of surface storage. Key results generated for each scenario include rock temperature at a given time calculated at a given radius from the central waste package (Section 5.2.1 and Appendix H, Section 3), the corresponding temperature at the interface of the waste package and EBS material, and at each EBS layer in between (Section 5.2.2 and Appendix H, Section 4). This information is vital to understand the implications of repository design (waste package capacity, surface storage time, waste package spacing, and emplacement drift or borehole spacing) by comparing the peak temperature to the thermal limits of the concentric layers surrounding the waste package; specifically 100 C for the bentonite buffer in granite and clay repositories, 100 C for rock wall in a clay repository and 200 C at the rock wall for a salt repository. These thermal limits are both preliminary and approximate, and serve as a means to evaluate design options rather than determining compliance for licensing situations. The thermal behavior of a salt repository is more difficult to model because it is not a concentric geometry and because the crushed salt backfill initially has a much higher thermal resistance than intact salt. Three models were investigated, namely a waste package in complete contact with crushed salt, secondly a waste package in contact with intact salt, and thirdly a waste package in contact with 75% intact and 25% crushed salt. The latter model best depicts emplacement of a waste package in the corner of an intact salt alcove and subsequently covered with crushed salt backfill to the angle of repose. The most conservative model (crushed salt) had temperatures much higher than the other models and although bounding, is too conservative to use. The most realistic model (75/25) had only a small temperature difference from the simplest (non-conservative, intact salt) model, and is the one chosen in this report (see Section 5.2.3). A trade-study investigating three key variables (surface storage time, waste package capacity and waste package spacing) is important to understand and design a repository. Waste package heat can be reduced by storing for longer periods prior to emplacement, or by reducing the number of assemblies or canisters within that waste package. Waste package spacing can be altered to optimize the thermal load without exceeding the thermal limits of the host rock or EBS components. By examining each of these variables, repository footprint (and therefore cost) can be optimized. For this report, the layout was fixed for each geologic medium based on prior published designs in the international community, but it will be varied in future work. Section 5.2.4 summarizes the conclusions based on varying two of the three parameters (storage time and waste package capacity), and the results are shown in Appendix H, Sections 5 and 6
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