Potential Benefits of Actinide Recycle to the Yucca Mountain Repository

This thesis contains an analysis of the Yucca Mountain Repository for high level nuclear wastes. A list of all the proposed waste materials was compiled. This list indicates that at the reference emplacement density of 57 kW/acre, the planned repository has insufficient capacity. Thus, incentives exist to increase the capacity by increasing the emplacement density. An alternative emplacement methodology utilizing a combination of actinide recycle, optimized geometry, and ventilated emplacement over an extended operation period promises to increase the capacity drastically. Using previously calculated values of the decay heat in spent fuel (SF) and high level wastes (HLW) from which the actinides have been removed, one and three dimensional heat transfer calculations were performed to quantify the capacity increases for several combinations of burnup, geometry changes, and repository operating schedules. These calculations indicate that the reference emplacement density of 57 kW/acre, which corresponds to 120 fuel assemblies per acre, is overly conservative. According to these calculations, the actual limit for SF emplaced in the reference geometry is 75 kW/acre, which corresponds to 159 fuel assemblies per acre. By removing the actinides, this maximum increases to 211 assemblies per acre. Calculations were performed for SF and HLW (SF From which the actinides have been removed via reprocessing) in optimized geometry. By spacing the radioactive material closer together, the maximum densities increase to 184 and 310 assemblies/acre for SF and HLW respectively. Similar calculations were performed for higher burnup materials, with no noticeable change in the relative results. Finally, staggered emplacement was analyzed. The maximum emplacement densities increase to 219 and 315 assemblies/acre for SF and HLW in standard geometry. In optimized geometry, the maximum densities are 222 and 590 assemblies/acre for SF and HLW. The results reported above correspond to the reference hot repository in which the waste packages reach temperatures greater than 200o C. Licensing difficulties associated with this hot repository content have created interest in a cold repository in which the emplacement horizon does not exceed the boiling point of water. Results for the cold repository in the standard emplacement geometry indicate the expected decrease in the allowable loadings: 68 and 91 assemblies/acre for SF and HLW respectively. For optimized geometry, the loadings increase to 93 and 133 assemblies/acre for SF and HLW. The results for staggered emplacement, however, do not show such a great decrease. In standard geometry, the loadings are 94 and 135 assemblies/acre for SF and HLW, and in optimized geometry, they are 142 and 253 assemblies/acre. This last result indicates that a cold repository which should prove easier to license, can contain all the identified wastes if one combines actinide removal with optimized emplacement geometry and ventilated operation over an extended operating period

mSHAP: SHAP Values for Two-Part Models

Two-part models are important to and used throughout insurance and actuarial science. Since insurance is required for registering a car, obtaining a mortgage, and participating in certain businesses, it is especially important that the models which price insurance policies are fair and non-discriminatory. Black box models can make it very difficult to know which covariates are influencing the results. SHAP values enable interpretation of various black box models, but little progress has been made in two-part models. In this paper, we propose mSHAP (or multiplicative SHAP), a method for computing SHAP values of two-part models using the SHAP values of the individual models. This method will allow for the predictions of two-part models to be explained at an individual observation level. After developing mSHAP, we perform an in-depth simulation study. Although the kernelSHAP algorithm is also capable of computing approximate SHAP values for a two-part model, a comparison with our method demonstrates that mSHAP is exponentially faster. Ultimately, we apply mSHAP to a two-part ratemaking model for personal auto property damage insurance coverage. Additionally, an R package (mshap) is available to easily implement the method in a wide variety of applications

Thin-Film Evolution Equation for a Strained Solid Film on a Deformable Substrate: Numerical Steady States

We consider the nonlinear behavior of the thin-film evolution equation for a strained solid film on a substrate. The evolution equation describes morphological changes to the film by surface diffusion in response to elastic energy, surface energy, and wetting energy. Due to the thin-film approximation, the elastic response of the film is determined analytically, resulting in a self-contained evolution equation which does not require separate numerical solution of the full three-dimensional elasticity problem. Using a pseudospectral predictor-corrector method we numerically determine the family of steady state solutions to this evolution equation which correspond to quantum dot and quantum ridge morphologies

A Performance-Based Framework for Structural Resilience to Blast-Induced Damage

This paper proposes a framework for establishing quantitative measures and mathematically reproducible definitions of structural resiliency as it pertains to a structure\u27s ability to minimize the potential for undesirable response to low-probability-high-consequence events. The resiliency assessment and design process follow a logical progression of steps starting with the characterization of hazards and continuing through analysis simulations, damage modeling, and loss assessment by balancing functional relationships between design tradeoffs and associated consequences. The outcomes of each subprocess are articulated through a series of generalized variables: topology, geometry, damage, and hazard intensity measures. A rigorous probabilistic framework permits consistent characterization of the inherent uncertainties throughout the process. The proposed framework is well suited to support the building design process through stochastic characterization of assessment measures. Using a stepwise approach, the framework facilitates a systemwide method to confront multihazard threat scenarios by establishing functional relationships between the development of appropriate models, design methods, damage acceptance criteria, and tools necessary for implementation. The proposed methodology can be implemented directly for assessment of project-specific performance criteria or can be used as a basis for establishing appropriate performance criteria and provisions to achieve resilient structural solutions at the outset of design