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Some Logistical Considerations in Designing a System of Deep Boreholes for Disposal of High-Level Radioactive Waste

Brady, Patrick V.; Arnold, Bill W.

Deep boreholes could be a relatively inexpensive, safe, and rapidly deployable strategy for disposing Americaś nuclear waste. To study this approach, Sandia invested in a three year LDRD project entitled “Radionuclide Transport from Deep Boreholes.” In the first two years, the borehole reference design and backfill analysis were completed and the supporting modeling of borehole temperature and fluid transport profiles were done. In the third year, some of the logistics of implementing a deep borehole waste disposal system were considered. This report describes what was learned in the third year of the study and draws some conclusions about the potential bottlenecks of system implementation.

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TYPE SAND Report YEAR 2012
DOIOSTI

Automated exploration of the mechanism of elementary reactions

Najm, Habib N.; Zador, Judit

Optimization of new transportation fuels and engine technologies requires the characterization of the combustion chemistry of a wide range of fuel classes. Theoretical studies of elementary reactions — the building blocks of complex reaction mechanisms — are essential to accurately predict important combustion processes such as autoignition of biofuels. The current bottleneck for these calculations is a user-intensive exploration of the underlying potential energy surface (PES), which relies on the “chemical intuition” of the scientist to propose initial guesses for the relevant chemical configurations. For newly emerging fuels, this approach cripples the rate of progress because of the system size and complexity. The KinBot program package aims to accelerate the detailed chemical kinetic description of combustion, and enables large-scale systematic studies on the sub-mechanism level.

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TYPE SAND Report YEAR 2012
DOIOSTI

First-Principles Flocculation as the Key to Low Energy Algal Biofuels Processing

Hewson, John C.; Mondy, Lisa A.; Murton, Jaclyn K.; O'Hern, Timothy J.; Parchert, Kylea J.; Pohl, Phillip I.; Williams, Cecelia V.; Wyatt, Nicholas B.; Barringer, David A.; Pierce, Flint; Brady, Patrick V.; Dwyer, Brian P.; Grillet, Anne M.; Hankins, Matthew G.; Hughes, Lindsey; Lechman, Jeremy B.

This document summarizes a three year Laboratory Directed Research and Development (LDRD) program effort to improve our understanding of algal flocculation with a key to overcoming harvesting as a techno-economic barrier to algal biofuels. Flocculation is limited by the concentrations of deprotonated functional groups on the algal cell surface. Favorable charged groups on the surfaces of precipitates that form in solution and the interaction of both with ions in the water can favor flocculation. Measurements of algae cell-surface functional groups are reported and related to the quantity of flocculant required. Deprotonation of surface groups and complexation of surface groups with ions from the growth media are predicted in the context of PHREEQC. The understanding of surface chemistry is linked to boundaries of effective flocculation. We show that the phase-space of effective flocculation can be expanded by more frequent alga-alga or floc-floc collisions. The collision frequency is dependent on the floc structure, described in the fractal sense. The fractal floc structure is shown to depend on the rate of shear mixing. We present both experimental measurements of the floc structure variation and simulations using LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). Both show a densification of the flocs with increasing shear. The LAMMPS results show a combined change in the fractal dimension and a change in the coordination number leading to stronger flocs.

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TYPE SAND Report YEAR 2012
DOIOSTI

Detectability of Neuronal Currents in Human Brain with Magnetic Resonance Spectroscopy

Jones, Howland D.T.; Thomas, Edward V.; Harper, Jason C.

Magnetic resonance spectroscopy has been used in a high-risk, high-payoff search for neuronal current (NC) signals in the free induction decay (FID) data from the visual cortex of human subjects during visual stimulation. If successful, this approach could make possible the detection of neuronal currents in the brain at high spatial and temporal resolution. Our initial experiments indicated the presence of a statistically significant change in the FID containing the NC relative to FIDs with the NC absent, and this signal was consistent with the presence of NC. Unfortunately, two follow-on experiments were not able to confirm or replicate the positive findings of the first experiment. However, even if the result from the first experiment were evidence of NC in the FID, it is clear that its effect is so small, that a true NC imaging experiment would not be possible with the current instrumentation and experimental protocol used here.

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TYPE SAND Report YEAR 2012
DOIOSTI

Probability of Loss of Assured Safety in Systems with Multiple Time-Dependent Failure Modes

Pilch, Martin; Sallaberry, Cedric J.

Weak link (WL)/strong link (SL) systems are important parts of the overall operational design of high-consequence systems. In such designs, the SL system is very robust and is intended to permit operation of the entire system under, and only under, intended conditions. In contrast, the WL system is intended to fail in a predictable and irreversible manner under accident conditions and render the entire system inoperable before an accidental operation of the SL system. The likelihood that the WL system will fail to deactivate the entire system before the SL system fails (i.e., degrades into a configuration that could allow an accidental operation of the entire system) is referred to as probability of loss of assured safety (PLOAS). Representations for PLOAS for situations in which both link physical properties and link failure properties are time-dependent are derived and numerically evaluated for a variety of WL/SL configurations, including PLOAS defined by (i) failure of all SLs before failure of any WL, (ii) failure of any SL before failure of any WL, (iii) failure of all SLs before failure of all WLs, and (iv) failure of any SL before failure of all WLs. The effects of aleatory uncertainty and epistemic uncertainty in the definition and numerical evaluation of PLOAS are considered.

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TYPE SAND Report YEAR 2012
DOIOSTI
Results 62101–62200 of 99,299
Results 62101–62200 of 99,299