Upgrading of primary alcohols by C-H bond breaking currently requires temperatures of >200 °C. In this work, new understanding from simulation of a temperature-programmed reaction study with methanol over a CeO(111) surface shows C-H bond breaking and the subsequent desorption of formaldehyde, even below room temperature. This is of particular interest because CeO is a naturally abundant and inexpensive metal oxide. We combine density functional theory and kinetic Monte Carlo methods to show that the low-temperature C-H bond breaking occurs via disproportionation of adjacent methoxy species. We further show from calculations that the same transition state with comparable activation energy exists for other primary alcohols; with ethanol, 1-propanol, and 1-butanol explicitly calculated. These findings indicate a promising class of transition states to search for in seeking low-temperature C-H bond breaking over inexpensive oxides.

In March 2018, the Savannah River National Laboratory (SRNL) notified Solid Waste Management (SWM) of new information that could potentially impact groundwater (GW) disposal limits and possibly require temporary protective measures (Crowley 2018). GW flow directions in the E-Area Low-Level Waste Facility (LLWF) Slit Trenches (STs), Engineered Trenches (ETs), and the Low Activity Waste Vault (LAWV) have notably changed in the new 2018 General Separations Area (GSA) flow model (Flach 2018a). The 2018 GSA flow model had been updated using 20 years of new hydrologic field data and model calibration methods that employed mathematical optimization software. It was later determined that the primary reason for the change in GW flow directions was due to the influence of low permeability caps that had been placed over the Old Burial Grounds and the Low Level Radioactive Waste Disposal Facility (LLRWDF). Updated flow directions in the model produce a higher degree of plume overlap for disposal units (DU's) in the southeastern portion of E-Area than had been predicted in the 2008 E-Area LLWF Performance Assessment (PA). SWM and SRNL outlined the scope for this Special Analysis (SA) and proposed a set of interim measures (IM's) to protect trench operations from exceeding Performance Objectives (PO's) during the preparation of this SA, both of which were approved by the SWM Performance Assessment Review Committee (PARC) (Mooneyhan 2018

ScopeA summary of the conceptual models to be used in representing slit (ST) and engineered trenches (ET) in PORFLOW (ACRi 2018) simulations as part of the performance assessment (PA) of the E-Area Low Level Waste Facility (ELLWF) is presented. Key details that are discussed include: model geometries, spatially dependent hydro-stratigraphic representations, model dimensionality, and boundary conditions (i.e., infiltration rates, cover overhangs, subsidence). Accounting for differences in the percent of noncrushable materials, eighteen unique models, defined by seven hydro-stratigraphic groupings, will be used to represent slit and engineered trenches. DiscussionThe relevance of several hydro-stratigraphic and design features specific to the ELLWF has been evaluated using PORFLOW to assist in the development and implementation of the vadose zone conceptual models to be used in the PA. In the following subsections, a summary of these evaluations is presented to highlight the actions and decisions in the development and implementation of the proposed conceptual models. Disposal Unit LengthThe longest footprint in the ELLWF is ST1 (675.3 feet). While the length of the majority of STs and ETs fall within 3% of the length of ST1, the lengths of ST10, ST11, ST21, ST22, and ET3 are substantially different (i.e., greater than 10%, and up to 33% different). Therefore, a series of PORFLOW simulations were performed to confirm that a generic model of any length could be used to represent any trench without impacting the flux to the water table. A generic 2D model with waste uniformly distributed across 600-, 500-, 400-, 300-, 200-, and 100-foot lengths was used to calculate steady-state flow and transient transport solutions to obtain the flux to the water table for the list of nine radionuclide species investigated in Hamm et al. 2018. Because the specified quantity of the radionuclide species is the same regardless of length, and no solubility limitations are imposed, all differences in the peak flux to the water table were negligible (<~3%) and attributed to numerical dispersion. Therefore, one generic waste zone length can be used for all disposal units (DUs) in the ELLWF.

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We propose a wavelet-based scheme that encodes the essential dynamics of discrete microscale surface reactions in a form that can be coupled with continuum macroscale flow simulations with high computational efficiency. This makes it possible to simulate the dynamic behavior of reactor-scale heterogeneous catalysis without requiring detailed concurrent simulations at both the surface and continuum scales using different models. Our scheme is based on the application of wavelet-based surrogate time series that encodes the essential temporal and/or spatial fine-scale dynamics at the catalyst surface. The encoded dynamics are then used to generate statistically equivalent, randomized surrogate time series, which can be linked to the continuum scale simulation. We illustrate an application of this approach using two different kinetic Monte Carlo simulations with different characteristic behaviors typical for heterogeneous chemical reactions.