Studies in Nuclear Energy: Low Risk and Low Carbon

The amount of greenhouse gas emissions mitigation required to prevent the most dramatic climate change scenarios postulated in the 2014 IPCC Synthesis Report is substantial. Prior analyses have examined the potential for nuclear energy to play a role in decarbonizing the energy sector, one of the largest contributors to emissions worldwide. However, advanced, non-light water reactors, while often touted as a viable alternative for development, have languished. Large light water development projects have a repeated history of extended construction timelines, re-work delays, and significant capital risk. With few exceptions, large-scale nuclear projects have demonstrated neither affordability nor economic competitiveness, and are not well suited to nations with smaller energy grids, or to replace fossil generation in the industrial process heat sector. If nuclear power is to play a role in decarbonization, new policy and technical solutions will be needed. In this manuscript, we examine key aspects of past performance across the nuclear enterprise and explore the future potential of nuclear energy worldwide, focusing on policy and technical solutions that may be needed to move nuclear power forward as a part of a low-carbon energy future. We do so first at a high level, examining the history of nuclear power research and development in the United States, the nation that historically has led the way in the development of this generating technology. A significant portion of our analysis is focused on new developments in this technology – advanced non-light water reactors and small modular reactors. We find that while there are promising technical solutions available, improved funding and focus in research and new models of deployment may be needed if nuclear is to play a continuing or future role. We also find that in examining potential new markets for the technology, a continuing focus on institutional readiness is critical.</p

Molecular Considerations for Mesophase Interaction and Alignment of Lyotropic Liquid Crystalline Semiconducting Polymers

Intermolecular interactions in conjugated polymers influence crystallinity, self-assembly, and packing motif, factors which in turn crucially impact charge transport properties such as carrier mobility in organic electronic devices. Correlated alignment of molecular and crystalline morphologies provides direct pathways for charge carriers to follow; however, the role of intermolecular interactions in achieving this is unexplored. Herein, we synthesize a series of lyotropic liquid crystalline conjugated polymers with variable side-chain structure to lend distinct steric repulsion and van der Waals attractive forces to each mesophase. We use this to investigate the role of intermolecular interactions on mesophase alignment. The strength of intermolecular interaction for each mesophase is compared by measuring melting temperature, π-stacking distance, and the Maier–Saupe interaction parameter. In general we find that side-chain structure can impact interaction strength by varying steric repulsion and backbone attractions and that the Maier–Saupe interaction parameters correlate with higher degrees of alignment after shearing, achieving a dichroic absorbance ratio of up to 2. This observation is used to develop equilibrium processing methods for fabricating macroscopically aligned polymer substrates used in transistors, improving mobility by a factor of 3 compared to spin-coated devices

Localized Probing of Gas Molecule Adsorption Energies and Desorption Attempt Frequencies

Gas-mediated electron beam induced etching (EBIE) and deposition (EBID) can be used to measure activation energies that are interpreted as the adsorption energies of surface-adsorbed precursor molecules. However, the measured quantities often disagree with adsorption energies measured by conventional analysis techniques such as thermally programmed desorption and have anomalous dependencies on parameters such as the electron beam current used to perform EBID. Here, we use the theory of EBIE and EBID rate kinetics to explain this behavior and identify conditions under which the activation energies and the associated pre-exponential factors correspond to gas molecule adsorption energies and desorption attempt frequencies, respectively. Under these conditions, EBIE and EBID can be used as robust, nanoscale techniques for the analysis of adsorbates

Proportion and samples size of natural (Nat.) and the three types of hatchery steelhead and unknown hatchery fish detected as spawning in the Chiwawa River, Nason Creek, or Other/unknown spawning location.

<p>Proportion and samples size of natural (Nat.) and the three types of hatchery steelhead and unknown hatchery fish detected as spawning in the Chiwawa River, Nason Creek, or Other/unknown spawning location.</p

Broodstock History Strongly Influences Natural Spawning Success in Hatchery Steelhead (<i>Oncorhynchus mykiss</i>)

<div><p>We used genetic parentage analysis of 6200 potential parents and 5497 juvenile offspring to evaluate the relative reproductive success of hatchery and natural steelhead (<i>Onchorhynchus mykiss</i>) when spawning in the wild between 2008 and 2011 in the Wenatchee River, Washington. Hatchery fish originating from two prior generation hatchery parents had <20% of the reproductive success of natural origin spawners. In contrast, hatchery females originating from a cross between two natural origin parents of the prior generation had equivalent or better reproductive success than natural origin females. Males originating from such a cross had reproductive success of 26–93% that of natural males. The reproductive success of hatchery females and males from crosses consisting of one natural origin fish and one hatchery origin fish was 24–54% that of natural fish. The strong influence of hatchery broodstock origin on reproductive success confirms similar results from a previous study of a different population of the same species and suggests a genetic basis for the low reproductive success of hatchery steelhead, although environmental factors cannot be entirely ruled out. In addition to broodstock origin, fish size, return time, age, and spawning location were significant predictors of reproductive success. Our results indicate that incorporating natural fish into hatchery broodstock is clearly beneficial for improving subsequent natural spawning success, even in a population that has a decades-long history of hatchery releases, as is the case in the Wenatchee River.</p></div

Illustration of the study design.

<p>Reproductive success (offspring per spawner) was measured in generation 2 by counting offspring in generation 3. Generation 3 was sampled only at the juvenile life-stages. Hatchery fish in generation 1 were produced in one of three ways: crossing two natural fish (H_NN), a natural fish and a prior generation hatchery fish (H_HN), or two prior generation hatchery fish (H_HH). Fish in the population returned to spawn primarily at ages 3, 4 and 5.</p

Smoothed relationships (with two standard error confidence bands) between reproductive success (offspring numbers) and length (cm), for ocean age 1 (red) and ocean age 2 (black) fish.

<p>Smoothed relationships (with two standard error confidence bands) between reproductive success (offspring numbers) and length (cm), for ocean age 1 (red) and ocean age 2 (black) fish.</p

Proportion and samples size of natural (Nat.) and the three types of hatchery steelhead and unknown hatchery fish detected as spawning in the Chiwawa River, Nason Creek, or Other/unknown spawning location.

<p>Proportion and samples size of natural (Nat.) and the three types of hatchery steelhead and unknown hatchery fish detected as spawning in the Chiwawa River, Nason Creek, or Other/unknown spawning location.</p

Estimates of <i>F</i>_ST among the four hatchery types of generation 2 hatchery fish and natural fish.

<p>Estimates of <i>F</i>_ST among the four hatchery types of generation 2 hatchery fish and natural fish.</p

Proportions of spring and summer run timing for natural origin steelhead (Nat.) and the three hatchery broodstock cross types.

<p>The proportion returning in each season differs significantly among categories for both males and females (chi-square contingency tests, <i>p</i> < 0.0001).</p