736 research outputs found
Underground nuclear power plant siting
This study is part of a larger evaluation of the problems associated with siting nuclear power plants in the next few decades. This evaluation is being undertaken by the Environmental Quality Laboratory of the California Institute of Technology in conjunction with The Aerospace Corporation and several other organizations. Current efforts are directed toward novel approaches to siting plants within the State of California. This report contains the results of efforts performed by The Aerospace Corporation to provide input information to the larger evaluation relative to underground siting of large central station nuclear power plants.
Projections of electric power demand in California and the country as a whole suggest that a major increase in generating capacity will be required. The problem is complicated beyond that of a large but straightforward extension of capital investment by increased emphasis on environmental factors combined with the early stage of commercial application and regulation of nuclear power sources. Hydroelectric power generation is limited by the availability of suitable sites, and fossil fueled plants are constrained by the availability of high quality fuels and the adverse environmental and/or economic impact from the use of more plentiful fuels. A substantial increase in the number of nuclear power plants is now under way. This source of power is expected to provide the maj or portion of increased capacity. Other power sources such as geothermal and nuclear fusion are unlikely to satisfy the national needs due to technical problems and the lack of a comprehensive development program.
There are several problems associated with meeting the projected power demand. Chief among these is the location of acceptable and economic plant sites. Indeed a sufficient number of sites may not be found unless changes occur in the procedures for selecting sites, the criteria for accepting sites, or the type of site required. Placement of a nuclear plant underground has been suggested as an alternative to present siting practices. It is postulated that the advantages of underground siting in some situations may more than compensate for added costs so that such facilities could be preferred even where surface sites are available. By virtue of greater safety, reduced surface area requirements, and improved aesthetics, underground sites might also be found where acceptable surface sites are not available.
Four small European reactors have been constructed partially underground but plans for large size commercial plants have not progressed. Consequently, the features of underground power plant siting are not well understood. Gross physical features such as depth of burial, number and size of excavated galleries, equipment layout, and access or exit shafts/tunnels must be specified. Structural design features of the gallery liners, containment structure, foundations, and gallery interconnections must also be identified. Identification of the nuclear, electrical, and support equipment appropriate to underground operation is needed. Operational features must be defined for normal operations, refueling, and construction. Several magazine articles have been published addressing underground concepts. but adequate engineering data is not available to support an evaluation of the underground concept.
There also remain several unresolved questions relative to the advantages of underground siting as well as the costs and other possible penalties associated with this novel approach to siting. These include the degree of increased safety through improved containment; the extent and value of isolation from falling objects, e. g. aircraft; the value of isolation from surface storms and tidal waves; the value of protection from vandalism or sabotage; the extent by which siting constraints are relieved through reduced population-distance requirements or aggravated by underground construction requirements; and the value to be placed upon the aesthetic differences of a less visible facility.
The study described in this report has been directed toward some of these questions and uncertainties. Within the study an effort has been made to identify viable configurations and structural liners for typical light water reactor nuclear power plants. Three configurations are summarized in Section 3. A discussion of the underground gallery liner design and associated structural analyses is presented in Section 4. Also addressed in the study and discussed in Section 5 are some aspects of containment for underground plants. There it is suggested that the need for large separations between the plant and population centers may be significantly reduced, or perhaps eliminated.
Section 6 contains a brief discussion of operational considerations for underground plants. The costs associated with excavation and lining of the underground galleries have been estimated in Section 7. These estimates include an assessment of variations implied by different seismic loading assumptions and differences in geologic media. It is shown that these costs are a small percentage of the total cost of comparable surface plants. Finally, the parameters characterizing an acceptable underground site are discussed in Section 8. Material is also included in the appendices pertaining to foreign underground plants, span limits of underground excavations, potential siting areas for underground plants in the State of California, pertinent data from the Underground Nuclear Test Program, and other supporting technical discussions
Welding-base metal investigation Final report, 27 Jun. 1964 - 28 Jul. 1965
Weld defects associated with aluminum alloys - monitoring weld shielding gas purit
Simultaneous Embeddings with Few Bends and Crossings
A simultaneous embedding with fixed edges (SEFE) of two planar graphs and
is a pair of plane drawings of and that coincide when restricted to
the common vertices and edges of and . We show that whenever and
admit a SEFE, they also admit a SEFE in which every edge is a polygonal curve
with few bends and every pair of edges has few crossings. Specifically: (1) if
and are trees then one bend per edge and four crossings per edge pair
suffice (and one bend per edge is sometimes necessary), (2) if is a planar
graph and is a tree then six bends per edge and eight crossings per edge
pair suffice, and (3) if and are planar graphs then six bends per edge
and sixteen crossings per edge pair suffice. Our results improve on a paper by
Grilli et al. (GD'14), which proves that nine bends per edge suffice, and on a
paper by Chan et al. (GD'14), which proves that twenty-four crossings per edge
pair suffice.Comment: Full version of the paper "Simultaneous Embeddings with Few Bends and
Crossings" accepted at GD '1
Spitzer Secondary Eclipse Observations of Five Cool Gas Giant Planets and Empirical Trends in Cool Planet Emission Spectra
In this work we present Spitzer 3.6 and 4.5 micron secondary eclipse
observations of five new cool (<1200 K) transiting gas giant planets:
HAT-P-19b, WASP-6b, WASP-10b, WASP-39b, and WASP-67b. We compare our measured
eclipse depths to the predictions of a suite of atmosphere models and to
eclipse depths for planets with previously published observations in order to
constrain the temperature- and mass-dependent properties of gas giant planet
atmospheres. We find that the dayside emission spectra of planets less massive
than Jupiter require models with efficient circulation of energy to the night
side and/or increased albedos, while those with masses greater than that of
Jupiter are consistently best-matched by models with inefficient circulation
and low albedos. At these relatively low temperatures we expect the atmospheric
methane to CO ratio to vary as a function of metallicity, and we therefore use
our observations of these planets to constrain their atmospheric metallicities.
We find that the most massive planets have dayside emission spectra that are
best-matched by solar metallicity atmosphere models, but we are not able to
place strong constraints on metallicities of the smaller planets in our sample.
Interestingly, we find that the ratio of the 3.6 and 4.5 micron brightness
temperatures for these cool transiting planets is independent of planet
temperature, and instead exhibits a tentative correlation with planet mass. If
this trend can be confirmed, it would suggest that the shape of these planets'
emission spectra depends primarily on their masses, consistent with the
hypothesis that lower-mass planets are more likely to have metal-rich
atmospheres.Comment: 16 pages, 14 figures, accepted for publication in Ap
Investigating Trends in Atmospheric Compositions of Cool Gas Giant Planets Using Spitzer Secondary Eclipses
We present new 3.6 and 4.5 μm secondary eclipse measurements for five cool (T 1000 K) transiting gas giant planets: HAT-P-15b, HAT-P-17b, HAT-P-18b, HAT-P-26b, and WASP-69b. We detect eclipses in at least one bandpass for all planets except HAT-P-15b. We confirm and refine the orbital eccentricity of HAT-P-17b, which is also the only planet in our sample with a known outer companion. We compare our measured eclipse depths in these two bands, which are sensitive to the relative abundances of methane versus carbon monoxide and carbon dioxide, respectively, to predictions from 1D atmosphere models for each planet. For planets with hydrogen-dominated atmospheres and equilibrium temperatures cooler than ~1000 K, this ratio should vary as a function of both atmospheric metallicity and the carbon-to-oxygen ratio. For HAT-P-26b, our observations are in good agreement with the low atmospheric metallicity inferred from transmission spectroscopy. We find that all four of the planets with detected eclipses are best matched by models with relatively efficient circulation of energy to the nightside. We see no evidence for a solar-system-like correlation between planet mass and atmospheric metallicity, but instead identify a potential (1.9σ) correlation between the inferred CH₄/(CO + CO₂) ratio and stellar metallicity. Our ability to characterize this potential trend is limited by the relatively large uncertainties in the stellar metallicity values. Our observations provide a first look at the brightness of these planets at wavelengths accessible to the James Webb Space Telescope, which will be able to resolve individual CH₄, CO, and CO₂ bands and provide much stronger constraints on their atmospheric compositions
(Against a) Theory of Audience Engagement with News
Audience engagement has become a key concept in contemporary discussions on how news companies relate to the public and create sustainable business models. These discussions are irrevocably tied to practices of monitoring, harvesting and analyzing audience behaviours with metrics, which is increasingly becoming the new currency of the media economy. This article argues this growing tendency to equate engagement to behavioural analytics, and study it primarily through quantifiable data, is limiting. In response, we develop a heuristic theory of audience engagement with news comprising four dimensions—the technical-behavioural, emotional, normative and spatiotemporal—and explicate these in terms of different relations of engagement between human-to-self, human-to-human, human-to-content, human-to-machine, and machine-to-machine. Paradoxically, this model comprises a specific theory of audience engagement while simultaneously making visible that constructing a theory of audience engagement is an impossible task. The article concludes by articulating methodological premises, which future empirical research on audience engagement should consider
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