26 research outputs found
Ocean Acidification Summary for Policymakers:Third Symposium on the Ocean in a High-CO2 World
Ozeanversauerung: Zusammenfassung für Entscheidungsträger
Third Symposium on the Ocean in a High-CO2 Worl
Sodium fast reactor fuels and materials : research needs.
An expert panel was assembled to identify gaps in fuels and materials research prior to licensing sodium cooled fast reactor (SFR) design. The expert panel considered both metal and oxide fuels, various cladding and duct materials, structural materials, fuel performance codes, fabrication capability and records, and transient behavior of fuel types. A methodology was developed to rate the relative importance of phenomena and properties both as to importance to a regulatory body and the maturity of the technology base. The technology base for fuels and cladding was divided into three regimes: information of high maturity under conservative operating conditions, information of low maturity under more aggressive operating conditions, and future design expectations where meager data exist
Sodium fast reactor safety and licensing research plan. Volume II.
Expert panels comprised of subject matter experts identified at the U.S. National Laboratories (SNL, ANL, INL, ORNL, LBL, and BNL), universities (University of Wisconsin and Ohio State University), international agencies (IRSN, CEA, JAEA, KAERI, and JRC-IE) and private consultation companies (Radiation Effects Consulting) were assembled to perform a gap analysis for sodium fast reactor licensing. Expert-opinion elicitation was performed to qualitatively assess the current state of sodium fast reactor technologies. Five independent gap analyses were performed resulting in the following topical reports: (1) Accident Initiators and Sequences (i.e., Initiators/Sequences Technology Gap Analysis), (2) Sodium Technology Phenomena (i.e., Advanced Burner Reactor Sodium Technology Gap Analysis), (3) Fuels and Materials (i.e., Sodium Fast Reactor Fuels and Materials: Research Needs), (4) Source Term Characterization (i.e., Advanced Sodium Fast Reactor Accident Source Terms: Research Needs), and (5) Computer Codes and Models (i.e., Sodium Fast Reactor Gaps Analysis of Computer Codes and Models for Accident Analysis and Reactor Safety). Volume II of the Sodium Research Plan consolidates the five gap analysis reports produced by each expert panel, wherein the importance of the identified phenomena and necessities of further experimental research and code development were addressed. The findings from these five reports comprised the basis for the analysis in Sodium Fast Reactor Research Plan Volume I
A giant impact as the likely origin of different twins in the Kepler-107 exoplanet system
Measures of exoplanet bulk densities indicate that small exoplanets with
radius less than 3 Earth radii () range from low-density sub-Neptunes
containing volatile elements to higher density rocky planets with Earth-like or
iron-rich (Mercury-like) compositions. Such astonishing diversity in observed
small exoplanet compositions may be the product of different initial conditions
of the planet-formation process and/or different evolutionary paths that
altered the planetary properties after formation. Planet evolution may be
especially affected by either photoevaporative mass loss induced by high
stellar X-ray and extreme ultraviolet (XUV) flux or giant impacts. Although
there is some evidence for the former, there are no unambiguous findings so far
about the occurrence of giant impacts in an exoplanet system. Here, we
characterize the two innermost planets of the compact and near-resonant system
Kepler-107. We show that they have nearly identical radii (about
), but the outer planet Kepler-107c is more than twice as
dense (about ) as the innermost Kepler-107b (about
). In consequence, Kepler-107c must have a larger iron core
fraction than Kepler-107b. This imbalance cannot be explained by the stellar
XUV irradiation, which would conversely make the more-irradiated and
less-massive planet Kepler-107b denser than Kepler-107c. Instead, the
dissimilar densities are consistent with a giant impact event on Kepler-107c
that would have stripped off part of its silicate mantle. This hypothesis is
supported by theoretical predictions from collisional mantle stripping, which
match the mass and radius of Kepler-107c.Comment: Published in Nature Astronomy on 4 February 2019, 35 pages including
Supplementary Information materia
The effect of vertical and horizontal dilution on fertilized patch experiments
A great deal of attention, both negative and positive, has been directed at the potential of large-scale iron fertilization schemes to sequester carbon by inducing phytoplankton blooms that would, in theory, result in significant export of organic carbon to the deep ocean in high nitrogen - low chlorophyll regions. A suite of iron manipulation or `patch' experiments have been performed over length-scales of 10s of km. Here, we use a physical-ecological-chemical model, with prognostic nitrogen, silica and iron dynamics, to study one of the most successful of these experiments,the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES), focusing on the vertical export of organic material, which is difficult to observe in the field. The implications of large-scale fertilization, i.e. increasing patch size, are investigated. Our results agree with the general conclusions obtained from the field experiments. Only a modest export of organic carbon occurs (less than 25% of carbon uptake by phytoplankton) at the base of the mixed layer. Furthermore, we show that lateral and vertical supply of silicic acid is necessary to fuel a sustained phytoplankton bloom. Increasing patch size results in less lateral nutrient supply relative to patch area and so a decrease, not only in total production (per unit area), but in the contribution by large phytoplankton due to silica limitation. Most importantly, the export of organic carbon (per unit area) decreases substantially, by nearly an order of magnitude as scales of 1000 km are approached