Behavior of the melt pool in the lower plenum of the reactor pressure vessel - review of experimental programs and background of the LIVE program

Das Verhalten eines Schmelze-Pools im unteren Plenum eines Reaktordruckbehälters – Überblick über experimentelle Programme und Grundlagen für das LIVE-Versuchsprogramm Die Rückhaltung der Kernschmelze im unteren Plenum des Reaktordruckbehälters (RDB) ist eine der in den letzten Jahren intensiv untersuchten Strategien, um einen hypothetischen Kernschmelzunfall zu beherrschen. In verschiedenen Institutionen weltweit wurden deshalb Experimente durchgeführt, um diese Strategie, welche bereits für das KKW Loviisa (Finnland) und den AP 600 (USA) genehmigt wurde, weiterzuentwickeln. Die wichtigsten Experimente waren dabei: • COPO-Experimente in Fortum Nuclear Services und CEA (Frankreich) • BALI-Experimente bei CEA (Frankreich) • SIMECO-Experimente im KTH (Schweden) • ACOPO-Experimente an der Universität von Kalifornien, Santa Barbara (USA) Diese Untersuchungen wurden nicht nur durchgeführt, um die Möglichkeit der Schmelze-Rückhaltung im RDB zu untersuchen, sondern auch, um das Verhalten eines Schmelzepools im unteren Plenum des RDB grundlegend zu verstehen. Die Ergebnisse dieser Untersuchungen wurden dazu verwendet, Modelle bzw. Korrelationen zu ermitteln, die in Rechencodeszur Untersuchung schwerer Unfälle verwendet werden können. Das Forschungszentrum Karlsruhe beteiligt sich mit der Versuchsanlage LIVE (Late In-Vessel Phase Experiments) an diesen Untersuchungen. Das Hauptziel dieses Berichtes ist es, die Ergebnisse anderer experimenteller Programme zum Schmelzeverhalten im unteren Plenum des RDB’s zusammenzufassen und damit ein Bild des derzeitigen Kenntnisstandes zu geben. Weiterhin soll gezeigt werden, wie die noch offenen Fragen im LIVE-Programm untersucht werden können

Guided ion beam and theoretical studies of the reaction of Ru+ with CS2 in the gas-phase: thermochemistry of RuC+, RuS+, and RuCS+

Journal ArticleAbstract: The gas-phase reactivity of the atomic transition metal cation, Ru+, with CS2 is investigated using guided-ion beam mass spectrometry (GIBMS). Endothermic reactions forming RuC+, RuS+, and RuCS+ are observed. Analysis of the kinetic energy dependence of the cross sections for formation of these three products yields the 0 K bond energies of D0(Ru+-C) = 6.27 ? 0.15 eV, D0(Ru+-S) = 3.04 ? 0.10 eV, and D0(Ru+-CS) = 2.59 ? 0.18 eV, and consideration of previous data leads to a recommended D0(Ru+-C) bond energy of 6.17 ? 0.07 eV. A detailed reaction coordinate surface for these processes is determined by quantum chemical calculations and shows that all three reactions take place by insertion to form a S-Ru+-CS intermediate. Although multiple spin states are available, the reaction appears to occur primarily on the quartet ground state surface, although coupling to a sextet surface is required to form the RuS+(6?+) + CS(1?+) ground state products. Calculations are used to locate the approximate crossing points between the quartet and sextet surfaces, finding them in both the bending coordinate of the S-Ru+-CS intermediate and in the exit channel. Elimination of S2 to form RuC+ follows a much more complicated pathway involving a cyclic RuCSS+ intermediate, consistent with the energetic behavior of the experimental RuC+ cross section

Guided ion beam and theoretical studies of the reaction of Ag+ with CS2: gas-phase thermochemistry of AgS+ and AgCS+ and insight into spin-forbidden reactions

Journal ArticleThe gas-phase reactivity of the atomic transition metal cation, Ag+, with CS2 is investigated using guided-ion beam mass spectrometry. Endothermic reactions forming AgS+ and AgCS+ are observed but are quite inefficient. This observation is largely attributed to the stability of the closed shell Ag+(1S,4d10) ground state, but is also influenced by the fact that the reactions producing ground state AgS+ and AgCS+ products are both spin forbidden. Analysis of the kinetic energy dependence of the cross sections for formation of these two products yields the 0 K bond energies of D0(Ag+uS)=1.40±0.12 eV and D0(Ag+uCS)=1.98±0.14 eV. Quantum chemical calculations are used to investigate the electronic structure of the two product ions as well as the potential energy surfaces for reaction. The primary mechanism involves oxidative addition of a CS bond to the metal cation followed by simple AguS or AguCS bond cleavage. Crossing points between the singlet and triplet surfaces are located near the transition states for bond activation. Comparison with analogous work on other late second-row transition metal cations indicates that the location of the crossing points bears directly on the efficiency of these spin-forbidden processes

Separated Oscillatory Fields for High-Precision Penning Trap Mass Spectrometry

Ramsey's method of separated oscillatory fields is applied to the excitation of the cyclotron motion of short-lived ions in a Penning trap to improve the precision of their measured mass. The theoretical description of the extracted ion-cyclotron-resonance line shape is derived out and its correctness demonstrated experimentally by measuring the mass of the short-lived $^{38}$Ca nuclide with an uncertainty of $1.6\cdot 10^{-8}$ using the ISOLTRAP Penning trap mass spectrometer at CERN. The mass value of the superallowed beta-emitter $^{38}$Ca is an important contribution for testing the conserved-vector-current hypothesis of the electroweak interaction. It is shown that the Ramsey method applied to mass measurements yields a statistical uncertainty similar to that obtained by the conventional technique ten times faster.Comment: 5 pages, 4 figures, 0 table

A balancing act: Evidence for a strong subdominant d-wave pairing channel in Ba0.6K0.4Fe2As2{\rm Ba_{0.6}K_{0.4}Fe_2As_2}

We present an analysis of the Raman spectra of optimally doped ${\rm Ba_{0.6}K_{0.4}Fe_2As_2}$ based on LDA band structure calculations and the subsequent estimation of effective Raman vertices. Experimentally a narrow, emergent mode appears in the $B_{1g}$ ($d_{x^2-y^2}$) Raman spectra only below $T_c$, well into the superconducting state and at an energy below twice the energy gap on the electron Fermi surface sheets. The Raman spectra can be reproduced quantitatively with estimates for the magnitude and momentum space structure of the s$_{+-}$ pairing gap on different Fermi surface sheets, as well as the identification of the emergent sharp feature as a Bardasis-Schrieffer exciton, formed as a Cooper pair bound state in a subdominant $d_{x^2-y^2}$ channel. The binding energy of the exciton relative to the gap edge shows that the coupling strength in this subdominant $d_{x^2-y^2}$ channel is as strong as 60% of that in the dominant $s_{+-}$ channel. This result suggests that $d_{x^2-y^2}$ may be the dominant pairing symmetry in Fe-based sperconductors which lack central hole bands.Comment: 10 pages, 6 Figure

Calcium isotope fractionation in alpine plants

In order to develop Ca isotopes as a tracer for biogeochemical Ca cycling in terrestrial environments and for Ca utilisation in plants, stable calcium isotope ratios were measured in various species of alpine plants, including woody species, grasses and herbs. Analysis of plant parts (root, stem, leaf and flower samples) provided information on Ca isotope fractionation within plants and seasonal sampling of leaves revealed temporal variation in leaf Ca isotopic composition. There was significant Ca isotope fractionation between soil and root tissue \Updelta^{44/42}\hbox{Ca}_{\rm root-soil} \approx -0.40\,\permille in all investigated species, whereas Ca isotope fractionation between roots and leaves was species dependent. Samples of leaf tissue collected throughout the growing season also highlighted species differences: Ca isotope ratios increased with leaf age in woody species but remained constant in herbs and grasses. The Ca isotope fractionation between roots and soils can be explained by a preferential binding of light Ca isotopes to root adsorption sites. The observed differences in whole plant Ca isotopic compositions both within and between species may be attributed to several potential factors including root cation exchange capacity, the presence of a woody stem, the presence of Ca oxalate, and the levels of mycorrhizal infection. Thus, the impact of plants on the Ca biogeochemical cycle in soils, and ultimately the Ca isotope signature of the weathering flux from terrestrial environments, will depend on the species present and the stage of vegetation successio

Relativistic quark models of baryons with instantaneous forces

This is the first of a series of three papers treating light baryon resonances (up to 3 GeV) within a relativistically covariant quark model based on the three-fermion Bethe-Salpeter equation with instantaneous two- and three-body forces. In this paper we give a unified description of the theoretical background and demonstrate how to solve the Bethe-Salpeter equation by a reduction to the Salpeter equation. The specific new features of our covariant Salpeter model with respect to the usual nonrelativistic quark model are discussed in detail. The purely theoretical results obtained in this paper will be applied numerically to explicit quark models for light baryons in two subsequent papers

Creutzfeldt-Jakob disease and homocysteine levels in plasma and cerebrospinal fluid

Background: There is evidence that homocysteine contributes to various neurodegenerative disorders. Objective: To assess the values of homocysteine in patients with Creutzfeldt-Jakob disease (CJD) in both cerebrospinal fluid (CSF) and plasma. Methods: Study design: Case control study. Total homocysteine was quantified in CSF and plasma samples of CJD patients (n = 13) and healthy controls (n = 13). Results: Mean values in healthy controls: 0.15 mumol/l +/- 0.07 (CSF) and 9.10 mumol/l +/- 2.99 (plasma); mean values in CJD patients: 0.13 mumol/l +/- 0.03 (CSF) and 9.22 mumol/l +/- 1.81 (plasma). No significant differences between CJD patients and controls were observed (Mann-Whitney U, p > 0.05). Conclusions: The results indicate that the CSF and plasma of CJD patients showed no higher endogenous levels of homocysteine as compared to normal healthy controls. These findings provide no evidence for an additional role of homocysteine in the pathogenetic mechanisms underlying CJD neurodegeneration. Copyright (C) 2005 S. Karger AG, Basel

Raman-Scattering Detection of Nearly Degenerate ss-Wave and dd-Wave Pairing Channels in Iron-Based Ba0.6_{0.6}K0.4_{0.4}Fe2_2As2_2 and Rb0.8_{0.8}Fe1.6_{1.6}Se2_2 Superconductors

We show that electronic Raman scattering affords a window into the essential properties of the pairing potential $V_{\mathbf{k},\mathbf{k^{\prime}}}$ of iron-based superconductors. In Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ we observe band dependent energy gaps along with excitonic Bardasis-Schrieffer modes characterizing, respectively, the dominant and subdominant pairing channel. The $d_{x^2-y^2}$ symmetry of all excitons allows us to identify the subdominant channel to originate from the interaction between the electron bands. Consequently, the dominant channel driving superconductivity results from the interaction between the electron and hole bands and has the full lattice symmetry. The results in Rb$_{0.8}$Fe$_{1.6}$Se$_2$ along with earlier ones in Ba(Fe$_{0.939}$Co$_{0.061}$)$_2$As$_2$ highlight the influence of the Fermi surface topology on the pairing interactions.Comment: 5 pages, 4 figure