Study of tritium transport characteristics in a transportable fluoride‐salt‐cooled high‐temperature reactor

Tritium management is one of the most critical issues that limit the development of fluoride‐salt‐cooled high‐temperature reactor (FHR); therefore, it is important to figure out the tritium transport characteristics in FHRs. In this paper, 3 works concerning about tritium in FHR are conducted: first, the tritium transport characteristics in the primary loop of FHRs are introduced, including tritium production and speciation, the absorption and desorption by graphite, dissolution and diffusion in molten salt, and permeation through structural materials. Second, the physical and mathematical models are established for tritium transport characteristic analysis in a transportable FHR (TFHR). The tritium transport characteristic analysis code (TAPAS) for TFHR is developed and benchmarked. The results prove the fidelity and accuracy of TAPAS. Finally, the tritium transport characteristics in the TFHR are analyzed systematically by TAPAS. Three conclusions are obtained: (1) tritium in the primary coolant loop is mainly in the form of T₂; (2) when TFHR operates at steady state, the permeation rate of T₂ can be regarded as a constant (9.03 × 10⁹ Bq ? EFPD^?1 ); and (3) ⁷Li enrichment and redox potential of molten salt have great influence on the tritium distribution. This work might provide contribution to the tritium control in FHRs.     

Synergistic microwave and structural studies of C-type Ho2Si2O7

Ho₂Si₂O₇ material exists in four polymorphs, a triclinic low temperature phase (type-B), a monoclinic modification (type-C), high temperature monoclinic (type-D), and high temperature orthorhombic modification (type-E). The structural properties are measured by XRD and the morphology is noted through scanning electron microscopy (SEM). The dc electrical resistivity (ρ) as a function of temperature and dielectric properties of C-type Ho₂Si₂O₇ in the microwave region is measured. The activation energy is calculated from ln ρ versus 1/k_BT plot. The activation energy is 0.119 ± 0.001 eV. Both the real (?′) and imaginary parts of permittivity (?″) decrease slightly as the frequency increases up to 1.5 GHz, after that ?′ increases while ?″ decreases as the frequency increases. At around 2.45 GHz, resonance is observed.     

Features of Capacitance and Mobility of Injected Carriers in Organic Layers Measured by Impedance Spectroscopy

Transport of charge carriers in organic layers plays a relevant role in the performance of electronic devices such as light-emitting diodes, solar cells, and photodetectors. The presence of energetically distributed traps severely affects the measured transport coefficient and the charge-storage features in the film. We summarize recent theoretical work on impedance spectroscopy models for space–charge limited current of a single carrier in a multiple trapping model, which describes the experimental behavior usually observed in organic layers with injected charge carriers well. Two main physical effects are obtained from the numerical and analytical treatment. First, carriers in slow traps that do not follow alternating current modulation provide an increase in the capacitance at low frequency, and second, those in fast traps remain in equilibrium with the transport state increasing the transit time. Analysis also provides a unified interpretation of models with field- or carrier-density dependence on mobility.     

Proton Conduction in Dense and Porous Nanocrystalline Ceria Thin Films

The electrical conductivity of ceria thin films (epitaxial as well as dense and porous nanocrystalline) is investigated in dry and wet atmosphere at temperatures below 500 °C. For the epitaxial and the fully dense nanocrystalline samples, no significant differences can be observed between dry and wet conditions. In marked contrast, the nanocrystalline porous films obtained via spin coating exhibit a considerable enhancement of the protonic conductivity below 300 °C in wet atmosphere. This outcome reveals that the residual open mesoporosity plays the key role for the enhancement of the proton transport at low temperatures and not the high density of grain boundaries. The quantitative analysis of the various pathways, along which the proton transport can take place, indicates that the observed proton conduction can arise not only from bulk water adsorbed in the open pores but also from the space charge zones on the water side of the water/oxide interface.     

Protecting against corner impacts: sensitivities discovered during a rail cask impact limiter design

Type B packages for the transportation of radioactive materials must remain ‘essentially leak tight’ under severe regulatory accident conditions, defined in the US Nuclear Regulatory Commission’s 10 CFR 71·73 and the International Atomic Energy Agency’s TS-R-1. The 9-m free drop test requirement onto an unyielding surface is performed in an orientation ‘for which maximum damage is expected’. Analytical techniques are used to evaluate various possible impact orientations before testing, and historically these maximal damage orientations have been side, slap-down, end, and centre-of-gravity over corner. Other orientations are rarely considered. Sandia National Laboratories (SNL) was asked by Equipos Nucleares SA (ENSA) to design, analyse, and test an impact limiter system for a newly designed rail cask. During the conceptual design process, SNL performed due diligence and evaluated a wide spectrum of possible impact orientations, in order to assure that peak cask body acceleration design goals were not exceeded. However, design of the impact limiter, including not only crush strength of constituent materials (which can be orientation and temperature dependent), but also the shape of the impact limiter, greatly affects peak acceleration response during 9-m drops in various orientations. Although many impact limiter design shapes resemble truncated right circular cylinders attached to each end of the cask, some tend to round the outer corners or truncate those corners with conical sections. SNL’s original conceptual design followed a similar theme, intending to use polyurethane foam or aluminium honeycomb within a bevelled corner shaped cylindrical shell. Detailed finite element analyses indicated excellent impact resistance at regulatory cold temperatures in the stereotypically tested side, slap-down, end, and CGOC impact orientations. Shortly before proceeding to engineering design, a rarely-considered impact orientation of 45° from horizontal indicated that cask body acceleration levels jumped unexpectedly, exceeding the design goal due to insufficient crushable material protecting the sharp corner of the cask. A complete re-design of the impact limiter was necessary, and the lessons learned from this experience could have implications for future impact limiter designs, and possibly existing designs that may not have considered this atypical impact orientation during the design process.     

Genistein Inhibits Osteoclastic Differentiation of RAW 264.7 Cells via Regulation of ROS Production and Scavenging

Genistein, a phytoestrogen, has been demonstrated to have a bone-sparing and antiresorptive effect. Genistein can inhibit the osteoclast formation of receptor activator of nuclear factor-κB ligand (RANKL)-induced RAW 264.7 cells by preventing the translocation of nuclear factor-κB (NF-κB), a redox-sensitive factor, to the nucleus. Therefore, the suppressive effect of genistein on the reactive oxygen species (ROS) level during osteoclast differentiation and the mechanism associated with the control of ROS levels by genistein were investigated. The cellular antioxidant capacity and inhibitory effect of genistein were confirmed. The translation and activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 1 (Nox1), as well as the disruption of the mitochondrial electron transport chain system were obviously suppressed by genistein in a dose-dependent manner. The induction of phase II antioxidant enzymes, such as superoxide dismutase 1 (SOD1) and heme oxygenase-1 (HO-1), was enhanced by genistein. In addition, the translational induction of nuclear factor erythroid 2-related factor 2 (Nrf2) was notably increased by genistein. These results provide that the inhibitory effects of genistein on RANKL-stimulated osteoclast differentiation is likely to be attributed to the control of ROS generation through suppressing the translation and activation of Nox1 and the disruption of the mitochondrial electron transport chain system, as well as ROS scavenging through the Nrf2-mediated induction of phase II antioxidant enzymes, such as SOD1 and HO-1.     

Incorporating Both Physical and Kinetic Limitations in Quantifying Dissolved Oxygen Flux to Aquatic Sediments

Traditionally, dissolved oxygen (DO) fluxes have been calculated using the thin-film theory with DO microstructure data in systems characterized by fine sediments and low velocities. However, recent experimental evidence of fluctuating DO concentrations near the sediment-water interface suggests that turbulence and coherent motions control the mass transfer, and the surface renewal theory gives a more mechanistic model for quantifying fluxes. Both models involve quantifying the mass transfer coefficient (k) and the relevant concentration difference (ΔC). This study compared several empirical models for quantifying k based on both thin-film and surface renewal theories, as well as presents a new method for quantifying ΔC (dynamic approach) that is consistent with the observed DO concentration fluctuations near the interface. Data were used from a series of flume experiments that includes both physical and kinetic uptake limitations of the flux. Results indicated that methods for quantifying k and ΔC using the surface renewal theory better estimated the DO flux across a range of fluid-flow conditions.     

A fugacity based continuous and dynamic fate and transport model for river networks and its application to Altamaha River

In this paper, a continuous and dynamic fugacity-based contaminant fate and transport model is developed. The dynamic interactions among all phases in the physical domain are addressed through the use of the fugacity approach instead of the use of concentration as the unknown variable. The full form of Saint Venant equations is used in order to solve for the hydrodynamic conditions in the river network. Then a fugacity-based advection-dispersion equation is modeled to examine the fate and transport of contaminants in the river network for all phases.The fugacity-based, dynamic and continuous contaminant fate and transport model developed here is applied to Altamaha River in Georgia, USA to demonstrate its use in environmental exposure analysis. Altamaha River is the largest river system east of Mississippi which offers habitat for many species, including about 100 rare endangered species, along its 140 mile course. Polychlorinated biphenyls (PCBs), a highly hydrophobic and toxic chemical ubiquitous in nature, and atrazine, the most commonly-used agricultural pesticide are modeled as contaminants in this demonstration. Through this approach the concentration distribution of PCBs and atrazine in the water column of Altamaha River as well as the sediments can be obtained with relative ease, which is an improvement over concentration based analysis of phase distribution of contaminants.     

Microcrystalline silicon, grain boundaries and role of oxygen

The authors report on the correlation of the oxygen content for three high growth-rate series of thin Si films crossing the boundary between amorphous and microcrystalline growth together with the evolution of the prefactor and the activation energy of the dark d.c. conductivity. The different roles of oxygen, such as doping, alloying or defect passivation, are discussed in the framework of the model of transport based on the formation of large grain boundaries with an increased band gap due to hydrogen and/or oxygen alloying.