Analysis of the MOX critical experiments BASALA by pin-by-pin core analysis method using three-dimensional direct response matrix

An analysis of the MOX critical experiments BASALA was performed to verify the pin-by-pin core analysis method using a three-dimensional direct response matrix. The BASALA experiments simulate full MOX BWR cores, and they were carried out in the EOLE critical facility of the French Atomic Energy Commission (CEA) by the Nuclear Power Engineering Corporation (NUPEC) in collaboration with CEA. The BASALA experimental cores are very heterogeneous because their size is much smaller than that of commercial power plants. The main features of the pin-by-pin core analysis method using the three-dimensional direct response matrix are that the response matrix can reflect the intra-assembly heterogeneous effect, the diffusion approximation is not involved, and the fuel rod fission rate can be directly evaluated. The maximum difference of the critical k-effective values among all nine cores analyzed was about 0.4% Δk. The root mean square differences between the calculated and measured radial fuel rod fission rate distributions in the test assembly of all cores were within 1.8% and nearly comparable to measurement error. The calculated results of the reactivity worth agreed with the measured results within 9%. These good agreements mean that the pin-by-pin core analysis method using the three-dimensional direct response matrix accurately reflects the effects of the intra- and inter-assembly heterogeneities in heterogeneous systems like the BASALA experimental cores.     

Atom devices based on single dopants in silicon nanostructures

Silicon field-effect transistors have now reached gate lengths of only a few tens of nanometers, containing a countable number of dopants in the channel. Such technological trend brought us to a research stage on devices working with one or a few dopant atoms. In this work, we review our most recent studies on key atom devices with fundamental structures of silicon-on-insulator MOSFETs, such as single-dopant transistors, preliminary memory devices, single-electron turnstile devices and photonic devices, in which electron tunneling mediated by single dopant atoms is the essential transport mechanism. Furthermore, observation of individual dopant potential in the channel by Kelvin probe force microscopy is also presented. These results may pave the way for the development of a new device technology, i.e., single-dopant atom electronics.     

一种新的精炼太阳能级多晶硅工艺的热力学分析(英文)

提出了一种新的硅精炼工艺生产太阳能级多晶硅,即Si-Al熔体低温凝固精炼硅技术。通过杂质在固相硅和Si-Al熔体中的分离热力学分析研究了采用Si-Al熔体分区凝固精炼硅的可行性。用温度梯度区域熔炼法来测定磷和硼的分离比,采用热力学计算金属杂质的分离比。新工艺具有很小的杂质低温分离比,表明其有很好的精炼能力。采用感应加热分区凝固实验进行验证;对Si-Al合金定向凝固中硅晶体生长进行了研究,结果表明,硅晶体的生长过程是受扩散控制的。     

Adsorption removal of boron in aqueous solutions by amine-modified tannin gel

A tannin gel (TG) synthesized from condensed tannin molecules has a remarkable ability to adsorb various metal ions in aqueous solutions. In the present study, the adsorption removal of boron in solutions at various pHs and temperatures has been examined using the TG and the amine-modified tannin gel (ATG) prepared with ammonia treatment of the TG. The adsorption amounts of boron for the TG and the ATG were relatively small and almost constant below pH 7, whereas the boron adsorption amounts increased with increasing pH in the range of pH above 7. Considering that in aqueous solutions above pH 7, the mole fraction of boric acid decreases while that of tetrahydroxyborate ion increases with increasing pH, the boron adsorption onto both gels takes place probably through the chelate formation of tetrahydroxyborate ion with the hydroxy and the amino groups in the gels. Besides, the adsorbability of the ATG for boron was higher than that of the TG due to the stable coordination bond between boron and nitrogen of the amino group in the ATG. The adsorption kinetics were adequately described by the pseudo-second order kinetic equation while the adsorption isotherms followed both the Langmuir and the Freundlich equations. The boron adsorbability of both the TG and the ATG at low boron concentration were comparable or fairly good compared with other adsorbents.     

Investigation of Settlement and Load Sharing on Piled Rafts by Monitoring Full-Scale Structures

This paper offers five recent case histories of piled raft foundations in Japan. The buildings are 19 to 162 m in height above the ground surface and were completed in 2005-2009. The piled rafts were designed based on a numerical analysis using the simplified method developed by Yamashita et al. (1998) with soil deformation parameters evaluated from the soil's shear modulus at very small strains. To confirm the validity of the foundation design, field measurements were performed on the foundation settlements and the load sharing between the rafts and the piles by monitoring the five structures from the beginning of their construction to 17 to 60 months after the end of their construction. The measured settlements were 19 to 24 mm, and the ratios of the load carried by the piles to the effective load of each structure in the tributary area, α′_p, were estimated to be 0.61 to 0.93 at the end of the observation period. The predicted maximum settlements and angular rotations of the rafts in the design were generally consistent with the measured values, and the ratios of the load carried by the piles to the total load assumed in the design were also consistent with those estimated from the measurements. Based on the measurement results from ten case histories, namely, five previously published case histories and five from the present study, it has been found that the value of α′_p generally decreases as the pile spacing ratio is increased. The value of α′_p seems to decrease gradually with a pile spacing ratio larger than about six, whereas the value of α′_p seems to decrease significantly as the pile spacing ratio is increased from about four to six. Based on the measurement results, it is suggested that piled rafts work more effectively at a pile spacing ratio of larger than about six, where at least 30% of the effective load of the structure can be carried by the rafts.     

A Simplified Image Analysis Method to Study LNAPL Migration in Porous Media

A novel Simplified Image Analysis Method was developed and tested to assess the saturation distribution values for water and LNAPLs (Light Non-Aqueous Phase Liquids) in granular soils subjected to fluctuating groundwater conditions. This method, based on the Beer-Lambert Law of transmissivity, determines the saturation of water (S_w) and LNAPLs (S_o) by comparing the average optical densities (D_i) for each matrix element of the tested domain to the corresponding average optical densities for three base pictures of the same domain taken with two digital cameras attached to two different band-pass filters (λ=450 nm and 640 nm). Two equations with two unknowns (S_w and S_o) are defined for each mesh element, which enables the saturation distribution to be calculated under dynamic conditions. The three base conditions for the domain are: (i) fully saturated with water (D_i¹⁰), (ii) fully saturated with LNAPL (D_i⁰¹), and (iii) completely dry (D_i⁰⁰). The Simplified Image Analysis Method was then applied to analyze the behavior of two fluctuating groundwater systems, namely, two-phase air-water and three-phase air-water-LNAPL, in a one-dimensional column, 3.5×3.5×50 cm, filled with Toyoura sand. The mass balance of the drainage-imbibition three-phase air-water-LNAPL system showed a difference of just 4.7% in LNAPL, demonstrating that this non-intrusive and non-destructive method is reliable for providing water and LNAPL saturation distributions throughout the domain when studying the effects of porous soil contamination by LNAPLs subjected to dynamic conditions.     

Numerical study on flow fields of tornado-like vortices using the LES turbulence model

Flow fields of tornado-like vortices generated by a numerical tornado simulator have been investigated using the LES turbulence model for two typical swirl ratios. The core radii of simulated vortices with swirl ratios of 0.31 and 0.65 showed favorable agreement with visualized vortices by a laboratory tornado simulator. Mean velocity fields were examined to obtain detailed corner flow patterns. It was found that an one-cell type vortex with a central upward flow appears for the case of low swirl ratio and vertical velocities show peaks at the center of the vortex, while a two-cell type vortex with a central downward flow emerges for the case of high swirl ratio and the maximum tangential velocity appears near ground. The formations of one-cell and two-cell type vortices were investigated by examining the axisymmetric time averaged Navier-Stokes equations. The vertical pressure gradient generates vertical velocities at the center of vortex in the one-cell type vortex, whereas the centrifugal force balances with the radial pressure gradient and the vertical advection term of the radial velocity in case of the two-cell type vortex.     

Evaluation of Pulmonary Toxicity of Zinc Oxide Nanoparticles Following Inhalation and Intratracheal Instillation

We conducted inhalation and intratracheal instillation studies of zinc oxide (ZnO) nanoparticles in order to examine their pulmonary toxicity. F344 rats were received intratracheal instillation at 0.2 or 1 mg of ZnO nanoparticles with a primary diameter of 35 nm that were well-dispersed in distilled water. Cell analysis and chemokines in bronchoalveolar lavage fluid (BALF) were analyzed at three days, one week, one month, three months, and six months after the instillation. As the inhalation study, rats were exposed to a concentration of inhaled ZnO nanoparticles (2 and 10 mg/m³) for four weeks (6 h/day, 5 days/week). The same endpoints as in the intratracheal instillation study were analyzed at three days, one month, and three months after the end of the exposure. In the intratracheal instillation study, both the 0.2 and the 1.0 mg ZnO groups had a transient increase in the total cell and neutrophil count in the BALF and in the expression of cytokine-induced neutrophil chemoattractant (CINC)-1, CINC-2, chemokine for neutrophil, and heme oxygenase-1 (HO-1), an oxidative stress marker, in the BALF. In the inhalation study, transient increases in total cell and neutrophil count, CINC-1,-2 and HO-1 in the BALF were observed in the high concentration groups. Neither of the studies of ZnO nanoparticles showed persistent inflammation in the rat lung, suggesting that well-dispersed ZnO nanoparticles have low toxicity.     

The Roles of the Ge‐Te Core Network and the Sb‐Te Pseudo Network During Rapid Nucleation‐Dominated Crystallization of Amorphous Ge2Sb2Te5

Ge₂Sb₂Te₅ (GST) has demonstrated its outstanding importance among rapid phase‐change (PC) materials, being applied for optical and electrical data storage for over three decades. The mechanism of nanosecond phase change in GST, which is vital for its application, has long been disputed: various, quite diverse scenarios have been proposed on the basis of various experimental and theoretical approaches. Nevertheless, one central question still remains unanswered: why is amorphous GST stable at room temperature for long time while it can rapidly transform to the crystalline phase at high temperature? Here it is revealed for the first time, by modelling the amorphous structure based on synchrotron radiation anomalous X‐ray scattering data, that germanium and tellurium atoms form a “core” Ge‐Te network with ring formation. It is also suggested that the Ge‐Te network can stabilize the amorphous phase at room temperature and can persist in the crystalline phase. On the other hand, antimony does not contribute to ring formation but constitutes a “pseudo” network with tellurium, in which the characteristic Sb–Te distance is somewhat longer than the covalent Sb–Te bond distance. This suggests that the Sb‐Te pseudo network may act as a precursor to forming critical nuclei during the crystallization process. The findings conclude that the Ge‐Te core network is responsible for the outstanding stability and rapid phase change of the amorphous phase while the Sb‐Te pseudo network is responsible for triggering critical nucleation.