Development of the evaluation methodology for the material relocation behavior in the core disruptive accident of sodium-cooled fast reactors

The in-vessel retention (IVR) of core disruptive accident (CDA) is of prime importance in enhancing safety characteristics of sodium-cooled fast reactors (SFRs). In the CDA of SFRs, molten core material relocates to the lower plenum of reactor vessel and may impose significant thermal load on the structures, resulting in the melt-through of the reactor vessel. In order to enable the assessment of this relocation process and prove that IVR of core material is the most probable consequence of the CDA in SFRs, a research program to develop the evaluation methodology for the material relocation behavior in the CDA of SFRs has been conducted. This program consists of three developmental studies, namely the development of the analysis method of molten material discharge from the core region, the development of evaluation methodology of molten material penetration into sodium pool, and the development of the simulation tool of debris bed behavior. The analysis method of molten material discharge was developed based on the computer code SIMMER-III since this code is designed to simulate the multi-phase, multi-component fluid dynamics with phase changes involved in the discharge process. Several experiments simulating the molten material discharge through duct using simulant materials were utilized as the basis of validation study of the physical models in this code. It was shown that SIMMER-III with improved physical models could simulate the molten material discharge behavior, including the momentum exchange with duct wall and thermal interaction with coolant. In order to develop an evaluation methodology of molten material penetration into sodium pool, a series of experiments simulating jet penetration behavior into sodium pool in SFR thermal condition were performed. These experiments revealed that the molten jet was fragmented in significantly shorter penetration length than the prediction by existing correlation for light water reactor conditions, due to the direct contact and thermal interaction of molten materials with coolant. The fragmented core materials form a sediment debris bed in the lower plenum. It is necessary to remove decay heat safely from this debris bed to achieve IVR. A simulation code to analyze the behavior of debris bed with decay heat was developed based on SIMMER-III code by implementing physical models, which simulate the interaction among solid particles in the bed. The code was validated by several experiments on the fluidization of particle bed by two-phase flow. These evaluation methodologies will serve as a basis for advanced safety assessment technology of SFRs in the future.     

Construction of the Quasi-ternary Phase Diagram in the NdO1.5-BaO-CuOx System in an Air Atmosphere: Part I, Equilibrium Tie Lines in the Nd1+xBa2−xCu3O6+δ Solid Solution and Liquid Region

Quasi-ternary phase diagrams of the NdO_1.5-BaO-CuO _x system near the CuO _x corner have been constructed near the peritectic temperature in air of the Nd_{1+ x} Ba_{2− x} Cu₃O_6+delta (Nd123) solid-solution phase. Liquidus curves were determined by measuring the temperature dependences of the neodymium, barium, and copper solubilities in Nd-Ba-Cu-O solutions with different BaO:CuO ratios. Solidus line compositions and equilibrium tie lines were determined by analyzing the compositions of the Nd123 solid solution equilibrated with the melt by quenching samples held isothermally. Based on the tie-line features in the Nd123-and- liquid two-phase field, the Nd123 solid solution with the smaller substitution content was observed to be equilibrated with the solution melt with a higher BaO:CuO ratio, even in an air atmosphere. Nd123 crystal with a substitution content of ∼0.02 could be formed from the solution with the BaO:CuO ratio of greaterthan equal to0.75, which resulted in higher critical superconducting transition temperatures.     

Iodide sorption and partitioning in solid, liquid and gas phases in soil samples collected from Japanese paddy fields

Sorption kinetics of iodide (I(-)), which is one of the major inorganic chemical forms of iodine in soil environments, were studied under four sets of experimental conditions characterised by temperature or biological activity. We compared partitioning ratios in solid, liquid and gas phases in soils as well as soil-soil solution distribution coefficients (K(d)s) at two different temperatures 4 and 23 °C, for 63 paddy soil samples collected throughout Japan. Interestingly, (125)I emission from soil was observed; the partitioning ratios in gas phase ranged from 0 to 27 % at 4 °C and from 0 to 42 % at 23 °C. In addition, the authors found that K(d) values at 23 °C had good correlation with pH though there was no correlation between K(d) values at 4 °C and pH because of the difference in biological activity.     

Three-dimensional islands of Si and Ge formed on SiO2 through crystallization and agglomeration from amorphous thin films

The crystallization process was examined for amorphous thin films of silicon (a-Si) and germanium (a-Ge) on quartz glass (SiO₂) substrate. Three-dimensional crystalline islands were formed through crystallization and agglomeration. These islands indicated a bimodal size distribution. The mechanism of crystalline island (c-Si, c-Ge) formation was discussed on the basis of thermodynamics. In studying the crystallization of the thin films, the influence of the film-substrate interfacial energy should be taken into consideration. It was found that the thickness of the as-deposited amorphous films is an essential factor in determining the crystallization behavior and in controlling island size. Above all, a high size uniformity of crystalline islands could be obtained under moderate thermal annealing conditions.     

Non-destructive inspection for weld joint of steel structure

Friction stir welding (FSW) succeeded in producing high quality dissimilar welds with AA5083 and A6N01 by evaluation of the microstructure and the root bend testing. A6N01 with a wide optimum range of welding condition should be placed on the retreating side to weld a sound joint between AA5083 and A6N01. The optimum welding condition of FSW for the dissimilar alloys between AA5083 and A6N01 was wider than that of AA5083. In the opposite orientation, A6N01 on the advancing side can hardly flow into AA5083 on the retreating side in front of the tool. As the pores on inappropriate welding conditions were observed, large pores on a lower tool rotation speed were different from small discontinuous pores on a higher tool rotation speed.     

锯齿型单壁碳纳米管的光电性质

应用基于广义梯度近似的密度泛函理论中的简化广义梯度近似方法(PBE)对(7,0)至(18,0)锯齿型单壁碳纳米管在极化与非极化条件下从紫外波段到近红外波段的光电性质分别做了理论计算,得到了锯齿型碳纳米管的各光学常数峰值和各光学常数峰值所对应的波长与其手性参数n之间的对应关系和变化趋势。结果表明:除反射率和损耗外的各光学常数的峰值是随着n的增大而减小的;除反射率峰值对应波长外,其它光学常数的峰值对应的波长值随着n的增大逐渐趋于一个恒定值。     

Cell surface hydrophobicity and colony morphology of Trichosporon asahii clinical isolates

Trichosporon asahii is a pathogenic basidiomycetous yeast. Individual strains of T. asahii have different colony morphologies. However, it is not clear whether cell surface phenotypes differ among the colony morphologies. Here we characterized the cell surface hydrophobicity and analysed the carbohydrate contents of the cell surface polysaccharides in T. asahii clinical isolates with various colony morphologies. Among the three distinctive colony morphologies obtained from one clinical isolate, the white‐type morphology exhibited higher hydrophobicity. The hydrophobicity of heat‐killed T. asahii cells was greatly reduced after periodate oxidation of the cell surface carbohydrates. Furthermore, the cell wall and extracellular polysaccharide components differed among the morphologies. Our results suggest that T. asahii cell surface hydrophobicity is affected by cell surface carbohydrate composition. Copyright © 2016 John Wiley & Sons, Ltd.     

Via-Shape-Control for Copper Dual-Damascene Interconnects With Low-k Organic Film

Copper dual-damascene (DD) interconnects are fabricated with low-k organic film (SiLKtrade) without any etch-stop layers by use of dual hard mask (dHM) process combined with sidewall-hardening etching step. It is a key point to reduce shoulder loss during trench etching at connecting regions of vias and trenches, so that hardening of the via-sidewall by fluorocarbon plasma during via etching is implemented. Careful designs of dual hard mask structures and their patterning sequence are carried out for the process without etch-stop layer under the trench. The two-layered interconnect with low-k structure has achieved low via-resistance of 0.65 Omega at 0.28 mumOslash with keeping large tolerance of misalignment up to 0.1 mum.     

Numerical analysis of an axial-mode zigzag antenna

The radiation characteristics of an axial-mode zigzag antenna are evaluated on the basis of the numerically determined current distribution. It is revealed that the frequency at which the maximum gain is obtained decreases as the number of zigzag cells is increased, and that an antenna of two zigzag cells has a high power gain of about 11 dB with a bandwidth of about 11%, although the number of zigzag cells is extremely small.