Cathodic polarization curves of the oxygen reduction reaction on various structural materials of boiling water reactors in high temperature–high purity water

Cathodic polarization curves of the O₂ reduction reaction were measured by using electrodes made from typical structural materials of boiling water reactors (BWRs) to evaluate the effects of kind of material on the electrochemical corrosion potential (ECP) calculation. To estimate ECPs at any region in the BWRs on the basis of the BWR environmental conditions, anodic and cathodic polarization curves should be obtained in advance under relevant conditions. The concentration of oxidants such as O₂ and H₂O₂ in coolant changes depending on the region in which they exist. As well, reduction reaction rates might differ depending on the kind of materials. In this work, the cathodic polarization curves of type 316L stainless steel (316L SS) and Alloy 182 were measured in high purity water at 553 K with different O₂ concentrations and compared with those of type 304 SS (304 SS). The results showed that the cathodic polarization curves differed depending on the kind of materials at the activation-controlled region. But, the difference in the ECP vs. O₂ concentration relationship was small when the ECPs were calculated by using both anodic and cathodic polarization curves measured on the objective material.     

Bacteria contributing to behaviour of radiocarbon in sodium acetate

An acetate-utilising bacterium was isolated and identified from deionised water that was used for flooding of paddy soils in this study's batch culture experiments. Bacteria in the deionised water samples formed colonies on agar plates containing [1,2-(14)C] sodium acetate, and the autoradiograms showed that all the colonies were positive for (14)C utilisation. Then one of the acetate-utilising bacteria was isolated. The isolate was characterised by phylogenetic analysis, cell morphology, Gram staining and growth at 30 °C. Phylogenetic analysis based on 16S rRNA sequencing showed that the isolate belonged to the genus Burkholderia. The bacterium was gram-negative rods and grew at 30 °C under aerobic conditions. Based on these characteristics, the isolate was identified as Burkholderia gladioli. Because B. gladioli is often found in soil, water and the rhizosphere, attention must be paid to the relationships between bacteria and the behaviour of (14)C to for the safety assessment of geological disposal of transuranic waste.     

Liquid Crystalline Inorganic Nanosheet Colloids Derived From Layered Materials

Inorganic layered crystals such as clay minerals, layered niobates, and graphite are exfoliated in solvents to form colloidal dispersions of extremely thin inorganic nanosheets. Recently, the liquid crystal phases of these “nanosheet colloids” have been rediscovered and are attracting interest as new types of inorganic liquid crystals. The huge anisotropy of the mesogenic nanosheets compared to other liquid crystal systems is an important feature of the nanosheet liquid crystals for fundamental studies in the fields of colloid science and soft matter physics. In addition, the rich functionalities intrinsic to inorganic materials open a variety of applications such as smart colloids and composite materials with structural regularity. In this article, the recent progress of the emerging new materials of inorganic nanosheet liquid crystals is reviewed with a focus on the behaviors of each system, alignment by external field, and theoretical aspects.     

Analysis of perfluorinated acids at parts-per-quadrillion levels in seawater using liquid chromatography-tandem mass spectrometry

Perfluorinated acids (PFAs) and their salts have emerged as an important class of global environmental contaminants. Determination of sub-parts-per-trillion or parts-per-quadrillion concentrations of perfluorinated acids in aqueous media has been impeded by relatively high background levels arising from procedural or instrumental blanks. To understand the role of the oceans in the transport and fate of perfluorinated acids, methods to determine ultratrace levels of these compounds in seawater are needed. In this study, sources of procedural and instrumental blank contamination by perfluorinated acids have been identified and eliminated, to reduce background levels in blanks and thereby improve limits of quantitation. The method developed in this study is capable of detecting perfluorooctanesulfonate (PFOS), perfluorohexanesulfonate (PFHS), perfluorobutanesulfonate (PFBS), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), and perfluorooctanesulfonamide (PFOSA) at low pg/L levels in oceanic waters. PFOA is the major perfluorinated compound detected in oceanic waters, followed by PFOS. Further studies are being conducted to elucidate the distribution and fate of perfluorinated acids in oceans.     

Efficient decomposition of environmentally persistent perfluorocarboxylic acids by use of persulfate as a photochemical oxidant

Photochemical decomposition of persistent perfluorocarboxylic acids (PFCAs) in water by use of persulfate ion (S2O8(2-)) was examined to develop a technique to neutralize stationary sources of PFCAs. Photolysis of S2O8(2-) produced highly oxidative sulfate radical anions (SO4-), which efficiently decomposed perfluorooctanoic acid (PFOA) and other PFCAs bearing C4-C8 perfluoroalkyl groups. The major products were F- and CO2; also, small amounts of PFCAs with shorter than initial chain lengths were detected in the reaction solution. PFOA at a concentration of 1.35 mM (typical of that in untreated wastewater after an emulsifying process in fluoropolymer manufacture) was completely decomposed by a photochemical system with 50 mM S2O8(2-) and 4 h of irradiation from a 200-W xenon-mercury lamp. The initial PFOA decomposition rate was 11 times higherthan with photolysis alone. All sulfur-containing species in the reaction solution were eventually transformed to sulfate ions by this method. This method was successfully applied to the decomposition of perfluorononanoic acid contained in a floor wax solution.     

Efficient decomposition of environmentally persistent perfluorooctanesulfonate and related fluorochemicals using zerovalent iron in subcritical water

Decomposition of perfluorooctanesulfonate (PFOS) and related chemicals in subcritical water was investigated. Although PFOS demonstrated little reactivity in pure subcritical water, addition of zerovalent metals to the reaction system enhanced the PFOS decomposition to form F-ions, with an increasing order of activity of no metal approximately equal Al < Cu < Zn < Fe. Use of iron led to the most efficient PFOS decomposition: When iron powder was added to an aqueous solution of PFOS (93-372 microM) and the mixture was heated at 350 degrees C for 6 h, PFOS concentration in the reaction solution fell below 2.2 microM (detection limit of HPLC with conductometric detection), with formation of F-ions with yields [i.e., (moles of F- formed)/(moles of fluorine content in initial PFOS) x 100] of 46.2-51.4% and without any formation of perfluorocarboxylic acids. A small amount of CHF3 was detected in the gas phase with a yield [i.e., (moles of CHF3)/(moles of carbon content in initial PFOS) x 100] of 0.7%, after the reaction of PFOS (372 microM) with iron at 350 degree C for 6 h. Spectroscopic measurements indicated that PFOS in water markedly adsorbed on the iron surface even at room temperature, and the adsorbed fluorinated species on the iron surface decomposed with rising temperature, with prominent release of F- ions to the solution phase above 250 degrees C. This method was also effective in decomposing other perfluoroalkylsulfonates bearing shorter chain (C2-C6) perfluoroalkyl groups and was successfully applied to the decomposition of PFOS contained in an antireflective coating agent used in semiconductor manufacturing.     

Persistent perfluorinated acids in seafood collected from two cities of China

As an initial survey of human exposure to perfluorinated acids through food consumption in China, seven types of seafood collected from fish markets in two coastal cities were analyzed. Nine perfluorinated compounds were determined using HPLC coupled with ESI-MS/MS. Perfluorooctane sulfonate (PFOS) was the predominant fluorochemical and was found in all 27 seafood samples, including fish, molluscs, crabs, shrimp, oysters, mussels, and clams. Concentrations of PFOS in seafood samples ranged from 0.3 to 13.9 ng/g wet weight, with the highest concentration in mantis shrimp. The hazard ratios of noncancer risk through seafood consumption based on PFOS and perfluorooctanoic acid concentrations were calculated and were less than unity.     

Stewanrt平台的运动奇异性与力奇异性研究

Stewart平台运动时,平台可能发生运动奇异性和力奇异性。通过对平台运动方程Jacobian矩阵和力平衡方程Jacobian矩阵的分析,给出了两Jacobian矩阵的元素、行列式和条件数之间的联系,并对比了两种奇异面方程。数学分析与实例说明,Stewart平台的运动学第三类奇异性与力的奇展示性同时发生。     

Alpha-particle-induced collected charge model in SOI-DRAM's

We have developed a model for collected charges induced by an alpha-particle for SOI-DRAMs which assumes that the body capacitance equals the gate capacitance and that holes do not recombine with electrons. The validity of our model was supported by three-dimensional (3-D) device simulations that considered various gate lengths, gate oxide thicknesses, and flat-band voltages. The work function difference between the gate and body materials caused a significant increase in the current gain. The vertical band of the body region should therefore be flat to suppress the collected charge. A thinner gate oxide would also suppress the collected charge during a refresh interval. This finding could not be obtained from the conventional equation     

Prediction of Type IV creep failure of a seam-welded mod. 9Cr-1Mo elbow based on microscopic damage simulation

Utilising the random-fracture-resistance model of grain boundaries, micro-macro combined creep damage simulation was applied to the prediction of the distribution of small defects in the FGHAZ (fine-grained heat-affected zone) of longitudinal welds in an actual-size elbow of modified 9Cr-1Mo (9Cr-1MoVNb) steel subject to internal pressure at 923 K. Based on the simulation results, a prediction scheme for the final rupture life of welds was considered using the damage mechanics concept together with effective stress. The applicability of nonlinear fracture mechanics was also discussed, assuming the initial crack length determined from the microscopic simulation results. The results thus obtained are summarized as follows: As the simulation results showed, the peaks of small defect density in the subsurface could be predicted, corresponding well with the observed results. Final failure life prediction based on the damage mechanics concept was found to be applicable, by considering both the final failure surface connecting the weakest grain boundaries and the effective stress against this surface. The fracture mechanics approach was also found applicable when assuming the initial crack length from the high peaks of the simulated small defects in the last stage of creep life.