Multi-component diffusion analysis and assessment of GAMMA code and improved RELAP5 code

A loss-of-coolant accident (LOCA) has been considered a critical event for very high temperature gas-cooled reactor (VHTR). Following helium depressurization, it is anticipated that unless countermeasures are taken, air will enter the core through the break by molecular diffusion and ultimately by natural convection leading to oxidation of the in-core graphite structure. Thus, without any mitigating features, a LOCA will lead to an air ingress event, which will lead to exothermic chemical reactions of graphite with oxygen, potentially resulting in significant increases of the core temperature.New and safer nuclear reactors (Generation IV) are now in the early planning stages in many countries throughout the world. One of the reactor concepts being seriously considered is the VHTR. To achieve public acceptance, these reactor concepts must show an increased level of inherent safety over current reactor designs (i.e., a system must be designed to eliminate any concerns of large radiological releases outside the site boundary).A computer code developed from this study, gas multi-component mixture analysis (GAMMA) code, was assessed using a two-bulb experiment and in addition the molecular diffusion behavior in the prismatic-core gas-cooled reactor was investigated following the guillotine break of the main pipe between the reactor vessel and the power conversion unit. The RELAP5 code was improved for the VHTR air ingress analysis and was assessed using inverse U-tube and NACOK natural circulation data.     

Chlorine stable isotopes: a comparison of dual inlet and thermal ionization mass spectrometric measurements

Chlorine stable isotope ratios, 37Cl/35Cl, currently are measured using dual-inlet and thermal-ionization mass spectrometry. These two different analytical techniques, however, have never been cross calibrated. A set of samples with chlorine stable isotope delta values ranging from -4.4 to +0.3 % relative to standard mean ocean water chloride has been analyzed using both of these techniques. Our data show that both techniques can yield similar results within analytical uncertainty. CsCl thermal ionization data are extremely sensitive to the amount of chlorine being measured and cannot be used to determine absolute ratios without an independent means of correcting for machine-induced mass fractionation. As long as standards and samples are of equivalent size, however, the differences between samples measured by thermal ionization remain constant Dual inlet stable isotope mass spectrometry is suited best for samples of > 10 micromol Cl, yielding chlorine stable isotope data with < or =0.1% reproducibilities (2sigma). Thermal ionization mass spectrometry easily accommodates samples of approximately0.1-0.3 micromol Cl, with achievable uncertainties of < or =0.2% (2sigma).     

Rectification of “restrained vs unrestrained”

For furnace testing of fire-resistant floor and roof assemblies in the United States, the ASTM E 119 standard (and similarly the UL 263 standard) permits two classifications for boundary conditions: “restrained” and “unrestrained.” When incorporating tested assemblies into an actual structural system, the designer, oftentimes a fire protection or structural engineer, must judge whether a “restrained” or “unrestrained” classification is appropriate for the application. It is critical that this assumption be carefully considered and understood, as many qualified listings permit a lesser thickness of applied fire protection for steel structures (or less concrete cover for concrete structures) to achieve a certain fire resistance rating if a “restrained” classification is confirmed, as compared with an “unrestrained” classification. The emerging standardization of structural fire engineering practice in the United States will disrupt century-long norms in the manner to which structural behavior in fire is addressed. For instance, the current edition of the ASCE/SEI 7 standard will greatly impact how designers consider restraint. Accordingly, this paper serves as an exposé of the “restrained vs unrestrained” paradigm in terms of its paradoxical nature and its controversial impact on the industry. More importantly, potential solutions toward industry rectification are provided for the first time in a contemporary study of this paradigm.     

Airborne Particulate Matter and Human Health: A Review

Results of recent research show that particulate matter (PM) composition and size vary widely with both space and time. Despite the variability in PM characteristics, which are believed to influence human health risks, the observed relative health risk estimates per unit PM mass falls within a narrow range of values. Furthermore, no single chemical species appears to dominate health effects; rather the effects appear to be due to a combination of species. Non-PM factors such as socioeconomic status and lifestyle are also believed to affect the health risk, although accounting for these confounding factors is challenging. Airborne PM is also responsible for a number of effects aside from human health, such as alterations in visibility and climate. Because the PM problem is associated with a range of societal issues such as energy production and economic development, making progress on reducing the effects of PM will require integrated strategies that bring together scientists and decision makers from different disciplines to consider tradeoffs holistically.     

Molecules that target beta-amyloid

The devastating effects of Alzheimer's and related amyloidogenic diseases have inspired the synthesis and evaluation of numerous ligands to understand the molecular mechanism of the aggregation of the beta-amyloid peptide. Our review focuses on the current knowledge in this field with respect to molecules that have been demonstrated to interact with either oligomeric or fibrillar forms of the beta-amyloid peptide. We describe natural proteins, peptides, peptidomimetics, and small molecules that have been found to interfere with beta-amyloid aggregation. We also detail recent efforts in selecting molecules that target beta-amyloid isolated from antibody, protein, and peptide libraries. These new molecules will likely aid in deciphering the details of the aggregation pathway for the beta-amyloid peptide and provide reagents that may stabilize relevant oligomeric intermediates which likely have bearing on the pathophysiology of Alzheimer's disease. Moreover, the described anti-amyloid molecular toolbox will also provide an avenue for designing new diagnostic and therapeutic reagents.     

Ionic strength-induced formation of smectite quasicrystals enhances nitroaromatic compound sorption

Sorption of organic contaminants by soils is a determinant controlling their transport and fate in the environment. The influence of ionic strength on nitroaromatic compound sorption by K+- and Ca2+ -saturated smectite was examined. Sorption of 1,3-dinitrobenzene by K-smectite increased as KCl ionic strength increased from 0.01 to 0.30 M. In contrast, sorption by Ca-smectite at CaCl2 ionic strengths of 0.015 and 0.15 M remained essentially the same. The "salting-out" effect on the decrease of 1,3-dinitrobenzene aqueous solubility within this ionic strength range was <1.5% relative to the solubility in pure water. This decrease of solubility is insufficient to account for the observed increase of sorption by K-smectite with increasing KCl ionic strength. X-ray diffraction patterns and light absorbance of K-clay suspensions indicated the aggregation of clay particles and the formation of quasicrystal structures as KCI ionic strength increased. Sorption enhancement is attributed to the formation of better-ordered K-clay quasicrystals with reduced interlayer distances rather than to the salting-out effect. Dehydration of 1,3-dinitrobenzene is apparently a significant driving force for sorption, and we show for the first time that sorption of small, planar, neutral organic molecules, namely, 1,3-dinitrobenzene, causes previously expanded clay interlayers to dehydrate and collapse in aqueous suspension.     

Protective effect of dietary tomatine against dibenzo[a,l]pyrene (DBP)-induced liver and stomach tumors in rainbow trout

The potential anti-carcinogenic effects of tomatine, a mixture of commercial tomato glycoalkaloids alpha-tomatine and dehydrotomatine (10:1), were examined in the rainbow trout chemoprevention model. Prior to the chemoprevention study, a preliminary toxicity study revealed that tomatine in the diet fed daily at doses from 100 to 2000 parts per million (ppm) for 4 weeks was not toxic to trout. For the tumor study, replicate groups of 105 trout were fed diets containing dibenzo[a,l]pyrene (DBP) alone (224 ppm), (N = 3), DBP plus tomatine at 2000 ppm (N = 2), tomatine alone (N = 2), or control diet (N = 2) for 4 weeks. The fish were then returned to control diet for 8 months and necropsied for histopathology. Dietary tomatine was found to reduce DBP-initiated liver tumor incidence from 37.0 to 19.0% and stomach tumor incidence from 46.4 to 29.4%. Tomatine also reduced stomach tumor multiplicity. The tomatine-containing diets did not induce mortality, change in fish weights, or liver weights. No adverse pathological effects in the tissues of the fish on the tomatine diets were observed. Dose-response and chemopreventive mechanisms for tomatine protection remain to be examined. This is the first report on the anticarcinogenic effects of tomatine in vivo.     

Electrostimulation as a prosthesis for repair of information flow in a computer model of neocortex

Damage to a cortical area reduces not only information transmitted to other cortical areas, but also activation of these areas. This phenomenon, whereby the dynamics of a follower area are dramatically altered, is typically manifested as a marked reduction in activity. Ideally, neuroprosthetic stimulation would replace both information and activation. However, replacement of activation alone may be valuable as a means of restoring dynamics and information processing of other signals in this multiplexing system. We used neuroprosthetic stimulation in a computer model of the cortex to repair activation dynamics, using a simple repetitive stimulation to replace the more complex, naturalistic stimulation that had been removed. We found that we were able to restore activity in terms of neuronal firing rates. Additionally, we were able to restore information processing, measured as a restoration of causality between an experimentally recorded signal fed into the in silico brain and a cortical output. These results indicate that even simple neuroprosthetics that do not restore lost information may nonetheless be effective in improving the functionality of surrounding areas of cortex.     

Surveys of natural radiation exposure in UK dwellings with passive and active measurement techniques

A representative sample of over 2,000 UK dwellings was monitored for a year using thermoluminescent and etchable plastic dosemeters to measure gamma-ray dose rates and radon concentrations. The survey was carried out by post. Each householder completed a questionnaire on the type of dwelling and its characteristics. These data will be used in the assessment of the factors affecting indoor exposure. The mean gamma-ray dose rates were 0.062 and 0.057 μGy h^?1 in air and the mean radon concentrations were 25 and 18 Bq m^?3 for living areas and bedrooms respectively. Other results of the preliminary data analysis are given.More detailed surveys were conducted in areas where the local geology indicated that elevated exposures to natural radiation might occur. Over 800 dwellings were visited and measurements made of several parameters. The mean gamma-ray dose rates varied from 0.05 to 0.10 μGy h^?1 in air. The mean radon concentrations varied from 14 Bq m^?3 to 520 Bq m^?3. Other findings related to equilibrium factors and regional differences are discussed.