Analysis of Granular Flow in a Pebble-Bed Nuclear Reactor

Pebble-bed nuclear reactor technology, which is currently being revived around the world, raises fundamental questions about dense granular flow in silos. A typical reactor core is composed of graphite fuel pebbles, which drain very slowly in a continuous refueling process. Pebble flow is poorly understood and not easily accessible to experiments, and yet it has a major impact on reactor physics. To address this problem, we perform full-scale, discrete-element simulations in realistic geometries, with up to 440,000 frictional, viscoelastic 6cm-diameter spheres draining in a cylindrical vessel of diameter 3.5m and height 10m with bottom funnels angled at 30 degrees or 60 degrees. We also simulate a bidisperse core with a dynamic central column of smaller graphite moderator pebbles and show that little mixing occurs down to a 1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local ordering and porosity (from Voronoi volumes), the residence-time distribution, and the effects of wall friction and discuss implications for reactor design and the basic physics of granular flow.Comment: 18 pages, 21 figure

The New Center for Advanced Energy Studies

A secure and affordable energy supply is essential for achieving U.S. national security, in continuing U.S. prosperity and in laying the foundation to enable future economic growth. The next generation energy workforce in the U.S. is a critical element in meeting both national and global energy needs. The Center for Advanced Energy Studies (CAES) was established in 2005 in response to U.S. Department of Energy (DOE) requirements. CAES, located at the new Idaho National Laboratory (INL), will address critical energy education, research, policy study and training needs. CAES is a unique joint partnership between the Battelle Energy Alliance (BEA), the State of Idaho, an Idaho University Consortium (IUC), and a National University Consortium (NUC). CAES will be based in a new facility that will foster collaborative academic and research efforts among participating institutions

Velocity profile of granular flows inside silos and hoppers

We measure the flow of granular materials inside a quasi-two dimensional silo as it drains and compare the data with some existing models. The particles inside the silo are imaged and tracked with unprecedented resolution in both space and time to obtain their velocity and diffusion properties. The data obtained by varying the orifice width and the hopper angle allows us to thoroughly test models of gravity driven flows inside these geometries. All of our measured velocity profiles are smooth and free of the shock-like discontinuities ("rupture zones") predicted by critical state soil mechanics. On the other hand, we find that the simple Kinematic Model accurately captures the mean velocity profile near the orifice, although it fails to describe the rapid transition to plug flow far away from the orifice. The measured diffusion length $b$, the only free parameter in the model, is not constant as usually assumed, but increases with both the height above the orifice and the angle of the hopper. We discuss improvements to the model to account for the differences. From our data, we also directly measure the diffusion of the particles and find it to be significantly less than predicted by the Void Model, which provides the classical microscopic derivation of the Kinematic Model in terms of diffusing voids in the packing. However, the experimental data is consistent with the recently proposed Spot Model, based on a simple mechanism for cooperative diffusion. Finally, we discuss the flow rate as a function of the orifice width and hopper angles. We find that the flow rate scales with the orifice size to the power of 1.5, consistent with dimensional analysis. Interestingly, the flow rate increases when the funnel angle is increased.Comment: 17 pages, 8 figure

Fatty acid composition and sensory properties of Wels catfish (Silurus glanis) hot smoked with different sawdust materials

This study aims to compare chemical, physical and sensorial parameters of the Wels catfish (Silurus glanis), hot smoked using vine, poplar, lemon tree and oak sawdust as well as corncob. Significant differences (P < 0.05) in proximate composition were found between fresh and smoked samples; however, the changes in fatty acid composition were less significant. In the fatty acid composition of control group, monounsaturated fatty acids (41.60%) had the highest share in fatty acids, which was followed by saturated fatty acids (29.95%) and polyunsaturated fatty acids (28.34%). The major fatty acids were observed to be C16:0, C18:0; C16:1 n-7, C18:1 n-9c, C18:1 n-9t and C18:2 n6c. There were significant differences (P < 0.05) between the groups considering their colour measurement results. General preference criteria such as appearance, odour, texture, colour and taste were chosen for the sensorial analysis, which were rated by the panellists. According to the results of overall appearance, the fillet pieces smoked with lemon tree (9.00), poplar (8.66), corncob (8.00), oak (7.33) and vine (5.33) sawdust were determined as the most preferred, in order. © 2010 The Authors. International Journal of Food Science and Technology © 2010 Institute of Food Science and Technology

Antioxidative and antimicrobial activities of shrimp chitosan on gilthead sea bream (Sparus aurata) during refrigerated storage

Summary: This study aims to determine the effects of chitosan obtained from Metapenaeus stebbingi shells on the shelf life of refrigerated gilthead sea bream. It was determined that 1% chitosan-coated samples had the lowest thiobarbituric acid (TBA) (3.05 mg malondialdehyde (MDA) kg-1) and free fatty acids (FFA) value (2.79% oleic acid), while the control group had the highest TBA (5.08 mg MDA kg-1) and FFA value (6.13% oleic acid) on the 27th day of storage. In the last day of storage, TVB-N was found higher in control group (25.62 mg 100 g-1) than chitosan-coated samples (14.57 mg 100 g-1). Total viable count value of the control group exceeded maximum permissible limit on the 27th day of storage. However, it was lower than 7.0 log CFU/g in chitosan-coated samples during the refrigerated storage. As a result of this study, it was determined that shelf life of refrigerated gilthead sea bream can be increased up to 27 days with chitosan. © 2012 The Authors. International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology

NOx and extremely low temperatures of charging

The basis of basic research consists in the influence monitoring of unconventional (extremely low temperatures) charging intercooling on the selected ecological and economical parameters of a turbocharged internal combustion engine in the specific operational conditions (periodic starts and stops). The paper deals with the influence of the mentioned temperatures from the point of view of the harmful gaseous emissions production withfocus on NOx. The theoretical analysis, consequential mathematical modelling (in Fluent) of the utilizing of the extremely low temperatures of charging after the intercooler in the range from 30°C to near above zero temperatures of the turbocharged engine should define the changes trends in its power parameters and exhaust gas emissions production mostly NOx. At the same time it should consider the influence of the extremely low temperatures of charging on the engine inner corrosion at the periodic engine starts and stops. The mathematical model should allow alternatively solving possible risks resulting from the proposal newness and originality. From the proposal it is expected to obtain more effective energy utilization, the decrease of the environment ecological load compared with the standard solution and the possibility of creation of the permanent sustainable energetic system. The possibilities of the design solution for the system of extremely low temperatures of air fuel mixture are also presented in the paper

Comparison Between Air and Helium for Use as Working Fluids in the Energy-Conversion Cycle of the MPBR

A comparison between air and helium for use as working fluids in the energy-conversion cycle of the MPBR is presented. To date, helium has been selected in the MPBR indirect-cycle working reference design. Air open- and closed-cycle variants are considered in this thesis in order to identify relative advantages in cycle efficiency, component efficiency, size, and possible development work required for deployment. The results of this comparison indicate that the helium cycle results in the smallest-sized plant, uses well-established technology, has a high busbar efficiency, and thus best meets the design priorities of the MPBR. The open-cycle-air variant employs turbomachinery components with the greatest amount of industrial experience, the least amount of development work required, and a 6% advantage in busbar efficiency when compared with the helium cycle. However, it results in a plant roughly 5 times the size of the helium plant. The closed-air cycle has a 5% advantage in busbar efficiency over the helium plant, but results in a plant roughly 2.5 times the size of the helium plant and requires approximately the same amount of development work for near-term MPBR deployment