Simulation of pellet-cladding thermomechanical interaction and fission gas release

This paper summarizes the present status of a computer code that describes some of the main phenomena occurring in a nuclear fuel rod throughout its life. Temperature distribution, thermal expansion, elastic and plastic strains, creep, mechanical interaction between pellet and cladding, fission gas release, gas mixing, swelling, and densification are modeled. The modular structure of the code allows for the incorporation of models to simulate different phenomena and material properties. Collapsible rods can be also simulated.The code is bidimensional, assumes cylindrical symmetry for the rod and uses the finite element method to integrate the differential equations. The stress–strain and heat conduction problems are nonlinear due to plasticity and to the temperature dependence of the thermal conductivity. The fission gas inventory is calculated with a diffusion model, assuming spherical grains and using a one-dimensional finite element scheme. Pressure increase, swelling and densification are coupled with the stress field.Good results are obtained for the simulation of the irradiation tests of the first argentine prototypes of MOX fuels, where the bamboo effect is clearly observed, and of the FUMEX series for the fuel centerline temperature, the inside rod pressure and the fractional gas release.     

Comparison of crumb microstructure from pound cakes baked in a microwave or conventional oven

Imaging, light microscopy and scanning electron microscopy were used to compare the microstructure of crumbs from pound cakes baked in a microwave or conventional oven. The microwave baking conditions for pound cake (240 W, 5 min) were established in previous research, conventional baked pound cakes were obtained using a swing oven at 180 °C for 40 min. Statistical differences in total cell, cell/cm² and mean cell area (P?0.05) were observed in the image analysis. Cells from microwaved pound cake crumbs were 20% larger. However, factor shape was 0.81 for both microwave and conventionally baked crumbs, and crumbs from both oven types were similar in appearance. Light microscopy revealed birefringence in crumbs from both types of pound cakes. Scanning electron microscopy revealed that the conventionally baked product had a greater amount of protein matrix however; the matrix structure of the crumb was comparable between microwave-baked and conventionally baked pound cakes. In conclusion, our results suggest that the unique aspects of pound cake dough, including its high content of fat, sugar and moisture, make it well suited to microwave baking.     

On the reduction of dodging in mice: A comparison of food wrenching and dodging in rats (Rattus norvegicus) and mice (Mus musculus).

Rats attempt to steal food from conspecifics by approaching them from the side to wrench the food from the victims' paws, but victims dodge laterally away to protect their food. Given the pervasive necessity of obtaining food, it might be expected that the behaviors of food wrenching and dodging would be common to many animals, but this idea has not been examined. In the present study, food wrenching and dodging were compared in Long-Evans and Sprague-Dawley rats (Rattus norvegicus) and out-crossed CDF1 and inbred C57b mice (Mus musculus). Mice stole food using a strategy very similar to that of rats, but they did not dodge in an open field test and dodged less in a home cage test and ran away or fought more than rats. There were no strain differences in rats, but C57b mice dodged less than CDF1 mice. Given that dodging is a component not only of food defensive behavior but also of play, sexual, and aggressive behavior, the species and strain difference may be a marker (or a key element) of changes in social behaviors that have occurred since the evolutionary separation of rats and mice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electroconductive nylon 6 and copper composites

A study is reported on the effect of the filler size and concentration on the electrical resistivity, density, and hardness of composites made of copper powder embedded in nylon 6 matrix by means of compression molding. The electrical resistivity of the composites is > 10¹¹ ohm·cm unless the metal content reached the percolation threshold, beyond which the resistivity decreased markedly by as much as 10¹². The percolation concentration was found to decrease with a decrease in the average particle diameter. The density of the composites was measured and compared with values calculated assuming different void levels within the samples. However, there is no sharp variation in the density due to the onset of percolation. Furthermore, it is shown that a percolation concentration can be also defined in the hardness/metal concentration curves as the intercept of linear regression curves of the low and high metal content regimes, respectively.     

Effects of calf diet, antioxidants, packaging type and storage time on beef steak storage

The effect of basal dietary supplemented with vegetable oils plus vitamin E (sunflower, soybean, linseed and a basal diet control), type of packaging (MAP or vacuum), addition of natural antioxidant (grape seed, rosemary) and storage time (0, 7, 14 and 21 days) on lipid oxidation, color stability, vitamin E content, and total aerobic bacterial counts in steaks of Longissimus thoracis was studied. The triple interaction diet × time × packaging affected oxidative stability, redness and yellowness of the meat. TBARS values did not increase with time in vacuum-packaged samples for all dietary treatments. However, samples from MAP and control showed the highest TBARS values after 21 days of storage (0.72 mg MDA/kg of meat, P < 0.05). Both exogenous antioxidant extracts and MAP maintained low total aerobic counts in steaks until the 21st day. Calves should be fed a diet supplemented with L-VE, stored in MAP and treated with grape seed extract to extend the shelf life of their meat.     

The benefits of flexible team interaction during crises.

Organizations increasingly rely on teams to respond to crises. While research on team effectiveness during nonroutine events is growing, naturalistic studies examining team behaviors during crises are relatively scarce. Furthermore, the relevant literature offers competing theoretical rationales concerning effective team response to crises. In this article, the authors investigate whether high- versus average-performing teams can be distinguished on the basis of the number and complexity of their interaction patterns. Using behavioral observation methodology, the authors coded the discrete verbal and nonverbal behaviors of 14 nuclear power plant control room crews as they responded to a simulated crisis. Pattern detection software revealed systematic differences among crews in their patterns of interaction. Mean comparisons and discriminant function analysis indicated that higher performing crews exhibited fewer, shorter, and less complex interaction patterns. These results illustrate the limitations of standardized response patterns and highlight the importance of team adaptability. Implications for future research and for team training are included. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Positron annihilation lifetime study of vapor sorption in polypropylene and polytetrafluoroethylene

Positron annihilation lifetime (PAL) spectra were measured for two different kinds of polymers: polypropylene (PP) and polytetrafluoroethylene (PTFE), during sorption of vapors of the following molecules: n-hexane, cyclohexane, benzene, methyl methacrylate, acrylic acid, and water. The behavior of ortho-positronium (o-Ps) annihilation parameters: lifetime, τ₃, and intensity, I₃, can be explained by considering different sorption mechanisms in rubbery and glassy polymers. The mean size of the intermolecular-space holes and the relative free-volume fraction of PP and PTFE were estimated before and during the sorption process from the o-Ps parameters obtained. Sorption of n-hexane, cyclohexane, and benzene in both polymers affect the o-Ps component in a systematic way, for PP τ₃ and I₃ tend to decrease, while in PTFE, τ₃ stay almost constant and I₃ diminishes. These effects are interpreted in relation to the different states of the polymers studied: rubbery for PP and glassy for PTFE. In case of methyl methacrylate molecules, the behavior of o-Ps parameters was more complicated. For acrylic acid and water, their associated polarity provokes a diminution in I₃, which is explained from the viewpoint of the spur model of positronium formation. Large changes in the mean size and the fraction of free volume, as well as their constant behavior in some cases, were interpreted to be due to positive or negative interactions, respectively, between vapor molecules and PP and PTFE, which could be correlated with the solvent-interaction parameters calculated. © 1995 John Wiley & Sons, Inc.     

A model to describe the interaction between UO2 and zircaloy in the temperature range 1000–1700°C

During high temperature transients the Zircaloy claddings in a nuclear power reactor may chemically interact with their environment, either on the internal or on the external surfaces. The external oxidation due to the interaction with the coolant has been extensively studied and described in models. However, the internal oxide-metal interaction is less well known and has not yet been satisfactorily described in models. In this paper the internal oxidation, which results from the reduction of the UO₂ pellets by the Zircaloy cladding material is analyzed. A model is developed which solves only the oxygen diffusion problem in the five phases which are formed due to the UO₂/Zircaloy interaction, without taking into account zirconium and uranium diffusion. The oxygen diffusion coefficients of four of the phases are determined and the oxygen concentrations at some of the interfaces are adjusted in order that the interface movements be in accordance with the experimental data published in the literature for the temperature range 1000 to 1700°C. The model attempts only to simulate the kinetics of the system during the first stages of the process when all the interface movements obey parabolic rate laws.