TRANSIENT HEAT TRANSFER ANALYSIS UP TO DRYOUT IN 3D FUEL RODS UNDER UNIDEAL CONDITIONS THROUGH THE DEVELOPMENT OF A COMPUTER CODE

In this paper we analyze a conjugated transient heat transfer problem consisting of a nuclear reactor’s fuel rod and its intrinsic coolant channel. Our analysis is made possible through a computer code being developed at the Instituto de Engenharia Nuclear (IEN/CNEN). This code is meant to study the temperature behavior in fuel rods which exhibit deviation from their ideal conditions, that is, rods in which the cladding is deformed or the fuel is dislocated. It is also designed to avoid the use of the computationally expensive Navier-Stokes equations. For these reasons, its physical model has as basis a three-dimensional fuel rod coupled to a one-dimensional coolant channel, which are discretized using the finite element method. Intending to study accidental conditions in which the coolant (light water) transcends its saturation temperature, turning into vapor, a homogeneous mixture is used to represent the two-phase flow, and so the coolant channel’s energy equation is described using enthalpy. Owing to the fact that temperature and enthalpy are used in the physical model, it became impractical to generate a fully coupled method for solving the pertinent equations. Thus, the conjugated heat transfer problem is solved in a segregated manner through the implementation of an iterative method. Finally, as study cases for this paper we present analyses concerning the behavior of the hottest fuel rod in a Pressurized Water Reactor during a shutdown wherein the residual heat removal system is lost (loss of the reactor’s coolant pumps). These studies contemplate cases in which the fuel rod’s geometry is ideal or curved. Analyses are also performed for two circumstances of positioning of the fuel inside the rod: concentric and eccentric.In this paper we analyze a conjugated transient heat transfer problem consisting of a nuclear reactor’s fuel rod and its intrinsic coolant channel. Our analysis is made possible through a computer code being developed at the Instituto de Engenharia Nuclear (IEN/CNEN). This code is meant to study the temperature behavior in fuel rods which exhibit deviation from their ideal conditions, that is, rods in which the cladding is deformed or the fuel is dislocated. It is also designed to avoid the use of the computationally expensive Navier-Stokes equations. For these reasons, its physical model has as basis a three-dimensional fuel rod coupled to a one-dimensional coolant channel, which are discretized using the finite element method. Intending to study accidental conditions in which the coolant (light water) transcends its saturation temperature, turning into vapor, a homogeneous mixture is used to represent the two-phase flow, and so the coolant channel’s energy equation is described using enthalpy. Owing to the fact that temperature and enthalpy are used in the physical model, it became impractical to generate a fully coupled method for solving the pertinent equations. Thus, the conjugated heat transfer problem is solved in a segregated manner through the implementation of an iterative method. Finally, as study cases for this paper we present analyses concerning the behavior of the hottest fuel rod in a Pressurized Water Reactor during a shutdown wherein the residual heat removal system is lost (loss of the reactor’s coolant pumps). These studies contemplate cases in which the fuel rod’s geometry is ideal or curved. Analyses are also performed for two circumstances of positioning of the fuel inside the rod: concentric and eccentric.In this paper we analyze a conjugated transient heat transfer problem consisting of a nuclear reactor’s fuel rod and its intrinsic coolant channel. Our analysis is made possible through a computer code being developed at the Instituto de Engenharia Nuclear (IEN/CNEN). This code is meant to study the temperature behavior in fuel rods which exhibit deviation from their ideal conditions, that is, rods in which the cladding is deformed or the fuel is dislocated. It is also designed to avoid the use of the computationally expensive Navier-Stokes equations. For these reasons, its physical model has as basis a three-dimensional fuel rod coupled to a one-dimensional coolant channel, which are discretized using the finite element method. Intending to study accidental conditions in which the coolant (light water) transcends its saturation temperature, turning into vapor, a homogeneous mixture is used to represent the two-phase flow, and so the coolant channel’s energy equation is described using enthalpy. Owing to the fact that temperature and enthalpy are used in the physical model, it became impractical to generate a fully coupled method for solving the pertinent equations. Thus, the conjugated heat transfer problem is solved in a segregated manner through the implementation of an iterative method. Finally, as study cases for this paper we present analyses concerning the behavior of the hottest fuel rod in a Pressurized Water Reactor during a shutdown wherein the residual heat removal system is lost (loss of the reactor’s coolant pumps). These studies contemplate cases in which the fuel rod’s geometry is ideal or curved. Analyses are also performed for two circumstances of positioning of the fuel inside the rod: concentric and eccentric

Reproductive biology of Pseudotocinclus tietensis (Siluriformes: Loricariidae: Hypoptopomatinae), a threatened fish species

Pseudotocinclus tietensis is endemic to the Upper Tietê River basin and classified as vulnerable. The reproductive biology of this species is still unknown, therefore, we investigated its reproductive strategy and gonad development during its annual reproductive cycle. The fish were collected throughout one year, and histology of the gonads, fecundity and oocyte diameter was conducted. Three phases of gonad maturation were found in males and females (immature, developing, and spawning capable), and the development stages of the gametes were identified within each stage. In the testes, four stages of gamete development were distinguished: spermatogonia, spermatocytes, spermatids and spermatozoa. During spermiation, the spermatozoa were released into the tubular lumen and then continued through the efferent ducts. In the ovaries, five stages of gamete development were identified: chromatin nuclear, perinucleolar, yolk vesicle formation, vitellogenic and ripe. The minimum diameter of ovulating oocytes was 297 µm, and the absolute fecundity was 64 to 306 oocytes. Males with spermatozoa in the lobular lumen and females with vitellogenic and ripe oocytes were found throughout the year. Pseudotocinclus tietensis has asynchronous ovarian development and gametes with fertilization capacity can be eliminated throughout the annual cycle

Mitochondrial Preconditioning: A Potential Neuroprotective Strategy

Mitochondria have long been known as the powerhouse of the cell. However, these organelles are also pivotal players in neuronal cell death. Mitochondrial dysfunction is a prominent feature of chronic brain disorders, including Alzheimer's disease (AD) and Parkinson's disease (PD), and cerebral ischemic stroke. Data derived from morphologic, biochemical, and molecular genetic studies indicate that mitochondria constitute a convergence point for neurodegeneration. Conversely, mitochondria have also been implicated in the neuroprotective signaling processes of preconditioning. Despite the precise molecular mechanisms underlying preconditioning-induced brain tolerance are still unclear, mitochondrial reactive oxygen species generation and mitochondrial ATP-sensitive potassium channels activation have been shown to be involved in the preconditioning phenomenon. This review intends to discuss how mitochondrial malfunction contributes to the onset and progression of cerebral ischemic stroke and AD and PD, two major neurodegenerative disorders. The role of mitochondrial mechanisms involved in the preconditioning-mediated neuroprotective events will be also discussed. Mitochondrial targeted preconditioning may represent a promising therapeutic weapon to fight neurodegeneration

Galactomannans from novel sources blended with collagen as edible coatings for fruits

The biggest losses (25 % to 80 %) in the quality and amount of fresh fruits occur between their harvest and consumption. Further, one of the most important problems in fruit conservation is their short shelf life. Preservation can be extended by reducing respiration and transpiration rates. This is done by controlling factors such as temperature, relative humidity, gas composition, light and mechanical/physical stress. The galactomannan films and coatings have a no greasy/oily aspect, together with a low caloric content. They became popular in the agriculture due to their permeability to CO2 and/or O2. On the other hand, collagen coatings have been used on meats and sausages to reduce gas and/or water vapour permeability. Blending has become an economical and versatile way to obtain materials with a wide range of desirable properties. In this work galactomannan/collagen blends were studied as coatings from mango and apple fruits. The galactomannans were extracted from Caesalpinia pulcherrima and Adenathera pavonina and mixed with collagen and glycerol. These new galactomannans have mannose:galactose ratios between 2:1 and 3:1, which significantly improve their mechanical properties when used as coatings. The work started by characterizing the surface properties of the fruits and the wetting capacity of the coatings (as determined by the sessile drop method) as well as the fruits respiration rate (determined by measurement of O2 - with an O2 electrode and CO2 - by gas chromatography - in a chamber). The coating composition which presented the best values of wettability was identified for each of the fruits under consideration. Such coatings were characterized in terms of their water vapor, O2 and CO2 permeability values. Results have shown that it is possible to coat mango and apple with galactomannan/collagen blends. However, further research must be undertaken to improve the mechanical properties of these new materials.info:eu-repo/semantics/publishedVersio

Social policies, personal and regional income inequality in Brazil: an I-O analysis of the "Bolsa Família" program

The study presents a Leontief-Miyazawa model to study personal and regional income inequality in Brazil. The economy is divided into 31 sectors, in 5 macro regions; households are allocated into 10 income brackets. The study identifies the contribution of different sectors to inequality. The model is used to simulate the capacity of social policies to reduce personal and regional inequality in the country. The analysis is conducted using the pro-poor “Bolsa Família” program which is a social program that provides direct income transfers to poor (with per capita income between BRL 60,01 and BRL 120,00) and extreme poor households (with per capita income below BRL 60,00). The results show that in the short run, the “Bolsa Família” program has proven to produce positive results, both at the personal income level and at the regional concentration level, and has surely paid large dividends in electoral terms. Solving inequality problems, however, might need other mid and long run policies which could improve competitiveness of lagging regions

Social policies, personal and regional income inequality in Brazil: an I-O analysis of the "Bolsa Família" program

The study presents a Leontief-Miyazawa model to study personal and regional income inequality in Brazil. The economy is divided into 31 sectors, in 5 macro regions; households are allocated into 10 income brackets. The study identifies the contribution of different sectors to inequality. The model is used to simulate the capacity of social policies to reduce personal and regional inequality in the country. The analysis is conducted using the pro-poor “Bolsa Família” program which is a social program that provides direct income transfers to poor (with per capita income between BRL 60,01 and BRL 120,00) and extreme poor households (with per capita income below BRL 60,00). The results show that in the short run, the “Bolsa Família” program has proven to produce positive results, both at the personal income level and at the regional concentration level, and has surely paid large dividends in electoral terms. Solving inequality problems, however, might need other mid and long run policies which could improve competitiveness of lagging regions