The nuclear industry needs of prediction of behavior and life-time, for a wide range of normal, off-normal and accident conditions for safe and economic operation. Among different thermo-mechanical properties that can...The nuclear industry needs of prediction of behavior and life-time, for a wide range of normal, off-normal and accident conditions for safe and economic operation. Among different thermo-mechanical properties that can be predictable, the knowledge on the radial temperature distribution of the UO2 （uranium dioxide） nuclear fuel during the operation of nuclear reactors is essential for safety as different mechanical and thermal-hydraulic thresholds should be respected. One of the attributes of the Brazilian CNEN （Nuclear Energy Commission） is to assess the performance of the fuel rods used in these reactors in high-bumup regimes. The effective removal of the heat generated in the fuel rods constitutes one of the primary points to consider in the design of nuclear reactors. One of the important physical parameters in the study of heat conduction from the nuclear fuel to the coolant in a PWR （pressurized water reactor） is its thermal conductivity. It is therefore desirable that the empirical models, updated for the calculation of thermal conductivity in the fuel region be developed from new sets of experimental data from the irradiated fuel rods in controlled environments This paper presents the obtained results of implementing of a new model for thermal conductivity of the UO2 in the FRAPCON code.展开更多
This study was motivated by the world interest in the development of advanced processes of waste decomposition, due to the need of safer decomposition processes, particularly for the POPs （Persistent Organic Polluta...This study was motivated by the world interest in the development of advanced processes of waste decomposition, due to the need of safer decomposition processes, particularly for the POPs （Persistent Organic Pollutants） and the organochlorines. A tendency observed at several countries is the adoption of progressively more demanding legislation for the atmospheric emissions from the waste decomposition processes. The suitable final disposal of hazardous organic wastes such as PCBs （Polychlorinated Biphenyls）, pesticides, herbicides and hospital residues constitutes a serious problem. In some point of their lifecycles, these wastes should be destroyed, in reason of the risk that they represent for the human being, animals and plants. The process involves a chemical reactor containing molten salts, such as sodium carbonate or some alkaline carbonates mixtures to decompose the organic waste. The decomposition is performed by submerged oxidation. Waste is injected below the surface of a turbulent salt bath along with the oxidizing agent. Decomposition of halogenated compounds, among which some pesticides, is particularly effective in molten salts. The process presents properties such as intrinsically safe control of organochlorine emissions. This work describes the process developed at IPEN/CNEN-SP （Nuclear and Energetic Research Institute/Brazilian Nuclear Energy Commission） for complete thermal decomposition of hazardous wastes through oxidation submerged in molten salts.展开更多
The calculation of the Doppler broadening function and of the interference term are important in the generation of nuclear data. In a recent paper, Goncalves and Martinez proposed an analytical approximation for the c...The calculation of the Doppler broadening function and of the interference term are important in the generation of nuclear data. In a recent paper, Goncalves and Martinez proposed an analytical approximation for the calculation of both functions based in sine and cosine Fourier transforms. This paper presents new approximations for these functions, and , using expansions in Fourier series, generating expressions that are simple, fast and precise. Numerical tests applied to the calculation of scattering average cross section provided satisfactory accu- racy.展开更多
In the past, stainless steel was utilized as cladding in many PWRs （pressurized water reactors）, and its performance under irradiation was excellent. However, stainless steel was replaced by zirconium-based alloy as...In the past, stainless steel was utilized as cladding in many PWRs （pressurized water reactors）, and its performance under irradiation was excellent. However, stainless steel was replaced by zirconium-based alloy as cladding material mainly due to its lower neutron absorption cross section. Now, stainless steel cladding appears as a possible solution for safety problems related to hydrogen production and explosion as occurred in Fukushima Daiichi accident. The aim of this paper is to discuss the steady-state irradiation performance using stainless steel as cladding. The results show that stainless steel rods display higher fuel temperatures and wider pellet-cladding gaps than Zircaloy rods and no gap closure. The thermal performance of the two rods is very similar and the neutron absorption penalty due to stainless steel use could be compensating by combining small increase in U-235 enrichment and pitch size changes.展开更多
This paper presents the experimental pressure loss of water flow through perforated plates with geometry similar to the ones of the bottom end piece of a Pressurized Water Reactors （PWR） fuel element. Geometric feat...This paper presents the experimental pressure loss of water flow through perforated plates with geometry similar to the ones of the bottom end piece of a Pressurized Water Reactors （PWR） fuel element. Geometric features like the number, pattern and diameter of holes were evaluated as well as different inlet chamfers. The recovering pressure profile downstream of the plates was also measured. The experimental results were compared with numerical modeling performed with the commercial Computational Fluid Dynamics （CFD） code CFX 11.0. The analysis of the results shows that the standard k-e turbulence model presents the best compromise between computing time and accuracy for the calculation of the total pressure loss through the perforated plates tested.展开更多
文摘The nuclear industry needs of prediction of behavior and life-time, for a wide range of normal, off-normal and accident conditions for safe and economic operation. Among different thermo-mechanical properties that can be predictable, the knowledge on the radial temperature distribution of the UO2 （uranium dioxide） nuclear fuel during the operation of nuclear reactors is essential for safety as different mechanical and thermal-hydraulic thresholds should be respected. One of the attributes of the Brazilian CNEN （Nuclear Energy Commission） is to assess the performance of the fuel rods used in these reactors in high-bumup regimes. The effective removal of the heat generated in the fuel rods constitutes one of the primary points to consider in the design of nuclear reactors. One of the important physical parameters in the study of heat conduction from the nuclear fuel to the coolant in a PWR （pressurized water reactor） is its thermal conductivity. It is therefore desirable that the empirical models, updated for the calculation of thermal conductivity in the fuel region be developed from new sets of experimental data from the irradiated fuel rods in controlled environments This paper presents the obtained results of implementing of a new model for thermal conductivity of the UO2 in the FRAPCON code.
文摘This study was motivated by the world interest in the development of advanced processes of waste decomposition, due to the need of safer decomposition processes, particularly for the POPs （Persistent Organic Pollutants） and the organochlorines. A tendency observed at several countries is the adoption of progressively more demanding legislation for the atmospheric emissions from the waste decomposition processes. The suitable final disposal of hazardous organic wastes such as PCBs （Polychlorinated Biphenyls）, pesticides, herbicides and hospital residues constitutes a serious problem. In some point of their lifecycles, these wastes should be destroyed, in reason of the risk that they represent for the human being, animals and plants. The process involves a chemical reactor containing molten salts, such as sodium carbonate or some alkaline carbonates mixtures to decompose the organic waste. The decomposition is performed by submerged oxidation. Waste is injected below the surface of a turbulent salt bath along with the oxidizing agent. Decomposition of halogenated compounds, among which some pesticides, is particularly effective in molten salts. The process presents properties such as intrinsically safe control of organochlorine emissions. This work describes the process developed at IPEN/CNEN-SP （Nuclear and Energetic Research Institute/Brazilian Nuclear Energy Commission） for complete thermal decomposition of hazardous wastes through oxidation submerged in molten salts.
文摘The calculation of the Doppler broadening function and of the interference term are important in the generation of nuclear data. In a recent paper, Goncalves and Martinez proposed an analytical approximation for the calculation of both functions based in sine and cosine Fourier transforms. This paper presents new approximations for these functions, and , using expansions in Fourier series, generating expressions that are simple, fast and precise. Numerical tests applied to the calculation of scattering average cross section provided satisfactory accu- racy.
文摘In the past, stainless steel was utilized as cladding in many PWRs （pressurized water reactors）, and its performance under irradiation was excellent. However, stainless steel was replaced by zirconium-based alloy as cladding material mainly due to its lower neutron absorption cross section. Now, stainless steel cladding appears as a possible solution for safety problems related to hydrogen production and explosion as occurred in Fukushima Daiichi accident. The aim of this paper is to discuss the steady-state irradiation performance using stainless steel as cladding. The results show that stainless steel rods display higher fuel temperatures and wider pellet-cladding gaps than Zircaloy rods and no gap closure. The thermal performance of the two rods is very similar and the neutron absorption penalty due to stainless steel use could be compensating by combining small increase in U-235 enrichment and pitch size changes.
文摘This paper presents the experimental pressure loss of water flow through perforated plates with geometry similar to the ones of the bottom end piece of a Pressurized Water Reactors （PWR） fuel element. Geometric features like the number, pattern and diameter of holes were evaluated as well as different inlet chamfers. The recovering pressure profile downstream of the plates was also measured. The experimental results were compared with numerical modeling performed with the commercial Computational Fluid Dynamics （CFD） code CFX 11.0. The analysis of the results shows that the standard k-e turbulence model presents the best compromise between computing time and accuracy for the calculation of the total pressure loss through the perforated plates tested.
