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《Journal of Nuclear Science and Technology》2013,50(11):1395-1405
In the present paper, homogenization procedures for fast critical assembly analyses are investigated. Errors caused by homogenizations are evaluated by the exact perturbation theory. In order to obtain reference solutions, three-dimensional plate-wise transport calculations are performed. It is found that the angular neutron flux along plate boundaries has a significant peak in the fission source energy range. To treat this angular dependence accurately, the double-Gaussian Chebyshev angular quadrature set with S24 is applied. It is shown that the difference between the heterogeneous leakage theory and the homogeneous theory is negligible, and that transport cross sections homogenized with neutron flux significantly underestimate neutron leakage. The error in criticality caused by a homogenization is estimated at about 0.1%Δ/k/kk' in a small fast critical assembly. In addition, the neutron leakage is overestimated by both leakage theories when sodium plates in fuel lattices are voided. 相似文献
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钠空泡反应性效应是钠冷快堆核设计和安全分析的重要内容。本文基于多群节块扩散法,采用微扰理论推导出钠空泡反应性的计算方法,对1 000 MWe钠冷快堆MOX燃料堆芯的总钠空泡反应性、空间分布、物理分项进行了计算。结果表明,钠空泡反应性主要来源于中子泄漏的增加和能谱的硬化,两者一正一负,且空间分布规律相反,导致钠空泡反应性具有强烈的空间依赖性;对于所计算的MOX燃料堆芯钠空泡反应性高达3 $左右。计算和分析结果阐明了钠空泡反应性的产生机理和分布规律,可为低钠空泡的设计提供参考。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(7):419-427
The analysis of sodium void reactivity measurements has been performed. The measurements were made in the FCA V-1, which is a fast critical assembly intended for physics mock-up of the experimental fast reactor “JOYO”. The voided zones were the central region of the core and channel drawers extending throughout the core height. The calculations were performed using the JAERI set with 70- group structure. As a result it was found that the conventional two-dimensional calculations underestimate measurements by about 10–40% in the core region. However, if the axial streaming effects are considered, the ratio between calculations and experimental results become about 0.9 for almost all cases of channel void. The streaming effects are calculated with use of Benoist's formula of anisotropic diffusion coefficients. The heterogeneity effects on the spatial neutron flux distribution are taken into consideration by the collision probability method. The effect is large in the central part of the core (about 20% negative reactivity). The elastic removal cross sections are precisely obtained for the predominant resonances of light elements and compared with the conventional set. The influence on sodium void reactivity is not so large in this assembly. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(4):538-546
The paper is devoted to studies on the influence of the sodium void reactivity effect (SVRE) on the safety and technical and economical characteristics of the BN-1200-type reactor. Different core options are considered for application to this reactor. These core options differ in design, dimensions, and, hence, SVRE value. It is shown by the analysis that the most flattened core with sodium plenum at the top assures reactor self-protection under beyond-design-basis accident conditions. Sodium plenum abandonment and core height increase causing an SVRE value increase deteriorate reactor self-protection, but at the same time, improve some technical and economical characteristics of the reactor. Self-protection means the possibility to avoid rapid core meltdown under conditions of the above-listed beyond-design accidents. The possibility of controlling beyond-design accidents (for instance, by restoring the power supply of the main pumps in a rather short time) is taken into account. Issues of choosing the optimal core design under these conditions are discussed. 相似文献
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组件替换反应性价值定义为测量位置组件替换成相应组件时引入的反应性变化。中国实验快堆物理启动试验中组件替换反应性价值测量试验方案中,试验测量了8个典型位置,其中6个位置为燃料组件替换成不锈钢组件,另外两个为不锈钢组件替换成燃料组件。测量结果显示,燃料组件替换反应性价值由内至外依次减少,内圈燃料组件替换反应性价值约-980 pcm,外圈燃料组件替换反应性价值约-470 pcm,补偿棒棒组测量和单根补偿棒测量的结果差别微小。使用CITATION程序对试验方案进行了理论计算,结果表明,计算结果与实验值符合良好,检验了CITATION程序的工程设计实用性。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(9):755-764
We have investigated cell calculation models to be used in the analysis of neutronic characteristics of a heterogeneous fast critical assembly. As cell models we have considered a single drawer model with a critical buckling, a single drawer model with group dependent bucklings and a multidrawer model which consists of some fuel and blanket drawers. We have compared the cell averaged cross sections obtained from these cell models with the results of a reference transport calculation and estimated the effects of the cell models on k eff, reaction rate ratios, reaction rate distributions and sodium void worths in the heterogeneous fast critical assembly ZPPR-13A. The multidrawer model and the single drawer model with group dependent buckling give reasonable cell averaged cross sections and have large effects on k eff and 238U fission rate distribution. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(3):203-213
A simple mechanistic model is presented to evaluate the subcooled void reactivity effect under a Reactivity Initiated Accident (RIA) at cold critical condition of BWR. This model consists of a drift flux model for vapor velocity and a vapor mass conservation model with a term of vapor source on a heated wall, and it was incorporated into a homogeneous and equilibrium thermal-hydraulic code EUREKA-JINS. A sample analysis by this model showed that the subcooled void reactivity effect leads to reduction of the maximum fuel enthalpy by about 20 cal/g UO2 in the case of RIA at cold critical condition. Though the reduced value is dependent on the reactor core condition, this result indicates the significance of subcooled void reactivity effect in the accident, while the effect can be neglected in the hot stand-by case where, at most, only 4 cal/g UO2 is reduced for the maximum fuel enthalpy. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(3):163-169
Fast cross section sets are prepared for the analysis of fast critical assemblies to test the agreement of calculated and measured integral parameters. Modifications are brought to fissile element cross sections making use of recently measured cross section data, and these updated cross section data are utilized to compare the calculated integral parameters of these assemblies, and to determine the effect brought to the calculated results by the differences between the data. The results are presented for the eigenvalue, central fission ratios and centra] sample reactivity in the 239Pu fueled assemblies ZPR- 3-48, 49, 50 and ZEBRA-6A, whose spectra simulate those of large fast reactors. In addition, for ZPR- 6-7 and ZPPR-2, which are large fast critical assemblies intended for testing the calcul ational procedures of practical demonstration reactor design, the results of analysis obtained with the updated cross section set are compared with experiments. It is found that the cross section for 241Pu recommended here satisfactorily agrees with the experimental reactivity worth. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(8):467-481
An attempt is made of applying the shielding factor method with a coarse-group structure to cell calculations for plate-type fast reactor assemblies. The 24-group collision probability calculations based on the shielding factor method derived from the basic equation is shown to give results of practical validity for heterogeneity and bunching reactivities, as proved by comparisons with 1950-group collision probability calculations and experiments in the FCA assemblies V-2 and VI-2. The mechanism of the heterogeneity effect in the two assemblies is examined in detail. Most part of the heterogeneity reactivity is found to be due to the flux heterogeneity effect, whereas the reactivity associated with the change of plate pattern is mostly caused by the change of the flux heterogeneity effect in the case of the assembly V-2, and by the change of the heterogeneous shielding effect in the case of the assembly VI-2. In comparison with experiment the calculated results on the streaming of neutrons in the entire assembly would tend to be closer to isotropic condition, which differs from prediction based on the anisotropic diffusion coefficients obtained in cell calculations. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(6):497-504
Abstract The introduction of zirconium-hydride (ZrH1.7) layer between the seed and blanket is very effective in reducing the coolant-void reactivity of steam-cooled FBR. The void reactivity reduction is attributed to the rapid increase of neutron absorption and to the decrease of neutron production in the blanket due to the moderation through the layer. The reason is that the neutron multiplication factor decreases, reflecting the neutron balance of the whole core. It is effective even the layer thickness is 1 or 2 cm. Compared with the conventional uniform introduction of this moderator into the seed, the fixed layer concept is more effective in reducing void reactivity and hardly deteriorate the breeding ratio. The negative void reactivity is proved for the non-flat large-sized radial heterogeneous core where the layers are placed between the seeds and blankets. The neutron absorption rate increases, the fast fission rate decreases in the central, inner and radial blankets. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(3):139-145
The effect of group collapsing applied to the perturbation theory for sample worth analysis in fast reactor systems is theoretically and numerically examined assuming the validity of the thin sample approximation. As a result, the calculated worths of scattering predominant materials placed at the center of core are found to be strongly influenced by the group collapsing. The effect on the sample worth when the sample is placed in positions off the core center decreases with increasing distance from the center. It is noted that the reactivity perturbation due to inelastic scattering is also affected significantly by group collapsing especially near the core-blanket interface. Based on the above observations, it is concluded that the perturbation theory with about 70 energy groups appropriately arranged is necessary to reproduce the experimental values of Na, O and Fe sample reactivity worths with accuracy efficient for ordinary purposes. 相似文献