摘要:

AbstractThe thermohydraulic behavior of the liquid-metal target of the spallation neutron source at Paul Scherrer Institute has been investigated. The configuration is a natural-circulation loop in a concentric double-tube-type container. The model is based on a one-dimensional loop analysis, and the thermohydraulic behavior of the target liquid, as well as the total performance of the target, are studied analytically and numerically. These results are verified by two experiments using liquid metal. The results show that the natural-circulation loop concept is valid for the design phase of the target construction, and the current specified design criteria will be fulfilled with the proposed parameter values.

ISSN:0029-5639    

DOI:10.13182/NSE93-A15329

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractResults are presented from laboratory experiments that examined the ability of dilute aqueous solutions of polyfethylene oxide) (PEO), a soluble drag-reducing polymer, to suppress spontaneous vapor explosions of molten tin. Polyfethylene oxide) with an average molecular weight of 4x106was used to prepare aqueous solutions with polymer concentrations from 10 weight parts per million (wppm) up to∼525 wppm, with resulting solution viscosity ratios of 1.01≥ηr≥2.00 at 25°C, whereηr=ηsolution/ηwater. Twelve-gram masses of molten tin at temperatures of 600, 700, 800, 900, and 1000°C were poured from a height of 60 cm into a cylindrical Plexiglas vessel (12.5-cm i.d.) containing 1ℓof coolant solution at 25°C. The experiment was repeated ten times with each solution to check consistency and repeatability. The maximum pressures recorded for each experiment are reported and are used to compare the relative violence of spontaneous vapor explosions in each solution.Experiments with pure water were carried out to provide a reference of comparison for the polymer solutions. The peak pressures measured in the most dilute PEO solutions (1.02≥ηr≥1.13) spanned a much wider range than those for water, and pressures many times larger than any recorded in pure water were recorded–up to 240 kPa. When the solution viscosity ratio was 1.25 or larger, however, spontaneous explosions were markedly suppressed; aboveηr= 2.00, they were entirely eliminated.

ISSN:0029-5639    

DOI:10.13182/NSE93-A15330

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractWhile the reactor physicists were fine-tuning the Monte Carlo paradigm for particle transport in regular geometries, the computer scientists were developing rendering algorithms to display extremely realistic renditions of irregular objects ranging from the ubiquitous teakettle to dynamic Jell-O. For many years, the modeling commonality of these apparently diverse disciplines was either largely ignored or unnoticed by many members in both technical communities. Apparently, with the exception of a few visionaries such as the Mathematical Application Group, Inc. (MAGI), each community was not sufficiently aware of what the other was doing. This common basis included the treatment of neutral particle transport through complicated geometries in three-dimensional space. In one instance, it is called the Boltzmann transport equation, while in the other, it is commonly referred to as the rendering equation.Even though the modeling methods share a common basis, the initial strategies each discipline developed for variance reduction were remarkably different. Initially, the reactor physicist used Russian roulette, importance sampling, particle splitting, and rejection techniques. In the early stages of development, the computer scientist relied primarily on rejection techniques, including a very elegant hierarchical construction and sampling method. This sampling method allowed the computer scientist to viably track particles through irregular geometries in three-dimensional space, while the initial methods developed by the reactor physicists would only allow for efficient searches through analytical surfaces or objects.As time goes by, it appears there has been some merging of the variance reduction strategies between the two disciplines. This is an early (possibly first) incorporation of geometric hierarchical construction and sampling into the reactor physicists’Monte Carlo transport model that permits efficient tracking through nonuniform rational B-spline surfaces in three-dimensional space. After some discussion, the results from this model are compared with experiments and the model employing implicit (analytical) geometric representation.

ISSN:0029-5639    

DOI:10.13182/NSE93-A15331

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractStatistical uncertainties for neutron transport calculations using the Monte Carlo method are typically evaluated during the calculation by using the first and second moments of the tallies. There are concerns that these statistical uncertainties may be substantially nonconservative in some classes of problems, especially reactor eigenvalue problems with the additional complication of a generation-to-generation source. Optimization of the Monte Carlo random walks may introduce further nonconservatism. Calculations are reported that quantify the reliability of the uncertainty by comparing an ensemble of Monte Carlo predictions of means and uncertainties to the true means for a liquid-metal fast reactor. It was found that the number of samples falling beyond a 90% confidence limit interval was typically not far from the expected 10%. However, 2 samples out of∼300 were beyond four standard deviations, while for a normal distribution there is<1 chance in 10 000 that a sample will be beyond four standard deviations.

ISSN:0029-5639    

DOI:10.13182/NSE93-A15332

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractA new approach for treating the sensitivity and uncertainty in the secondary energy distribution (SED) and the secondary angular distribution (SAD) has been developed, and the existing two-dimensional sensitivity/uncertainty analysis code, FORSS, was expanded to incorporate the new approach. The calculational algorithm was applied to the9Be(n,2n) cross section to study the effect of the current uncertainties in the SED and SAD of neutrons emitted from this reaction on the prediction accuracy of the tritium production rate from6Li (T6) and7Li (T7) in an engineering-oriented fusion integral experiment of the U.S. Department of Energy/Japan Atomic Energy Research Institute Collaborative Program on Fusion Neutronics in which beryllium was used as a neutron multiplier. In addition, the analysis was extended to include the uncertainties in the integrated smooth cross sections of beryllium and other materials that constituted the test assembly used in the experiment. This comprehensive two-dimensional cross-section sensitivity/uncertainty analysis aimed at identifying the sources of discrepancies between calculated and measured values for T6and T7. Without considering the uncertainties in the SED and SAD of the9Be(n,2n) cross section, the uncertainties in T6are∼2 to 3% in the Li2Obreeding zone, whereas they are∼10% when the uncertainties in the SED and SAD are included. The contribution from the uncertainties in the SAD was small (∼1%) compared with the contribution from the uncertainties in the SED. As for T7, the uncertainties in the Li2Ozone with and without considering the SED and SAD results are 4 to 7 and 2 to 5.5%, respectively. The estimated uncertainties in T6and T7could partly cover the observed discrepancies between calculations and measurements, although other sources have been identified. Although the approach followed to complete the uncertainty analysis is not standard because of the absence of an existing file that contains the uncertainty information in the SED and SAD of the9Be(n,2n) reaction, the results obtained by introducing approximations to these data clearly demonstrate the importance of accounting for the uncertainties in the SED and SAD when a complete cross-section sensitivity/uncertainty analysis is to be performed.

ISSN:0029-5639    

DOI:10.13182/NSE93-A15333

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractExposure buildup factors, energy spectra, and angular flux distributions for plane-normal incident and point isotropic source gamma rays of 0.1, 0.5, 1, 3, 6, and 10 MeV penetrating two-layer water-lead and lead-water shields are calculated with the point Monte Carlo code EGS4 The effects of bremsstrahlung and fluorescent radiation are included.The value of the buildup factor in the second layer lies between those for infinite media of both materials in two source geometries in the 0.5- to 3-MeV energy range. However, this behavior varies remarkably and is enhanced with a bremsstrahlung contribution, when the source energy is higher than that corresponding to the minimum in the attenuation coefficient of lead. This varies equally with the fluorescent contribution when the source energy is close to the K edge of lead.

ISSN:0029-5639    

DOI:10.13182/NSE92-52

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor