摘要:

AbstractThe use of the one-dimensional two-phase flow six-equation model requires knowledge of mass, momentum, and energy transfers between the phases. These transfers can be expressed from the flow parameters and their derivatives.The first part of this paper is devoted to the formulation of the entropy production at the interface as a function of the velocity, Gibbs potential and temperature of each phase. It is assumed that each transfer can be expressed in the formwhere R is the reversible part andδR the irreversible part of the transfer R. The linear theory of irreversible thermodynamics allows the formulation ofδR. The expression of R may include differential terms.In the second part of this paper, we show how to write interfacial transfer terms to reduce the six-equation model into a lower order model.The last part of this paper presents an original method for computing critical flow, taking into account the flow blockage phenomenon, which is observed when variations of downstream conditions do not produce any significant effect on the upstream flow, even though the fluid velocity is less than the sound velocity.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19590

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractStationary two-phase flow experiments at pressures up to 13 MPa and temperatures up to 600 K have been performed in a converging nozzle. The experiment is specially designed for the assessment of two-phase computer codes used in reactor safety analysis, in particular for loss-of-coolant accident blowdown calculations. An assessment by the codes DUESE, DRIX-2D, and RELAP4/MOD6 is reported.The shape of the nozzle, the instrumentation, and the experimental program are such that models and empirical parameters of a wide range of codes can be tested and determined, respectively. Results show the influence and magnitude of models and parameter variations, the effect of the dimensionality and the difference scheme of the code, and the relevance of the models as a function of the initial conditions.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19591

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractAn advanced methodology for performing systematic uncertainty analysis of time-dependent nonlinear systems is presented. This methodology includes a capability for reducing uncertainties in system parameters and responses by using Bayesian inference techniques to consistently combine prior knowledge with additional experimental information. The determination of best estimates for the system parameters, for the responses, and for their respective covariances is treated as a time-dependent constrained minimization problem. Three alternative formalisms for solving this problem are developed. The two“off-line”formalisms, with and without“foresight”characteristics, require the generation of a complete sensitivity data base prior to performing the uncertainty analysis. The“online”formalism, in which uncertainty analysis is performed interactively with the system analysis code, is best suited for treatment of large-scale highly nonlinear time-dependent problems.This methodology is applied to the uncertainty analysis of a transient upflow of a high pressure water heat transfer experiment. For comparison, an uncertainty analysis using sensitivities computed by standard response surface techniques is also performed. The results of the analysis indicate the following.Major reduction of the discrepancies in the calculation/experiment ratios is achieved by using the new methodology.Incorporation of in-bundle measurements in the uncertainty analysis significantly reduces system uncertainties.Accuracy of sensitivities generated by response-surface techniques should be carefully assessed prior to using them as a basis for uncertainty analyses of transient reactor safety problems.Conclusions about the future applicability of the uncertainty analysis methodology presented in this work are also discussed.

ISSN:0029-5639    

DOI:10.13182/NSE82-3

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe ion beam-pellet interaction is investigated by using a time-dependent particle tracking algorithm for the slowing down of the bombarding ions. Model equations for energy and momentum deposition are developed and solved with the aid of a numerical code that describes the beam-pellet interaction as well as the subsequent heating and compression of the target. Results of calculations carried out for solid deuterium-tritium pellets using beams of deuterons, alpha particles, and lithium ions are presented and discussed.Two main conclusions are found to hold, namely:Consideration of the finite thermalization time of the ion in the transport process results in slower heating and compression of the pellet as well as in smaller thermonuclear yield ratios.Taking into account the momentum deposition of the bombarding ions in the pellet also provides different thermonuclear yields for low initial ion energies; for high initial ion energies, the effect of the momentum deposition is negligible.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19593

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe influence of different representations of the unresolved resonances of238U on the computed self-shielding factors is examined. It is shown that the evaluated infinitely diluted average capture cross section does not provide sufficient information to determine a unique set of unresolved resonance parameters; different sets of unresolved resonance parameters equally consistent with the evaluated average capture cross section yield significantly different computed self-shielding factors. In the conclusion it is recommended that the resolved resonance description of the evaluated238U cross sections be extended to higher energies and that thick sample transmission data and self-indication data be used to improve the evaluation of the unresolved resonance region.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19594

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe neutron collision escape probability from a medium depends on the shape of spatial distribution of the source. The case of a uniform or flat source distribution has been investigated extensively from time to time. In the present work, the case of bare homogeneous reactor assemblies having a centrally peaked neutron source distribution has been analyzed for predicting collision escape probability as a function of assembly size measured in terms of the optical mean chord length. An approximation, known as the modified Wigner rational approximation, is derived and is given bywhere pE(W) stands for the collision escape probability from a bare homogeneous reactor assembly;ϵ1andϵ2are geometry-dependent parameters. These parameters have been determined for infinite slab, infinite cylinder, sphere, cube, and finite cylinders of height-to-diameter ratio varying from 0.1 to 20. It is shown that it is possible to predict the collision escape probability within approximately±2% of the exact value for, ranging from 0 to 20 mean-free-paths (mfp). Generally, for a giventhe collision escape probability value for the centrally peaked source is lower than that for the uniform source. But it is found that for very thin infinite slab assemblies of optical mean chord length1.5 mfp, the collision escape probability for centrally peaked source distribution is higher than that for uniform source distribution. The reason for this anomaly is discussed.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19595

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractMethods for treating nuclear plus interference elastic scattering of light charged particles in continuous energy or multigroup transport calculations are given. These methods conserve the rate of projectile energy loss and maintain energy balance by ensuring that, on the average, the rate of projectile energy loss equals the rate of target energy gain. It is shown that this approach is equivalent to conserving the P0and P1moments of the angular distribution of scattered projectiles and targets in the center-of-mass system. We include an approximate method that corrects for the temperature of the medium.To illustrate the application of these methods to a multigroup problem, we give multigroup data for all 25 projectile/target combinations of protons, deuterons, tritons,3He ions, and alpha particles based on an example 10-group energy structure. The results are in a compact form from which the group-to-group transfer matrices can be easily calculated.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19596

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractAfter a short presentation of the Boltzmann-Fokker-Planck (BFP) equation, which was derived in a previous work, two numerical approaches to solve this equation are investigated-the multigroup method and a diamond scheme applied in a consistent way to space and energy variables. Because of the parabolic nature of the Fokker-Planck operator, it is shown that the standard neutron transport codes cannot solve such an equation. With the one-dimensional time-dependent BFP-1 code, many numerical results have been produced. All deal with the transport of charged particles in dense plasmas because such a problem is very severe from a numerical point of view. Other applications can be imagined since the BFP formalism is quite general.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19597

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractPresented in this paper is the asymptotic analysis of the time-independent neutron transport equation in the second-order variational formulation. The small parameter introduced into the equation is an estimate of the ratio of absorption and leakage to scattering in the system considered. When the ratio tends to zero, the weak solution to the transport problem tends to the weak solution of the diffusion problem, including properly defined boundary conditions. A formula for the diffusion coefficient different from that based on averaging the transport mean-free-path is derived.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19598

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThree topics are considered. First, the Langevin approach to neutron noise is used as a basis and guide to develop solutions and solution techniques for the Chapman-Kolmogorov forward equation approach to neutron noise. The approach followed throughout this first part is that of solution by means of Green's functions. A particular form for the binary operator Green’s function was picked on the basis of the Langevin method. Second, the basic solution technique using the particular Green's function form mentioned above is proven to be a correct and a general result. It is proven that the binary operator is always separable and that the Green’s function could be written as the product of two single operator Green’s functions. This is a new result. Third and finally, the forward equation approach of Chapman-Kolmogorov is generalized to include time allowing differential equations for second and higher order correlation functions to be developed directly. The principal result of the last section, the differential equation for correlation function of the neutron density, is new. Its derivation is really outside of or broader than the scope indicated by the title of the paper.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19599

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor