摘要:

AbstractBy reviewing several publications on frictional pressure drop and interface drag in the two-phase flow of liquid metals, it is found that acceleration loss by droplets has a considerable effect on the hydraulic models, due to the high-density and the high-slip ratios. A one-dimensional, steady-state flow model is developed for vertical upward annular-dispersed flow under adiabatic conditions to account for acceleration loss by droplets. The results show that, if acceleration of droplets is considered, the two-phase multiplier and interface drag coefficient of the liquid film fall around correlations developed for ordinary fluids.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19387

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractA new form of the one-equation turbulence model has been developed and verified by application to fully developed turbulent flow in smooth, bare rod bundles. The present model allows for the effect of anisotropic eddy viscosities on turbulent flow quantities. The finite element method has been used to predict local values of velocity and turbulent kinetic energy right up to the wall. A variational principle is applied to develop the finite element relationships. The resulting set of nonlinear algebraic equations for the nodal parameters is linearized by the successive-substitution scheme and solved by the frontal solution technique. The numerical results are shown to be in good agreement with available experimental data.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19388

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractA formal approach for the optimization of the final design of reload cores has been devised and verified. The method is based on applying the calculus of variations (Pontryagin’s principle) to the normal flux and depletion system equations. The resulting set of coupled system, Euler-Lagrange (E-L), and optimality equations are solved iteratively. This is done by assuming a loading pattern for the old fuel, first solving the system equations, and then the E-L equations. The pattern is then modified by using the optimality (or Pontryagin) condition, and the process is repeated until no further improvements can be made.A computer program, OPMUV, implementing these procedures has been written and verified. The code can handle two-dimensional, quarter-core symmetric configurations with up to 241 assemblies and 4 nodes per assembly with modified one-group theory. It also has the capability of optimizing over the entire depletion cycle as well as just at the beginning of cycle (BOC).The results show that the procedure does work. In all cases tried, the method led to a reduction in nodal peaks of 1 to 3% over the final designer-obtained loading pattern within a couple of iterations. These savings carry over to comparable reductions in pin peaks when the optimized patterns are used in four-group, fine-mesh calculations. Since the changes on each iteration are limited to ensure convergence, the method is thus well suited for the final fine tuning of the normally obtained patterns to gain an extra few percent in power flattening.

ISSN:0029-5639    

DOI:10.13182/NSE82-4

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractUsing the Oak Ridge Electron Linear Accelerator pulsed neutron source and a 1-mm-thick lithium glass detector, neutron transmission spectra through232Th have been measured at 22- and 40-m flight paths. At 22 m, transmission spectra through samples of five thicknesses were measured from 7 meV to 15 eV. At 40 m, spectra through samples of eight thicknesses were measured from 15 eV to 4 keV. The resulting total cross section from 0.1 to 20.0 eV is smaller than that given by the ENDF/B-V evaluation. Least-squares shape analysis of the transmissions up to 2.0 keV gives larger neutron widths above 0.5 keV than those previously reported. An average radiation width of 25.2 meV is obtained for 19 low-energy s-wave resonances.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19390

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractWe prove a mathematically rigorous theorem that asserts, under certain carefully stated hypotheses, the validity of the Goertzel and Otsuka conclusions that, in a thermal nuclear reactor that has a minimum critical mass, the fuel must be distributed so that the product of the thermal neutron flux and the adjoint thermal neutron flux is a constant in the core and does not exceed that constant in the reflector. We also furnish some examples that illustrate the necessity of imposing some mathematical hypotheses to obtain the desired conclusions.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19391

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractWe prove two mathematically rigorous theorems that assert, under certain carefully stated hypotheses, the validity of the Goertzel and Otsuka conclusions that, in a thermal nuclear reactor that has a minimum critical mass, the fuel must be distributed so that the product of the thermal neutron flux and the adjoint thermal neutron flux is a constant in the core and does not exceed that constant in the reflector. These theorems differ from that in the preceding paper in the sense that some of the hypotheses of the earlier theorem have been strengthened and some weakened. The hypotheses can be weakened still further if we restrict attention to a fixed core and are not interested in results concerning the reflector. We also study the second variation of the critical mass functional. Finally, we show that, under some explicitly stated conditions, the multigroup diffusion theory for a thermal reactor can be treated as a special case of our general theory.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19392

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractExperiments were performed with a 122-cm-diam sphere to determine criticality of aqueous solutions of plutonium in a system having low-neutron leakage. The plutonium in the chemical form of Pu(NO3)4had a240Pu content of 2.52 wt%. The critical-sphere concentration obtained in this experiment was analyzed along with data from eight additional critical experiments to evaluate the minimum critical concentration for plutonium. The limiting critical concentration was determined to be 7.62 g Pu/ℓ, for Pu(NO3)4without excess acid and 7.59 g Pu/ℓfor a239Pu-water mixture. From these data, the Maxwellian-averaged thermal value of the number of fission neutrons emitted per neutron absorbed by239Pu, eta, was determined to be 2.056±0.037. The value at 2200 m/s is 2.100±0.041.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19393

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe discrete angle technique is a customary method for selecting scattering angles from such scattering laws that are given through their Legendre coefficients up to some finite order. In this technique, discrete scattering angles are selected with certain probabilities. In low-order Pntruncations, however, this method can lead to unwanted ray effects during the first few free flights of the random walk. We propose a method in which a linear combination of some arbitrary density function, having the same first 2n moments as the truncated expansion, and of a discrete density function will yield samples that conserve the first (2n + 2) moments of the truncated series. Bounds are derived on the possible ranges of the combination coefficient. The method is applied to construct a semicontinuous density function (continuous + Dirac delta functions) having the first four moments prescribed, i.e., being given by its first three Legendre coefficients.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19394

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractSolving problems of reactor physics is well developed for typical pressurized water and boiling water reactor geometries but less developed for high-temperature gas-cooled reactor, liquid-metal fast breeder reactor, and WWER (BB϶P) geometries. Several problems of reactor physics can be formulated in a geometry-independent fashion with the help of symmetry considerations, which allows the solution to be decomposed into eigenfunctions of the symmetry operations.An analytic coarse-mesh solution is derived without resorting to the cross leakage concept. The method is applicable to arbitrary geometries. A second-stage homogenization based on the Bloch theorem is presented. It is shown that the solution of the transport equation can always be made up from a cell problem set (microfunctions) and from an overall solution to the diffusion equation (macrofunction).

ISSN:0029-5639    

DOI:10.13182/NSE82-338

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractIn the considerations of recriticality of molten fuel assemblies, the presence of bubbles in the fuel plays an important role. In such a situation, there are two opposing contributions to reactivity from (a) the phenomenon of neutron streaming in bubbles (negative contribution) and (b) the phenomenon of changing neutron self-multiplication in the fuel (positive contribution). It is not possible to accurately calculate the individual reactivity contributions of the two phenomena using multidimensional transport theory or Monte Carlo codes. A simple diffusion theory expression given by Nicholson and Goldsmith for estimating reactivity contribution due to neutron streaming alone has been used extensively. As a part of the present contribution, first an attempt has been made to improve the applicability of the Nicholson-Goldsmith work by expressing extrapolation length in terms of the root-mean-square free path in the assembly. It is found that the application of the Trombay criticality formula, particularly its“modified Wigner rational variant,”leads to an expression for bubble reactivity worth, due to neutron streaming alone, that yields the closest agreement with the bubble worth values computed from the two-dimensional transport theory code TWOTRAN and the Monte Carlo code KENO.

ISSN:0029-5639    

DOI:10.13182/NSE82-A19396

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor