Search Results

Advanced search parameters have been applied.
open access

Neutron and gamma transport effects by heterogeneous core designs. [LMFBR]

Description: The use of diffusion theory for the prediction of power production near a reactor core-blanket interface and the assumption that gammas are absorbed in situ can lead to substantial errors. This is primarily due to the breakdown of Fick's law for neutron diffusion near the core-blanket boundary, and the gamma leakage from the core into the blanket. These considerations are more pronounced in a situation where a large number of internal blanket assemblies are present, such as in the large heterog… more
Date: January 1, 1977
Creator: Lam, S.K.
Partner: UNT Libraries Government Documents Department
open access

An optimized algorithm for solving the nodal diffusion method on shared memory multiprocessors

Description: Nodal methods play a special role in reactor physics calculations. In recent papers the high computational efficiency of nodal methods has been established and the development of more efficient algorithms tailored to the advanced architectures of modern day computers proposed. The rapidly changing architectures of today's computer influence the way codes have to be programmed so that reasonable speed up and efficiency are attained. We have applied these concepts in solving the one-group neutron… more
Date: January 1, 1990
Creator: Kirk, B.L. & Azmy, Y.Y.
Partner: UNT Libraries Government Documents Department
open access

Variational methods in steady state diffusion problems

Description: Classical variational techniques are used to obtain accurate solutions to the multigroup multiregion one dimensional steady state neutron diffusion equation. Analytic solutions are constructed for benchmark verification. Functionals with cubic trial functions and conservational lagrangian constraints are exhibited and compared with nonconservational functionals with respect to neutron balance and to relative flux and current at interfaces. Excellent agreement of the conservational functionals u… more
Date: January 1, 1983
Creator: Lee, C.E.; Fan, W.C.P. & Bratton, R.L.
Partner: UNT Libraries Government Documents Department
open access

Solving the uncommon reactor core neutronics problems

Description: The common reactor core neutronics problems have fundamental neutron space, energy spectrum solutions. Typically the most positive eigenvalue is associated with an all-positive flux for the pseudo-steady-state condition (k/sub eff/), or the critical state is to be effected by selective adjustment of some variable such as the fuel concentration. With sophistication in reactor analysis has come the demand for solutions of other, uncommon neutronics problems. Importance functionss are needed for s… more
Date: January 1, 1980
Creator: Vondy, D.R. & Fowler, T.B.
Partner: UNT Libraries Government Documents Department
open access

Asymptotic Analysis of Time-Dependent Neutron Transport Coupled with Isotopic Depletion and Radioactive Decay

Description: We describe an asymptotic analysis of the coupled nonlinear system of equations describing time-dependent three-dimensional monoenergetic neutron transport and isotopic depletion and radioactive decay. The classic asymptotic diffusion scaling of Larsen and Keller [1], along with a consistent small scaling of the terms describing the radioactive decay of isotopes, is applied to this coupled nonlinear system of equations in a medium of specified initial isotopic composition. The analysis demonstr… more
Date: September 27, 2006
Creator: Brantley, P S
Partner: UNT Libraries Government Documents Department
open access

Spin correlations in Au/sub 0. 85/Fe/sub 0. 15/

Description: Neutron diffuse scattering measurements were used to study the spin correlations in Au-15 at. % Fe. Single-crystal data were obtained in the first Brillouin zone for an (001) orientation at temperatures of 10 K and 295 K. The results indicate free-spins at 295 K with the development of spin correlations below about 200 K. The cross section at 10 K is similar to that observed by x-rays with diffuse streaks in (210) directions and diffuse peaks both at (000) and (1 1/2 0). Intercomparison of the … more
Date: January 1, 1987
Creator: Cable, J.W.; Parette, G. & Tsunoda, Y.
Partner: UNT Libraries Government Documents Department
open access

Differencing asymptotic diffusion theory

Description: A diffusion theory is presented which extends asymptotic diffusion to non-uniform material properties. Finite difference methods for the diffusion theory naturally result in jump conditions on interfaces when appropriate.
Date: June 7, 1979
Creator: Zimmerman, G.B.
Partner: UNT Libraries Government Documents Department
open access

Nodal method for fast reactor analysis

Description: In this paper, a nodal method applicable to fast reactor diffusion theory analysis has been developed. This method has been shown to be accurate and efficient in comparison to highly optimized finite difference techniques. The use of an analytic solution to the diffusion equation as a means of determining accurate coupling relationships between nodes has been shown to be highly accurate and efficient in specific two-group applications, as well as in the current multigroup method.
Date: January 1, 1979
Creator: Shober, R.A.
Partner: UNT Libraries Government Documents Department
open access

Alternate differencing technique for the synthetic method

Description: Larsen and coworkers have shown that the effectiveness of the synthetic method is often determined by the techniques used to difference the diffusion equation, the equation taken, in current forms of the synthetic method, as the low-order approximation. They have also developed their own differencing technique. On the other hand, the Los Alamos (LA) approach generates point-centered diffusion difference equations, a feature which is inconvenient for the many people now using box-centered codes.… more
Date: January 1, 1983
Creator: Gelbard, E.M. & Khalil, H.
Partner: UNT Libraries Government Documents Department
open access

Gain from a mixed finite-difference formulation for three-dimensional diffusion-theory neutronics

Description: The advantage of a mixed differencing scheme for representing the diffusion theory approximation to neutron transport in three-dimensional triangular-Z geometry is demonstrated for a fast reactor. Most of the early codes employed the mesh edge difference formulation as is used in the German D3E code. A mesh centered formulation was chosen for use on a routine basis with mesh points located at the centers of the finite difference elements instead of at the corners where the internal material int… more
Date: January 1, 1981
Creator: Vondy, D.R. & Fowler, T.B.
Partner: UNT Libraries Government Documents Department
open access

Geometry-independent approach to coarse-mesh neutron diffusion calculations

Description: This summary describes the development of a boundary coarse-mesh nodal method applicable to arbitrary geometries using the boundary integral technique coupled with nodal source expansion. (JDB)
Date: January 1, 1986
Creator: Kohut, P.
Partner: UNT Libraries Government Documents Department
open access

Blackness coefficients, effective diffusion parameters, and control rod worths for thermal reactors - methods

Description: Simple diffusion theory cannot be used to evaluate control rod worths in thermal neutron reactors because of the strongly absorbing character of the control material. However, reliable control rod worths can be obtained within the framework of diffusion theory if the control material is characterized by a set of mesh-dependent effective diffusion parameters. For thin slab absorbers the effective diffusion parameters can be expressed as functions of a suitably-defined pair of blackness coefficie… more
Date: January 1, 1984
Creator: Bretscher, M.M.
Partner: UNT Libraries Government Documents Department
open access

Geometry-independent approach to coarse-mesh neutron diffusion calculations

Description: Powerful coarse-mesh and nodal methods have been recently developed to calculate accurate node-average fluxes and eigenvalues. The nodal methods solve for the node-average flux by reducing the multidimensional diffusion problem to a coupled system of 1-D equations. These schemes are mainly limited to rectangular (xyz) nodes and cannot easily be extended to other geometries. The polynomial-based coarse-mesh methods have been applied to thetaRZ and HEXZ geometries. This summary describes the deve… more
Date: June 1, 1985
Creator: Kohut, P.
Partner: UNT Libraries Government Documents Department
open access

An improved quasistatic option for the DIF3D nodal kinetics code

Description: An improved quasistatic scheme is formulated for solution of the time-dependent DIF3D nodal equations in hexagonal-z geometry. This scheme has been implemented, along with adiabatic and point kinetics solution options, in the DIF3D hexagonal-z nodal kinetics code. The improved quasistatic method is shown to permit significant reduction in computing time, even for transients involving pronounced changes in flux shape. The achievable computing time reduction, in addition to being problem dependen… more
Date: January 1, 1991
Creator: Taiwo, T. A. & Khalil, H. S.
Partner: UNT Libraries Government Documents Department
open access

Performance of a parallel algorithm for solving the neutron diffusion equation on the hypercube

Description: The one-group, steady state neutron diffusion equation in two- dimensional Cartesian geometry is solved using the nodal method technique. By decoupling sets of equations representing the neutron current continuity along the length of rows and columns of computational cells a new iterative algorithm is derived that is more suitable to solving large practical problems. This algorithm is highly parallelizable and is implemented on the Intel iPSC/2 hypercube in three versions which differ essential… more
Date: January 1, 1989
Creator: Kirk, B.L. & Azmy, Y.Y.
Partner: UNT Libraries Government Documents Department
open access

A nodal integral method for the neutron diffusion equation in cylindrical geometry

Description: This Summary reports recent progress in deriving and numerically implementing a nodal integral method (NIM) for solving the neutron diffusion equation in cylindrical, r-z, geometry. Comparisons of numerical solutions to two test problems with those obtained by the code EXTERMINATOR-2 indicate the superior accuracy of the nodal integral method solutions on much coarser meshes. 6 refs., 1 fig., 1 tab.
Date: January 1, 1987
Creator: Azmy, Y.Y.
Partner: UNT Libraries Government Documents Department
open access

Priori local grid refinement in the multigrid method

Description: In this work we study the possibility of a priori local grid refinement in the multigrid method for the single group neutron diffusion equation. (WHK)
Date: January 1, 1983
Creator: Dendy, Joel E.
Partner: UNT Libraries Government Documents Department
open access

Neutronics Computational Applications of Symmetry Algebras

Description: Lie groups of point transformations and their corresponding symmetry algebras are determined for a general system of second order differential equations, special cases of which include the multigroup diffusion equations and the ''FLIP form'' of the P/sub L/ equations. It is shown how Lie symmetry algebras can be used to motivate, formulate and simplify double sweep algorithms for solving two-point boundary value problems that involve systems of second order differential equations. A matrix Ricc… more
Date: January 1, 1989
Creator: Axford, R. A.
Partner: UNT Libraries Government Documents Department
open access

Response-matrix directional diffusion coefficients for application within large cavities

Description: A deterministic definition of the directional diffusion coefficient is proposed which allows diffusion theory codes to adequately reproduce the transport effects within a large cavity. The methodology has been tested satisfactorily upon the TREAT Upgrade hodoscope slot. This preliminary testing illustrates that the directional diffusion coefficients were applicable to a wide range of perturbations of the original model, thus exhibiting a high degree of versatility.
Date: January 1, 1980
Creator: Malloy, D.J.
Partner: UNT Libraries Government Documents Department
open access

Neutron wave propagation in heterogeneous media and the interpretation of neutron noise in BWRs

Description: Experimental data from boiling water reactors (BWRs) show that the phase of the cross-power spectral density between pairs of axially separated neutron detectors varies linearly with frequency (characteristic of a pure delay process) for frequencies greater than approx. 1 Hz. The interpretation of this fact is of relevance to application of noise techniques to measure the average velocity of the vapor phase in the moderator. It is shown that the homogeneous approximation is inadequate to interp… more
Date: January 1, 1980
Creator: Difilippo, F.C.
Partner: UNT Libraries Government Documents Department
open access

Three-dimensional nodal diffusion and transport methods for the analysis of fast-reactor critical experiments

Description: This paper describes two new nodal methods for solving the multigroup neutron diffusion and transport equations in three-dimensional Cartesian geometry. These methods have been developed for the global analysis of fast-reactor critical experiments once cell-averaged multigroup cross sections for each matrix position or drawer have been computed using appropriate cell-homogenization procedures. Brief descriptions of the nodal diffusion and transport schemes are presented, along with results of t… more
Date: January 1, 1984
Creator: Lawrence, R. D.
Partner: UNT Libraries Government Documents Department
open access

An improved quasistatic option for the DIF3D nodal kinetics code

Description: An improved quasistatic scheme is formulated for solution of the time-dependent DIF3D nodal equations in hexagonal-z geometry. This scheme has been implemented, along with adiabatic and point kinetics solution options, in the DIF3D hexagonal-z nodal kinetics code. The improved quasistatic method is shown to permit significant reduction in computing time, even for transients involving pronounced changes in flux shape. The achievable computing time reduction, in addition to being problem dependen… more
Date: December 31, 1991
Creator: Taiwo, T. A. & Khalil, H. S.
Partner: UNT Libraries Government Documents Department
open access

Error analysis of the quartic nodal expansion method for slab geometry

Description: This paper presents an analysis of the quartic polynomial Nodal Expansion Method (NEM) for one-dimensional neutron diffusion calculations. As part of an ongoing effort to develop an adaptive mesh refinement strategy for use in state-of-the-art nodal kinetics codes, we derive a priori error bounds on the computed solution for uniform meshes and validate them using a simple test problem. Predicted error bounds are found to be greater than computed maximum absolute errors by no more than a factor … more
Date: February 1, 1995
Creator: Penland, R. C.; Turinsky, P. J. & Azmy, Y. Y.
Partner: UNT Libraries Government Documents Department
Back to Top of Screen