TWODANT

A Code Package for Two-Dimensional, Diffusion-Accelerated, Neutral-Particle Transport
by Ray E. Alcouffe, Forrest W. Brinkley, Duane R. Marr , and R. Douglas O'Dell

Usage: xtwodant < input > output

Function

TWODANT solves the two-dimensional multigroup transport equation in x-y, r-z, and r-theta geometries. Both regular and adjoint, inhomogeneous (fixed source and homogeneous (k-effective and eigenvalue search) problems subject to vacuum, reflective, periodic, white, or inhomogeneous boundary flux conditions are solved. General anisotropic scattering is allowed and anisotropic inhomogeneous sources are permitted.

Method of Solution

TWODANT numerically solves the two-dimensional, multigroup form of the neutral-particle, steady-state Boltzmann transport equation. The discrete-ordinates form of approximation is used for treating the angular variation of the particle distribution and the diamond-difference scheme is used for space-angle discretization. Negative fluxes are eliminated by a local set-to-zero-and-correct algorithm. A standard inner (within-group) iteration, outer (energy-group-dependent source) iteration technique is used. Both inner and outer iterations are accelerated using the diffusion synthetic acceleration method. The diffusion solver uses the multigrid method and Chebychev acceleration of the fission source.

Restrictions

The code is thoroughly variably dimensioned with a flexible, sophisticated data management and transfer capability. The code is designed for a three-level hierarchy of data storage: a small, fast core central memory (SCM), a fast-access peripheral large core memory (LCM), and random-access peripheral storage. (For computing systems based on a two-level hierarchy of data storage - a large fast core and random-access peripheral storage - a portion of fast core is designated as a simulated LCM to mimic the three-level hierarchy). Random-access storage is used only if LCM (or simulated LCM) storage requirements are exceeded. Normally, an SCM of about 40 000 words of storage and an LCM (or simulated LCM) of a few hundred thousand words or less storage are sufficient to eliminate the need for using random-access storage.

Running Time

Running time is directly related to problem size and to central processor and data transfer speeds. On the CRAY-1, a four group, adjoint calculation of the eigenvalue of an R-Z model of the Fast Test Reactor (FTR) took 15 seconds. The calculation used transport corrected P0 cross sections, an S4 angular quadrature, and a 31 by 68 spatial mesh.

Unusual Features of the Program

The TWODANT code package is modularly structured in a form that separates the input and the output (edit) functions from the main calculational (solver) section of the code. The code makes use of binary, sequential data files, called interface files, to transmit data between modules and submodules. Standard interface files whose specifi- cations have been defined by the Reactor Physics Committee on Computer Code Coordination are accepted, used, and created by the code. The ONEDANT free-field card-image input capability is provided for the user. The code provides the user with con- siderable flexibility in using both card-image or sequential file input and also in controlling the execution of both modules and submodules. Separate versions of the code exist for short- word and long-word machines.