**1. NAME AND TITLE**

GBANISN: One-Dimensional Discrete Ordinates Transport Code System with Anisotropic Scattering with the Group-Band Option.

GBANISN (GroupBand-ANISN) is a sister program of CCC-254/ANISN-ORNL which superseded DTF-II (NAA-SR-10951, March 1966) and followed a series of one-dimensional Sn code developmental efforts over a period of years. An early Sn code, DSN, was developed in the FLOCO language by Bengt Carlson of the Los Alamos Scientific Laboratory. A revision of DSN, called DTK, was written to incorporate improved convergence technique and ease of operation. DTF was a FORTRAN version of DTK written by UNC and LASL personnel. DTF-II evolved from DTF at Atomics International and in turn evolved into ANISN.

**2. CONTRIBUTORS**

Oak Ridge National Laboratory, Oak Ridge, Tennessee.

Lawrence Livermore National Laboratory, Livermore, California.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN 77, ANSI C; IBM RS 6000 (C00628IRISC00).

**4. NATURE OF PROBLEM SOLVED**

GBANISN is closely related to ANISN(CCC-254) and solves the one-dimensional Boltzmann transport equation for neutrons or gamma rays in slab, spherical, or cylindrical geometry. The source may be fixed, fission, or a subcritical combination of the two. Selective criticality searches may be performed on any one of several parameters. Cross sections may be weighted using the space and energy dependent flux generated in solving the transport equation. A main difference is a randomizing of user-select energy group fluxes within a "band" at all interfaces between dissimilar materials and a reduction in the number of outer iterations for problems involving neutron upscatter into higher energy groups. The workstation version of GBANISN is also included in CCC-650/DOORS 3.1.

**5. METHOD OF SOLUTION**

The solution technique is an advanced discrete ordinates method which represents a generalization of the method originated by G. C. Wick and greatly developed and extended to curvilinear geometry by B. G. Carlson at Los Alamos Scientific Laboratory.

GBANISN solves deep-penetration problems in which angle-dependent spectra are calculated in detail and problems involving neutron upscatter. GBANISN uses a programming technique with optional data-storage configurations which allows execution of small, intermediate, and extremely large problems requiring fewer outer iterations than ANISN. This is achieved by performing "inner iterations" over energy groups within a "band" and converging those groups before moving to the next band. These "inner" iterations slightly resemble outer iterations in ANISN. Thus, a calculation with upscatter and no fission can be solved with one traditional outer iteration. GBANISN, like ANISN, includes a technique for handling general anisotropic scattering, pointwise convergence criteria, and alternate step function difference equations that effectively remove the oscillating flux distributions sometimes found in discrete ordinates solutions.

**6. RESTRICTIONS OR LIMITATIONS**

1. Problem size is limited only by machine memory size.

2. The option IEVT = 2 (alpha calculation) is unchecked and possibly not valid with GBANISN.

3. The option IDAT2 which allows diffusion theory and infinite media calculations must equal zero (no effect). This restriction was necessary because of the interface boundary conditions.

4. No outer iteration acceleration is done. Properly implemented acceleration schemes may help to solve upscatter problems efficiently.

5. For adjoint problems, the 1$ array (groupband array) should be input in the inverted order.

**7. TYPICAL RUNNING TIME**

Depending on problem size, type, and convergence, running time has varied from less than one minute to several hours.

The IBM RS/6000 took approximately 5 seconds to run the sample problem.

**8. COMPUTER HARDWARE REQUIREMENTS**

GBANISN is operable on IBM RS/6000 computers.

**9. COMPUTER SOFTWARE REQUIREMENTS**

The AIX XLF FORTRAN 2.2 compiler and linker was used to compile and link the FORTRAN source code. The AIX XLC 2.2 compiler was used for the C source subroutines. The GIP program (from the CCC-543/TORT-DORT package) was used to mix the supplied cross-section library and is not included on the distribution diskette.

**10. REFERENCES**

R. L. Childs and D. E. Cullen, "GROUPBAND-ANISN: A Code to Perform Multiband Calculations," Informal Notes (June 1994).

W. W. Engle, Jr., "ANISN, A One-Dimensional Discrete Ordinates Transport Code with Anisotropic Scattering," K-1693 (March 1967).

W. W. Engle, M. A. Boling, and B. W. Colston, "DTF-II, A One-Dimensional, Multigroup Neutron Transport Program," NAA-SR-10951 (March 1966).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced documents and a diskette written in DOS format which contains the source codes, compile and link batch file, sample input and output for both the GIP mixing code and GBANSN, and a sample data file, written in DOS files.

**12. DATE OF ABSTRACT**

July 1995.

**KEYWORDS**: DISCRETE ORDINATES; NEUTRON; GAMMA-RAY; ONE-DIMENSION;
MULTIGROUP; CYLINDRICAL GEOMETRY; ADJOINT; WORKSTATION.