**1. NAME AND TITLE**

TESS: Multigroup Discrete Ordinates Code System for Slab and Spherical Geometries.

TESS is an extension/modification of CCC-71/MIST.

**2. CONTRIBUTOR**

Argonne National Laboratory, Argonne, Illinois, through the Argonne Code Center (ACC Abstract 513).

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; CDC 3600.

**4. NATURE OF PROBLEM SOLVED**

TESS provides the multigroup real and adjoint solutions to the transport equation in the S_{n}
approximation for one-dimensional slab and spherical geometry. Highly generalized boundary-condition capabilities make the system quite suitable for photon-transport problems. Integrals of
flux and adjoint for perturbation analysis can be calculated. Reaction rates may be computed for
specified isotopes as a function of space.

**5. METHOD OF SOLUTION**

A direct method of solution for each outer iteration is used for maximum efficiency in slowly converging problems. A double SN formulation in slab geometry, which allows the code to treat discontinuities more efficiently in the angular flux at interfaces, yields more accurate results with fewer angles. TESS contains a sophisticated cross-section homogenization routine, which permits cross-section collapse in both space and energy by six different prescriptionsthree by real flux weighting, and three by flux and adjoint weighting. In addition, two different methods of providing for cell leakage make the code convenient for fast-reactor, critical-facility heterogeneity studies.

**6. RESTRICTIONS OR LIMITATIONS**

TESS permits a maximum of 150 mesh points, 26 groups, 20 angular intervals, 12 isotropic downscatter groups, 1 P1 downscatter group, 40 regions, 25 materials. There is no restriction on angles except that they be symmetric about PI/2" (MU = 0). No upscatter is allowed.

**7. TYPICAL RUNNING TIME**

Approximately .5 millisecond is required (point-group-angular order squared) per iteration.

**8. COMPUTER HARDWARE REQUIREMENTS**

TESS is operable on the CDC 3600 computer, with 50K available storage and 10 tape units.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A FORTRAN IV compiler with a SCOPE 6,2114 operating system is required.

**10. REFERENCES**

a. Included in the documentation:

R. W. Goin and J. P. Plummer, "TESS, A One-Dimensional SN Transport-Theory Code for the CDC 3600," ANL 7406 (December 1971).

b. Background information:

G. E. Putnam and D. M. Shapiro, "MIST (Multigroup Internuclear Slab Transport)," IDO-16856 (May 1963).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document (10.a) and one (1.2MB) DOS diskette which contains the source code and sample problem input.

**12. DATE OF ABSTRACT**

June 1973; updated July 1975.

**KEYWORDS: ** DISCRETE ORDINATES; NEUTRON; GAMMA-RAY; ONE-DIMENSION;
SLAB; SPHERICAL GEOMETRY; MULTIGROUP