**1. NAME AND TITLE**

TRIDENT: Two-Dimensional Multigroup Discrete Ordinates Transport Code System(x,y) and (r,z) Geometries.

**2. CONTRIBUTOR**

Los Alamos National Laboratory, Los Alamos, New Mexico.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV and Assembler language; IBM 360/370 (A) and CDC 7600 (B).

**4. NATURE OF PROBLEM SOLVED**

TRIDENT solves the two-dimensional multigroup transport equations in rectangular (x-y) and
cylindrical (r-z) geometries using a regular triangular mesh. Regular and adjoint, inhomogeneous
and homogeneous (k_{eff} and eigenvalue searches) problems subject to vacuum, reflective, white, or
source boundary conditions are solved. General anisotropic scattering is allowed and anisotropic-distributed sources are permitted.

**5. METHOD OF SOLUTION**

The discrete-ordinates approximation is used for the neutron directional variables. An option is included to append a fictitious source to the discrete-ordinates equations that is defined such that spherical-harmonics solutions (in x-y geometry) or spherical-harmonics-like solutions (in r-z geometry) are obtained. This option is useful for cases in which ray-effect distortions are severe. A spatial-finite-element method is used in which the angular flux is expressed as a linear polynomial in each triangle that is discontinuous at triangle boundaries. Both inner (within-group) and outer iteration cycles are accelerated by either whole-system or fine-mesh rebalance.

Provision is made for creation of standard interface output files for S_{N} constants, angle-integrated (scalar) fluxes, and angular fluxes. Standard interface input files for S_{N} constants,
inhomogeneous sources, cross sections, and the scalar flux may be read. Subroutines DRED and
DRIT perform information transfers between LCM and random disk. Data transfer between large
and small core are performed by CRED and CRIT. Sequential operations are performed by SEEK,
REED, and RITE. Flexible edit options as well as a dump and restart capability are provided.

**6. RESTRICTIONS OR LIMITATIONS**

Variable dimensioning is used so that any combination of problem parameters leading to a container array less than MAXLEN can be accommodated. On CDC machines MAXLEN can be about 40,000 words of Small Core Memory (SCM) and Large Core Memory (LCM) is used for most group-dependent data. On IBM machines, TRIDENT executes in double precision (8 bytes per word) so that MAXLEN can be on the order of 100,000 or more. Although most problems can be fast core contained on the IBM machine and SCM and LCM contained on the CDC machine, an option exists to automatically overflow the storage of selected large arrays to random disk if necessary.

**7. TYPICAL RUNNING TIME**

A six group, S_{2}, 1,700 triangle, k_{eff} calculation of an EBR-II core modeled in x-y geometry
requires approximately 4.4 min of CDC 7600 time. This is approximately the same as the
TRIPLET running time. Running times vary almost linearly with the total number of unknowns.
When the ray-effect correction option is used, the running time is increased by a factor of
approximately two, depending upon the problem.

Ten sample problems ran in 9.88 min on the IBM 360/91.

**8. COMPUTER HARDWARE REQUIREMENTS**

A maximum of three interface units, open at once, and three system input/output units are required. One random-disk unit is required if the automatic-data-overflow option is used. A large bulk memory, such as the CDC-7600 LCM, is assumed by the code. This function may, however, be replaced by a portion of fast-core memory with IBM 360/370 machines or by disk, drum, or tape storage.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A FORTRAN IV compiler is required.

**10. REFERENCES**

T. J. Seed, W. F. Miller, Jr., F. W. Brinkley, Jr., "TRIDENT: A Two-Dimensional, Multigroup, Triangular Mesh Discrete Ordinates, Explicit Neutron Transport Code," LA-6735-M (March 1977).

D. Carson "Core to Core Conversion," ANL-K250S-1, (Revision, February 1970).

**11. CONTENTS OF CODE PACKAGE**

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

**12. DATE OF ABSTRACT**

December 1981.

**KEYWORDS: ** TWO-DIMENSIONS; MULTIGROUP; DISCRETE ORDINATES; NEUTRON; TRIANGULAR MESH; GAMMA-RAY