1. NAME AND TITLE

TRIGON: Two-Dimensional Multigroup Diffusion Code SystemTrigonal or Hexagonal Mesh.

2. CONTRIBUTOR

Nuclear Engineering Laboratory, Technical Research Centre of Finland, Helsinki, Finland.

3. CODING LANGUAGE AND COMPUTER

FORTRAN V; UNIVAC 1108.

4. NATURE OF PROBLEM SOLVED

TRIGON solves the multigroup time-independent neutron diffusion equations with arbitrary group-to-group scattering in two space dimensions. In addition to homogeneous or k-effective calculations, inhomogeneous or fixed source calculations can be made. The problem may be specified with both external and internal logarithmic derivative boundary conditions. Using the pointwise flux distribution, the program automatically calculates the average flux and power distributions over equal hexagons of arbitrary size into which the area of solution is divided by the user.

5. METHOD OF SOLUTION

The diffusion theory equations are approximated by 7-point difference equations for the uniform triangular or hexagonal mesh grid. In the former case, the mesh points are situated at the cross-sections of the mesh lines separating different materials and in the latter case at the center points of the homogeneous mesh hexagons. The difference equations are solved iteratively by the line over-relaxation technique utilizing an exponential over-relaxation procedure. Coarse mesh rebalancing and special asymptotic flux extrapolation are used to improve the convergence.

6. RESTRICTIONS OR LIMITATIONS

Due to variable dimensioning of arrays, the only restriction on problem size is the available core storage. The program requires about 27,000 words on the UNIVAC 1108. This can be reduced to less than 15,000 words by segmentation. In addition, a minimum of approximately 10,000 words must be available for variable dimensioned arrays.

7. TYPICAL RUNNING TIME

The basic running time is about 0.2 minutes per space-energy point per iteration when the calculation is performed entirely within the core storage. Usually, some 100 iterations will be enough for convergence.

If the problem involves the use of auxiliary storage devices (tapes, discs, or drums) during the calculation, the running time will be increased due to the fact that computation and data transfer are not performed simultaneously.

8. COMPUTER HARDWARE REQUIREMENTS

TRIGON is designed to operate on a UNIVAC 1108 computer with 64 K words of core storage. A maximum of six auxiliary files will be used. These can be either tape, disc, or drum files. The clock is sampled.

9. COMPUTER SOFTWARE REQUIREMENTS

TRIGON was designed for the EXEC-8 operating system. The UNIVAC 1108 library routine NTRAN is used to perform unbuffered data transfer between core storage and auxiliary files. The CLOCK routine requires Assembly Language.

10. REFERENCE

E. Kaloinen, "TRIGON, A Two-Dimensional Multigroup Diffusion Code for Triagonal or Hexagonal Mesh," Technical Research Centre of Finland, Nuclear Engineering Laboratory, VTT-YDI-1 (May 1973).

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.

12. DATE OF ABSTRACT

December 1981.