**1. NAME AND TITLE**

TPHEX: Transmission Probability Code System for Calculating Neutron Flux Distributions in Hexagonal Geometry.

**AUXILIARY ROUTINES**

SNOOPY: Finds and prints desired items from the debug output file of TPHEX.

TPHEXTR: Flux extrapolation routine for TPHEX.

TPHXPND: Expands the results of TPHEX into point fluxes.

TPCURR-T2: Prints interface currents calculated by TPHEX and calculates and sums net currents through specified cell faces.

**2. CONTRIBUTORS**

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

Argonne National Laboratory, Argonne, Illinois.

**3. CODING LANGUAGE AND COMPUTER**

Fortran IV, Fortran 77; CDC CYBER (A), CRAY XMP (B).

**4. NATURE OF PROBLEM SOLVED**

TPHEX calculates the multigroup neutron flux distribution in an assembly of hexagonal cells using a transmission probability (interface current) method. It is primarily intended for calculations on hexagonal LWR fuel assemblies but can be used for other purposes subject to the qualifications mentioned in Item 6.

**5. METHOD OF SOLUTION**

The equation system is solved using inner-outer iteration with successive overrelaxation. Various renormalization options intended to accelerate convergence are available but are usually not worthwhile. For optically large systems, the auxiliary routine TPHEXTR may possibly be useful.

**6. RESTRICTIONS OR LIMITATIONS**

The optical thicknesses of the individual cells must lie between 0.1 and 5.0. The accuracy of TPHEX appears to be best when the optical thicknesses do not lie close to these limits. Some extension of the permitted range can be achieved through modification of the coefficient library TABU and minor reprogramming, but a major extension would necessitate revision of the physical approximations.

Strong and extensive flux gradients, such as are encountered in shielding problems, appear to have a deleterious effect on the accuracy of TPHEX.

There are no fixed limits on the number of cells, groups, etc., since variable dimensioning is used, but problems with appreciably more than a few hundred cells and a dozen groups may require storage exceeding 64 K words and running times longer than a few minutes.

**7. TYPICAL RUNNING TIME**

On a UNIVAC 1108 or CDC CYBER 173:

7 groups × 36 cells: less than one minute

7 groups × 169 cells: slightly more than 4 min.

On the Cray XMP/14, sample input 1 took 1.5 seconds; sample input 2 took .59 second; sample input 3 took .42 second and sample input 4 took .52 second of CPU time.

**8. COMPUTER HARDWARE REQUIREMENTS**

TPHEX is operable on the CDC CYBER 170 series computers and the Cray XMP computers.

**9. COMPUTER SOFTWARE REQUIREMENTS**

Fortran IV and 77 compilers and the standard CYBER 173 operating system are required. On the Cray XMP, the CFT77 compiler is used under the UNICOS operating system.

**10. REFERENCES**

F. Wasastjerna, "TPHEX User's Manual," Technical Research Centre of Finland, Nuclear Engineering Laboratory, Report 47 (1980).

F. Wasastjerna, "TPCURR-T, A Program for Printing Cell-to-Cell Partial Currents Calculated by the Stand-Alone Version of TPHEX," REP 5/82 (March 1982).

F. Wasastjerna, "TPCURR-T2, A Program for Printing Cell-to-Cell Partial Currents Calculated by the Stand-Alone Version of TPHEX," REP-17/85 (August 1985).

F. Wasastjerna and Ivan Lux, "TPHEX Programmer's Manual, Nuclear Engineering Laboratory," Report 149 (October 1982).

F. Wasastjerna, "Validation of TPHEX," REP-22/85 (November 1985).

F. Wasastjerna, "An Application of the Transmission Probability Method
to the Calculation of Neutron Flux Distributions in Hexagonal Geometry,"
*Nucl. Sci. Eng.* 72, 9-18 (1979).

F. Wasastjerna and Ivan Lux, "A Transmission Probability Method for Calculation of Neutron Flux Distributions in Hexagonal Geometry," Nuclear Engineering Laboratory, Report 46 (March 1980).

**11. CONTENTS OF CODE PACKAGE**

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

**12. DATE OF ABSTRACT**

June 1982; updated March 1986 and September 1989, January 1991.

**KEYWORDS: **NEUTRON; ONE-DIMENSION; TRANSMISSION PROBABILITY