NEA-1591 OMEGA.

1. NAME OR DESIGNATION OF PROGRAM:  OMEGA.

3. DESCRIPTION OF PROBLEM OR FUNCTION

OMEGA is a Monte Carlo code for the solution of the stationary neutron transport equation with k-eff as the eigenvalue. A three-dimensional geometry is permitted consisting of a very general arrangement of three basic shapes
(columns with circular, rectangular, or hexagonal cross section with a finite height and different material layers along their axes). The main restriction is that all the basic shapes must have parallel axes. Most real arrangements of fissile material inside and outside a reactor (e.g., in a fuel storage or transport container) can be described without approximation. The main field of application is the estimation of criticality safety. Many years of experience and comparison with reference cases have shown that the code together with the built-in cross section libraries gives reliable results. The following results can be calculated:
- the effective multiplication factor k-eff
- the flux distribution
- reaction rates
- spatially and energetically condensed cross sections for later use in a subsequent OMEGA run. A running job may be interrupted and continued later, possibly with an increased number of batches for an improved statistical accuracy. The geoetry as well as the k-eff results may be visualized. The use of the code is demonstrated by many illustrating examples.

4. METHOD OF SOLUTION

The Monte Carlo method is used with neutrons starting from an initial source distribution. The histories of a generation (or batch) of neutrons are followed from collision to collision until the histories are terminated by capture, fission, or leakage. For the solution of the eigenvalue problem, the starting positions of the neutrons for a given generation are determined by the fission points of the preceding generation. The summation of the results starts only after some initial generations when the spatial part of the fission source has converged. At present the code uses the BNAB-78 subgroup library of the Obninsk data group (26 energy groups with subgroups in the resonance region) for epithermal and fast neutron energies. Spatially dependent resonance self-shielding is accounted for by the so-called subgroup method using the information given by the subgroup parameters of the library. A THERMOS type library is used for thermal energies where upscattering and molecular binding effects (e.g., for light water) are taken into account. The reliability of the data base for criticality problems was shown by many comparisons with reference cases.

The batch file sample.bat executes the ten examples inp1,...,inp10 (see report VKTA-36/May 1996).
A single case (say inp8) may be started by omega inp8.

            test 1 : 0.94 min.
            test 2 : 0.74 min.
            test 3 : 0.43 min.
            test 4 : 0.80 min.
            test 5 : 1.52 min.
            test 6 : 1.74 min.
            test 7 : 0.63 min.
            test 8 : 2.12 min.
            test 9 : 1.70 min.
            test 10 :1.73 min.

The batch file all16.bat executes the 16 examples cas01,...cas16 (see report VKTA-54/April 1998).

           cas 01 :  0.66 min.
           cas 02 : 19.56 min.
           cas 03 :  3.14 min.
           cas 04 :  2.04 min.
           cas 05 :  5.59 min.
           cas 06 :  6.72 min.
           cas 07 :  3.17 min.
           cas 08 : 53.89 min.
           cas 09 : Stopped on error (SQRT argument negative in module transp)
           cas 10 : 58.33 min.
           cas 11 :  4.10 min.
           cas 12 :  3.80 min.
           cas 13 :  3.75 min.
           cas 14 :  3.50 min.
           cas 15 :  3.70 min.
           cas 16 : Program stops without any error message.

7. UNUSUAL FEATURES: UNUSUAL FEATURES OF THE PROGRAM

8. RELATED AND AUXILIARY PROGRAMS

All  files which are necessary for running the program (libraries, executable files) are included in this package. The code is ready to use. All source files are also included.

- E. Seifert:
  A PC Version of the Monte Carlo Criticality Code OMEGA.
  VKTA-36 (May 1996)
- E. Seifert:
  MCNP and OMEGA Criticality Calculations.
  VKTA-54 (April 1998)

11. MACHINE REQUIREMENTS:  PC (486 or  Pentium).

File storage is not more than 10 MByte disk memory.

13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:  PC-DOS

15. NAME AND ESTABLISHMENT OF AUTHOR

          E. Seifert
          VKTA
          Rossendorf e.V.
          Postfach 510119
          D-01314 Dresden, GERMANY

omega.inf     this information file
NEA_1591_1.pdf    Documentation file

Directory SR:C
omega.for     OMEGA source
flix.for      FLIX source
slconv.for    source of fast library conversion (ASCII to binary)  
tlconv.for    source of thermal library conversion (ASCII ti binary)
sl25card      fast library (ASCII form)
tl21card      thermal library (ASCII form)
library.bat   batch file for library conversion
compil1.bat   batch file for OMEGA compilation
compil2.bat   batch file for FLIX compilation

Directory VKTA36:
omega.bat     batch file for executing the examples
samples.bat   batch file for executing 10 samples
inp1..inp10   10 input files (see VKTA-36, May 1996)
inp7flix      input file for program Flix
auth1 to auth10 10 author output
exaauth7.set  Flix output, Omega input for test 7
nea1 to nea10   10 NEA output files
exanea7.set   Flix output, Omega input for test 7

Directory VKTA54:
all16.bat     batch file for executing 16 cases
cas01 to cas16  16 input files (see VKTA-54, April 1998)
casnea01 to casnea16  16 NEA output files

Directory TEST1:
testjob1.bat  batch file for executing the 1th testjob
x1 to x3        input files for test1
x10.out to x30.out  author output files for test1
x10.set       author output file for test1
xnea1.out to xnea3.out  NEA output files for test1
xnea1.set     NEA uotput file for test1
testnea1.dif  difference file between NEA output and files X10..X30

Directory TEST2:
testjob2.bat  batch file for executing the 2th testjob
inp1 to inp10   10 input files for test2
inp7flix      input file for program Flix
auth1 to auth10 10 author output
exaauth7.set  Flix output, Omega input for test 7
nea1 to nea10   10 NEA output files
exanea7.set   Flix output, Omega input for test 7
out1 to out10   output reference files
testnea2.dif  difference file between NEA output and reference files