NAME OR DESIGNATION OF PROGRAM, COMPUTER, DESCRIPTION OF PROBLEM OR FUNCTION, METHOD OF SOLUTION, RESTRICTIONS, CPU, FEATURES, RELATED AND AUXILIARY PROGRAMS, STATUS, REFERENCES, MACHINE REQUIREMENTS, LANGUAGE, OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED, OTHER RESTRICTIONS, NAME AND ESTABLISHMENT OF AUTHOR, MATERIAL, CATEGORIES

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Program name | Package id | Status | Status date |
---|---|---|---|

OMEGA | NEA-1591/01 | Tested | 12-MAR-1999 |

Machines used:

Package ID | Orig. computer | Test computer |
---|---|---|

NEA-1591/01 | IBM PC | PC Pentium II 400 |

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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.

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.

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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 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.

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NEA-1591/01

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.

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NEA-1591/01, included references:

- 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)

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NEA-1591/01

File storage is not more than 10 MByte disk memory.[ top ]

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NEA-1591/01

omega.inf this information fileNEA_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

Keywords: Monte Carlo method, criticality, flux distribution, neutron transport equation, reaction rates, three-dimensional.