NEA-0628 THERMOS-OTA.

1. NAME OR DESIGNATION OF PROGRAM:  THERMOS-OTA.

3. DESCRIPTION OF PROBLEM OR FUNCTION

THERMOS-OTA uses the collision  probability method to solve the integral transport equation for the  thermal neutron density in slab or cylindrical geometry in connec- tion with fuel rod lattice problems.

4. METHOD OF SOLUTION

The method used in THERMOS for solving the multigroup integral transport equation by a collision probability approach is kept unchanged in THERMOS-OTA with a few exceptions which include treatment of vacuum regions and making (optional) transport corrections to the cross sections. The latter modifica- tion is to approximately take into account the effect of anisotropic scattering and is realized 1) by replacing the total cross section in each group by the transport cross section when calculating the transport kernel and 2) by subtracting from the diagonal elements of the isotropic scattering matrix the term equal to the average cosine of angle of scattering times the total scattering cross section.

However, the main modifications are in the output part of the code and in the programming technique: THERMOS-OTA can generate with one  run a data library containing cross section data that has been hom-  ogenised and condensed as specified by the user. This data library can be used in a subsequent run, e.g. a fuel rod cell calculation may first be made and then, using the data library from this run, a  whole assembly calculation in cylindrical geometry to derive diffu-  sion theory parameters for specified regions. Such data libraries can also be constructed for materials not present in the cell. One run can produce a data library and/or diffusion parameters for various homogenisations and condensations specified by the user.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

THERMOS-OTA makes use of the dynamic storage allocation technique, i.e. the central memory space for most arrays is allocated from one large array (40 Kwords typically). So the exact restrictions on the complexity of the problem cannot be given. The number of core storage words requested in a case depends mainly on the number of space points and energy groups.

6. TYPICAL RUNNING TIME:  Strongly case dependent.

7. UNUSUAL FEATURES OF THE PROGRAM:

8. RELATED AND AUXILIARY PROGRAMS

THERMOS-OTA is an improved version  of the THERMOS code. Auxiliary programs are THEPSL which lists the data library output from THERMOS-OTA, and THECOM which combines several such data libraries.

THERMLIB is an independent program which generates, revises and expands the data library that is input to THERMOS-OTA.

10. REFERENCES

- H.C. Honeck:
  The original THERMOS code
  BNL-5826 (1961).

- Eero Patrakka:
  A 48 Group THERMOS-OTA Library
  YDI 1974, Memo 3 (Translation from Finnish)
- Jaako Saastamoinen, Frej Wasastjerna:
  THERMOS-OTA, A Revised Version of the THERMOS Program for Thermal
  Lattice Calculations with the Auxiliary Programs THEPSL and THECOM
  Nuclear Engineering Laboratory, Report 10, Otaniemi, January 1974

11. MACHINE REQUIREMENTS

59 Kwords (with a storage allocation array size of 40 Kwords).

13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:  UNIVAC 1108 EXEC  8, CDC CYBER NOS.

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS:  Over-
lay structure defined in report of code.

15. NAME AND ESTABLISHMENT OF AUTHOR

          J. Saastamoinen and F. Wasastjerna
          Nuclear Engineering Laboratory
          Technical Research Centre of Finland
          Otaniemi, Finland.

source program   mag tape                                           SRCTP
test-case data   mag tape                                           DATTP
test-case output mag tape                                           OUTTP
source program   mag tapeTHECOM Source                              SRCTP
source program   mag tapeTHEPSL Source                              SRCTP
symb data lib    mag tapeData Library in formatted form             LBSTP
source program   mag tapeLIBCON4 Source                             SRCTP
source program   mag tapeLIBCON2 Source                             SRCTP
report                                                              REPPT