NEA-0043 THERMOS.

1. NAME OR DESIGNATION OF PROGRAM:  THERMOS.

3. NATURE OF PHYSICAL PROBLEM SOLVED

Computes the scalar thermal neutron spectrum as function of position in a one-dimensional slab (THERMOS-1) or cylindrical cell (THERMOS-2).
Isotropic neutron scattering in the laboratory system is assumed.
The slowing down source is computed from elastic scattering of the neutrons in a 1/E epithermal flux.
Either a reflecting or vacuum boundary can be chosen.

4. METHOD OF SOLUTION

The velocity and space variables are replaced by discrete values. Scattering and collision probability matrices are computed and the neutron balance equation is solved by iterative techniques. A combination of a Gauss iteration, renormalization and extrapolation is used to accelerate convergence.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

Maximum 30 velocity groups, 20 space points, 5 mixtures (assigned arbitrarily to the space points) composed of maximum 10 isotopes. An additional 10 isotopes can be specified for activation calculations and cross section averaging.

6. TYPICAL RUNNING TIME

a) IBM 7090 - approximately 12.n.k.(n+k+5)/100000 minutes.
b) IBM 704  - approximately n.k.(n+k+5)/1000 minutes.
Where n is the number of space points, and k is the number of velocity groups. With n = 20 and k = 30 the time required by IBM 7090 is about 4 minutes.

7. UNUSUAL FEATURES OF THE PROGRAM

Designed for production running.
Library tape and/or on-line cross section input. Arbitrary space and velocity mesh. The scattering model is arbitrary but a free gas model is built into the programme. Output contains the velocity dependent neutron density and a number of velocity integrated or velocity averaged quantities such as reaction rates, average velocities and cross sections.

8. RELATED AND AUXILIARY PROGRAMS

LIBP is used to prepare a library tape containing cross sections and scattering matrices for isotopes used frequently. GAKER computes the scattering matrix, according to the Nelkin model, for protons bound in water.
GAKER may also be used for heavy water or polyethylene.
MERGE may combine specified portions of different scattering matrices into a composite matrix to be used in THERMOS.
LASER is a combination of THERMOS and MUFT-4.

10. REFERENCES

- H.C.Honeck:
  THERMOS, A Thermalization Transport Theory Code for Reactor Lattice Calculations
  BNL 5826 (September 1961).

- Herman I. de Wolde:
Remarks on THERMOL 360 Version (June 1969)
- Errors found in THERMOL (Technical University of Helsinki)
- Herman I. de Wolde:
THERMOL, A Fortran IV Code to Compose Libraries for The THERMOS Code

11. MACHINE REQUIREMENTS

32k (fast memory), 5 tapes.
The 7040 version is for a 16k memory.

13. OPERATING SYSTEM OR MONITOR UNDER WHICH PROGRAM IS EXECUTED

FORTRAN II monitor (IBM 7090).
IBM 7040/44 Operating System.
IBM 360 Operating System.

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

ANY OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

15. NAME AND ESTABLISHMENT OF AUTHOR

        Henry C.Honeck
        Brookhaven National Laboratory
        Upton, New York

The Library has received the 7090 version of this programme through the CETIS programmotheque. The 7040 version was written by the Universite libre de Bruxelles.
ALGOL version was offered by Delft (Reactor Instituut Delft, Netherlands).
A version for ICL computer was received from Central Research Institute for Physics of the Hungarian Academy of Sciences Budapest, Hungary.

source program   mag tape                                           SRCTP
test-case data   mag tape                                           DATTP
test-case output mag tape                                           OUTTP
user's guide                                                        WRKPT