**1. NAME AND TITLE**

THERMOS-OTA: Multigroup Integral Transport Code System for Thermal Lattice Calculations using Collision Probability Method for Slabs and Cylinders.

**AUXILIARY ROUTINE**

ETOTO: A program to process data from ENDF/B to THERMOS-OTA and FACEL.

THERMOS-OTA is based on the THERMOS code which was developed at Brookhaven National
Laboratory, Upton, New York. It is, to a large extent, a reprogrammed version of THERMOS
including the dynamic storage allocation facility. Thus, the range of program applicability has been
greatly increased.

**2. CONTRIBUTOR**

Technical Research Centre of Finland, Nuclear Engineering Laboratory, Helsinki, Finland,
through the OECD NEA Data Bank, Gif-sur-Yvette, France.

**3. CODING LANGUAGE AND COMPUTER**

Fortran IV, UNIVAC-1108 (A); Fortran V, CYBER 173 (B); Fortran 77, CYBER 740 (C).

**4. NATURE OF PROBLEM SOLVED**

THERMOS-OTA solves the integral transport equation for the thermal neutron density in slab or
cylindrical geometry. It allows condensed cross section sets to be obtained for various nuclides and
mixtures and they can be stored in mass storage as pseudo material libraries.

**5. METHOD OF SOLUTION**

The method used in THERMOS for solving the multigroup integral transport theory Boltzmann
equation by collision probability approach is kept unchanged in THERMOS-OTA with a few small
exceptions. These include treatment of vacuum regions and making transport correction to the cross
sections. THERMOS-OTA uses successive overrelaxation, renormalization, and extrapolation.

**6. RESTRICTIONS OR LIMITATIONS**

Due to the use of dynamic storage allocation, it is difficult to specify limits for the problem size.
However, as a rule of thumb, the product of the number of groups and the number of space points
should be less than about 600 if 40,000 words are used for dynamic storage. The amount of storage
space reserved by the program can be changed.

**7. TYPICAL RUNNING TIME**

For a small system, such as a fuel rod cell, the running time on a UNIVAC 1108 is typically about
1 minute without the transport correction and perhaps 2 minutes with it. For large systems such as
50 mean free paths in radius with many groups, convergence is poor leading to running times on the
order of 20 minutes. On the CDC 740, THERMOS-OTA runs in 70 CPU seconds.

**8. COMPUTER HARDWARE REQUIREMENTS**

THERMOS-OTA is operable on the UNIVAC 1108 computer (A) or the CYBER 740 computer
(B). On the UNIVAC 1108, with 46,000 words used for dynamic storage, 64 K of core storage will
suffice. THERMOS-OTA uses 2 auxiliary storage files of arbitrary type. The CYBER 740 main
storage was 170,000 octal words.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A Fortran IV compiler is required (A). A Fortran 77 compiler is required for version (B).

**10. REFERENCES**

J. Saastamoinen and F. 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 (January 1974).

E. Patrakka, ETOTO, "A Program to Process Data from ENDF/B to THERMOS-OTA and FACEL," Nuclear Engineering Laboratory, Report 7 (September 1973).

E. Patrakka, "A 48 Group THERMOS-OTA Library," Nuclear Engineering Laboratory (From YDI
1974 Memo 3).

**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 the THERMOS-OTA Library.

**12. DATE OF ABSTRACT**

March 1984; reviewed May 1984, updated September 1985, August 1986.

**KEYWORDS: ** MULTIGROUP CROSS SECTION PROCESSING; NEUTRON CROSS
SECTION PROCESSING