1. NAME AND TITLE

NASIF-NARES: A Code System for Computing Shielding Factors from ENDF/B Tapes.

2. CONTRIBUTOR

Israel Atomic Energy Commission, Tel-Aviv, Israel.

3. CODING LANGUAGE AND COMPUTER

Fortran, Fortran IV; IBM 360/370.

4. NATURE OF PROBLEM SOLVED

NASIF-NARES is a supplement to PSR-120/NANICK which generates infinite-dilution group cross sections. NASIF-NARES computes group shielding factors from resolved and statistical resonance parameters. The shielding factors are temperature and background cross-section dependent.

NASIF computes the shielding factors with variable number of side resonances (up to 24) while NARES computes the shielding factors with 24 side resonances; the contributions of 22 resonance-wings are lumped and approximated by a parabola.

5. METHOD OF SOLUTION

NASIF-NARES processes an entire ENDF/B-III tape in a single run. It searches for the data file of the first isotope requested, processes it, searches for the data of the next isotope, etc., until the list of isotopes requested is exhausted.

Resolved resonance parameters are used directly in the resolved region. The ladder of resonances is continued into the unresolved region by the Monte Carlo method using the unresolved parameters. This ladder of pseudo-resolved resonances, containing resonances of all (l,j) series, is used to compute the shielding factors. The computation involves calculation of temperature-dependent cross sections for each energy point.

6. RESTRICTIONS OR LIMITATIONS

Up to 30 energy groups, 4 background cross-sections, one temperature, and as many isotopes as there are on the ENDF/B tape may be processed in one run.

7. TYPICAL RUNNING TIME

On the IBM 370/165 computer, with 3 contributing resonances, energy range up to 1.1 keV, NASIF runs in about 40 sec and in about 4 minutes for the same with 25 contributing resonances, per fissile element.

NARES runs in about 60 sec for energy range up to 1.1 keV, per fissile element.

8. COMPUTER HARDWARE REQUIREMENTS

NASIF-NARES is operable on the IBM 360/370 computers.

9. COMPUTER SOFTWARE REQUIREMENTS

Fortran and Fortran IV compilers are required.

10. REFERENCE

Y. Gur and S. Yiftah, "NASIF - A Fully Automatic Code for the Calculation of Shielding Factors from ENDF/B-III Tapes," IA-1292 (November 1973).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document and one (1.2MB) DOS diskette which contains the source code and sample problem input and output.

12. DATE OF ABSTRACT

March 1984.