1. NAME AND TITLE

XLACS-IIA: A Modified Version of XLACS-II for Processing ENDF Data into Multigroup Neutron Cross Sections in AMPX Master Library Format.

AUXILIARY ROUTINES

The output from XLACS-IIA is in AMPX master library format. Resonance processing must be done using the NITAWL module of PSR-063/AMPX-II, which produces cross section libraries in working format to be used in discrete ordinates codes such as XSDRN-PM and ANISN. Many of the other AMPX modules which manipulate multigroup data would be useful in handling output from XLACS-IIA.

2. CONTRIBUTOR

Australian Atomic Energy Commission, Sutherland, N.S.W., Australia.

3. CODING LANGUAGE AND COMPUTER

Fortran IV; IBM 3031/3033.

4. NATURE OF PROBLEM SOLVED

XLACS-IIA calculates fine-group averaged neutron cross sections from ENDF data. Its primary purpose is to produce full range multigroup libraries for the XSDRN-PM program. It also serves this purpose in the AMPX system. Provisions are included for treating fast, resonance, and thermal ENDF/B data. Fine-group energy structures and expansion orders used to represent differential cross sections for XSDRN can be arbitrarily specified by the user. Cross sections can be averaged over an arbitrary user-supplied weighting function or by any of several built-in weighting functions.

5. METHOD OF SOLUTION

This program is a modified version of XLACS-II included in the PSR-063/AMPX-II code package. The major change is in the treatment of thermal scattering, but quite extensive changes have also been made in the resonance treatment.

XLACS-IIA can treat fast, resonance, and thermal ENDF/B data in a single calculation. Energy group structure and expansion orders used to represent differential cross sections can be arbitrarily specified by the user. Smooth cross sections can be averaged over an arbitrary user-supplied weighting function or over any of several built-in weighting functions. The multigroup data produced are in AMPX master library format. Many improvements have been made since the original release of XLACS. The following improvements should be specifically noted: discrete inelastic levels are processed anisotropically to the order specified, all forms of angular distribution data given in ENDF File 4 are processed, anisotropic matrices for ``continuum'' inelastic processes are produced, AMPX master library management features included in XLACS have been removed and execution time and I/O requirements have been significantly reduced for some cases.

In XLACS-IIA, the treatment of thermal scattering has been changed by virtually rewriting the FLANGE section of the code. The documentation explains the changes made to both the thermal scattering and the resonance treatment. The changes produce thermal data joining smoothly onto the slowing down data without using an ultrafine group structure. At the same time the running time for the program was decreased.

6. RESTRICTIONS OR LIMITATIONS

The principal restriction is the availability of adequate core storage. The program is variably dimensioned, which means that array sizes are set for the particular problem at execution time. Core storage requirements are not affected by the number of nuclides in a case.

7. TYPICAL RUNNING TIME

The sample problem was run on an IBM 3033 computer and required less than 2 minutes of CPU time.

8. COMPUTER HARDWARE REQUIREMENTS

The PSR-063/AMPX-II version of XLACS-II was developed on the IBM 360 computer. The contributors made the modifications to this program on the IBM 3031. The sample problem required 488 K in the GO step on the IBM 3033.

9. COMPUTER SOFTWARE REQUIREMENTS

The sample problem was executed using the Fortran H enhanced compiler under MVS.

10. REFERENCES

G. S. Robinson, "Notes on the AAEC Version of XLACS-II," Informal Memo (9/3/81).

Section 3.0 of PSR-063/AMPX-II document, pages 31-56.

N. M. Greene, J. L. Lucius, J. E. White, R. Q. Wright, C. W. Craven, Jr., and M. L. Tobias, "XLACS: A Program to Produce Weighted Multigroup Neutron Cross Sections from ENDF/B," ORNL/TM-3646 (April 1972).

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 output.

12. DATE OF ABSTRACT

May, 1982.