**1. NAME AND TITLE**

COMBINE-PC: Code System to Compute Neutron Spectra and ENDF/B Version 5 Based Multigroup Neutron Constants.

**2. CONTRIBUTOR**

Idaho National Engineering Laboratory, Idaho Falls, Idaho.

**3. CODING LANGUAGE AND COMPUTER**

Fortran 77; all IBM PC's and all computers in general.

**4. NATURE OF PROBLEM SOLVED**

COMBINE computes the neutron spectra and ENDF/B Version 5 based neutron multigroup constants suitable for use in diffusion and transport theory neutronics analysis. The equations solved for the energy-dependent fast and thermal neutron spectra are based on the B-1 or B-3 approximation to the Boltzmann transport equation.

**5. METHOD OF SOLUTION**

The energy range is broken into 166 discrete points for the spectrum calculation. The resulting matrix of flux equations is then solved using standard numerical techniques to obtain the spectral weight function for generation of group-averaged constants. Resolved resonance shielding of the fine mesh cross section data is performed using a table lookup technique or the Nordheim method. The unresolved range is treated using a statistical averaging technique.

**6. RESTRICTIONS OR LIMITATIONS**

This version can be used for neutron energy range .001 eV to 16.9 MeV. The number of coalesced (broad) groups output to the cross section interface file is limited to 99 or fewer, not 118 as indicated in the manual. COMBINE/PC will run on 32 or 60 or 64 bit computers.

**7. TYPICAL RUNNING TIME**

Variable from a few minutes to 3 hours on IBM PC, depending on the number and type of resonance shielding calculation. On Cray, Apollo and CDC hardware , run times vary from a few seconds to a few minutes. At RSIC, the code was installed on an IBM PC/XT with 640 K of main memory and 20 mb hard disk, running at 4.7 megahertz under Dos 3.3. Installation of the fast neutron library took about 1 hour; the resonance broadening table took about 1 hour and 10 minutes; the thermal library took about 2 hours. The following run times were noted:

C01.INP - 1 hour and 25 minutes

C09.INP - 2 hours and 25 minutes

C11.INP - 10 minutes

**8. COMPUTER HARDWARE REQUIREMENTS**

IBM PC and compatibles with math co-processor, 640 K of addressable memory and at least 20 MB of fixed storage.

**9. COMPUTER SOFTWARE REQUIREMENTS**

The code was written in Fortran 77 and uses Lahey F77L and PLINK86 overlay linker for the IBM PC version. A Fortran 77 compiler is required for the mainframe versions.

**10. REFERENCES**

D. W. Nigg, ``Correction to EGG-2589,'' (July 10, 1991).

``READ.ME,'' Informal notes by Idaho National Engineering Laboratory on ``COMBINE-5/PC Version 5.23'' (1990).

Robert A. Grimesey, David W. Nigg and Richard L. Curtis, *COMBINE/PC - A Portable
ENDF/B Version 5 Neutron Spectrum and Cross Section Generation Program*, EGG-2589 (April
1990).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced documents and seven DS/HD diskettes.

**12. DATE OF ABSTRACT**

October 1990, revised August 1991.

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