**1. NAME AND TITLE**

RAFFLE 2: A General Purpose Monte Carlo Code System for Neutron Transport with
Mixed Zone Geometry Option.

**AUXILIARY ROUTINES**

PSICHI: Data Processing Routine.

IHCECOMH: Data Processing Routine.

RAND: Data Processing Routine.

**DATA LIBRARIES**

FDL: Fast Cross-Section Data Library.

TDL: Thermal Cross-Section Data Library.

RAFFLE has gone through a series of development levels. The packaged version is RAFFLE
2, MOD 2.

**2. CONTRIBUTOR**

Idaho National Engineering Laboratory, Idaho Falls, Idaho.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; IBM 360/370.

**4. NATURE OF PROBLEM SOLVED**

RAFFLE 2 solves the neutron transport equation in general geometry. The types of surfaces
allowed include planes parallel to the z-axis, cylinders with the axis parallel to the z-axis, spheres,
and planes perpendicular to the z-axis. On the exterior surfaces of the problem, reflective albedos
may be set to 0.0 (no return) or 1.0 (mirror reflection).

**5. METHOD OF SOLUTION**

RAFFLE 2 solves either iteration-type problems by Monte Carlo methods to obtain the multiplication factor (k) and normal-mode fluxes, or external-source problems. The external sources may be distributed volume sources of general shape or may be incoming current sources specified on particular surfaces. The current sources may have any energy and angular distributions. For external source problems, fission daughters can be subsequently generated from the source neutrons. For any type of problem, the neutron slowing-down treatment can be as detailed as desired. Inelastic discrete-level and evaporation-model scattering; resolved resonance absorption, scattering and fission; and elastic scattering with any degree of anisotropic angular scattering can be treated. Multiple thermal groups are optional and can be used for thermal systems. Also, for resonance problems, temperature can be spatially dependent.

RAFFLE 2 allows three types of scoring techniques. The path technique uses a Richtmeyer-type estimator which is essentially an averaged path length estimator and is the scoring technique
well suited to most problems. The ray technique is used, where the uncollided neutron beam is
followed, at each event, until the contribution falls below some cutoff weight. The KENO
technique is available, in which cross sections of all regions are made equal and delta-type
scattering is allowed. RAFFLE 2 uses both multigroup cross sections and pointwise cross sections.
The resolved resonance interactions are treated by use of the single-level Breit-Wigner formula for
the pointwise cross sections which are then Doppler-broadened using a Maxwellian distribution for
the nucleus velocity. The code system contains standard biasing techniques which may be
employed to decrease running time for some classes of problems. Weight reduction in which, at a
collision, a neutron always undergoes a scattering, may be used. Neutron splitting may be used in
regions where more accurate detailed information is desired. Russian roulette may be played in
various degrees, dependent upon the particular group and region.

**6. RESTRICTIONS OR LIMITATIONS**

This version requires 600 K bytes for execution on the IBM 360/370 computers. The code is
presently set up to handle a maximum of 100 energy groups, 400 regions, 4 fission spectra, and
200 surfaces. Other restrictions are given in the referenced documentation. Much of the data is
dynamically stored such that simple limits on individual data cannot be specified.

**7. TYPICAL RUNNING TIME**

Execution is usually terminated by specification of a maximum CPU limit. Running times are
extremely problem dependent and may vary from 1 minute to several hours. Adequate convergence on k may be obtained in as little as 1 minute on the IBM 360/195 for a simple fast system
such as a bare metal sphere. Complicated thermal systems have been analyzed and runs made in
which 2 to 3 million particles were processed in one hour on the IBM 360/195.

**8. COMPUTER HARDWARE REQUIREMENTS**

RAFFLE 2 uses three input units including the card reader, the fast library tape (or disk or
drum) and the thermal library tape (or disk or drum). During input preparation an intermediate
scratch disk is also employed.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A FORTRAN IV compiler and assembler are required. All non-standard software is included
in the code package.

**10. REFERENCES**

F. J. Wheeler, S. A. Easson, R. A. Grimesey, and D. W. Wessol, "The RAFFLE V General Purpose Monte Carlo Code for Neutron and Gamma Transport," EGG-PHYS-6003, Rev.1 (October 1983).

R. S. Marsden, F. J. Wheeler, and D. E. Wessol, "A Mixed Zone Geometry Option for the RAFFLE General Purpose Monte Carlo Code," ANCR-1206 (February 1975).

W. E. Vesely, R. J. Wheeler, and R. S. Marsden, "The RAFFLE General Purpose Monte
Carlo Code," ANCR-1022 (April 1973).

**11. CONTENTS OF CODE PACKAGE**

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

**12. DATE OF ABSTRACT**

August 1977; revised March 1982, January 1983, February 1985.

**KEYWORDS: ** MONTE CARLO; NEUTRON; MULTIGROUP; COMPLEX GEOMETRY,
CRITICALITY CALCULATIONS