**1. NAME AND TITLE**

O5R: A General-Purpose Monte Carlo Neutron Transport Code System.

**PROTOTYPES**

O5R-STATEST: Sample Shielding Calculation

O5R-K: Sample Reactor Calculation; Multiplication Constant.

**PRIMARY ROUTINE**

O5R-Generator: Collision Tape Generator.

**AUXILIARY ROUTINES**

XSECT: Cross Section Handling Code.

LEGENDRE: Data Generator.

STATEST: Statistical EstimationSpecial Analysis Routine for Sample Problem.

O5R was originally written in FAP for the IBM 7090. This original version was incorporated
into the NTC code (CCC-7), and later modified for the IBM 360 and incorporated into CCC-161/NMTC and in CCC-178/HETC. O5R was followed by CCC-128/O6R and later by CCC-203/MORSE, which is recommended over the early technology. O5R, still in use in connection
with other computing technology, is held by RSIC but not generally recommended. It should be
noted that during its "active" period, 19641976, it was distributed by RSIC 427 times. It was also
distributed through the OECD Nuclear Energy Agency (NEA) Data Bank.

**2. CONTRIBUTOR**

Engineering Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee.

**3. CODING LANGUAGE AND COMPUTER**

RAM CCC-17A: FORTRAN and Assembly language; IBM 360/370.

**4. NATURE OF PROBLEM SOLVED**

The O5R code system was designed to calculate, by Monte Carlo methods, any quantity related to neutron transport in reactor or shielding problems. The system is represented by two examples: O5R-STATEST which calculates the neutron flux, for various energy bins, at various points by statistical estimation; and O5R-K which calculates the multiplication constant of a chain-reacting system.

Sources may have arbitrary spatial, energy, and angular distributions via a subroutine written
by the user. Arbitrary three-dimensional geometries bounded by quadric surfaces may be treated.
Anisotropic scattering can be included for both elastic and inelastic processes. Fissionable as well
as non-fissionable media can be treated. Several variance reduction techniques are available.

**5. METHOD OF SOLUTION**

For maximum flexibility, a calculation generally consists of two main operations. The code O5R-Generator is used to generate neutron case histories and produce ``collision tapes'' on which are written any, or all, of 34 distinct parameters describing each collision. These tapes are subsequently processed by "analysis" routines to produce Monte Carlo estimates of any desired quantity. The analysis routine STATEST is supplied as part of a prototype of the O5R system as applied to shielding problems. Statistical estimation of the flux in energy bins is computed for an array of space points. The multiplication constant is estimated in the reactor prototype O5R-K by obtaining Monte Carlo estimates of the number of neutrons emerging from successive generations. The special subroutine OUTPT is used and no analysis of a collision tape is required.

A batch system of generating case histories is employed to obtain a very detailed table of cross sections in fast memory. The cross sections in memory at one time encompass only a small energy range. All collisions of a batch, for which these cross sections are needed, are generated before reading from tape another group of cross sections. Cross-section data is prepared for use in O5R by XSECT, a code which performs a variety of manipulations: preparing, updating, and editing a master tape, and performing cross-section arithmetic.

Source data is generated by subroutine SOURCE, usually written by the code package user for his specific problem. A source generator is included in the package for the sample problem.

A very general geometry subroutine permits the treatment of complicated geometries. As many
as 16 media are permitted and boundaries may be either planes or quadric surfaces, arbitrarily
oriented and intersecting in arbitrary fashion.

**6. RESTRICTIONS OR LIMITATIONS**

Number of different media allowed: 16

Number of scatterers allowed per medium: 8

Number of anisotropic scatterers allowed: 10

Energy range covered: 77.13 MeV to 0.07 x 10-13 eV.

Treatment of thermal neutrons is limited to a one-velocity approximation unless the user
supplies subroutines for thermal scattering.

**7. TYPICAL RUNNING TIME**

Running time for O5R on various types of problems varies with the problem and with the
computer used.

**8. COMPUTER HARDWARE REQUIREMENTS**

IBM 360/370. In addition to tape units needed for input, output and systems, a maximum of
four units are needed for a reactor problem, and three units for a shielding problem.

**9. COMPUTER SOFTWARE REQUIREMENTS**

The codes are almost entirely written in FORTRAN, with a few small assembly language routines for random number generation, word packing and unpacking, etc.

All library-type routines are standard.

Logical tape numbers of auxiliary tapes may be specified as input to a given problem. The
standard input, output and systems tapes are used.

**10. REFERENCES**

R. R. Coveyou, J. G. Sullivan, H. P. Carter, D. C. Irving, R. M. Freestone, Jr., and F. B. K. Kam, "O5R, a General-Purpose Monte Carlo Neutron Transport Code," ORNL-3622 (February 1965).

D. C. Irving, V. R. Cain, and R. M. Freestone, Jr., "An Amplification of Selected Portions of the O5R Monte Carlo Code User's Manual," ORNL-TM-2601 (May 1969).

Y. Caseau, "Geometric Treatment of Trajectories in the O5R Program," CEN/FAR 17 (ORNL-tr-1379) (April 1966).

F. B. K. Kam and K. D. Franz, "ACTIFK, A General Analysis Code for O5R," ORNL-3856 (September 1966).

D. C. Irving and G. W. Morrison, "PICTURE: An Aid in Debugging GEOM Input Data," ORNL-TM-2892 (May 1970).

D. C. Irving, W. E. Kinney, and P. Rea, "LEGENDRE, A Program to Calculate Legendre Coefficients from Angular Distributions," ORNL-TM-1241 (November 1965).

J. T. Mihalczo, G. W. Morrison, and D. C. Irving, "SOURCE, A Neutron Distribution Routine for the O5R Monte Carlo Code," ORNL-TM-1192 (July 1965).

W. E. Kinney, "Program STATEST, An Application of the Method of Statistical Estimation to the Calculation of Neutron Flux in Anisotropically Scattering Media by Monte Carlo," ORNL-3715 (November 1964).

E. A. Straker and V. R. Cain, "A Note on Subroutine CEASE (O5R:EVAP), A Modification of EVAP in O5R", ORNL-TM-1552 (August 1966).

G. R. Handley and J. N. McLeod, "A Users Manual for HANDY, a Fortran IV Program for
Calculating Numerical Coefficients of the General Second-Degree Equation in Three Variables, Y-1615" (June 1968).

**11. CONTENTS OF CODE PACKAGE**

The package contains the following items: a) the referenced documents, b) sample data sheets
and additional written material, c) one (1.2MB) DOS diskette on which is written in separate files:
the source card decks and input and output for a sample problem, d) a library of cross sections.

**12. DATE OF ABSTRACT**

January 1966, updated July 1981.

**KEYWORDS: ** MONTE CARLO; COMPLEX GEOMETRY; NEUTRON; TIME-DEPENDENT