**1. NAME AND TITLE**

TIMOC-72: Monte Carlo Three-Dimensional Neutron Transport Code System.

**AUXILIARY ROUTINES**

CODAC-2: ENDF Format to TIMOC Format Data Generator.

PLOTGEOM: Geometry Diagnostic Display.

GEOM: Optional Geometry Routines.

RN: Random Number Generator Package.

TIMOC and CODAC were originally packaged in 1970; with a complete replacement in RSIC in 1972. ENDF/B-III data are used in this version and, other the sample problem input, must be supplied by the user.

**2. CONTRIBUTOR**

Euratom, Ispra, Italy through the OECD NEA Data Bank, Gif-sur-Yvette, France.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; IBM 360/370. Some library and other routines in Assembler are included.

**4. NATURE OF PROBLEM SOLVED**

TIMOC-72 solves the energy- and time-dependent (or stationary) homogeneous or inhomogeneous neutron transport equation in three-dimensional geometries. The program can treat absorption and all commonly used scattering kernels, such as: fission, isotropic and anisotropic scattering, level excitation, the evaporation model, and the energy transfer matrix model, which includes (n,2n) reactions. The exchangeable geometry routines consist of: (a) periodical multilayered slab, spherical, and cylindrical lattices; (b) an elaborate three-dimensional cylindrical geometry, which allows all kinds of subdivisions; and (c) the flexible 05R geometry routine which is able to describe any body or body combinations with surfaces of second order.

The program calculates the stationary or time-, energy-, and region-dependent fluxes as well as the transmission ratios between geometrical regions and the following integral quantities or eigenvalues: the leakage rate, the slowing down density, the production to source ratio, the multiplication factor based on flux and collision estimator, the mean production time, the mean destruction time, time distribution of production and destruction, the fission rates, the energy dependent absorption rates, and the energy deposition due to elastic scattering for the different geometrical regions.

A special option allows the calculation of geometrical perturbation effects. In such calculations the differential effect does not depend on the total variance of the considered quantity. The sampling of these differential effects is based on the method of similar flight paths.

CODAC-72 converts ENDF/B data into group-averaged cross sections in the form needed by
Monte Carlo codes. It generates the mean values of sigma_{EXP}, sigma_{el}, sigma_{in}, sigma_{fiss}, and nu for
any group structure by using specified weighting spectra. In the case of anisotropic elastic
scattering either the average cosine (mu) or the angular distribution function dsigma(mu)/dmu is
calculated for each energy group. The inelastic scattering is described by a transfer matrix which
can also include (n,2n) reactions.

**5. METHOD OF SOLUTION**

TIMOC, Monte Carlo method, uses several partially optional variance reducing techniques, such as: the method of expected values (weight factor), Russian Roulette, the method of fractional generated neutrons, double sampling, semi-systematic sampling, and the method of expected leakage probability. The neutron histories are assigned a discrete energy value after each collision process. The nuclear data input is done, however, by group-averaged cross sections.

The program can generate the neutron fluxes either resulting from an external source or in the form of fundamental mode distributions by a special source iteration procedure. In this latter case, the calculations of eigenvalues are based on the life-cycle concept.

TIMOC is linked to the ENDF/B data file via CODAC, which generates, for any desired group
structure, the nuclear parameters and group-averaged cross sections needed. Averaging is done by
using a weighting spectrum to be input. Group-averaged cross sections are calculated by summing
up the smooth contributions and the contributions of the resolved and unresolved resonances, using
the methods of the ETOG-ETOM codes and of MC^{2} at zero temperature. Anisotropic elastic
secondary angular distribution is calculated optionally as mu_{Lab}, Legendre expansion, or point by
point along the mu-axis. The inelastic secondary energy distribution is computed as transfer
matrix.

Anisotropic elastic scattering secondary angle distribution can optionally be calculated in three different ways: as Legendre expansion in the c.m. system, point by point along the mu-axis in the c.m. system, as averaged cosine in the lab system. In calculating, nearly isotropic scattering is assumed in and below the resonant region.

**6. RESTRICTIONS OR LIMITATIONS**

The following limits apply:

In TIMOC: number of energy groups < 50, number of isotopes < 20, number of mixtures < 20.

CODAC will handle any number of ENDF/B materials during one run. The number of energy groups is limited to 50. The output formats of CODAC correspond to the input formats of TIMOC.

**7. TYPICAL RUNNING TIME **

The running of TIMOC depends very much on the problem tested and to some extent on the options specified.

Estimated running time of the packaged sample CODAC problem: GO STEP on the IBM 360/75, 85 seconds.

**8. COMPUTER HARDWARE REQUIREMENTS**

The codes were originally designed for the IBM 7090 and were converted to run on the IBM 360 series.

CODAC is built in an overlay structure where it requires 155,600 bytes (38,900 words) on the 360/65. Without overlay, 221,400 bytes (55,350 words) are necessary. It requires two I/O devices for reading and printing, one I/O device for the ENDF/B library tape, and one on which the TIMOC library is written. One additional I/O device is necessary if the program is loaded from tape.

**9. COMPUTER SOFTWARE REQUIREMENTS**

The codes are operable on the IBM 360/75/91 Operating System using an OS-360 FORTRAN H compiler and the overlay feature. A library of ENDF cross sections is required. The package includes only those elements needed by the sample problem; data taken from the ENDF master files.

**10. REFERENCES**

R. Jaarsma and H. Rief, "TIMOC 72 Code Manual," EUR-5016.e (1973).

H. Kschwendt and H. Rief, "TIMOCA General Purpose Monte Carlo Code for Stationary and Time Dependent Neutron Transport," EUR-4519.3 (1970).

F. Beonio-Brocchieri and C. Daolio, "CODAC 2, A New Version of the CODAC Code Which Accepts ENDF/B Data for the Production of a Few Group Library for TIMOC," EUR/C-IS/81672e (1972).

H. Krainer, "CODAC, A FORTRAN IV Programme to Process a TIMOC Library from the ENDF/B File," EUR-4521.e (1970).

**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, and library routines in Assembler.

**12. DATE OF ABSTRACT**

February 1972; revised August 1982.

**KEYWORDS: ** MONTE CARLO; COMPLEX GEOMETRY; NEUTRON