**1. NAME AND TITLE**

TIMEX: One Dimensional, Time Dependent Multigroup Explicit Discrete Ordinates Radiation Transport Code System with Anisotropic Scattering.

**DATA LIBRARY**

CRD: Critical Radius Data (for sample problems 3 and 5, CDC-7600).

TIMEX was initially packaged in 1976 (A and B versions); was converted to run on the UNIVAC in 1982 (C); the CRAY version was added in 1983 (D). ONETRAN (CCC-266) may be utilized to provide compatible initial conditions to TIMEX.

**2. CONTRIBUTORS**

Los Alamos Scientific Laboratory, Los Alamos, New Mexico (A, B, D).

Ciudad University, Madrid, Spain (C).

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; IBM 360/370 (A), CDC 7600 (B), UNIVAC 1106 (C), and CRAY (D).

**4. NATURE OF PROBLEM SOLVED**

TIMEX solves the time-dependent, one-dimensional multigroup transport equation with delayed neutrons in plane, cylindrical, spherical, and two-angle plane geometries. Both regular and adjoint, inhomogeneous and homogeneous problems subject to vacuum, reflective, periodic, white, albedo or inhomogeneous boundary flux conditions are solved. General anisotropic scattering is allowed and anisotropic inhomogeneous sources are permitted.

**5. METHOD OF SOLUTION**

The discrete ordinates approximation for the angular variable is used with the diamond (central) difference approximation for the angular extrapolation in curved geometries. A linear discontinuous finite element representation for the angular flux in each spatial mesh cell is used. Negative fluxes are eliminated by a local set-to-zero and correct algorithm. The time variable is differenced by an explicit technique that is unconditionally stable so that arbitrarily large time steps can be taken. Because no iteration is performed, the method is exceptionally fast in terms of computing time per time step. Two acceleration methods, exponential extrapolation and rebalance, are utilized to improve the accuracy of the time differencing scheme.

Provision is made for creation of standard interface output files for angular fluxes and angle-integrated fluxes. Standard interface input files for Sn constants, inhomogeneous sources, cross sections, and initial angular fluxes may be read.

**6. RESTRICTIONS OR LIMITATIONS**

Variable dimensioning is used so that any combination of problem parameters leading to a container array less than MAXCOR can be accommodated. On CDC machines MAXCOR can be about 25,000 words and peripheral storage is used for most group-dependent data.

**7. TYPICAL RUNNING TIME**

The running time for TIMEX is highly problem-dependent but varies almost linearly with the total number of unknowns and time steps. A 16-group 30 interval mesh requires 4 1/2 minutes on the CDC 7600 for 200 times steps.

**8. COMPUTER HARDWARE REQUIREMENTS**

Five interface units (optional), five output units, and two system input/output units are required. A large bulk memory is desirable, but may be replaced by disk, drum, or tape storage.

**9. COMPUTER SOFTWARE REQUIREMENTS**

Software used for versions A-D: (A) IBM FORTRAN H compiler, (B) CDC RUN compiler, (C) UNIVAC FORTRAN IV compiler, and (D) the LLNL CTSS operating system, using the CFT FORTRAN compiler. Modification to the dynamic memory management is probably required for CRAY facilities using the COS (CRAY Operating System).

**10. REFERENCES**

CRAY ONETRAN and TIMEX Codes (informal note).

T. R. Hill and W. H. Reed, "TIMEX: A Time-Dependent Explicit Discrete Ordinates Program for the Solution of Multigroup Transport Equations with Delayed Neutrons," LA-6201-MS (February 1976).

TIMEX Test Problem Set (informal document).

**11. CONTENTS OF CODE PACKAGE**

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

**12. DATE OF ABSTRACT**

November 1981; revised September 1983, December 1983, January 1984, January 1985.

**KEYWORDS: ** ONE-DIMENSION; TIME-DEPENDENT; MULTIGROUP; DISCRETE
ORDINATES; CYLINDRICAL GEOMETRY; SPHERICAL GEOMETRY;
ADJOINT; ALBEDO