**RSICC
CODE PACKAGE CCC-754 **

** **

**1. NAME AND TITLE**

VIM 5.1: Continuous Energy Neutron/Photon Transport Code System.

**AUXILIARY
CODES:**

- XSEDIT2 edits or performs binary conversion of processed physics data.
- RETALLY repeats the statistical analysis of tally data, optionally collapsing energy groups and/or spatial regions, or skipping early generations.
- KEFCODE repeats the statistical analysis of keff tallies.
- ISOVIM produces multigroup VIM material files from COMPXS or ISOTXS interface files, or from CASMO ASCII output.
- REBATCH regroups tally records to encompass more generations to permit assessment of serial correlation of reaction rate and flux estimates.
- Slicer, a C++ program, generates color 2D shapshots of a specified VIM geometry.

**2. CONTRIBUTOR**

Argonne National Laboratory, Argonne, Illinois.

**3. CODING LANGUAGE
AND COMPUTER**

VIM5.1 is written in Fortran 90 with a few subprograms in C. The geometry visualization program, Slicer, is written in C++. Machines: Linux PC, Sun, Mac Pro. (C00754/MNYWS/01).

**4. NATURE OF
PROBLEM SOLVED**

VIM is a continuous-energy criticality, reactor physics, and shielding code. It solves the transport problem for neutrons or photons, includes thermal neutron scattering effects, either in the eigenvalue mode or for photon or neutron fixed source. VIM features flexible geometry and neutron physics data carefully constructed from ENDF/B data. Special neutron physics capabilities in VIM include unresolved resonance probability tables, and direct treatment of resolved resonances described with Reich-Moore parameters. It has been extensively benchmarked, using both experiments and other accurate codes.

VIM solves the steady‑state neutron or photon transport problem in any detailed three‑dimensional geometry using either continuous energy‑dependent ENDF nuclear data or multigroup cross sections. Neutron transport is carried out in a criticality mode, or in a fixed source mode (optionally incorporating subcritical multiplication). Photon transport is simulated in the fixed source mode. The geometry options are infinite medium, combinatorial geometry, and hexagonal or rectangular lattices of combinatorial geometry unit cells, and rectangular lattices of cells of assembled plates. Boundary conditions include vacuum, specular and white reflection, and periodic boundaries for reactor cell calculations.

The VIM 5.1 (April 2009) release includes data from ENDF/B-IV, ENDF/B-V, ENDF/B-VI and ENDF/B-VII.0. ASCII data libraries and a convenient means to convert them to binary on a target machine are included.

**5. METHOD OF
SOLUTION**

VIM uses standard Monte Carlo methods for particle tracking with several optional variance‑reduction techniques. These include splitting/Russian roulette, non‑terminating absorption with nonanalog weight cutoff energy. The keff is determined by the optimum linear combinations of two of the three eigenvalue estimates ‑ analog, collision, and track length. Resonance and smooth cross sections are specified pointwise with linear ‑ linear interpolation, frequently with many thousands of energy points. Unresolved resonances are described by the probability table method, which allows the statistical nature of the evaluated resonance cross sections to be incorporated naturally into the representation of self-shielding effects. Neutron interactions are elastic, inelastic and thermal scattering, (n,2n), fission, and capture, which includes (n,γ), (n,p), (n,α), etc. Photon interaction data for pair production, coherent and incoherent scattering, and photoelectric events are taken from MCPLIB. Trajectories and scattering are continuous in direction, and anisotropic elastic and discrete level inelastic neutron scattering are described with probability tables derived from evaluated nuclear data. VIM has an automatic restart capability to permit user‑directed statistical convergence. In eigenvalue calculations, the beginning source sites are from a random (flat) guess, or can be provided via ASCII input, or from a previous calculation. The starting neutrons for each subsequent generation are randomly selected from the potential fission sites in the previous generation.

Track‑length or collision estimates of reaction rates are automatically tallied by energy group and edit region to facilitate comparison to other calculations. Groupwise edits include isotopic and macroscopic reaction rates and cross sections, group‑to‑group scattering cross sections, net currents, and scalar fluxes. Particle pseudo‑collisions are used to estimate microscopic group‑to‑group (n,2n), inelastic, and PN elastic scattering. The serial correlation of eigenvalue estimates is computed to detect underestimated errors.

** **

**6. RESTRICTIONS OR
LIMITATIONS**

The maximum number of isotopes in one calculation is 100. The maximum of splitting surfaces is 60. All other problem characteristics are accommodated by variable dimensioning.

**7. TYPICAL RUNNING
TIME**

Varies widely, depending on geometric complexity, the number of isotopes, application of absorption weighting and splitting, overall scattering ratio, and desired statistics.

**8. COMPUTER
HARDWARE REQUIREMENTS**

VIM was developed on Sun workstations and has been run on PCs (Linux) and Mac Pro.

**9. COMPUTER
SOFTWARE REQUIREMENTS**

VIM5.1 is written in Fortran 90 with a few routines in C. No executables are included in the package. This system was developed on Sun Solaris workstations and was ported to Linux and Mac Pro at ANL. The Mac Pro testing was done with Intel Compiler Version 11 under Darwin 9. VIM was tested at RSICC on an AMD Opteron in 32-bit mode under RedHat Enterprise Linux 4 using the Intel Compiler 10.1.0.018. Modification may be required on other systems. Over 1 GB of disk space is required to expand all of the included cross sections.

**10. REFERENCE**

R. N. Blomquist, "VIM Monte Carlo Neutron/Photon Transport Code User's Guide Version 5.1," Web-based PDF file (March 2009).

**11. CONTENTS OF
CODE PACKAGE**

The package is transmitted on one CD-rom in a Unix tar file which contains installation instructions, Users Guide, Fortran source, data libraries, and test cases.

**12. DATE OF
ABSTRACT**

April 1998, revised December 1998, June 2001, March 2004, March 2009, April 2009.

**KEYWORDS:** COMBINATORIAL
GEOMETRY; REACTOR PHYSICS; CRITICALITY CALCULATIONS; MONTE CARLO; NEUTRON;
GAMMA-RAY; GAMMA-RAY HEATING; WORKSTATION