VIM, 3-D Monte-Carlo Analysis of Fast Critical Assemblies Using Point Cross-Sections

1 - Description of problem or function: VIM solves the three- dimensional steady-state multiplication eigenvalue or fixed source neutron or photon (VIM2/15) transport problem using continuous energy-dependent nuclear data. It was designed for the analysis of fast critical experiments. In VIM2/15, the photon interactions i.e., pair production, coherent and incoherent scattering, and photoelectric events, and photon heating are tallied by group, region, and isotope. 2 - Method of solution: VIM uses the Monte Carlo technique to estimate eigenvalues by collision, track length, and analog methods. Geometry options include infinite medium, plate cell lattice, general combinatorial geometry, and repeating lattices of hexagonal or rectangular cells constructed using combinatorial geometry. ENDF/B cross section data are used, including thermal scattering law data. Variance reduction options available include several splitting and Russian roulette techniques, any linear combination of analog and absorption neutron weighting, and combined eigenvalue estimators. An easy-to-use restart option is also available. In VIM2/15, photon cross sections are defined by composition independent microscopic datasets in the energy range from 1 KeV to 100 MeV. Coherent and incoherent scattering, pair production, and photoelectric cross section data are described by pointwise values with log-log interpolation. Photon heating numbers are specified pointwise with linear-log interpolation. Pair production is simulated by creation of a double-weighted photon of energy 0.511008 MeV, and production by fluorescence is treated explicitly. The Klein-Nishina distribution is sampled exactly for secondary angle and energy during incoherent scattering events. 3 - Restrictions on the complexity of the problem - Maximum of: 40 isotopes