4. Radiation Shielding

Introduction by D. E. Peplow and B. T. Rearden

The Monaco with Automated Variance Reduction using Importance Calculations (MAVRIC) fixed-source radiation transport sequence is designed to apply the multigroup and continuous energy fixed-source Monte Carlo code Monaco to solve problems too challenging for standard, unbiased Monte Carlo methods.i The intention of the sequence is to calculate fluxes and dose rates with low uncertainties in reasonable times even for deep penetration problems. MAVRIC is based on the Consistent Adjoint Driven Importance Sampling (CADIS) methodology, which uses an importance map and biased source that are derived to work together. MAVRIC generates problem-dependent cross section data and then automatically performs a coarse mesh 3D discrete ordinates transport calculation using Denovo to determine the adjoint flux as a function of position and energy. MAVRIC then applies the information to optimize the shielding calculation in Monaco. In the Forward-Weighted CADIS (FW-CADIS) methodology, an additional Denovo calculation is performed to further optimize the Monaco model to obtain uniform uncertainties for multiple tally locations. Sources can be input using many spatial and energy distributions, or they can be imported from a previously generated mesh file. Responses can be generated from cross section reaction rates, flux-to-dose conversion factors, or user-defined functions; responses are tallied on geometry regions, Cartesian or cylindrical grids, or as point detectors.

MAVRIC enables users to import spent fuel isotopics from ORIGEN binary concentrations files such as those generated with ORIGAMI and to import gamma emission spectral data directly from the ORIGEN nuclear data files to streamline analysis and reduce the opportunity for human error.

Several utility modules are also provided for data introspection and conversion.