Woodruff School of Mechanical Engineering

NRE 8011/8012 and MP 6011/6012 Seminar

Nuclear & Radiological Engineering and Medical Physics Programs




Dr. Scott Mosher


Reactor/Nuclear Systems Division (ORNL)


Thursday, March 17, 2011 at 11:00:00 AM


Boggs Building, Room 3-47, 3rd FL




Current “state-of-the-art” tools and methods used to perform commercial reactor analyses have several undesirable features, the most significant of which is the non-rigorous spatial decomposition scheme. Monte Carlo methods, which allow detailed and accurate modeling of the full geometry and are considered the “gold standard” for radiation transport solutions, are playing an ever-increasing role in correcting and/or verifying the deterministic, multi-level spatial decomposition methodology in current practice. However, the prohibitive computational requirements associated with obtaining fully converged, system-wide solutions restrict the role of MC to benchmarking deterministic results at a limited number of state-points for a limited number of relevant quantities. The goal of this research is to change this paradigm by enabling the direct use of MC for full-core reactor analyses. The most significant of the many technical challenges that must be overcome are the slow, non-uniform convergence of system-wide MC estimates and the memory requirements associated with detailed solutions throughout a reactor (problems involving hundreds of millions of different material and tally regions due to fuel irradiation, temperature distributions, and the needs associated with multi-physics code coupling). To address these challenges, our research has focused on the development and implementation of a hybrid deterministic/MC method for determining high-precision fluxes throughout the problem space in k-eigenvalue problems and an efficient MC domain-decomposition (DD) algorithm that partitions the problem phase space onto multiple processors for massively parallel systems. The presentation will provide a review of hybrid methods at ORNL for fixed-source calculations, extension of the hybrid methods for reactor analyses, and the MC DD algorithm and implementation within a new MC code.


Dr. Scott Mosher is an R&D Staff Member in the Radiation Transport Group of the Reactor and Nuclear Systems Division at the Oak Ridge National Laboratory. Scott received his Bachelors, M.S., and Ph.D. degrees in Nuclear Engineering from Georgia Tech. His Ph.D. dissertation, advised by Dr. Rahnema, was entitled, “A Variational Transport Theory Method for Two-Dimensional Reactor Core Calculations.” His thesis described the development and implementation of a heterogeneous coarse-mesh transport method for the calculation of the neutron flux distribution in large-scale, two-dimensional models of nuclear reactor cores. After graduation, Scott joined the Computational Physics Group at Los Alamos National Laboratory in 2004. At LANL, Scott performed research on non-linear thermal X-ray transport and contributed to a parallel Monte Carlo code system for the same. Since joining ORNL in 2008, Scott has been involved in research on hybrid (Monte Carlo / deterministic) transport methods for shielding and radiation detection applications. He is the current lead developer of the ADVANTG code system, which automates the generation of variance reduction parameters for use in MCNP/MCNPX simulations. In recent work, Scott is leading an internally-funded research project to extend ORNL’s hybrid methods to eigenvalue transport problems in reactor applications.