Joint International Topical Meeting on Mathematics & Computation and Supercomputing in Nuclear Applications (M&C + SNA 2007) Monterey, California, April 15-19, 2007, on CD-ROM, American Nuclear Society, LaGrange Park, IL (2007) UNÌC: Ultimate Neutronic Investigation Code G. Palmiotti, M. Smith, C. Rabiti, M. Leclere Nuclear Engineering Division D. Kaushik, A. Siegel, B. Smith Mathematics and Computer Science Division Argonne National Laboratory 9700 South Cass Avenue Argonne, Illinois 60439 E. E. Lewis Northwestern University Department of Mechanical Engineering Evanston, Illinois 60208 Email contact: GPalmiotti@anl.gov ABSTRACT A code called UNÌC is currently under development at Argonne National Laboratory (ANL). The aim of the code is to provide a neutronic solver with the same geometrical flexibility of Monte Carlo codes and without the approximations (homogenization and energy condensation) associated with the common multi-step approach currently used. Moreover, UNÌC will offer the capability of multi-resolution in phase space. At the moment, two methodologies are implemented: a second order spherical harmonics (P N ) form of the transport equation and the first order method of characteristics. To improve overall performance (per-processor and scalability to thousands of processors) and reduce memory requirements, we are developing some specialized implementations of key PETSc preconditioners and matrix objects. Key Words: neutronics, P n , method of characteristics, PETSc 1. INTRODUCTION Current neutronics analysis requires two or more homogenization and energy group collapsing steps. Typically, the first step involves a local calculation to obtain the spectral self-shielding for the individual pin. The second step requires an assembly-level calculation to obtain the spectral self-shielding for each assembly and to produce homogenized parameters for each unique assembly in the reactor. These assembly-level cross sections are then used in a whole-core diffusion or transport calculation to obtain the flux solution for a targeted reactor system.