The core simulator supported by the USNRC and used throughout the world. Originally developed for analysis of LWRs, recent improvements have allowed the modeling of HWRs, Hexagonal LWRs, Graphite moderated reactors, and Gas reactors (Cylindrical & Hexagonal Geometries).


The U.S. DOE CASL project and the University of Michigan are the primary sponsors for the development of the MPACT code. The underlying approach is an MOC method for high fidelity 2-D or 3-D transport simulations of a reactor core.  Aggressive development is ongoing and upcoming features include coupled TH feedback, depletion, and multiphysics modeling applications.


The USNRC, in anticipation of gas reactor licensing, supported the development of AGREE. Both Pebble and hexagon block type gas reactors can be modeled with AGREE. Several HTR benchmarks have been completed with the code, which shows good agreement with other gas reactor system codes. Development has slowed somewhat, but maintenance continues.


The PARCS code utilizes a so-called PMAXS cross section library. The GenPMAXS code converts the output of various lattice level transport codes to the PMAXS format. Currently supported outputs include: TRITON (ONRL-SCALE), HELIOS (Studsvik), CASMO (Studsvik), SERPENT (Finland-VTT), CONDOR (Argentina – INVAP), WIMS (Canada-AECL)

Testing is underway for the future release of the POLARIS lattice physics code, which is being developed for the USNRC by ORNL.


PARCS utilizes a 4-equation hydraulic feedback module for steady state BWR analysis. This code is benchmarked against experimental data and compared to TRACE. Originally developed for BWR depletion analysis, development continues for tight-pitch BWR cores, hexagonal geometry, and improved TWPS water tables. Planned development will expand PATHS to PWRs and VVERS as well.


Development of DeCART has generally stopped in favor of MPACT. DeCART is now used principally to provide results for testing MPACT. This DeCART code is not associated with the versions found at KAERI or ANL.