MCNPX version 2.5.0 is currently available from RSICC, The Radiation Safety Information Computational Center at Oak Ridge national Laboratory. It will soon be available from OECD/NEA, The European Community Organization for Economic Cooperation and Development / Nuclear Energy Agency.
For code access, contact RSICC or OECD/NEA for copies.
MCNPX is under active development and newer versions are available to beta testers under a beta test agreement. Those wishing access to the beta testing program should contact the MCNPX team, mcnpx@lanl.gov, for information.
Beta testers can access the code by using Beta Release access.
For sponsors and MCNPX developers, intermediate developmental versions are available. Developers can access the code by using developer access.