The Probabilistic System Assessment Group (PSAG) (formerly the Probabilistic System Assessment Code (PSAC) User Group was established in 1985 by the Nuclear Energy Agency (NEA) of the Organisation for Economic Co-operation and Development (OECD). The principal purpose of this group is to further the development in OECD member countries of computer codes for the Probabilistic Safety Assessment (PSA) of radioactive waste disposal systems.