FONESYS (Forum & Network of SYS-TH Codes in Nuclear Reactor Thermal-Hydraulics) is a Network for cooperation among developers of system thermal-hydraulics codes adopted worldwide for nuclear reactor analysis.

Network connects Institutions and Organizations that are involved in the development and the application of SYS-TH codes to support the Best Estimate Plus Uncertainty safety assessment and the design of water-cooled nuclear reactor.

Network has been created to strengthen the current technology, cooperate and share recent advances, identify and discuss further ways of improvements in SYS-TH code development.

The San Piero a Grado Nuclear Research Group (GRNSPG) of the University of Pisa serves as Host Institution for FONESYS.

The company N.IN.E. Nuclear and Industrial Engineering (NINE) provides administrative support for the operation of FONESYS.