[en] The safety assessment and licensing of nuclear reactor plants by the United States Nuclear Regulatory Commission (USNRC) depend partially on analytical computer programs to predict the response of safeguard systems to accident conditions. CONTEMPT4/MOD2 is a new computer code to predict the long-term thermal hydraulic behavior of water-cooled nuclear reactor containment systems during postulated loss-of-coolant accident (LOCA) conditions. Written in FORTRAN IV, the new code was developed at the Idaho National Engineering Laboratory by EG and G Idaho, Inc., under the sponsorship of the USNRC. The paper describes the features and analytical models available in the code. Comparisons of calculated results with experimental data are also presented which demonstrate the range of containment problems applicable to CONTEMPT4/MOD2