Numerical simulations are nowadays increasingly used to assess the thermal-hydraulic behavior of a steam boiler instead of carrying out expensive tests in experimental facilities. In the present work, the Relap5/Mod3.2 thermal-hydraulic computer code, which is largely used in the nuclear engineering framework, is used to carry out a tube rupture transient of a high power industrial steam boiler. For this purpose a Relap5 model was developed and qualified at the steady-state conditions using the plant available data. The control and regulation systems are also modeled. The main outcome of this work is a successful application of a thermal-hydraulic system code in predicting the main key parameters of an industrial radiant steam boiler under steady and transient operating conditions. (C) 2013 Elsevier Ltd. All rights reserved.