One of the key safety issues for nuclear hydrogen production is the heat transfer tube rupture in intermediated heat exchangers (IHX) which provide heat to process heat applications. This study focused on the detection method and system behaviour assessments during the IHX tube rupture scenario (IHXTR) in the HTTR coupled with IS process hydrogen production system (HTTR-IS system). The results indicate that monitoring the integral of secondary helium gas supply would be the most effective detection method. Furthermore, simultaneous actuation of two isolation valves could reduce the helium gas transportation from primary to secondary cooling systems. The results of system behaviour show that evaluation items do not exceed the acceptance criteria during the scenario. Maximum fuel temperature also does not exceed initial value and therefore the reactor core was not seriously damaged and cooled sufficiently.