| The development of HTGR obliges the usage of nuclear class graphite as essential structure of core reactor, nuclear class graphite requires an in-service inspection of NDT process to determine the declining rate of properties due to the used up amount of time. One of the frequently used NDT methods is ultrasonic method. Yet up to this moment, NDT ultrasonic is merely used limited to metal, and therefore the purpose of this research is to analyze the capability of ultrasonic flaw detector as an in-service inspection for nuclear class graphite. The method used in this measurement is the contact method by using the ultrasonic flaw detector with 2 MHz dan 5 MHz . In this measurement, the capability of ultrasonic flaw detector could be seen from some parameters such as velocity, attenuation, and aslo the maximum propagation distance of ultrasonic flaw detector to nuclear class graphite. The results of this measurement shows that the ultrasonic flaw detector may be well-functioned for the nuclear class graphite in the velocity of 2450 m/s and the attenuation of 0,93 dB/mm. Beside that, the simulation result shows that the maximum propagation distance of the ultrasonic flaw detector may only reach up to the distance of 50 mm with the intensity of 31,5 dB for frequency 2 MHz and 49,5 dB for frequency 5 MHz. |