A fission gas sampling device for selectively locating leaking TRIGA reactor fuel elements was developed. The device, and the associated scintillation spectrometer, measures the radioactivity of the particulate daughter products of the fission gases escaping from a single failed fuel element. Details of the design of the device and the operating procedures are described. Several different approaches for locating faulty elements were evaluated and the most suitable one was used to locate a fuel element cladding break in the TRIGA reactor of the University of Texas at Austin.