Abstract: An inspection system for detecting leakage from for example the primary vessel (11) of a nuclear reactor includes a camera (29) carried by an umbilical cable (28) which can be fed through a duct assembly (22) comprising a series of tubular sections (23) connected endwise by flexible bellow (24). A guide track (18) extends around the top of the vessel (11) and each duct section (23) is provided with wheels (25) which engage the track (18). A curved guide tube (17) feeds the duct sections (23) from a vertical entry position (15) in the roof (13) into a horizontal track-engaging disposition. The track (18) includes spaced flanges (20b, 21b) through which the umbilical cable can extend and depend downwardly into the annular space between the primary vessel (11) and a surrounding guard vessel (12).