Positioning and inspection apparatuses for use in nuclear reactors

Devices position inspection and operation tools in a nuclear reactor without use of a bridge or other maintenance structure well above the reactor core. Devices can selectively join to in-reactor structures like steam dams through clamping that permits limited movement. Positioning assemblies may be supported by the devices. The positioning assembly includes a mast that moves relative to the positioning assembly. Rollers of the positioning assembly may so move the mast. The positioning assembly may be rotated with a sun gear having an exterior surface about which the mast and rollers can revolve. A local motor or external drive may provide power for this rotation and/or revolving as well as rotation of the rollers to move the mast and assembly. Devices are useable underwater or submerged in fluid and may include instruments with powering lines or mechanical extensions that permit powering or direct interfacing from operators outside the reactor.