Devices position inspection and operation tools in a nuclear reactor without use of a bridge or other refueling structure well above the reactor core. Devices can selectively join to in-reactor structures like steam dams through clamping that permits limited movement. Clamps can include one or more rollers that allow for controlled, accurate positioning of the devices relative to the structures. Devices include an extension to which the tools can be affixed. Through selective disengagement of joining structures, devices can move over obstacles on the mounting structure. Devices further include controls so that operators positioned outside the reactor can move the device while mounted on a static structure. The controls can further move the inspection tool in other directions with the extension. Devices are useable underwater or submerged in other fluid and may include powering lines or mechanical extensions that permit powering or direct interfacing from operators outside the reactor.