Patent Number: 052689409
Section: summary

FIELD AND BACKGROUND OF THE INVENTION The present invention is generally related to the inspection of nuclear reactors and more particularly to an apparatus for inspecting the upper internals containing the control rod guide structures in a nuclear reactor. In nuclear reactors, control rod assemblies are used to control the reactivity of the reactor. The upper internals and control rod guide structures house and guide the control rod assemblies as they are raised from or lowered into the core. The guide structure is generally formed by one or more horizontally positioned plates above the reactor core. A centrally located vertical aperture and radial channels through each plate house and guide the control rods and control rod assemblies. The known spider form of the assemblies passes through the slot-like channels as the rods are raised and lowered. The channels through the plate extend radially relative to the aperture. Each channel is provided with at least one cutout section that forms a C-shape or split tube shape in the channel. During normal reactor operation the control rod assemblies are withdrawn from the core. In this position, a relatively short length of the control rods extends into the core. The hydraulic flow of coolant through the upper internals causes the control rods to vibrate against the horizontal plate of the guide structure. This vibration causes wear of the control rods and horizontal plate, especially at the cutout sections of the channels in the plate. Substantial wear of the guide plate can have an adverse effect on the normal operation of the control rods. Thus, it becomes important to know the extent of wear in the guide structure since proper reactor control is directly related to proper control rod movement. See, for example, U.S. Pat. Nos. 4,728,488, 4,863,678 and 4,902,468. Inspection of this plate presents special problems. The radial channels and central aperture are complex in shape. Difficulty in accessing the plates, radioactive contamination and high radiation levels, and the need for precise inspection measurements preclude a close visual inspection. SUMMARY OF THE INVENTION The present invention addresses the aforementioned problems in a straightforward manner. An inspection device is provided that detects the profile of the support plate in the upper internals, at interface points with the control rods. A probe body is attached to an outer housing support that is used to position the probe body axially for inspection of the upper internals support plate. The probe body is provided with upper and lower inflatable bladder sections that align and secure the probe body in the center of the upper internals support plate. Accordingly, an object of the present invention is to provide an inspection device for the upper internals of a nuclear reactor having a support plate with a central aperture, a plurality of radial channels extending outwardly from the central aperture, and at least one control rod aperture communicating with each channel, the device comprising an outer housing support for raising and lowering a probe body through the central aperture, a probe support connected to the probe body, rotation drive means connected to the probe support and probe body for rotating the probe body. A profile transducer senses the profile of a radial channel in the support plate, transducer drive means is connected between the probe body and the transducer for moving the transducer radially with respect to the probe body, and centering means is connected to the probe body for centering the probe body in the central aperture of the plate. With the probe body lowered by the outer housing support into the central aperture, the rotation drive means is operable to rotate the probe body into a rotational position for moving the transducer radially into one of the radial channels, and the transducer drive means is operable for moving the transducer radially into and along said one of the channels and the rod aperture. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.