Patent Number: 051568039
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to reactor vessels with a reactor core enclosed in a core shroud and more particularly, to an apparatus for inspection of a reactor vessel. Inspection of the interior of a reactor vessel typically includes the systematic inspection of weld joints in the reactor vessel and pipe sockets etc. Usually, an end effector comprising inspection members in the form of, for example, cameras, ultrasonic probes or the like is moved into the reactor vessel with the aid of special devices. These devices generally include a trolley, which is movable on the exposed upper flange of the vessel, provided with traversing wheels and a drive means. The trolley supports a support mast which is immersed into the reactor vessel substantially parallel to the vertical axis of the reactor vessel. The support mast supports the end effector which may be moved with the aid of a drive member. The device disclosed in U.S. Pat. No. 4,585,610, is well known in the art and includes a trolley with three or four wheels, which supports a support mast centrally insertable in the reactor vessel. Inspection of the vessel wall weld joints is accomplished by means of ultrasonic probes, which make contact with the vessel wall. However, the inspection depth is often limited by reactor components located at the wall of the vessel such as feed water spargers and/or core spray spargers which are not normally dismantled during inspection. Consequently, using this inspection technique weld joints and reactor components located towards the bottom portion of the reactor vessel are not accessible to inspection. It is also well known in the art to place the ultrasonic probes on an extension mast which is fixed to the lower part of the support mast and movable in the radial direction of the vessel. However, the support mast is lowered into the reactor vessel at such a large distance from the its wall that the support mast and the extension mast clear the feed water spargers. When the extension mast has cleared the spargers, the extension mast, by means of the trolley, is moved radially towards the vessel wall below the feed water spargers and also below any core spray spargers which may exist. Although this technique permits a certain increase in the available inspection depth, the inspection depth is limited by the fact that the extension mast cannot be made longer than the axial distance between the feed water spargers and the core shroud cover. In order for the extension mast of this conventional system to clear the feed water spargers, the extension mast must protrude within the annular space formed by the projection of the core shroud cover and the vessel wall. However, the extension mast can only be inserted into the reactor vessel to a point where it contacts the core shroud cover. Therefore, particularly in reactor vessels in which the distance between the core spargers and core shroud cover is relatively short, the space between the reactor vessel and the core shroud which is available for inspection is limited with use of the conventional inspection system. It is therefore an object of the present invention to provide an apparatus for inspection of a reactor vessel which is capable of being inserted into the lower portion of the annular space between the core shroud and the wall of the reactor vessel. It is also an object of the present invention to provide a reactor inspection apparatus which enables inspection of a greater area of the reactor vessel by providing for increased radial, tangential and axial movement of the end effector relative to the reactor vessel wall. SUMMARY OF THE INVENTION The aforementioned objects and advantages are achieved through use of the apparatus for inspection of a reactor vessel in accordance with the present invention. Compared with prior art devices, a device according to the present invention may increase the accessible part of the length of those weld joints which are positioned below the feed water spargers. The apparatus for inspection of a reactor vessel includes a support mast, a trolley for supporting the support mast to the wall flange of a reactor vessel and transporting the support mast along the inside side wall of the reactor vessel, an extension mast capable of vertically extending below the support mast, the extension mast being translated by means of a second trolley engaged between the extension mast and the support mast, an end effector means connected to the lower portion of the extension mast for inspecting the reactor vessel wall, and a tilting device connected to the support mast for varying the angle between the support mast and the reactor vessel wall. The tilting device may include an arm attached to the support mast, the arm being capable of being radially moved by a means for altering the angle between the support mast and the vessel wall. The means may include a compressed air cylinder. The tilting device may also include a support wheel connected to the arm for contacting the reactor vessel wall. The end effector may include a main frame, an upper drive device connected to the main frame, a lower drive device also connected to the main frame, a horizontal trolley affixed to a rack operatively connected to the upper drive device and capable of tangential movement relative to the main frame, a probe position trolley affixed to the horizontal trolley, and a probe holder capable of securing ultrasonic probes affixed to the probe position trolley by a shaft. The end effector may also comprise means for unlocking the probe holder from the probe position trolley to allow relative movement between the probe holder and probe position trolley. The means may include means for activating a spring loaded locking pin interfaced with the shaft, and a lower drive device adapted to rotate the probe position trolley around the shaft to unlock or lock the shaft from the horizontal trolley. The upper drive device may include an electric motor, a gear box operatively engaged with the motor, and a chain transmission means operationally engaged to the gear box and one or more gear wheels to displace the rack in the tangential direction. The apparatus may further include a support arm connecting the end effector means to the extension mast, a spring loaded bearing connecting the support arm to the extension mast for continuously applying a torque forcing the end effector means in a direction radially towards the reactor vessel wall, and means for forcing the end effector means in a direction radially opposite the reactor vessel wall. The means may be a compressed air cylinder. The apparatus may also include a locking pin affixed to the main frame and insertable into an aperture located on a front plate of the probe position trolley wherein the probe position trolley may be locked to the main frame when the pin is inserted into the aperture. Also, a rope affixed to the horizontal trolley and passing through a hole in an output shaft of the gear box of the upper drive device may be included, wherein applying a tension to the rope enables the horizontal trolley to be moved to a central position. The apparatus may further include a tangential direction fine positioning system and/or a radial direction fine positioning system comprising a rotatable member affixed to the trolley. The tangential direction fine positioning system may include a positioning arm pivotably affixed to the lower portion of the support mast, means for pivotably moving the position arm in an axial direction, and a distance measuring device affixed to the positioning arm for measuring the distance to a lug on the shroud of the reactor. The means may include a compressed air cylinder. The radial direction fine positioning system may include a nozzle within the member capable of radially displacing a beam relative to the member, the nozzle being affixed to the support mast. The apparatus may further include a simulation block located at the lower portion of the support mast for verifying the accuracy of probe on the probe holder. The apparatus, with the simulation block, may also include an arm pivotably affixed to the support mast, means for pivotably moving the arm from a retracted position to a verification position, and a simulation block holder located at the end of the arm for supporting the simulation block. The means may include a compressed air cylinder to cause the arm to extend into the verification position such that the simulation block will interface with the probes of the end effector for verification of the probes. The end effector may comprise a horizontal trolley for movement of the inspection members in a tangential direction in relation to the extension mast. This is particularly advantageous in those cases where, for example, jet pumps are placed in the gap between the reactor vessel and the core shroud since it makes possible inspection of at least parts of those weld joints which are situated between the jet pumps and the vessel wall. Other advantageous further developments of the invention will be clear from the following description and the appended claims.