Patent Number: 054835615
Section: description

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, an inspection apparatus 1 is shown. The apparatus includes a probe tube 2 having a diameter sufficient to pass through an opening of about 3 inches. The tube 2 has a pair of tapered ends 3 and 4. The tapered ends minimize binding when the tube is lowered or raised into a reactor internals package. The probe is substantially hollow and has a radial opening 5. The tube is hollow to allow passage of a signal wire 6 therethrough. The signal wire is attached at one end to a detection means 7 located in a distal end of the tube, adjacent to the opening 5. The detection means may comprise any sensor capable of detecting an improper connection to a fuel assembly or other internal structures in a nuclear reactor. Preferably, the detection means is one or more ultrasonic transducers, preferably two, which will operate in the frequency range of about 200 kilohertz and which are capable of operating in an environment of 30,000 rad for a period of several hours. The transducer should be designed to operate in an underwater environment and have a capability for locating an entanglement within 1 inch .+-. in a 12 foot diameter core. Such transducers are quite small, allowing an initial inspection to be undertaken when the package is lifted by from about 2-12 inches, well before serious damage could occur. The signal wire 6 exits the tube at the proximal end 4 and is of sufficient length to extend away from the nuclear reactor to a remote monitoring means. Preferably, the signal wire passes in conjunction with a cable 8 used to raise or lower the inspection apparatus. The cable may optionally be connected to a winch or other means for raising or lowering the inspection apparatus, though it may be lowered by hand. The signal wire 6 separates from the cable 8 at a termination box 9 with the signal wire connected to a monitoring means 10. With an ultrasonic transducer, an oscilloscope or other comparable device may be used to determine if there is an entanglement of a fuel assembly to a member being lifted. Included with the cable are means for rotating the inspection apparatus while in the inspection position. A hand wheel 11 incorporating a degree scale 12 is attached to the cable 8 and coordinated with the radial opening by a mark 13 such that a visual indication is obtained of the initial position of the radial opening. If, during rotation, an improper entanglement is detected, its location is precisely determined by reference to the degree scale and steps can be taken to disentangle the fuel assembly from the structure. Referring to FIG. 2, the apparatus is shown in an inspection position. A nuclear reactor 14 has a vessel 15, with a reactor core 16 disposed therein. Above the core is disposed an internals package 17. This may comprise various structures such as baffles or other devices, and the term "Package" is herein defined as any structures disposed above the core which may require periodic removal. These devices are attached to an upper flange 18 which rests on the containment vessel flange 19. To remove the package, the upper flange is lifted along guides 20, as shown. During this lifting process, it is possible that a fuel assembly will become entangled with the upper internal structure and be damaged during removal. Previously, it was necessary to raise the upper internals package above the reactor flange so a camera could be used to determine if an assembly was entangled. However, this distance of lift could cause damage before the entanglement is detected. Thus, such an inspection is inadequate. In this instance, the internal package has been partially raised about 12 inches. Once raised, the inventive apparatus is inserted through a passage 21 in the internal structure. For example, such an internal package typically includes a central drive shaft and after the shaft has been removed, the inventive apparatus can be disposed within the passage provided for that shaft. The tube 2 is lowered into the passage 21 via the cable 8 until the portion of the tube containing the radial opening 5, passes through a lowermost surface 22 of the internals package. Preferably, the cable includes a stop 23 which is a flat disk or plate which may be located, based on the length of the internals package, to assure that the radial opening exits the upper internal assembly bottom plane and maintains the tube in that position during subsequent rotation. This stop can be a clamp type device which is adjustable for different reactor internal assemblies or, if the package is of a standard depth, can be a disk or plate permanently affixed to the cable. The hand wheel 11 and the degree scale 12 are located above the top portion of the internals package so that it can be manipulated by hand. The signal cable 6 which exits the termination box 9 is connected to a detection device 10 such as an oscilloscope. At that time, the sensor is activated and the tube rotated a full 360.degree.below the internals package. If an ultrasonic transducer is used, this transducer will detect whether there is a metallic object disposed between the opening 5 and the vessel wall which would normally indicate that a fuel assembly 24 has become entangled and is being raised with the internals package. If such a signal is detected, the degree scale is consulted to determine where the hangup has occurred and the exact fuel assembly involved and steps are taken to disentangle the assembly before further lifting is attempted. If a decision is made to continue with the lift, the invention can be used periodically to determine if the assembly has disengaged at any time during the lift. If, after rotation, it is determined that there has been no hangup, the inspection apparatus is removed and the upper internals package is then lifted completely from the vessel. The cable is preferably a hollow core stainless steel torque resistant flexible cable of a fixed length such that the signal wire can pass through the cable to prevent damage to the delicate signal wire. Additionally, the probe can have a pair of screw type caps forming the tapered ends at both the proximal and distal portions to allow access to the sensor for removal and/or replacement. The tube and tapered portions are also preferably composed of stainless steel and weighted at the lower end to maintain an axial alignment within 1.degree.of the vertical to assure transducer report accuracy. The tube preferably has a diameter of about 2 inches and a length of about 3 feet to better control alignment of the probe during use and to prevent hang up inside the package. While a preferred embodiment of the present invention has been shown and described, it will be understood by those skilled in the art that various changes or modifications could be made without varying from the scope of the invention.