Patent Number: 044329318
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to a remote visual inspection system for certain areas of vessels which are not accessible for inspection by personnel. It particularly relates to the inspection of a storage arrangement wherein there is a primary vessel for containing a fluid and an outer vessel, generally referred to as the containment vessel, which surrounds the primary vessel to prevent loss of fluid in the event of a rupture or leak in the primary vessel. There are many reasons why a primary vessel containing a fluid would be contained within a secondary containment vessel. For example, if the fluid is hazardous or dangerous to the environment, the secondary vessel acts to catch and retain the fluid in the event of a leak. In addition, when the primary vessel contains a fluid which is at an extreme temperature, for example, either a cryogenic fluid or a high temperature fluid such as would be found in a nuclear reactor, the space between the primary and secondary vessels acts to provide insulation and minimize the loss of heat from the primary vessel to the environment. A nuclear reactor presents a particularly difficult inspection problem since the space between the two vessels is at a relatively high temperature, generally 200.degree. C. or more. In addition, the space between the primary and secondary vesels generally is maintained at a minimum. In the event of a rupture in the primary vessel, the fluid would drain into the area between the two vessels. This could create an extremely dangerous situation if the fluid level in the primary vessel became so low as to expose the reactor core. If the core were exposed, it would not receive sufficient convection coolant, with the result being fusion of the core. Thus, if the space between the two vessels is not maintained relatively small to prevent this possibility, the alternative is to maintain an extremely large inventory of coolant in the primary vessel. To ensure continued safe operation of, for example, a nuclear reactor, periodic inspection at least of the primary vessel outer wall is required. While various methods have been proposed for inspection of the interior of vessels, very few systems or methods are known for inspecting the narrow annulus that generally exists between a primary vessel and a containment vessel, particularly at the operating temperatures encountered in a nuclear reactor. In addition to being able to inspect the interior of such an annulus, it also is necessary to know at all times precisely where the visual inspection device is located in order to compare subsequent inspections with those made earlier when it was known that the structural integrity of the vessel was intact. Further, it generally is desired, particularly in the case of nuclear reactors, that there be no penetration in the containment vessel at any level below that of the uppermost portion of the reactor core, the reason for this being obvious in that any such penetration represents another potential failure point in the system. Accordingly, it is an object of the present invention to provide a system which permits precise location of a remote visual inspection device for examining the annular space between a primary vessel and a containment vessel. It is another object of the invention to provide a remote visual inspection system which can withstand exposure to an extreme range of temperatures. SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a system for remote visual inspection of a structure comprising a primary vessel surrounded by a containment vessel. Broadly, the system comprises at least one, and preferably more than one, substantially rigid fixed conduit member which terminates at a first end adjacent an upper portion of the vessel and at its second end adjacent an area to be inspected. The conduit member is provided with at least one aperture adjacent the area to be inspected. The system further includes a housing containing a camera and a light source for insertion into the first end of the conduit member and means for maintaining or controlling the temperature of the camera in the housing. There is also provided a support means for the housing which includes at least a first hollow, flexible hose member having a first end connected to the housing and a second end terminating adjacent an upper portion of the vessels. The support means further includes an electrical conduit for supplying electrical power to the camera and light source, and transmitting signals received from the camera to a display means remote from the camera for receiving said signals. There also is provided a pressurizing means for introducing a fluid into the flexible hose member in an amount sufficient to provide a desired amount of rigidity to the hose member to facilitate pushing the housing and the hose member through the fixed rigid conduit member to a desired location. In accordance with certain preferred embodiments of the invention, the rigid fixed conduit member extends along the length of a weld seam in one of the vessels, generally the primary vessel and is provided with a plurality of closely spaced apertures adjacent the length of the weld seam. Generally, there is provided more than one fixed conduit member to permit inspection of all of the weld seams and any other areas of interest. In accordance with yet another embodiment, the flexible hose member and housing are provided with some positioning means for maintaining the housing substantially in the center of the conduit member. Preferably, the positioning means includes rollers positioned about the periphery of the housing and hose member which also act to minimize frictional forces as the housing is pushed into the rigid conduit member. In acordance with yet another embodiment of the invention the support means further includes a second hollow, flexible hose member, one of said hose members being located about the periphery of and coaxial with the other hollow, flexible hose member. The inner surface of one hose member and the outer surface of the other hose member define an annular space therebetween, the first and second hose members cooperating to provide a flow path for fluid from the pressure means to the housing and back to an upper portion of the vessels. The fluid is passed in heat exchange relationship with the camera and provides the means for controlling the temperature of the camera. Preferably, the fluid is an inert gas such as nitrogen, helium, argon, or carbon dioxide.