Patent Number: 053713630
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting radiation within a pipe. More specifically, it relates to a device that is pulled through embedded piping to perform radiation surveys therein. 2. The Prior Art Nuclear facilities within the United States are licensed for operation by the Nuclear Regulatory Commission (NRC). The NRC specifies radiation contamination limits, for example, radioactive contamination limits that must be satisfied prior to termination of an NRC license. Modern nuclear power stations contain thousands of feet of exposed and embedded piping that must be surveyed in order to determine radioactive contamination levels. The cost of removing this piping is many millions of dollars, and therefore it would be advantageous to survey the internal pipe surfaces while the pipes remain embedded, for the purpose of allowing unconditional release of those pipes. The radiation survey is most effectively carried out by a pipe crawler or a device with radiation sensors that is located within the pipe. These devices are equipped with a variety of detectors, to count alpha, beta particles and/or gamma rays. A different size pipe crawler is required to survey each size of pipe and even each schedule of pipe size. Numerous patents have been issued pertaining to equipment for testing the integrity of pipes and pipe joints. For example, U.S. Pat. No. 4,131,081 to Muller et al, U.S. Pat. No. 4,548,785 to Richardson et al, and European Patent Application 039,922 disclose devices for ultrasonically inspecting pipes. U.S. Pat. No. 4,581,938 to Wentzell, U.S. Pat. No. 5,138,644 to McArdle et al, French Patent 2,652,650 and European Patent Application 078,072 disclose various other types of scanning and measuring equipment for pipes. However, none of these patents addresses the specific problems associated with detecting radiation within pipes. Therefore, it would be advantageous to have a device that can pass within piping and detect radiation contamination on the internal surfaces of those pipes. It would be further advantageous to have a device that can perform detailed radiological surveys at precise locations of internal pipe surfaces. It would further be advantageous to be able to survey different size pipes and different schedules of pipes. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a device for detecting radiation within a pipe that can be moved through the pipe. It is a further object of the present invention to provide such a device that can perform detailed radiological surveys at precise locations of internal pipe surfaces. It is a further object of the present invention to provide a device for conducting surveys in a variety of pipe sizes with detectors in the precise geometry required to satisfy the U.S. government criteria for the unconditional release of those pipes. It is yet another object of the present invention to provide a device in which the conditions and results of the surveys can be fully recorded and documented for inspection and record retention purposes. These and other related objects are achieved according to the invention by a device for detecting radiation on an interior pipe surface, including a carriage movable through the pipe hat has a longitudinal central axis and radii extending between the longitudinal central axis and the pipe. The device includes means for positioning the carriage centrally within the pipe. A set of radiation sensors are mounted about the central axis for detecting radiation on the interior pipe surface. The device further includes indexing means for rotating the sensor a fraction of the angle between adjacent sensors, so that a circumferential strip on the interior of the pipe in sensed. Cables are coupled to the device for moving it through the pipe and for transmitting sensor data from the device. The device maintains the radiation sensors in the geometry required for unconditional release surveys. In smaller sized pipes, indexing of the sensors is not possible due to the limited diameter of the pipes. In an alternate embodiment, there is provided a device for detecting radiation on the interior of these smaller diameter pipes. The device includes two or more carriages coupled in spaced relation along the central axis of the device and adapted for movement through the pipe. The device includes two or more sets of sensors. Each set of sensors is mounted on one of the carriages. Each set of sensors has an angular displacement about the longitudinal central axis, with respect to the other sets of sensors. The angular displacement is dependent on the number of carriages and the number of sensors per set, so that the entire interior pipe surface is covered as the device is moved through the pipe.