Patent Number: 052805077
Section: claims

1. The method of sensing obstructions in a tubular nuclear fuel rod or the like, and comprising the steps of providing a nozzle having high and low gas pressure sourced connected thereto, and providing a gas flow balance circuit directly communicating with the nozzle, said gas flow balance circuit including an outlet having a variable restriction,  calibrating the balance circuit and including positioning the nozzle in sealed relationship with one end of a fuel rod known to be free of internal obstructions, flowing a low pressure gas from the low pressure gas source through the nozzle and into and through the fuel rod, sensing the pressure of the flowing gas at a location in the nozzle so as to define a standardized pressure, flowing a balance circuit gas through the balance circuit while sensing the pressure of the gas within the balance circuit, and adjusting the variable restriction of the balance circuit so that the sensed pressure within the balance circuit equals the standardized pressure,  positioning the nozzle in sealed relationship with one end of a fuel rod to be tested,  flowing a low pressure gas from the low pressure gas source through the nozzle and then into and through the fuel rod to be tested,  flowing a balance circuit gas through the balance circuit to produce the standardized pressure,  sensing the pressure of the flowing low pressure gas in the nozzle, and  comparing the sensed pressure of the flowing low pressure gas with the standardized pressure of the balance circuit flowing gas and such that a difference between the sensed pressure of the low pressure gas flowing in the nozzle from the low pressure gas source and the standardized pressure of the balance circuit is indicative of an obstruction in the fuel rod being tested.  a nozzle adapted to engage one end of a fuel rod in an air tight sealed relationship,  means connected to said nozzle for flowing an initial high pressure gas flow through said nozzle and into a fuel rod positioned in an air tight sealed relationship with said nozzle so as to blow any obstructions from the interior of fuel rod,  means connected to said nozzle for flowing a low pressure ga flow through said nozzle and into a fuel rod positioned in an air tight sealed relationship with the nozzle,  means for sensing the pressure of the flowing low pressure gas in the nozzle when the low pressure gas is flowing through the nozzle,  a gas flow balance circuit directly communicating with the nozzle, said gas flow balance circuit including an outlet having a variable restriction,  means for flowing a balance circuit gas through the balance circuit, and  means for sensing the balance circuit gas flow and such that the pressure of the balance circuit gas flow equals a standardized pressure, and  means for comparing the sensed pressure of the flowing low pressure gas with the standardized pressure of the balance circuit gas flow, and such that a difference between the sensed pressure and the standardized pressure is indicative of an obstruction in the fuel rod. 2. An apparatus for sensing obstructions in a tubular nuclear fuel rod or the like, and comprising 3. The method as defined in claim 1 wherein the fuel rod and the outlet of the balance circuit both vent to the atmosphere, and so as to render the method insensitive to changes in atmospheric pressure. 4. The method as defined in claim 1 comprising the further step of generating a visible or audible alarm signal when the difference between the sensed pressure and the standardized pressure is greater than a predetermined value. 5. The method as defined in claim 1 comprising the further step of passing an initial high pressure gas from the high pressure gas source through the nozzle and into and through the fuel rod prior to the step of flowing the low pressure gas therethrough, and so as to blow any obstructions from the interior of the fuel rod. 6. The apparatus as defined in claim 2 wherein the fuel rod and the outlet of said balance circuit both vent to the atmosphere, and so as to render the apparatus insensitive to changes in atmospheric pressure. 7. The apparatus as defined in claim 2 wherein said comparing means includes means for generating a visible or audible alarm signal when the difference between the sensed pressure and the standardized pressure is greater than a predetermined value.