Patent Number: 041893484
Section: summary

This invention relates to nuclear fuel elements formed with a large number of depending fuel rod assemblies attached to and depending from an overhead support having a manifold system connected to each fuel rod assembly for the extraction of fission product gases generated by nuclear fuel during fission. Nuclear fuel rod assemblies having solid nuclear fuel therein are often supported or hung by their upper ends to a grid-like support formed of interconnected beams having a manifold passageway system within the beams connected to each of the respective fuel rod assemblies for conveying gases therefrom. Such a fuel rod manifold and support system is disclosed in U.S. Pat. Nos. 3,743,576 and 3,432,388; and, as disclosed therein, the fuel rod assemblies were welded to their overhead supporting beams with gas tight welds between the fuel rod assembly and the lower wall of the beam. Often, a large number of fuel rod assemblies comprise a given fuel element, e.g., as many as two hundred and seventy-one or more fuel rod assemblies per fuel element. Typically, these fuel rod assemblies are elongated pin-like structures, often called fuel pins, having an outer metallic cladding wall encircling the fuel and transferring heat to the coolant flowing past the outer surface of the cladding wall. Usually, the upper ends of fuel rod assemblies have a plug or shaft of metal which is hermetically sealed to the cladding wall and is formed with a central bore to allow fission product gases to flow upwardly to the manifold system in the supporting beams. To convey the fission product gases to the manifold system without leakage into the surrounding coolant, each of the upper plugs of the fuel rod assemblies were welded to their support beams. However, such a welding process is slow and expensive. Moreover, a leaking weld connection is difficult to correct particularly when it is located at an interior one of a large number of fuel rod assemblies attached to a common beam support. Heretofore, it has been proposed to drill and tap the beam support and to thread the upper ends of the fuel plugs for releasable threading of the fuel rod assemblies directly to the support beams. However, threading of the beams also was found to be costly, time-consuming and inefficient. Thus, there is a need for a new and improved releasable interconnection between the fuel rod assemblies and their support beams which also provides a tight leak-free seal between the fuel rod assemblies and the support. Accordingly, a general object of the present invention is to provide a new and improved fuel element having detachable fuel rod assemblies secured with a tight leak-free connection to a beam support having a manifold vent system therein.