GB953694A - Detection of faulty fuel elements in refuelling machines on nuclear reactors - Google Patents

Abstract

953,694. Nuclear fuel elements. PLESSEY CO. Ltd. Sept. 15, 1960 [June 24, 1959], No. 21633/59. Heading G6C. The fuel elements of a nuclear reactor are tested after removal from the reactor, and either before or after loading into the magazine of the reactor refuelling machine by monitoring the cooling gas flowing over a selected fuel element in order to detect the rare gas fission products krypton and xenon, the escape of which through any puncture or similar defect is greatly enhanced for a time by reducing the external pressure on the fuel element. The fuel elements are lifted by a grab and cable arrangement (not shown) through a charge tube into a loading shoot which is deflected horizontally in order that the elements may be lowered into the chambers 5 of a storage magazine 4 rotatable about a vertical axis. In the embodiment shown in Fig. 2, each chamber 5 is sealed, in the position to which it moves after loading, by two hinged plates 7, 8 and is then depressurised by means not shown. In an alternative embodiment (Fig. 2), a block 9 rotatable about a vertical axis and having two chambers 10, 11 is mounted above the magazine 4 with one chamber 10 aligned with a loading shoot of the reactor and with the magazine chamber 12 which is intended to receive the fuel element from the shoot after testing. The block 9 is rotated to position the chamber 10 together with a fuel element between plates 7, 8 while chamber 11 receives the next fuel element. When the block 9 is rotated back to its first position, the tested fuel element can be dropped into the chamber 12 and another element placed in the vacated chamber 10. The gas removed from the chambers on depressurisation is monitored by a precipitation type detector and, according to the cooling requirements of the fuel element, the gas sampling may be an intermittent or continuous flow process. The depressurising can induce incipient faults to fail so that weak elements can be rejected before being returned to the core, this being of particular importance in the case of metallic uranium elements, especially at higher burnups, where a serious type of failure can occur due to progressive accretion of oxide within the sheath at the site of a defect too small to be detectable by normal methods, but which may result in a sudden burst releasing large quantities of active oxide.