Patent Number: 046817298
Section: summary

BACKGROUND OF THE INVENTION This invention relates to the monitoring of temperature within a vessel, particularly vessels used for the long term storage of or transfer of nuclear fuel materials. In detecting outside a vessel a change in the temperature inside the vessel it is known to use a temperature probe to measure the temperature of the external surface of the vessel; to use an infra-red detector responsive to the surface temperature of the vessel; to receive outside the vessel radio signals from a temperature detection system in the vessel. The suitability of these known methods is in doubt especially in terms of long term storage of nuclear fuel materials. FEATURES AND ASPECTS OF THE INVENTION According to the invention there is provided a vessel provided internally with a device for enabling external detection of temperature changes within the vessel, said device comprising a permanent magnet, means mounting the magnet within the vessel for movement towards and away from a boundary wall of the vessel, means having sufficient magnetic coupling with the magnet to restrain the magnet against movement away from a predetermined position with respect to said boundary wall of the vessel, and temperature-responsive means for urging the magnet away from said predetermined position whereby, in the event of a substantial rise in temperature within the vessel, the latter means becomes effective to move the magnet relative to the boundary wall to vary the magnetic field strength detectable by detector means located on the external side of said boundary wall. The vessel may be open or closed. The vessel may for example be a nuclear fuel transport flask or a canister for nuclear fuel or a containment vessel for a reactor core. The detector means may comprise a Hall effect transducer responsive to the magnetic field produced by the permanent magnet outside the container. The detector means may alternatively comprise means for generating a time varying magnetic flux in said boundary wall of the vessel which interacts with the magnetic flux of the permanent magnet, and means for sensing magnetic flux external to said boundary wall. The temperature responsive means may include a thermal link so that on breaking of the link the permanent magnet is moved relative to said boundary wall by spring means. The link may be broken by an increase in temperature above a predetermined value or by corrosion.