Patent GB-1522531-A (GB)
Title: Method for locating defective fuel rods of a reactor fuel element
Inventor: JESTER ALFRED
IPC: G21C17/07
Filed: 1976-02-11
Abstract: 1522531 Testing fuel elements BABCOCKBROWN BOVERI REAKTOR GmbH and BROWN BOVERI & CIE AG 11 Feb 1976 [11 Feb 1975] 05444/76 Heading G6C In a method of locating leaky fuel rods within a multi-rod nuclear fuel element after irradiation in a liquid-cooled nuclear reactor, all the fuel rods are heated simultaneously at a rate sufficient to raise the temperature of a rod into which the reactor coolant has not leaked, above the boiling-point of the reactor coolant liquid, the respective temperatures of the heated fuel rods are monitored simultaneously, and any fuel rod whose temperature remains at the said boiling-point is determined to have a fault in its can through which the coolant has leaked into the rod. An apparatus for performing this method comprises a water tank 1 filled to the level 2 in which is mounted a rack 3 for accommodating a fuel element 4 which is to be tested. The rack 3 may be turned through 180 degrees so that fuel element 4 is inverted. A bell 5 is moved sideways in the broken line position while the rack 3 is being manipulated, the interior of the bell being kept dry by a stream of hot gas discharged from pipes 15. This prevents the formation of vapour in the bell 5, which vapour could endanger the functioning of a conventional thermographic infra-red measuring apparatus 6 mounted in the bell. The bell 5 is then moved by a crab (not shown) into the solid-line position. The rack 3 is raised by a lifting device (not shown) so that the fuel rods project by 30-100 mm. above the water level N in the ball 5. Fig. 2 shows an end region of a fuel rod 22 with a capillary structure 12 comprising a metal mesh, fleece or felt or a porous ceramic slug disposed in a cavity 21 in the end cap 11. Cooling water leaks during reactor operation into all defective fuel rods and collects in their bottom region after reactor shut-down. The capillary structure 12 in a leaky fuel rod becomes charged with water and, after the rack 3 is turned through 180 degrees, is disposed in the end cap 11 which projects into the bell 5. An alternative construction is shown in Fig. 3 in which a cup-shaped cap 19 of sheet metal is located in the end cap 11, open towards the end, and formed with a central port 20 for drainage of excess water on inversion of the fuel element. In a further construction (Fig. 4, not shown), a wick (24) projects through the fission gas space 25 as far as the fuel pellets 10 to convey any leakage water into the capillary structure 12. Such a fuel rod is tested without inversion, e.g. in situ in the reactor core. Heat radiation sources 15 disposed in the bell 5, and/or the hot gas discharged from pipes 15, uniformly heat the end faces of the end caps 11. During the time which elapses before any leakage water has evaporated, the absorption of latent heat of evaporation will cause the temperature of the end cap end faces to be maintained at 100 C. The heat radation sources 14 are able to heat the end cap end faces of non-defective rods to at least 125 C., the temperature difference #25 C. being detected by the infra-red temperature measuring apparatus 6. A monitor 16 connected to the apparatus 6 enables the positions of all defective rods to be located at a glance, defective rods appearing as dark areas 17 and non- defective rods as bright areas 18.