Holding down a sodium-cooled fast reactor fuel element - by suction device through which coolant flows to prevent damage resulting from fuel melt-down

摘要

Fuel element comprises a channel box contg. fuel rods and connected in leaktight manner to the lower grid plate. The box can be removed upwards out of the reactor vessel. The foot of the box or an insert which seals it to the lower grid plate contains a hydraulic holding-down device consisting of a lower and an upper tubular part connected respectively to the insert and to the fuel element foot or channel box by means of 2 sets of hollow ribs and which thus connect the interior of the holding-down device to the zone outside the channel box which is at lower coolant outlet pressure. The relative suction inside the holding-down device prevents uplift of the fuel element by the upward flowing coolant. The connection to the upper hollow ribs is provided by an upward tubular extension of the upper half of the holding down device, so that the openings of the two connections to the low pressure zone are as far apart vertically as possible. Natural or forced convection through the inside of the hydraulic holding-down device is afforded, so that it is kept cool, even if there is a fault which might cause molten fuel to drop onto the holding down device. Molten fuel would thus be kept inside the fuel elements and not allowed to spread.