ES331993A1 - Nuclear reactor - Google Patents

Abstract

A nuclear reactor is cooled by a coolant flow in channels of constant cross-section which are each occupied by a train of fuel cartridges, each cartridge being formed by a fuel element supported in a tubular jacket of moderator material, the jacket of at least the terminal cartridge at the channel end opposite that through which the cartridges are unloaded being of smaller cross-sectional area than the jackets of the cartridges in the channel nearest the end through which the cartridges are unloaded. By this means the force due to the coolant flow acting on the terminal cartridge when this is the last remaining during discharge of the cartridges is limited to an appropriate value. In the preferred embodiment, as shown in Fig. 3, a channel 4a of constant cross-section contains a stack of fuel cartridges all of similar construction, the terminal cartridge 17, for example, being formed by a graphite jacket 18a containing a fuel element 20a borne by a saddle 22a connected to the jacket by retaining wires 23a and centred by partitions 24a. The o.d. of the jacket 18a (like that of the jackets further up the channel) is such that only a slight gap exists between it and the channel wall and substantially all the cooling gas, e.g. CO 2 , flows between the jacket 18a and the fuel element 20a. At least the bottom cartridge 17 has a jacket 18a whose i.d. is greater than the i.d. of the jackets 18a11, 18a111 of the standard cartridges 1711, 17111 in the top part of the channel. The force experienced by the cartridges, more particularly by the fuel elements, is therefore less for the bottom cartridges 17 than for the standard cartridges. In an alternative embodiment, all the jackets have the same i.d., the upper jackets being in close contact with the channel wall whereas the lower jackets are spaced from the channel wall. During normal operation, therefore, substantially all the coolant flows between the jackets and the fuel elements but once the upper cartridges have been removed, a by-pass flow occurs between the lower jackets and the channel wall. The total flow through the channel increases but the pressure drop between the ends of the remaining cartridges, and the force experienced thereby, decreases because of the increased pressure losses due to the fixed elements of the channel, more particularly the debris collector at the bottom of the channel.