Patent Number: 055442048
Section: description

SPECIFIC DESCRIPTION FIG. 1 shows a nuclear reactor having a ring-shaped reactor core 10, a central column 11 and a main supply of coolant represented by the inlets 12 and 13 extending to a space 14 distributing the main coolant flow to passages 15 opening into the core 10. The main body of fissionable fuel is received in the core and the reactive zone is represented between the horizontal planes 16 and 17 and within the annular region represented by the generatrices 18 and 19. At the upper end of the reactor, passages 20 carry the heated coolant to an annular space 21 whence the coolant is lead away via the ducts 22 and 23 to the remainder of the main coolant circulation which can include an energy recovery system for producing electrical energy, heat-exchangers or the like for lowering the temperature of the coolant. According to the invention, a reactivity-controlling system is provided in the form of a vertical compartment 25 within the central column 11, an upper portion of which is in the reactive zone and a lower portion of which is outside the reactive zone and the neutron flux thereof. The compartment 25 is disposed above the annular space 26 which also forms a distributing space for a portion of the coolant which can be admitted into this space via an annular sieve structure 27 and axial-sieve structures 28. The coolant flow through the compartment 25 is branched from the main coolant stream as represented by the arrows 29. At the upper end of the chamber 25 is another sieve structure 30 which screens nuclear-fuel particles 31 in the compartment 25 from the branched coolant stream. The branched coolant stream which fluidizes masses of fuel particles 31 in the compartment 25 and forms an expanded bed thereof in the reactive zone, passes into a collecting chamber 32 from which the branched coolant returns at 33 to the main coolant flow. Within the compartment 25 gravity acts on the coated fuel particles 31 in the direction of arrow 34 and thus the flow of branched coolant through this compartment is in the direction of arrow 35. Arrows 36 represent the main coolant flow through the reactor. As can be seen from FIG. 1, moreover, the sieve-like structures 27, 28, 30 are so constructed that the fuel particles 31 cannot pass from the compartment 25 either upwardly or downwardly, but can be held suspended in the reaction region as long as the main coolant flow is sustained and, of course, as long as there is a branched fluidizing coolant flow. As can be seen from FIG. 2, however, should there be a failure of the coolant flow (note the lack of arrows 36 in the reactor), an accumulation S of the particles due to gravity in the space 26 removes the fuel particles from the reactive region and thus reduces the reactivity by the order of 0.5 to 1%, leading to hot shutdown of the reactor. In the embodiment of FIGS. 1 and 2, the branched flow passes through a region of the reactor which is free from nuclear fuel until fuel particles are entrained into it namely the upper part of column 11 above the particle-collecting space in arriving at and upon departing from the compartment 25, and in the case of a breeder reactor, can pass through the breed-blanket shell and in the case of a thermal reactor through the reflector as may be desired. The space 26 and the volume of the fuel particles S is such that the reduction in reactivity is the 0.5 to 1% indicated.