Support structure for the core of the reactor resonance a fast neutrons

摘要

1474646 Reactors COMMISSARIAT A L'ENERGIE ATOMIQUE 28 May 1975 [25 June 1974] 23314/75 Heading G6C A core support structure for a sodium-cooled, fast reactor comprising a horizontal diagrid supporting the reactor core fuel assemblies, has a tundish unit or core catcher mounted beneath the diagrid in such a manner as to ensure its direct cooling in the event of an accident condition involving melt-down of the reactor core. As shown in Fig. 2, the diagrid 7 is carried by a flooring structure 8 formed by an open metallic assembly, the periphery of which is applied against the internal surface of the reactor primary vessel 3, while beneath the diagrid 7 is fixed the tundish unit 9 which comprises a cylindrical shell 10 with lateral openings 10a and closed by a conical bottom wall 11 provided with holes 11a. The tundish unit 9 contains a receiving tray 12 for collecting the core in the event of a melt-down and formed by a series of successive cups each having a conical transverse profile and forming a series of troughs arranged in cascade from one cup to the next. The cups are provided with bottom openings 12a which permit free circulation of the liquid sodium through the tray 12. The interior of the tundish unit 9 is divided by a thin horizontal metallic plate 13 into two zones 14, 15. The zone 14 collects sodium leakages from a high pressure collector 28 at the level of recesses provided within the diagrid 7 for accommodating the fuel assembly end-fittings 17, the cold sodium being supplied under pressure through ducts 29 to an annular space 30 surrounding the internal surface of the primary vessel 3 and delimited by a parallel baffle-plate 31. Within the zone 15, the cold sodium at a lower pressure ensures suitable cooling of the tray 12 and of the diagrid support structure 8 during a normal period of reactor operation. In the event of a melt-down of the reactor core 6 and its collection within the tray 12 after destruction of the separating plate 13, a natural circulation of sodium by convection is automatically established around the tray 12 by causing the zone 15 to communicate with a cold sodium collector 24 located between the primary vessel 3 and an inner vessel 19 by means of a series of communication ducts 32 formed through the diagrid support structure 8. The ducts 32 are distributed around the structure 8 in such a way as to ensure that the hot sodium is permitted to flow towards the cold collector 24 through some of the ducts whilst the remaining duets serve to return the sodium towards the tray 12 after cooling by passing through and mixing within the collector, as illustrated in Fig. 2 respectively on the left- and right-hand sides of the tundish unit 9.