Patent Number: 041982711
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT In the construction shown in the drawing the reactor core 1 is submerged in a pool 2 of liquid sodium in a primary vessel 3. The primary vessel is suspended from the roof structure 4 of a containment vault 5 the rim of the primary vessel being sealed to the roof structure in order to contain an inert cover gas for the pool of coolant. There is a leak jacket 6 suspended from jacking means 4a of the roof structure by tie members 7 and it surrounds the primary vessel in order to catch any liquid metal coolant which may leak from the primary vessel. A plurality of control rods 8 (only one being shown in the drawing) is supported by the roof structure of the vault and the rods are insertable in the core to control reactivity. The reactor core is supported from the wall of the base region of the primary vessel by means of a strongback 9 diagrid 13 combination, the strongback 9 having an annular foot 10 which is secured to the primary vessel. Within the interspace designated 11 between the primary vessel 3 and the leak jacket 6 there is an annular shoe 12 disposed immediately below the foot 10 and there is a clearance designated `C` between the shoe 12 and the external surface of the primary vessel. The clearance `C` is adjustable by the jacking means 4a. In the event of deflection of the wall of the primary vessel downward displacement of the core relative to the control rods is limited to the clearance `C` and thereby avoids serious reactivity instability. In more detail, the nuclear reactor core 1 is a fast breeder reactor comprising a plurality of upstanding fuel element assemblies arranged side-by-side on the diagrid which serves as a coolant inlet plenum for the core. The core is surrounded by a shroud 14 or core tank and there is an intermediate annular neutron shield 15. Four pumps 16 and four heat exchangers 17 (only one of each being shown in the drawing) depend from the roof of the vault and are immersed in the pool of coolant. The pumps are arranged to deliver coolant drawn from the outer regions of the pool to the core by way of the diagrid 13. The coolant is heated in passage through the core and flows upwardly through the shroud 14 thence outwardly to the heat exchangers 17 subsequently being returned to the pool. The strongback has four arms 18 mounted on an annular skirt 19 which carries the foot 10. The diagrid 13 is of frustroconical shape and sits within a complementary socket defined by the strongback the socket having an annular shoe 20. The diagrid 13 is carried from the strongback by an annular skirt 21 such that there is a clearance between the shoe 20 and the diagrid 13. The skirt 21 and strongback 9 are imperforate to prevent downward flow of coolant from inside the shroud and the strongback is of double skin construction. The primary vessel houses a tray 22 for the collection of core debris and the primary vessel is externally clad with thermal insulation 23 to reduce heat transfer to the concrete vault structure 5. In the event of failure of the support skirt 21 for the core, displacement of the core is limited to the clearance between the diagrid 13 and the shoe 20. Instrumentation (not shown in the drawing) is provided for monitoring the clearances between the shoe 20 and the diagrid 13 and between the shoe 12 and the primary vessel 3. In the described construction both clearances are 6 mm.