Assembly a control bar to resonance reactor.

摘要

1321169 Controlling reactors COMMISSARIAT A L'ENERGIE ATOMIQUE 9 Dec 1971 [22 Dec 1970] 57174/71 Heading G6C A control rod assembly, in particular for a sodium-cooled fast reactor, comprises a stationary thimble 10 surrounding a control rod 12 having a head 32 in which is formed an annular recess engageable by handling tongs (not shown) of a control rod drive mechanism, a neutronabsorbing portion consisting of a cluster of pins 22 within a sleeve 24, and a lower end-fitting 26. The coolant enters the thimble 10 through apertures 20 in a nose 19 extending into the reactor diagrid 16, and passes upwardly (as indicated by the arrows), at least 70% entering the sleeve 24 through openings in the end-fitting 26 and flowing over the neutron-absorbing pins 22 before entering a tubular stem 30 and finally leaving the control rod 12 via holes 40 disposed between the head 32 and a flange 36. The control rod 12 is shown disengaged from the drive mechanism, beyond the bottom position in which the drive mechanism brings the rod into the position of maximum absorption, and supported by the engagement of the flange 36 against a collar 38 carried by the internal wall of the thimble 10. The remainder of the coolant flows up through the annular passage 44 between the thimble 10 and the control rod sleeve 24, this passage 44 being throttled by the small clearance between the collar 38 and the control rod stem 30. Each pin 22 comprises a can containing a lower portion 46 of tantalum and a much longer upper portion 48 of boron carbide. The thimble 10 may be provided immediately above the reactor core 14 with three inserts 42 to guide the control rod 12. When the control rod 12 is released and in the position shown, access is provided to an annular recess 18 in the upper end of the thimble 10 which can then be engaged by the fuel handling device for lifting the control rod assembly from the reactor core.