Control rod drives in LMFBR type reactors

Purpose: To prevent sodium vapors from depositing in a shielding sleeve by providing a gas blowing nozzle near the lower end of the shielding sleeve for flowing out cover gases downwardly to the inside of the reactor thereby turning back the cover gases. Constitution: In an LMFBR type reactor, cover gases, which tend to flow into annular spaces between a shielding sleeve and a driving shaft extension of a cover gas blow down mechanism provided in the portion of the plug in which a control rod drive mechanism is passed through, are turned back into the reactor by the blow down gases from a blowing port of a gas blow channel provided to the sleeve so as to blow out the gases downwardly. Accordingly, sodium vapors do not deposit on the inner wall of the shielding sleeve and the outer wall of the driving shaft extension, whereby undesirable ''biting'' in the annular space containing a labyrinth seal upon drive of the control rod is eliminated. (Seki, T.)