Device for installing dry PDD lances and for flushing out lance-housing tubes in boiling water reactors

In combination, a reactor pressure vessel of a boiling water reactor wherein reactor water is received, and a device for flushing out radioactive deposits accumulated in a lance-housing tube at least partly disposed in the reactor pressure vessel and for aligning in the lance-housing tube a dry power distribution detector lance which partly protrudes with a pressure-tight lance passthrough from an end flange on the lance-housing tube of the reactor pressure vessel and is supported in a seat on the end flange, comprising a tubular housing surrounding from below a part of the lance protruding from the reactor pressure vessel, said tubular housing being sealed by a lance protection tube and being fastened to the end flange;

• and a piston arranged in said tubular housing underneath the lance sealed in said tubular housing, and being vertically displaceable and rotatable so as to entrain and lift the lance out of said seat in which it is supported so that reactor water received in the reactor pressure vessel is admitted to the lance-housing tube, said piston being formed with a flow passage for the reactor water admitted to the lance-housing tube and including a valve disposed in said flow passage for controlling the flow of reactor water out of the reactor pressure vessel.