Abstract: In the operation of a power reactor having a pressure bessel (2) containing a core and a plurality of thimbles extending into the core to provide passages for a flux detector, a movable support member (12) located outside of the pressure vessel (2) and carrying a plurality of tubular members (10) each detachably connected to a respective thimble, and a transfer unit (20) normally coupled to the tubular members (10) for introducing a flux detector into a selected thimble via a respective tubular member (10), obstructions are removed from a selected thimble while the reactor remains in operation, by the steps of:disconnecting at least the respective tubular member from the transfer unit (20);introducing an obstruction removal device (40,42) into the respective tubular member (10); andadvancing the obstruction removal device (40,42) through the respective tubular member (10) and into the selected thimble to the location of the obstruction.

Abstract: In the operation of a power reactor having a pressure vessel (2) containing a core and a plurality of thimbles extending into the core to provide passages for a flux detector, a movable support member (12) located outside of the pressure vessel (2) and carrying a plurality of tubular members (10) each detachably connected to a respective thimble, and a transfer unit (20) normally coupled to the tubular members (10) for introducing a flux detector into a selected thimble via a respective tubular member (10), obstructions are removed from a selected thimble while the reactor remains in operation, by the steps of:disconnecting at least the respective tubular member from the transfer unit (20);introducing an obstruction removal device (40,42) into the respective tubular member(10); andadvancing the obstruction removal device (40,42) through the respective tubular member (10) and into the selected thimble to the location of the obstruction.