Method and apparatus for removing an incore neutron flux monitor

In a nuclear reactor wherein four square shaped fuel rod assemblies are disposed in respective square shaped openings defined by crossing grids of an upper supporting plate, and an in-core monitor is disposed at a cross-point of the grids, the in-core monitor is removed by removing four fuel rod assemblies adjacent the in-core monitor, removing one fuel rod assembly from each of three square shaped openings about the in-core monitor, inserting a holder-cutter assembly into a large vacant space formed by removing the four fuel rod assemblies for holding the upper portion of the in-core monitor, inserting a clamping device into one small vacant space formed by removing one of the three fuel rod assemblies which is diagonally opposite the removed fuel rod assembly for clamping a portion of the in-core monitor which is spaced apart from the portion thereof held by the holder of the holder-cutter assembly, severing the in-core monitor into two sections by operating the cutter, and removing to the outside of the reactor the severed two sections while they are held by the clamping device and the holder, respectively