Patent ID: 7769124

Claim:
A handling method associated with maintenance and inspection of a natural circulation boiling water reactor including a chimney having a cylindrical chimney shell disposed above a core in a reactor pressure vessel, a plurality of square tubes disposed so as to extend in the vertical direction in said chimney shell, and a grid support plate having a plurality of first grid holes and a plurality of second grid holes alternately arranged in rows and columns so that a lower end of each square tube is detachably supported by a corresponding second grid hole and said second grid hole faces an opening at said lower end of said square tube, and adjacent square tubes in a respective row and a respective column are initially separated from each other by an interval which exceeds a width of one square tube, wherein for enabling maintenance and inspection, the method comprises, during shut down of the reactor, and after opening of the reactor pressure vessel, and taking out in-reactor devices and removal of fuel assemblies, the steps of: detaching and removing a predetermined number of said plurality of square from said corresponding second grid holes of said grid support plate and shifting a respective one of said predetermined number of said plurality of square tubes to a respective one of said first grid holes within said interval between said plurality of initially separated square tubes; and performing maintenance and inspection via said corresponding one of said second grid holes from which said respective square tube has been removed.