Patent Number: 
Section: claims

1. A mounting method for core internals, comprising the steps of: carrying an integrated module of core internals having a new core shroud, a new jet pump and a new baffle plate into a reactor pressure vessel in which an old baffle plate and an old shroud support cylinder welded and fixedly secured to the reactor pressure vessel and an old shroud support leg fixedly secured to said old baffle plate and said old shroud support cylinder are left;  fixedly securing said new baffle plate to said old baffle plate; and  fixedly securing said new core shroud to said old shroud support cylinder. 2. The mounting method for core internals according to  claim 1 , wherein said integrated module of core internals having the new core shroud, the new jet pump and the new baffle plate is carried into said reactor pressure vessel through an opening provided in a roof of a reactor building for receiving said reactor pressure vessel. claim 1 3. The mounting method for core internals according to  claim 1 , wherein claim 1 said new jet pump comprises a new jet pump inlet mixer, a new jet pump riser and a new jet pump diffuser;  a lower end of said new jet pump diffuser is fixedly secured to said new baffle plate; and  said new jet pump riser is secured to said new shroud by a new jet pump riser brace mounted on an outer wall of said new shroud. 4. A mounting method for core internals, comprising the steps of: cutting an old core shroud and an old jet pump from an old shroud support cylinder and an old baffle plate and carrying the old core shroud and the old jet pump out from a reactor pressure vessel;  carrying an integrated module of core internals having a new core shroud, a new jet pump and a new baffle plate into the reactor pressure vessel in which the old baffle plate and the old shroud support cylinder welded and fixedly secured to the reactor pressure vessel, and said old baffle plate and said old shroud support cylinder are left;  fixedly securing said new baffle plate to said old baffle plate; and  fixedly securing said new core shroud to said old shroud support cylinder.