Patent Number: 
Section: claims

1. A method of forming an aperture portion of reactor building, wherein an isolation chamber is provided to a roof of said reactor building at a position between said roof of said reactor building and a traveling path of an overhead traveling crane in said reactor building, and  an aperture portion for passing a structure therethrough is formed at a location directly above said isolation chamber of said roof of reactor building. 2. A method of forming an aperture portion of reactor building as claimed in  claim 1 , wherein said isolation chamber is provided with doors which are passable of said structure. claim 1 3. A method of forming an aperture portion of reactor building as claimed in  claim 1 , wherein doors which are passable of said structure are provided to said isolation chamber after fixing said isolation chamber at said roof of said reactor building. claim 1 4. A method of forming an aperture portion of reactor building as claimed in  claim 1 , wherein said structure is a reactor vessel, and claim 1 said location of fixing said isolation chamber is a portion directly above said reactor vessel in said reactor building. 5. A method of forming an aperture portion of reactor building as claimed in claims  1 , wherein said isolation chamber has a structure to prevent dust generated by forming operation of said aperture portion from diffusing into said reactor building. 6. A method of forming an aperture portion of reactor building as claimed in  claim 1 , wherein a protecting apparatus covering the location where said aperture portion is to be assembled and having doors which are passable of said structure is provided onto said roof of said reactor building prior to forming of said aperture portion. claim 1