Shielding method upon exchange of reactor pressure vessel

A shielding material for shielding γ rays is filled to a space surrounded by the inner surface of a reactor pressure vessel and the outer surface of a shroud to shield the shroud and jet pumps as radiation sources. This can greatly reduce the thickness of an iron plate shield temporarily disposed upon exchange of the reactor pressure vessel. In addition, since shielding material in a granular form is filled to the space, it can be filled only by a required amount thereby enabling to reduce the weight of the shielding material to be filled. Further, since a shielding lid is disposed to the shroud, the height of the iron plate shield can be made substantially identical with the position of the top of the shroud, and this can greatly reduce the weight of the iron plate shield. With such procedures, there can be provided effects of reducing the volume of a large-sized crane and transporting vehicles for the exchanging operation. (T.M.)