PURPOSE: To enable decreasing shielding extent of radiation down to almost the same level of a shielding wall by providing a shielding member consisting of a γ-ray shielding material and a neutron shielding material, at one of outer and inner side penetration hole provided at a penetrating part.

CONSTITUTION: A shielding member 11 is placed outside a penetration hole 10 and the member 11 is constituted of rectangular flat plane shaped γ-ray shielding material 12 and a neutron shielding material 13 which are integrally fitted together. Also, this shielding member 11 is formed to be a size larger than an area which can be seen directly from outside a nuclear reactor shielding wall 4 to a nuclear reactor pressure vessel 2 side, and is supported by a supporter body 14 extending from the shielding wall 4, and floor 15. At a vicinity of the penetration hole 10, an access hole is provided and the access hole is constituted to be able to be freely opened and closed by a shield plug having no hollow part in it and therewith radiation from a reactor core part 3 does not pass through directly to outside the shielding wall 4.