Installation method for reactor core shroud and radiation shielding structure in reactor pressure vessel

A radiation shielding member is integrally combined on the inner circumference of a new reactor core shroud. The radiation shielding member is formed by combining a radiation shield to the new reactor core shroud and containing a seal tank between the shield and the reactor core shroud. The new shroud and the radiation shielding member are suspended in a pressure vessel of a BWR type reactor in a state where water is filled, and positioned on a shroud support. Water in the pressure vessel is entirely removed, and then the new reactor core shroud is seal-welded to the shroud support from the outer circumference. Water is supplied to a down comer and the seal tank to form an operation region surrounded by a radiation shielding member where an operator can work in the new reactor core shroud. A welding machine is transported to the operation region, and the new reactor core shroud is seal-welded to the shroud support from the inner side. (I.N.)