Method for temporary shielding of reactor vessel internals

Abstract

A first plurality of water filled shielding tanks is introduced through a nuclear reactor containment building hatch and placed between the stored core internals and the reactor vessel. A support structure for this vertical wall is previously shipped, disassembled, introduced into containment and erected between the reactor vessel and the stored internals. A second plurality of water filled shielding tanks is placed on the containment building operating floor level to cover the stored internals. Once in place, the tanks allow manned activity in the reactor vessel area, such as preparations for annealing. The method includes the steps of: removing the nuclear fuel from the reactor; storing both the upper and lower internals underwater; assembling the support structure and placing same in position in the refueling canal; introducing the vertical and horizontal tanks through the hatch; filling the vertical shielding tanks with water and placing same in the support structure; filling the horizontal shielding tanks with water and placing them above the stored internals and the vertical tanks; draining water from the refueling canal to the level of the reactor vessel flange; performing an operation requiring human intervention such as annealing; flooding the refueling canal to near the operating floor elevation; and decontaminating the tanks and support structure and removing same.