A containment building includes a wall made of a material of the concrete type that delimits a space and at least one viewing module, the viewing module including at least one window arranged in an opening in the wall, the window having a frame in which at least one optical unit that provides protection from high-energy and/or neutron radiation is placed, the frame being fitted in the opening, the viewing module also having a protective element that includes a sash bearing a pane and is arranged so as to close the opening at the face on the inside of the building, the viewing module thus including at least one interface between two surfaces. The containment building also includes at least one sealing system arranged at at least one interface.