Apparatus and methods for impingement cooling of a side wall of a turbine nozzle segment

For use in a gas turbine, a nozzle segment having outer and inner band portions and at least one vane extending between said band portions, at least one of said band portions having a nozzle wall defining in part a hot gas path through the turbine, a cover radially spaced from said nozzle wall defining a chamber therebetween and an impingement plate secured within said segment and disposed in said chamber defining with said cover a first cavity on one side thereof for receiving a cooling medium, said impingement plate on an opposite side thereof defining with said nozzle wall a second cavity, said impingement plate having a plurality of apertures therethrough for flowing cooling medium from said first cavity into said second cavity for impingement cooling said nozzle wall, said nozzle segment including a side wall extending generally radially between said nozzle wall and said cover and having an inturned flange, said inturned flange defining an undercut region adjacent said side wall, and a backing plate overlying a portion of said impingement plate, said backing plate and said impingement plate portion having aligned apertures therethrough for directing a flow of the cooling medium onto said side wall for impingement cooling thereof.