A wheel disk assembly, having a wheel disk, a plurality of blade devices, which are fastened along the outer circumference of the wheel disk, and a plurality of sealing plates, which are retained in two annular grooves radially spaced apart from each other, the first annular groove in the wheel disk and bounded axially outward by an annular projection, and the second annular groove defined by a plurality of annular-groove segments arranged adjacently, which are in the individual blade devices. At least one opening extends axially through the annular projection, the minimum width of which opening in the circumferential direction is greater than the width of the sealing plates at the inside diameter such that a sealing plate is axially insertable between the annular grooves through the opening and moveable in the circumferential direction while guided by the annular grooves. A method assembles such a wheel disk assembly.