Shield for a nuclear reactor

This patent describes a nuclear reactor having a core, a radial reflector, a reflector, an reflector, and a reactor vessel head, a shield in the reactor vessel head. It comprises: a primary region within the reactor vessel head containing a packed bed of spheres of zirconium hydride; a secondary region within the reactor vessel head adjacent to the primary region containing a packed bed of spheres of lithium borohydride; and a subregion of spheres of zirconium deuteride in the primary region