Chemical interaction of D9 alloy clad with B 4 C in liquid sodium: Studies employing XPS , XRD , and SEM

A cell representing typical control rod subassembly of the prototype fast breeder reactor is designed to probe the liquid sodium‐mediated chemical interaction of boron carbide (B 4 C) control rod with the D9 alloy clad. The cell was equilibrated at 973 K for 5000 hours with liquid sodium in the annular gap. XRD shows the formation of Cr 3 C 2 and Fe 2 B along with oxides of Ni, Cr, and Fe. XPS studies reveal the diffusion of boron and carbon up to a depth of about 160 and 120 μm, respectively. A boron‐rich region is observed up to a depth of about 40 μm which consists of B 3+ arising from oxides and a nearly constant elemental boron region, extending up to a depth of 160 μm. The highly reacted zone extends up to a depth of about 40 μm consisting of oxides of most of the elements of D9 clad exhibiting a higher valence states. As the cell is helium leak tested, oxygen out gassed from B 4 C at 973 K played a major role in chemical oxidation of the constituents of the D9 alloy which can be minimized by using high‐density B 4 C.