COMPARISON OF DPA AND HELIUM PRODUCTION IN CANDIDATE FUEL CLADDING MATERIALS FOR THE CANADIAN SCWR

Harsh conditions associated with high-temperature, high-pressure supercritical-water coolant in the Canadian supercritical water-cooled reactor (SCWR) necessitate the use of stainless steel or nickel-based alloys as fuel cladding material rather than more conventional zirconium-based alloys. In-core neutron irradiation is expected to produce helium in nickel-bearing alloys through the 2-step Ni-58(n,gamma)Ni-59(n,alpha)Fe-56 reaction. Increases in displacements per atom (DPA) associated with this reaction will also occur. It is important to quantify neutron-irradiation induced helium production and DPA to assess the consequences for fuel sheath material integrity. In this paper, neutron-flux induced helium production and displacement damage are estimated from lattice physics calculations for 5 candidate SCWR fuel clad materials, alloys 214, 625, 800 H, 347, and zirconium-modified 310 stainless steel, and compared for 2 fuel options, plutonium-thorium dioxide, (Pu-Th)O-2, and low enriched uranium-thorirum dioxide, (LEU-Th)O-2. It is found that helium production in the fuel clad material is proportional to nickel content in the fuel clad and is greater, (by a factor of approximately 2) for the (LEU-Th)O-2 fuel. DPA is found to be approximately independent of the composition of fuel clad with only a small variation (similar to 5%) between fuel materials.