Vanadium Alloys vs Stainless Steel for Sodium-Cooled Fast Reactor Cladding

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Abstract
The development of vanadium alloys as fuel element cladding materials in sodium-cooled, ceramic-fueled fast breeder reactors was reviewed. Compared to stainless steel, certain vanadium alloys have advantageous nuclear and thermal characteristics, elevated temperature strength, and potential resistance to fast-neutron embrittlement. The compatibility of vanadium alloys with flowing sodium and with ceramic fuels was identified as an area in which more data are necessary. A comparison of economics and performance was made for vanadium-alloy and stainless-steel cladding in a carbide-fueled LMFBR. The power costs depended strongly on the projected fabrication cost of vanadium-alloy and stainless-steel tubing. Several fabrication costs as well as different cladding thicknesses were considered. For a core coolant outlet temperature of 110°F in the vanadium designs, an economic break even point with 316-SS was reached at vanadium-alloy tubing costs of ∼$3.50/ft in the vented design and $2.85/ft in the nonvented design. Stainless steel was considered inadequate at that coolant temperature. With the core coolant outlet temperature at 1 000°F in all core designs, the economic break even vanadium tubing cost was ∼30% lower. Power costs were generally a few hundredths of a mill/kWh higher with vanadium cladding at the same burnup. This cost differential could be eliminated since vanadium alloys may be capable of a slightly higher burnup than stainless steel, due to their higher end-of-life ductility. Differences in nuclear performance characteristics such as fuel inventory, breeding ratio, and doubling time were <1% for all cladding materials and thicknesses studied. Doppler and sodium-void reactivity effects were 5 to 10% more favorable with vanadium-alloy cladding than with stainless steel. Based upon the available economic and performance data, a vanadium alloy appears to be an attractive potential alternate to stainless steel for LMFBR cladding.