Extending Sodium Fast Reactor Driver Fuel Use to Higher Temperatures

Abstract

Calculations of potential sodium-cooled fast reactor fuel temperatures were performed to estimate the effects of increasing the outlet temperature of a given fast reactor design by increasing pin power, decreasing assembly flow, or increasing inlet temperature. Based upon experience in the United States, both metal and mixed oxide (MOX) fuel types are discussed in terms of potential performance effects created by the increased operating temperatures. Assembly outlet temperatures of 600, 650, and 700°C were used as goal temperatures. Fuel-cladding chemical interaction (FCCI) and fuel melting, as well as challenges to the mechanical integrity of the cladding material, were identified as the limiting phenomena. For example, starting with a recent 1000 MW(thermal) fast reactor design, raising the outlet temperature to 650°C through pin power increase raised the MOX centerline temperature to more than 3300°C and the metal fuel peak cladding temperature to more than 700°C. These exceeded limitations to fuel performance; fuel melting was limiting for MOX and FCCI for metal fuel. Both could be alleviated by design “fixes,” such as using a barrier inside the cladding to minimize FCCI in the metal fuel, or using annular fuel in the case of MOX. Both would also require an advanced cladding material with improved stress rupture properties. Although some of these are costly, the benefits of having a high-temperature reactor that can support hydrogen production, or other missions requiring high process heat, may justify the extra costs.