Fuel Management of PWR Cores with Silicon Carbide Cladding

Abstract

The primary motivation for using silicon carbide rather than zirconium alloy cladding is its putative improvement in accident resistance, due to slow reactions with water, even at high temperatures. But, fuel management performance will also be an important consideration in its commercial acceptance. Whether backfittable 18- and 24-month cycles can be designed for existing light water reactors, their enrichments, operating characteristics, and fuel costs are questions that the present study undertakes to answer. Also evaluated is the possibility of leveraging silicon carbide’s ability to sustain higher fuel duty for increasing power levels and discharge burnups in pressurized water reactors. A preliminary design using fuel rods with the same dimensions as in typical Westinghouse fuel, but with fuel pellets having a 10 vol % central void, has been adopted to mitigate the higher fuel temperatures when silicon carbide is used. This allows design of 18- and 24-month cycles that meet present-day operating constraints on peaking factor, boron concentration, reactivity coefficients, and shutdown margin, while achieving batch average discharge burnups up to 80 MWd/kg U, as well as power uprates of 10% and possibly 20%. Control rod configuration modifications may be required to meet the shutdown margin criterion for the 20% uprate. For nonuprated cores, silicon carbide–clad fuel may have a fuel cost advantage, especially with increasing discharge burnup, provided the fuel manufacturing cost is close to that of Zircaloy tubes. The economics of the fuel cycle also improve with power uprates, as the value of the additional energy generated may substantially exceed the advantage from fuel cost alone.