Modeling of silicon carbide duplex cladding designs for high burnup light water reactor fuel

One of the current obstacles to enhancing light water reactor performance is fuel rod cladding degradation. As fuel is pushed to higher power density and burnup, the traditional zirconium alloy cladding becomes increasingly embrittled, corroded, and deformed. Silicon carbide may be a replacement for zircaloy because its strength and its radiation and chemical resistance may permit fuel to achieve higher burnup than is permissible today. In addition, SiC cladding can withstand higher temperatures during transients without yielding or undergoing significant reactions. The proposed cladding is a duplex design, consisting of an inner monolithic SiC tube surrounded by and bonded to a woven SiC fiber composite. The dimensions of this duplex tube would be comparable to LWR fuel rods currently in service. The thermo-mechanical behavior of a SiC-clad fuel rod has been investigated with a modified version of the FRAPCON steady-state fuel rod modeling code. This code was used to predict the temperature, geometry, stress, and fission gas release of the fuel rod up to very high burnup (100 GWd/MT) under anticipated PWR conditions, and compared it to a zircaloy-clad fuel rod under identical operating conditions. The effects of possible variations in the properties of the SiC cladding on fuel temperature were also explored. It is predicted that a SiC-clad fuel rod would have higher peak fuel temperatures than a comparable zircaloy-clad fuel rod. However, SiC that does not experience creep or significantly decreased elastic modulus with increased temperature, has an ultimate strength similar to zircaloy, and is resistant to oxidation. Therefore, at current peak linear heat rates, the SiC-clad fuel rods would provide acceptable performance, including operation up to 100 MWd/kg burnup without hard pellet-cladding contact. The properties of a composite SiC cladding, however, require verification in a radiation environment. (authors)