On the Potential Use of High Thermal-conductivity Fuels in Supercritical Water-cooled Reactors (SCWRS)

Abstract

Chosen as one of six Generation IV nuclear-reactor concepts, SuperCritical Water-cooled Reactors (SCWRs) will have thermal efficiencies within the range of 45-50% owing to high reactor-outlet temperatures.  A generic SCWR operates at a pressure of 25 MPa with inlet- and outlet-coolant temperatures of 350°C and 625°C.  On the other hand, the high operating temperatures of SCWRs leads to high fuel centerline temperatures.  Previous studies have shown that the fuel centerline temperature could exceed the industry limit of 1850°C when UO₂ or other low thermal-conductivity fuels such as ThO₂ or MOX are used in certain conditions.  Therefore, there is a need for alternative fuels for future use in SCWRs.The objective of this paper is to evaluate several high thermal-conductivity fuels, namely, uranium carbide, uranium nitride, and uranium dioxide composed of graphite fibers.  Consequently, the fuel centerline and sheath temperature profiles of these fuels have been calculated and compared against the industry accepted limits of 1850°C and 850°C for the fuel and the sheath, respectively.  Further, other factors such as thermal conductivity value and trend, melting point, uranium atom density, high temperature stability, chemical compatibility, thermal-shock resistance, steady-state and irradiation-induced creep, and volumetric swelling were considered to determine the most suitable fuel option for future use in SCWRs. The result showed that uranium carbide can be considered as a promising fuel option for SCWRs.