Simplified thermalhydraulic analysis of a dual-cooled annular fuel rod in a single subchannel

Annular fuel rods have been received increasing attention due to their advantages over the traditional solid fuel rods used in water and liquid metal cooled nuclear reactors. A significant increase in the power density can be achieved with use of the annular fuel rods. This work presents a simplified thermalhydraulic analysis of an annular fuel rod coupled with a single subchannel. The transient heat conduction in the inner cladding, annular fuel pellet, and outer cladding is modeled by an improved lumped parameter formulation based on Hermite approximations for integrals. The surface temperatures and heat fluxes are related to the average temperatures in the three regions by using the Hermite approximation H_1,1/H_0,0. The energy transport by the coolant is modeled by an integrated energy equation over the coolant subchannel. A system of four linear ordinary differential equations for the average temperatures in the fuel, inner and outer claddings, and of the coolant in the subchannel is solved analytically and numerically. Numerical results show excellent agreement between the analytical and numerical solutions. (author)