Pressure drop in dual-cooled annular and cylindrical solid fuel assemblies for pressurized water reactor

Dual-cooled annular fuel with inner and outer coolant channels is known to have a great advantage of significantly increasing the reactor power. To maintain all components in a conventional nuclear power system using cylindrical solid fuel, the pressure drop in a dual-cooled annular fuel bundle should be comparable to that in a cylindrical solid fuel bundle. In this work, the pressure losses in dual-cooled annular and cylindrical solid fuel assemblies were experimentally investigated. To simulate a dual-cooled annular fuel assembly, a 4 × 4 square rod array of P/D (Pitch-to-Diameter ratio) = 1.08 was prepared with plain and twist-vane spacer grids, and the friction factor in a bare rod bundle and the pressure loss coefficients at the spacer grids were then measured. For a cylindrical solid fuel assembly, a 5 × 5 square rod array of P/D = 1.35 was used with the plain, split-vane, and hybrid-vane spacer grids. The friction factor in a rod bundle and the pressure loss coefficients at the spacer grids in P/D = 1.08 were smaller than those in P/D = 1.35. Based on the present experimental results, the pressure drops in dual-cooled annular (12 × 12 rod bundle) and cylindrical solid (16 × 16 rod bundle) fuel assemblies were evaluated and compared under the nominal operating conditions of an optimized power reactor in the Republic of Korea, OPR1000. It was revealed that dual-cooled annular fuel could decrease the total pressure drop of a fuel assembly by about 15% for a plain spacer grid and about 7% for a spacer grid with a pair of mixing vanes, as compared to the cylindrical solid fuel.