Study on natural convection in core barrel; Experimental and numerical results for band type spacer pads

Hayashi, Kenji; Kawamata, Nobuhiro; Kamide, Hideki 

In a fast reactor an lnter-Wrapper Flow (IWF)is one of significant phenomena for decay heat removal under natural circulation condition, when a direct reactor auxiliary cooling system (DRACS)is adopted for decay heat removal system. Cold coolant provided by dipped heat exchangers (DHX) of DRACS can penetrate into the core barrel (region between the subassemblies)and it makes natural convection in the core barrel. Such IWF will depend on a spacer pad geometry of subassemblies. Water experiment, TRIF(Test Rig for inter-wrapper Flow),was carried out for IWF in a reactor core. The test section modeled a 1/12th sector of the core and upper plenum of reactor vesse1. Experimental parameters were the spacer pad geometry and flow path geometries connecting the upper plenum and core barrel. Numerical simulation using AQUA code was also performed to confirm applicability of a simulation method. An experimental series using a button type spacer pad had been carried out. Here a band type spacer pad was examined. Temperatures at subassembly wall were measured with parameter of the flow path geometries; one was a connection pipe between the upper plenum and core barrel and the other was flow hole in core former plates between the outermost subassemblies and the core barrel. It was found that these flow paths were effective to remove heat in the core in case of the band type spacer pad. A general purpose three dimensional analysis code, AQUA,was applied to the experimental analysis. Each subassembly and inter wrapper gap region were modeled by slab mesh geometry. Pressure loss coefficient at the spacer pad was set based on the geometry. The numerical simulation results were in good agreement with measured temperature profiles in the core.