Transient experiments on fast reactor core thermal-hydraulics and its numerical analysis Inter-subassembly heat transfer and inter-wrapper flow undernatural circulation conditions

Sodium experiments were conducted on core thermal-hydraulics simulating a s cram transient of a large scale fast breeder reactor using the test facilit y PLANDTL-DHX with seven fuel subassemblies. The influence of inter-subasse mbly heat transfer on temperature distribution in the subassembly was revea led via measurements. The flow in the gap between neighboring subassemblies called inter-wrapper flow (IWF) was also studied in relation to its capabi lity of cooling the subassemblies. A computational model is presented for p redicting the transient without IWF. The multi-dimensional numerical analys is model employs an empirical correlation to simulate mixing effects betwee n adjacent subchannels. It was shown that the present computational method could evaluate the transient behavior of thermal-hydraulics in the subassem blies accurately from forced to natural circulation accompanied by inter-su bassembly heat transfer and flow redistribution in the subassembly. The coo ling effects of IWF on the fuel subassemblies were found in spite of natura l circulation flow reduction in the primary loop attributable to temperatur e decreases in the upper non-heated section in the core. The inter-wrapper flow can effectively cool the core under extreme conditions of low flow rat es through the core. (C) 2000 Elsevier Science S.A. All rights reserved.