Development of whole core thermal-hydraulic analysis program ACT, 2; Development of core model and verification analysis

Otaka, Masahiko; Ohshima, Hiroyuki

Whole core thermal-hydraulic analysis program ACT is being developed for the purpose of evaluating detailed in-core thermal hydraulic phenomena of fast reactors under various operation conditions, e.g., normal operation and transition from forced to natural circulation. This second report describes the core model and its verification analysis. ACT consists of several thermal-hydraulic calculation modules related to the following regions: (1)subassemblies (fuel, blanket and control rods) (2)inter-subassembly gaps, (3)upper plenum and (4)primary heat transport system. The subassembly module is almost equivalent to the subchannel analysis code ASFRE-III, which was developed and validated at Thermal Hydraulic Research Section, and is applied to each subassembly of the core. The inter-subassembly gap module is used for calculating the flow and temperature fields in the gaps between the wrapper tubes (inter-wrapper flow) and was also developed based on ASFRE-IIl code (the first report described last year). The upper plenum and primary heat transport system modules are utilized to offer complicated boundary conditions to the whole-core analysis especially under natural circulation conditions with the operation of the direct reactor auxiliary coolant system. In this work, the core model as the main part of ACT was developed by coupling the subassembly modules and the inter-subassembly gap module and it has made possible to calculate flow and temperature fields in the whole core including thermal interaction between the inner subassemblies and the inter-subassembly gaps. The coupling was made explicitly through the heat exchange on the wrapper tube outer surface from the viewpoints of flexibility to model various core geometry and program parallelization for large-scale simulation. The core model was applied to the analysis of PLANDTL-DHX sodium experiment whose test section consisted of 7 subassemblies for code verification. It was confirmed that the predicted sodium ...