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全炉心熱流動解析コードACTの開発,2; 炉心詳細熱流動モデルの開発とナトリウム炉外実験による検証

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

大高 雅彦; 大島 宏之

Otaka, Masahiko; Ohshima, Hiroyuki

高速炉の定格および強制循環から自然循環へ移行する場合の過渡までを含む様々な運転モードに対し、炉心部の熱流力挙動を精度良く評価することを目的として全炉心熱流動解析コードACTの開発を実施している。本コードは複数の解析コードをカップリングすることで、炉心のみならずシステム全体を詳細にモデル化するものである。前報では、燃料集合体間の隙間(集合体間ギャップ部)に存在する冷却材の熱流動挙動を解析する炉心槽解析部の開発について報告した。今回は、集合体内の熱流動解析を行う燃料集合体解析部と炉心槽解析部をカップリングすることでACTの炉心詳細熱流動モデルの開発を実施した。併せてコードの並列化を行うことで大規模計算が可能なものとした。本モデルの開発によって、集合体間ギャップ部の熱流動を考慮した上で、集合体内の温度を精度良く評価することが初めて可能となった。開発したモデルの妥当性を確認するために、7体の集合体で炉心部を摸擬したナトリウム炉外実験データを用い検証解析を行った。その結果、集合体内の冷却材温度は実験誤差以内で一致しACTの炉心部の熱流動解析モデルとして適用できることを確認した。

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 ...

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