Development of Lagrangian particle method for temperature distribution formed by sodium-water reaction in a tube bundle system

管群体系中のナトリウム-水反応により形成された温度分布評価のためのラグランジュ粒子法の開発

小坂 亘  ; 内堀 昭寛 ; 岡野 靖; 柳沢 秀樹*

Kosaka, Wataru; Uchibori, Akihiro; Okano, Yasushi; Yanagisawa, Hideki*

ナトリウム冷却型高速炉における蒸気発生器(SG)の安全性評価及び設計について、SG内伝熱管からの加圧水のリーク及びその後の事象進展の評価は重要である。解析コードLEAP-IIIは半経験式や1次元保存式などの低計算コストなモデルで構成されるために短い計算時間で水リーク率等を評価でき、革新炉開発における多様なSG設計の探求を加速させることが期待される。しかし、現在の温度分布評価モデルには、過度な保守性を示す場合があること、及びチューニングのために予備的な実験又は詳細な数値解析が必要とされて準備に時間がかかることに課題がある。これらを改善するため、より単純な計算原理に従い、機構論的な側面を持ちつつも高速計算可能なラグランジュ粒子法コードの開発に取り組んでいる。今回は、本粒子法コードに実装されている粒子ペア探索手法の効率化、及び粒子ペア探索を用いずに同等の結果を得るためのモデルの開発を行った。テスト解析を通して、これらのモデル改良による計算時間短縮効果を確認し、また、伝熱管破損判定に重要な伝熱管周囲の代表温度について、詳細な機構論的解析コード(SERAPHIM)による評価結果とよい一致を示すことを確認した。

The leakage of pressurized water from a steam generator (SG) and the progress after that are a key issue in the safety assessment or design of a SG in sodium-cooled fast reactor. The analysis code LEAP-III can evaluate a rate of water leakage during the long-term event progress, i.e., from the self-wastage initiated by an occurrence of a microscopic crack in a tube wall to the water leak detection and water/water-vapor blowdown. Since LEAP-III consists of semi-empirical formulae and one-dimensional equations of conservation, it has an advantage in short computation time. Thus, LEAP-III can facilitate the exploration of various new SG designs in the development of innovative reactors. However, there are several problems, such as an excessive conservative result in some case and the need for numerous experiments or preliminary analyses to determine tuning parameters of models in LEAP-III. Hence, we have developed a Lagrangian particle method code, which is characterized by a simpler computational principle and faster calculation. In this study, we have improved the existing particle pair search method for interparticle interaction in this code and developed an alternative model without the pair search. Through the trial analysis simulating in a tube bundle system, it was confirmed that new models reduced the computation time. In addition, it was shown that representative temperatures of the heat-transfer tubes evaluated by this particle method code, which is used to predict the tube failure in LEAP-III, were good agreement with that by SERAPHIM, which is a detailed mechanistic analysis method code.