原子炉冷却系総合試験装置の基本仕様設定のための模擬燃料集合体内熱流動解析 -ASFRE-IIIコードによる燃料集合体内のパラメータ解析-

Thermal-hydraulic analysis for basic design of FBR large-scale sodium test facility; Parameter study on thermal-hydraulics in fuel subassembly using ASFRE-III

成田 均; 大高 雅彦; 大島 宏之; 家田 芳明 

not registered; Otaka, Masahiko; Ohshima, Hiroyuki; not registered

原子炉冷却系総合試験装置における燃料集合体基本仕様設定のバックデータを得るため、サブチャンネル解析コードASFRE-IIIを用いて、燃料集合体内熱流動特性に対するピン本数の依存性、除熱効果の影響、ダミーピンの影響等についてパラメータ解析を行った。その結果、以下の知見が得られた。・ラッパー管からの除熱が無い場合、37本以上のピンバンドル体系を用いれば燃料集合体内の温度プロファイルに大きな差異はない。・ラッパー管からの除熱がある場合、本解析の設定では、ピン本数が増えるにつれて(特に217本)、バンドル体系での周辺部の温度勾配が相対的に急峻になった。・除熱量にも依存するが、ピン本数が異なる場合の集合体間熱移行への影響については、ピンの本数が多いほど壁サブチャンネルファクタが小さくなる傾向があることから、幾分集合体間熱移行が起こりにくくなると考えられる。・ダミーピンについては、その配置によって温度極小値が発生し、集合体内流量配分も異なってくる可能性があるため、注目する現象によってはその影響に留意する必要がある。

Thermal-hydraulic analyses using a single-phase subchannel analysis code ASFRE-III were performed to reveal the design parameter effects on the steady-state thermohydraulics in an electrically heated fuel subassembly of the FBR large-scale sodium test facility, which is being planned to be, constructed in O-arai Engineering Center, and to set the specification of the fuel assemblies of the test facility. In the analysis, the number of heater pins simulating fuel pins in a subassembly and dummy (unheated) pins included, heater pin diameter, heat flux on the surface of heater pins, and averaged coolant velocity were varied as design parameters. Heat transfer through the wrapper tube wall was also considered to examine the influence on temperature distribution in the fuel subassembly. The results were summarized as follows: (1)In case of an a diabatic condition at the wrapper tube wall, similar coolant temperature profiles were obtained in fuel subassemblies which had more than 37 heater pins. From the viewpoint of the natural circulation simulation, at least 37 fuel pins should be set in a fuel subassembly. (2)The influence of heat transfer through the wrapper tube wall on the coolant temperature profiles in the peripheral area of the fuel assembly. The larger temperature gradient in this area resulted in the larger temperature difference between the center (maximum) and edge (minimum) subchannels. This tendency is stronger as the number of heater pins is increased, which means that larger pin bundle leads smaller inter-subassembly heat transfer because the wall subchannel factor is reduced. (3)In some cases, dummy pins caused local temperature decrease around them which might effect on the flow redistribution in a subassembly. If dummy pins are set in a subassembly, the number and position of them should be carefully determined to make their influence minimized.