平成7年度 実用リサイクル炉概念検討報告書; ダクトレス燃料炉心構造

Conceptual design study of the actinide recycle reactor; Study of core structural with ductless fuel assemblies

小川 伸太; 早船 浩樹; 戸澤 克弘; 一宮 正和; 林 秀行; 向坊 隆一

Ogawa, Shinta; Hayafune, Hiroki; Tozawa, Katsuhiro; Ichimiya, Masakazu; Hayashi, Hideyuki; Mukaibo, Ryuichi

60万kWeのMOX高燃焼度・長期運転リサイクル炉心を対象に,燃料集合体のダクトを削除したダクトレス燃料炉心の熱流動特性,機械的特性を評価し,ダクトレス炉心の基本概念を明らかにした。主な検討結果は,(1)ダクトレス燃料集合体の基本構造を設定し,その機械的性質を確認した。(2)ダクトレス燃料炉心では炉心領域の流量が一様となり,温度分布の出力分布依存性が高くなる。(3)集合体剛性はダクト型集合体に比べて大幅に低下し,また炉心領域での熱わん曲や照射わん曲が小さい。(4)炉心での自然対流による炉心冷却効果が高く,ピーク温度の低減,炉内温度分布の均一化等,ダクトレス燃料炉心固有の安全性を確認した。

It is required enhanced core safety characteristics, recycle cost reduction, mitigation of risk to the environment and nuclear non proliferation for the fast reactor at the commercial use age of actinide recycle. The ductless fuel assembly, which has no wrapper tube, is promising for these requirements. In this study, the thermal hydraulic and mechanical characteristics of the ductless fuel core are evaluated for 600MWe MOX core with high burnup and long operating cycle length, and conceptual structure of the ductless fuel assembly core was established. The results of the study are summarized as follows; (1)Structural of Ductless Fuel Assembly. Conceptual design of components of the ductless fuel assembly, e.g. grid spacer, tie rod, upper shielding, lower nozzle and mechanical hold down spring, were performed and conceptual structure was established. Detail study of fuel pin bundle stiffness are required in the following design study. (2)Thermo-hydraulic Characteristics of Ductless Core and Ductless Fuel Assembly. The bypass flow rate strongly depends on the gap between core region and core barrel. For this bypass flow, it is found that thermal hydraulic feasibility is expected when the gaps between core region and core barrel are decreased(1mm). Since the core flow distribution is uniform, a coolant temperature distribution depend on the power distribution into core region. For fuel assembly, if the gaps between fuel assemblies are enlarged, the maximum sodium temperature increases (20C/mm), therefore a proper gap design are needed. (3)Mechanical Characteristics of Ductless Core. The seismic safety of ductless core, in which a mechanical hold down are used, is assured. To decrease the impact force at spacer grid, however, some considerations on the grid design is necessary to avoid buckling. (4)Thermohydraulic Safety Characteristics. The maximum sodium temperatures are roughly evaluation under the condition of natural circulation and coolant ...