低減速軽水炉用燃料被覆管の力学的特性評価,1(受託研究)

Mechanical characteristics evaluation of fuel cladding tube for reduced-moderation water reactor, 1 (Contract research)

金子 哲治; 塚谷 一郎; 木内 清

Kaneko, Tetsuji; Tsukatani, Ichiro; Kiuchi, Kiyoshi

低減速軽水炉の炉心は、高転換比と超高燃焼度を同時に達成するために、MOX燃料とUOブランケットの各ペレット領域を多段に積層した燃料要素から構成される。その燃料要素の設計では、長手方向におけるトランジェントな熱出力分布に起因した局所的変形挙動の評価が重要となることから、実炉で想定される燃料被覆管の温度分布及び応力分布の数値解析を行い、局所的な変形挙動の評価試験条件を選定した。それをもとに、燃料被覆管の熱変形挙動評価試験装置の温度分布制御等の再現試験を行い、最適な実験条件を選定した。併せて、被覆管の熱変形挙動で想定される疲労及びクリープ及び熱物性等の基礎データを取得して、燃料被覆管の多軸応力場における力学的特性評価に必要となる試験・解析条件を整えた。

Fuel elements used in The Reduced-Moderation Water Reactor (RMWR) have the lamellar structure consisting of MOX pellets and UO blankets in order to attain the high breeding ratio and high burn-up simultaneously. It is a characteristic of the fuel elements that there is high thermal stress caused by inhomogeneous linear power density along the longitudinal direction of the fuel rod. Therefore, it is important to evaluate the local deformation behavior due to the transient temperature distribution. To estimate the thermal deformation behavior, the temperature and stress distribution of the fuel cladding tube assumed in the designed reactor were analyzed. Moreover, basic physical properties and mechanical properties for analyzing the deformation behavior were obtained by experiment using fuel cladding tubes made of candidate alloys. In addition, the appropriate experimental conditions for realizing the practical thermal deformation behavior of the fuel cladding tube was selected by adjusting the testing temperature distribution based on data obtained with thermal analysis.