高性能制御棒の検討; FBR大型炉の設計主要目に関する研究

Study on advanced control rod; Study on the main design parameters of large scale FBR core characteristics

菰田 成一*; 池上 哲雄*; 水野 朋保*; 鈴木 惣十*; 金城 勝哉*; 中西 征二; 谷山 洋*

not registered; not registered; not registered; not registered; not registered; Nakanishi, Seiji; not registered

61年度レファレンス炉心をベースとし、長寿命化、および出口冷却材温度高温化の観点で好適な、高性能制御棒仕様を明らかにするとともに、その性能を把握することを目的とした。制御棒当たり吸収ピン本数、ピン配列形状、B4Cペレットと被覆管間のギャップ幅、スペーサワイヤの径や巻付けピッチ等をパラメータとし、ACMI発生後の継続照射時の、被覆管フープ応力やピンバンドルと保護管の寸法干渉量(BDI)、また寿命初期の被覆管最高温度を評価した。ピン本数として37本程度を選定するならば、製作時のペレット被覆管間直径ギャップ幅を0.8㎜程度まで広げることができ、照射後約3年でACMIが開始する。さらに、約1年継続照射すると、BDIはワイヤ径1本分に達する。この間、被覆管のフープ応力は、照射クリープの寄与により、過大な値とならないが、炉停止時および炉外取出時には急増するとの結果が得られた。また、同芯円状配列の37本バンドルは、正三角形格子状配列の31本バンドルと比べて、出口冷却材温度高温化の観点で有利との結果が得られた。結論として、同芯円状配列の37本バンドルを採用することで、出口冷却材温度約450の達成見通しを得た。また、制御棒寿命を評価するためには、被覆管の照射クリープ特性明確化の必要性のあることが分かった。

The aims of this work are to give the specifications of the control rod having a good performance under a long term irradiation and a high temperature condition of outlet coolant, and also to get a rough estimation of the allowable maximum irradiation period and outlet temperature at the base of the reference core designed in the year before last. The hoop stress of a cladding tube and the dimension of interference between an absorber pin bundle and an inner duct tube surrounding the bundle (BDI) are evaluated in the period after the time that ACMI begins. In addition, the maximum temperature of a cladding tube is evaluated at the beginning stage of irradiation. These evaluations are done for the several specifications which change in the number of pins, the arrangement of pins, the gap width between BC pellet and cladding tube, the spacer wire thickness or wrapping pitch, etc. It is found that a diametral gap width between pellet and cladding tube may be expanded to about 0.8 mm if a 37 pins bundle is selected, and that ACMI begins at three years irradiation and BDI reaches the magnitude of wire thickness at additional one-year irradiation if that width of 0.8 mm is selected. Through the additional irradiation, the hoop stress of a cladding tube does not exceed the allowable maximum value owing to an irradiation creep, but it increases rapidly at a reactor shutdown or when the control rod is removed from the core. It is also found that the 37 pins bundle whose pins are located on concentric circles is superior in view of making an coolant outlet temperature high to the 31 pins bundle whose pins are located with a regular triangle lattice pattern. As a conclusion, the prospect is obtained that about 450C is realized as an coolant outlet temperature by selecting the 37 pins bundle whose pins are located on concentric circles. But it is found that the irradiation creep behavior of a cladding tube must be clarified in order to evaluate the ...