Irradiation test subassembly bent onto in-vessel storage rack in the experimental fast reactor "Joyo"

高速実験炉「常陽」炉内ラック位置での計測線付実験装置試料部の変形

関根 隆 ; 中野 朋之 

Sekine, Takashi; Nakano, Tomoyuki

高速実験炉「常陽」では、第15回施設定期検査中に発生した燃料交換機の荷重異常に伴い原子炉容器内を観察した結果、計測線付実験装置(MARICO-2)の試料部が炉内ラック上に突き出ていること、炉心上部機構下面の整流板及び案内スリーブが変形していることを確認した。本事象は、照射試験終了後、MARICO-2を照射位置である炉心第3列から炉内ラックに移動した後、保持部と試料部の切離作業を炉内ラックで実施したが、この際に試料部切離機構の設計不備により試料部を切り離せず、その後、試料部が接続された状態で回転プラグを操作したために生じたものである。

During the 15th periodical inspection of the experimental fast reactor "Joyo", in-vessel visual inspections were conducted because of the malfunction of a fuel handling machine. These inspection results confirmed that the test subassembly part of instrumented type irradiation test device "MARICO-2" has been bent onto the in-vessel storage rack, and the regulating grids and guide tubes on the bottom of Upper Core Structure (UCS) have been deformed. After finishing irradiation test, MARICO-2 was transferred from the irradiation position to an in-vessel storage rack. Then the disconnection work of MARICO-2 test subassembly part from the upper structure was carried out. However, disconnecting failure was occurred because of the design deficiency of the separation mechanism. When the rotating plug was returned to the original position, the upper structure of MARICO-2 which was installed in the UCS dragged the test subassembly, and the head of the irradiation test subassembly has been bent.