Cause investigation for thinning of anchor bolts and gaps between anchor bolt nuts and a flange plate at the JMTR Hot Laboratory exhaust stack

Shibata, Akira ; Kitagishi, Shigeru  ; Watashi, Katsumi; Matsui, Yoshinori ; Omi, Masao; Sozawa, Shizuo; Naka, Michihiro 

The exhaust stack of Japan Materials Testing Reactor Hot laboratory is a part of gaseous waste treatment system. It was built in 1970 and is 40 m in height. In 2015, thinning was found at some anchor bolts on base of the stack. When thinning of anchor bolts were investigated, gaps between anchor bolt nuts and flange plate was found. JAEA removed steel cylinder of stack which is 33 m in height for safety. In the end of investigation, thinning was found in all anchor bolts of the stack. Cause investigation for the thinning and the gaps were performed. It is concluded that the thinning was caused by water infiltration over a long period of time and the gaps were caused by elongation of thinning part of anchor bolts by the 2011 earthquake off the Pacific coast of Tohoku.