Tokyo Electric Power Co (Tepco) plans to begin dismantling the upper section of the joint exhaust stack for the unit 1 and 2 reactors at its Fukushima Daiichi NPP in fiscal 2018, company officials announced on April 25 during a meeting with the Nuclear Regulation Authority (NRA). NRA officials had advised Tepco to disassemble the structure because of fractures in its pillars that increased the risk of collapse, The Mainichi reported.
However, venting to reduce pressure inside the reactor containment vessels contaminated the stack during the 2011 nuclear disaster and radiation levels are extremely high. Radiation measurements conducted at the base of the structure in 2013 stood at an estimated 25 sieverts per hour.
As a result, the will be undertaken from a distance utilizing a large crane. It is expected to be completed in fiscal 2019. Tepco officials told NRA that fractures or deformities had been detected in eight different sections of the pillars' steel joints, which are found at approximately the 66 metre-mark of the 120-metre-high exhaust stack. The cracks are thought to have been caused by the hydrogen explosions that occurred during the disaster.
Tepco has said the structure "would not fall over even if an earthquake of the same intensity as that which struck during the Great East Japan Earthquake (an upper level 6 on the Japanese scale) were to occur again". However, it decided to dismantle the top section as it would have repercussions on the reactor decommissioning work taking place in the area in the unlikely event of the structure's collapse.