TEPCO to dismantle top of exhaust stack at Fukushima plant due to fractures

Tokyo Electric Power Co. (TEPCO) will begin dismantling the upper section of the joint exhaust stack for the No. 1 and 2 reactors of its Fukushima No. 1 Nuclear Power Plant 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 due to fractures in its pillars that increased the risk of it collapsing.

Because the vent to reduce the pressure of the nuclear reactor containment vessels contaminated the stack in the 2011 nuclear disaster at the plant, and it is releasing extremely high radiation, the work will be undertaken from a distance utilizing a large crane. The work is expected to be completed in fiscal 2019.

Explaining the dismantling plans during the NRA meeting, TEPCO officials said that fractures or deformities had been detected in a total of eight different sections of the pillars' steel joints, which are found at approximately the 66 meter-mark of the exhaust stack. The structure stands at a total height of around 120 meters.

The cracks are thought to have been caused by the hydrogen explosions that occurred during the disaster.

Radiation measurements conducted at the base of the structure in 2013 stood at an estimated 25 sieverts per hour -- an extremely high level that would kill nearly everyone exposed for that long.

While TEPCO has determined that 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," the utility 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.