The exhaust stack for the No. 1 and No. 2 reactors at Fukushima No. 1 nuclear plant will eventually be dismantled using equipment seen on both sides. (Keitaro Fukuchi)

Tokyo Electric Power Co. has delayed the start of work to dismantle a dangerous and highly contaminated exhaust stack at the Fukushima No. 1 nuclear power plant because of a calculation error.

The company said May 16 that work on the 120-meter-tall chimney, which was initially scheduled to begin on May 20, will be postponed until June at the earliest.

TEPCO found that the height of special cutting equipment lifted by crane would be 1.6 meters lower than under the original plan, making it unable to reach the top of the stack.

“We believe that the lifting angle of the crane arm turned out to be different from the original plan because of an error in measuring equipment,” a TEPCO official in charge of the operation said.

The company is now considering adjusting the angle and the crane position or extending the arm length after it is lowered.

The exhaust stack was used for the No. 1 and No. 2 reactors at the plant.

When the nuclear disaster unfolded in March 2011, vapor containing highly radioactive substances was released through the stack. Metal poles used to support the chimney were damaged apparently by a hydrogen explosion.

The area around the base of the stack contains levels of radiation that are too dangerous for humans to work in, so the dismantling work will be conducted by remote control.