How Work To Remove A Radioactive Tower At Fukushima Daiichi Went Wrong

Measure twice, cut once.

Work to remove the highly contaminated units 1-2 vent tower at Fukushima Daiichi took an unfortunate turn last month. The cutting rig had been tested at one of the research facilities and was determined ready to use. When the equipment was assembled on site and work was to commence, it was discovered the crane and cutting rig could not be lifted high enough to place it in the vent tower stack.

With the work now on hold, contractors involved tried to determine what went wrong. Three issues were found that created the cascading error.

The cables that attach the cutting rig to the crane were longer in real life than they were in the on paper design. This caused the cutting rig to sit 3 meters too low.

“When the demolition equipment was confirmed to be able to install at the top, the hanging fee * and actual hanging fee at the time of planning
There was a difference, and it was judged that it was necessary to increase the lifting height of the crane.
* Distance from the hook of the crane to the top of the exhaust cylinder”

“The difference of the plan and about 4m was found in the wire growth at the maximum hoisting from the measurement of the height of various places.
 The factor in which this difference occurred is that the limit switch wire is about 4m, accidentally on the hook from the crane tip
Because it had planned as a distance of about 4m to the end, the difference of about 4m is generated for the actual wire length about 8m did.

The crane being used on site was slightly different than what was assumed on paper, this impacted the height the rig could be lifted to.

“ After that, there was a plan that there was little room for crane height, and the cooperation company had no difference between the plan and the actual
To the maintenance company of the premises Crane, but the manufacturer and the model
The limit switch position was different, and understood the dimensions of the wrong position.”

The engineering survey of the site and ensuing blueprints incorrectly interpreted the total height of the tower by 1 meter. This was due to portions of the base and attachment of the vent tower on site being miscalculated. The base of the tower is obscured by concrete slabs and other shielding put in place after the extent of the dangerous radiation in the tower was better understood.

“ Since the base position of the exhaust tube was set at a 1m higher position than the actual, the planned value is The difference from the was about 3m.”

TEPCO further explains that there was no effort to confirm construction drawings vs. the conditions on site.

“The cause of wire growth at maximum hoisting is different from the plan.
 In the first stage of the plan, we will detail the Crane plan diagram that general Contractors was using in planning a separate construction
To a cooperating company that plans to dismantle the exhaust pipe without confirming the The plan was studied using the picture.
(At this point, there has been a difference between actual and planned
Raised height was insufficient)
 After that, there was a plan that there was little room for crane height, and the cooperation company had no difference between the plan and the actual
To the maintenance company of the premises Crane, but the manufacturer and the model
The limit switch position was different, and understood the dimensions of the wrong position.
(P.3) (the difference between the actual machine and the plan has increased further)
 We determine that the construction plan in the height direction can be confirmed by the plan diagram, and the position of the crane limit switch
Confirmation of the detailed position of the (Construction drawing and site confirmation) was not performed.
The reason why the basic position was planned about 1m higher than actual
 Since the G.L. ± 0 of the exhaust cylinder cannot be accurately confirmed, the cooperating company shall draw the base of the tower base.
I thought that I was surveying the height of the Tower Foundation crest at the site, but the actual survey position was from the Tower Foundation crest.
1m high position (root-wound concrete crest of the steel Tower), the erroneous information is reflected in the plan diagram, We did not confirm the setting grounds of the height in the construction drawing, etc.
(p.3)
 the roles of the company, the cooperating companies, and other affiliated companies in this construction are unclear, and
It is not limited to events, but also involves deep digging of the background factors including communication problems, and measures appropriately .”

 

The solution to part of the problem is to position the crane closer to the tower. This requires the addition of gravel fill to the area to provide the crane a elevated area to sit upon.

The series of miscalculations will cause the work to cut down the vent tower to be delayed until late July 2019.

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