High radiation means delays in decommissioning crippled Fukushima reactors

The decommissioning process at the Fukushima No. 1 nuclear power plant faces a further obstacle after Tokyo Electric Power Co. said radiation readings in the containment vessel of the No. 2 reactor were at fatal levels on March 27.

It said readings were detected as high as 72.9 sieverts per hour, which would be fatal to humans in the event of a leak.

That is also enough to affect electronics in robots or other remote-controlled equipment used to probe the reactor ahead of final decommissioning.

Junichi Matsumoto, acting general director of TEPCO’s Nuclear Power and Plant Siting Division, said, “We believe it is the effect from the fuel (that melted) and leaked into the containment vessel. For the decommissioning operation, we will need to develop equipment that can withstand high radiation levels.”

The March 27 announcement marked the first time TEPCO directly measured radiation levels within the containment vessel of the No. 1 to No. 3 reactors where reactor meltdowns occurred a year ago.

TEPCO workers inserted an industrial endoscope into the containment vessel of the No. 2 reactor and measured radiation levels at eight locations. The highest reading of 72.9 sieverts was recorded about 4.2 meters from the bottom of the vessel.

After the Fukushima nuclear disaster flared, the highest radiation level recorded was about 10 sieverts per hour last August around piping near the main exhaust duct of the No. 1 and No. 2 reactors.

At that time, the high radiation was considered the result of fuel leaking during the venting process. The latest reading is not only much higher but reinforces the possibility that the decommissioning process will be prolonged.

High radiation levels can cause electronic parts to malfunction. The latest measurement throws another spanner in the works: Much more work will need to be done to decontaminate the area to reduce radiation levels.

Decommissioning of the No. 1 to No. 3 reactors will involve the unprecedented process of collecting nuclear fuel that has melted into the containment vessel.

Decommissioning was initially expected to take around 30 years, but that estimate will likely now have to be revised.

ref: http://ajw.asahi.com/article/0311disaster/fukushima/AJ201203280034


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