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Fukushima Radioactive Sump Water Disappears

December 23, 2019

Radioactive water in the sump pit at the base of the unit 1-2 vent tower at Fukushima Daiichi escaped in November.

The base of the vent tower is one of the most radioactive locations at the disaster site. Water in this sump is normally pumped out into a truck to transport it for treatment. An automatic sensor system detects when the sump fills to a certain level then transfers water to the truck’s tank. TEPCO discovered that the water level in the sump had gone down but no transfer of water had taken place. The radioactive water is assumed to have left the sump pit. TEPCO did indicate rising radiation levels in two nearby groundwater control sump wells after the water escaped.

Rainwater is considered to be the main route for water to flow into the vent tower sump pit. When the upper vent tower removal work is completed, a cap will be placed on the vent pipe to prevent rainwater from flowing into the sump pit. There appears to be some amount of water transfer at the ground level between this sump pit and the surrounding soil. TEPCO did not address this further in their most recent report.

TEPCO document

https://www4.tepco.co.jp/decommission/information/committee/roadmap_progress/pdf/2019/d191128_06-j.pdf

http://www.simplyinfo.org/?p=17830&fbclid=IwAR1iUIvMl8bCua3SbG2PJfKjn73xCTPQsQ2pL30IYxFdY2UgNyKJuNamKzs

December 30, 2019 Posted by dunrenard | fukushima 2019 | Fukushima Daiichi, Radioactive Water, Vent Tower | Leave a comment

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

June 12, 2019

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.

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.

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.

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.

TEPCO’s Plan For Some Of The More Dangerous Work At Daiichi

Soon after the disaster workers at the plant discovered that their dosimeters would high radiation alarm then be unable to give a reading when they approached the unit 1-2 shared vent tower. This was an indication that radiation levels near the tower were so high that their dosimeters were unable to accurately read the level. One of the most dangerous places at Fukushima Daiichi may undergo work to reduce the ongoing risk.

One of the two units connected to this vent tower ejected considerable amounts of radioactive materials via the tower during the initial disaster. The area has been declared off limits with shielding walls installed. Closer inspection with cameras and drones showed that the tower had suffered structural damage and was at risk of collapse or further damage. Since then TEPCO and the research agencies tasked with disaster clean up at the site have been working on a plan to dismantle the tower.

The current plan includes a complex series of machines and equipment designed specifically for this task. The work would remove the upper portions of the vent tower then install a cap on the top of the remaining pipe. This is assumed to be used to prevent further release of radioactive materials or inflow of rainwater into the highly radioactive area. The actual demolition work is scheduled for fall of 2018 and could take a year to complete.

The graphic below shows the steps towards cutting down the tower in sections.

u1_2_vent_tower_dismantling 24 july 2018.jpg