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Work begins to topple dangerous exhaust stack at Fukushima plant

Dismantling work begins Aug. 1 to slice a highly contaminated exhaust stack into parts at the stricken Fukushima No. 1 nuclear power plant complex.
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A crane hoists a dismantling mechanism to the top of an exhaust stack at the Fukushima No. 1 nuclear power plant site.
 
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Work begins Aug. 1 to dismantle an exhaust stack at the Fukushima No. 1 nuclear power plant site.
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A crane lifts a dismantling mechanism toward the top of an exhaust chimney on the Fukushima No. 1 nuclear power plant site
 
August 2, 2019
Delicate work got under way Aug. 1 at the crippled Fukushima No. 1 nuclear power plant to dismantle an unstable exhaust stack that is so highly contaminated by radiation the task must be done by remote control.
Initial plans had called for the work to start in March, but the project was delayed by a failure among other things to confirm design plans that led operator Tokyo Electric Power Co. to deploy a crane that was not up to the task.
The exhaust stack, which is 120 meters tall and 3.2 meters in diameter, was used for the No. 1 and No. 2 reactors.
The work is regarded as a crucial phase in the decommissioning of the plant, a task that is projected to take decades and cost billions of yen.
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 found to have been damaged following a hydrogen explosion at the No. 1 reactor.
Radiation levels around the base of the stack are believed to be still too high for humans to work in, so the dismantling work must be done by remote control.
There are also concerns that the chimney could collapse. TEPCO plans to dismantle the upper half of the structure by the end of the current fiscal year.
A remote control room was set up in a large remodeled bus located about 200 meters from the site. Workers will operate the special cutting equipment while watching footage from 140 video cameras.
Immediately after the triple meltdown at the Fukushima No. 1 plant, radiation levels at the base of the chimney exceeded more than 10 sieverts per hour. In 2015, radiation levels still hovered at 2 sieverts per hour, the highest among all outdoor areas of the plant.
A 750-ton crane is being used to hoist the dismantling mechanism over the exhaust chimney.
The work was supposed to begin around 7:30 a.m. on Aug. 1 with the cutting of ladders and electric cables at the base of the chimney. But some of the equipment did not function properly because of problems with a telecommunications system.
Work finally started around noon.
From Aug. 2, the dismantling mechanism will be used to slice parts of the chimney from the top. The dismantled pieces will be stored in the grounds of the Fukushima No. 1 plant.
Although plans call for dismantling the upper part of the stack by the end of March 2020, strong winds and other weather conditions could cause delays.
The dismantling mechanism was developed and is being operated by construction company Able Co., based in Okuma, Fukushima Prefecture, where the Fukushima No. 1 plant is located.
It is unusual for a local company to be involved in such a key project on-site, but a company official said, “As a local company, we want to respond to the expectations of the local community by successfully completing the project without incident.”
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August 3, 2019 Posted by | fukushima 2019 | , , | Leave a comment

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.

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August 1, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

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

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.

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The fractured steel beam section of the exhaust stack pillar at the No. 1 and 2 reactors of the Fukushima No. 1 Nuclear Power Plant.

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.

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The joint exhaust stack for the No. 1 and 2 reactors of the Fukushima No. 1 Nuclear Power Plant, whose upper section has been fractured.

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.

http://mainichi.jp/english/articles/20160425/p2a/00m/0na/024000c

April 28, 2016 Posted by | Fukushima 2016 | , | Leave a comment