This Jan. 31, 2014, image released by Tokyo Electric Power Company Holdings shows the aerial view of the No. 3 reactor, with its roof blown off and shield plug (circle in the middle) exposed, in Okuma town, Fukushima prefecture, northeastern Japan. A draft investigation report into the 2011 Fukushima nuclear meltdown, adopted by Japanese nuclear regulators Wednesday, Jan. 27, 2021, says it has detected dangerously high levels of radioactive contamination at two of the three reactors, adding to concerns about decommissioning challenges.

Newly found Fukushima plant contamination may delay cleanup

January 27, 2021

TOKYO – A draft investigation report into the 2011 Fukushima nuclear meltdown, adopted by Japanese nuclear regulators Wednesday, says it has detected dangerously high levels of radioactive contamination at two of the three reactors, adding to concerns about decommissioning challenges.

The interim report said data collected by investigators showed that the sealing plugs sitting atop the No. 2 and 3 reactor containment vessels were as fatally contaminated as nuclear fuel debris that had melted and fell to the bottom of the reactors following the March 2011 tsunami and earthquake.

The experts said the bottom of the sealed plug, a triple-layered concrete disc-shaped lid 12 meters (39 feet) in diameter sitting atop the primary containment vessel, is coated with high levels of radioactive Cesium 137.

The No. 1 reactor lid was less contaminated, presumably because the plug was slightly knocked out of place and disfigured due to the impact of the hydrogen explosion, the report said.

The experts measured radiation levels at multiple locations inside the three reactor buildings, and examined how radioactive materials moved and safety equipment functioned during the accident. They also said venting attempt at Unit 2 to prevent reactor damage never worked, and that safety measures and equipment designs still need to be examined.

The lid contamination does not affect the environment as the containment vessels are enclosed inside the reactor buildings. The report did not give further details about if or how the lid contamination would affect the decommissioning progress.

Nuclear Regulation Commission Chairman Toyoshi Fuketa called the findings “extremely serious” and said they would make melted fuel removal “more difficult.” He said figuring out how to remove the lids would be a major challenge.

Removing an estimated 900 tons of melted fuel debris from three reactors is a daunting task expected to take decades, and officials have not been able to describe exactly when or how it may end.

The Fukushima plant was to start removing melted fuel debris from Unit 2, the first of three reactors, later this year ahead of the 10th anniversary of the accident. But in December, plant operator Tokyo Electric Power Co. and the government announced a delay until 2022. They said the development of a robotic arm for the debris removal — a joint project with Britain — has been delayed due to the pandemic.

Under the current plan, a remote-controlled robotic arm will be inserted from the side of the reactor to reach the molten fuel mixed with melted parts and concrete floor of the reactor. Eventually the lids also would have to be removed, but their contamination is a major setback.

The team of experts entered areas inside the three reactors that were previously highly contaminated and inaccessible after radiation levels came down significantly. They’re seeking data and evidence before they get lost in the cleanup.

Massive radiation from the reactors has caused some 160,000 people to evacuate from around the plant. Tens of thousands are still unable to return home.

https://www.local10.com/tech/2021/01/27/newly-found-fukushima-plant-contamination-may-delay-cleanup/

High radiation facilities inside Fukushima No. 1 nuclear power plant may delay decommissioning process

January 27, 2021

Ahead of the 10-year anniversary of the March 2011 accident at Tokyo Electric Power Company Holdings Inc.’s Fukushima No. 1 nuclear power plant, a panel of the Nuclear Regulation Authority on Tuesday released a draft interim report on the accident investigation, which resumed in September 2019. The on-site investigation found that there were areas with extremely high radiation levels near the fifth floor of the reactor buildings of Units 2 and 3. This may lead to a delay in the decommissioning process of the plant.

According to the draft report, high levels of contamination were found at the bottom of a concrete lid called a shield plug, located at the top of the reactor containment vessel. Radioactive cesium there was estimated to be giving off about 20 to 40 petabecquerels of radiation at Unit 2 and about 30 petabecquerels at Unit 3. (The prefix peta indicates 1,000 trillion.)

In terms of radiation dosage, this is likely to be equivalent to several sieverts per hour. If a person were to enter the area, a fatal dose would accumulate in just a few hours.

TEPCO plans to first remove the nuclear fuel debris, which is a mixture of melted nuclear fuel and other materials, from the Unit 2 reactor. Depending on the removal route, it may be necessary to remove the shield plug. The removal of this structure is expected to take a long time, not only because of the high radiation levels but also because the shield plug weighs a total of 465 tons.

Looking back at what had happened during the crisis at the plants in 2011, the panel also examined the effects of venting, or releasing steam containing radioactive materials into the atmosphere to reduce pressure, which was done to prevent damage to the containment vessels. As a result of examining the piping and other parts, the panel found that steam flowed back into the reactor buildings of Units 1 and 3, where the venting was successful.

They also analyzed the TV footage from that time and noted that there had been multiple hydrogen explosions at the Unit 3 reactor

https://the-japan-news.com/news/article/0007096152