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TEPCO: Fuel debris samples taken from damaged Fukushima Daiichi nuclear reactor

February 1, 2023

The operator of the crippled Fukushima Daiichi nuclear power plant says it has retrieved samples from inside the No. 1 reactor containment vessel. It says the samples are likely to contain fuel debris.

The plant suffered a triple meltdown in the March 2011 earthquake and tsunami.

Its operator, Tokyo Electric Power Company, or TEPCO, said on Wednesday that underwater robots successfully sucked water out from two locations inside the vessel.

The company has been examining the inside of the No.1 reactor containment vessel. It says the accumulated matter at the bottom is thought to contain fuel debris.

The project to collect samples initially began early last month, but was suspended due to technical errors. It was resumed on Tuesday.

Experts hope that a close analysis of the samples will help lead to successful removal of fuel debris — one of the greatest challenges in the plant’s decommissioning process.

TEPCO said it will try taking samples from two other locations inside the vessel. It also said it will spend about a year identifying the types and amounts of chemical elements contained in the samples.

The company also plans to send robotic cameras inside the pedestal, a structure that props up the reactor.

https://www3.nhk.or.jp/nhkworld/en/news/20230201_21/

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February 4, 2023 Posted by | Fuk 2023 | , , | Leave a comment

Concrete melted off ‘pedestal’ for damaged reactor in Fukushima

Rebars in the pedestal, which are normally covered with concrete, are seen exposed inside the No. 1 reactor at the Fukushima No. 1 nuclear power plant. (Provided by the International Research Institute for Nuclear Decommissioning and Hitachi-GE Nuclear Energy Ltd.)

November 30, 2022

The concrete support foundation for a reactor whose core melted down at the Fukushima No. 1 nuclear power plant has deteriorated so much that reinforcing bars (rebars) are now exposed.

Masao Uchibori, governor of Fukushima Prefecture, has expressed concerns about the earthquake resistance of the “pedestal” for the No. 1 reactor at the crippled plant operated by Tokyo Electric Power Co. (TEPCO).

Strong quakes struck off the coast of the prefecture in 2021 and 2022.

“There have been events that caused anxieties among residents of our prefecture, including damage to the foundation supporting the No. 1 reactor’s pressure vessel,” Uchibori told a prefectural assembly session in September. “We will check up on TEPCO’s efforts so the decommissioning work will proceed safely and steadily.”

The cylindrical pedestal, whose wall is 1.2 meters thick, is 6 meters in diameter. It supports the reactor’s 440-ton pressure vessel.

The interior of the No. 1 reactor’s containment vessel was inspected in May for TEPCO’s eventual plans to retrieve the melted nuclear fuel that dropped to the bottom of the vessel during the 2011 nuclear disaster.

The study found that the normally concrete-encased rebars were bare and the upper parts were covered in sediment that could be nuclear fuel debris.

The concrete likely melted off under the high temperature of the debris.

The International Research Institute for Nuclear Decommissioning (IRID), an entity set up by power utilities and nuclear reactor manufacturers, conducted a simulation in fiscal 2016.

IRID said seismic resistance would remain uncompromised even if about one-quarter of the pedestal was damaged.

However, only a part of the pedestal was inspected during the May study, and only from the outside.

The pedestal’s inside remains a mystery.

“The pedestal’s soundness is of foremost concern,” said Kiyoshi Takasaka, a former engineer with Toshiba Corp. who is now an adviser to the Fukushima prefectural government on nuclear safety issues. “It is important to first inspect the pedestal from the inside.”

TEPCO has prepared six types of robots to detect the fuel debris and perform other tasks in a series of inspections at the No. 1 reactor.

An internal study of the pedestal is planned toward the March end of the fiscal year as the final mission during the inspections. The task carries the risk of the robot hitting the sediment or other obstacles and being unable to return.

“We understand people’s concerns very well,” Akira Ono, president of TEPCO’s Fukushima Daiichi Decontamination & Decommissioning Engineering Co., told a news conference in October. “We hope to finish studies inside the pedestal by the end of this fiscal year.”

He said his company will scrutinize whether the previous assessment of seismic resistance is still applicable.

Haruo Morishige, who has been studying the Fukushima nuclear disaster, called for immediate emergency safety measures, such infusing concrete to reinforce the pedestal.

“There is a critical defect in terms of quake resistance,” said Morishige, based on a photo showing the interior of the No. 1 reactor. 

Morishige studied aseismic structural design for nuclear reactors when he worked for Mitsubishi Heavy Industries Ltd.

He also served as an on-site manager for the No. 3 reactor at the Ikata nuclear plant operated by Shikoku Electric Power Co., including when the reactor was being built.

The photo, released following the May inspection, shows how concrete covering the cylindrical “inner skirt” of the pedestal had melted off, laying bare part of the steel frame and rebars from the bottom to the top.

The inner skirt’s functions connect the reactor pressure vessel with the containment vessel. But the melting of the concrete has separated the pressure vessel from the containment vessel, and weakened the structure’s quake resistance, Morishige said.

The loss of concrete has also decoupled the pedetal’s walls from the floor, making it more prone to sway during seismic events, he added.

Morishige said that all concrete around the rebars inside the pedestal has likely melted away.

He also said fuel debris that flowed out from an aperture likely melted concrete around rebars over about a quarter of the outside circumference of the pedestal.

His simulation has shown that the support capability of the pedestal is now about three-eighths of the original level.

“In such a state, the reactor could topple over in an earthquake of upper 6 on the Japanese seismic intensity scale (of 7),” Morishige said.

He added that repeated exposure to seismic shocks could cause cracks in the remaining concrete, further undermining quake resistance.

“The very fact there are chances of the reactor toppling is unacceptable,” he said. “Officials should proceed with safety measures and inspections at the same time.”

(This article was written by Keitaro Fukuchi and Tetsuya Kasai.)

https://www.asahi.com/ajw/articles/14767569

December 4, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

Inside the Primary Containment Vessel of Fukushima Daiichi Nuclear Power Station Unit 1.

by Citizens’ Nuclear Information Center · Published September 30, 2022 · Updated September 30, 2022

Pedestal with Exposed Reinforcing Steel

By Kamisawa Chihiro (CNIC)

Survey of the pedestal exterior in the Unit 1 primary containment vessel

On February 9, 2022, Tokyo Electric Power Company Holdings, Inc. (TEPCO) and the International Research Institute for Nuclear Decommissioning (IRID) conducted a survey into the underground level of the primary containment vessel (PCV) of Fukushima Daiichi Nuclear Power Station (FDNPS) Unit 1, using an underwater remotely operated vehicle (ROV). The survey was intended to be a preliminary to investigating the conditions inside the vessel. The survey revealed that there were vast amounts of deposits, which were attributed to melted nuclear fuel, and exposed reinforcing steel, which appeared to be the skeletons of damaged concrete structures.

On March 14, the two parties started a close visual inspection along the periphery of the pedestal (reinforced concrete base on which the reactor pressure vessel was installed) with an ROV. However, on March 16, a serious earthquake of magnitude 7.4 occurred off the coast of Fukushima Prefecture. The water level in the PCV of Unit 1 declined due to the earthquake, and the inspection was suspended.

The two parties thereafter adjusted the water level by increasing the rate of water feed to the reactor, realizing the required water level in the PCV. On May 17, close inspection of the PCV interior was resumed using the ROV. The visual inspection was continued until May 21. The thickness of the deposits were also measured and thermal neutron flux measurements were conducted to learn whether the deposits were from nuclear fuel. It was confirmed that a major part of the deposits was from the fuel.

Fuel debris deposits and damaged wall concrete on the pedestal periphery

In the survey, the outside of the pedestal was visually inspected in detail with the underwater ROV camera along more than half the cylindrical surface of the pedestal (Figure 1).

Fig. 1: Overview of Pedestal Periphery Survey Using an Underwater ROV (Compiled from TEPCO and IRID Data)

The videos and photographs taken from the pedestal periphery show there are deposits that have accumulated deep on the PCV floor (Photograph 1).

The lower periphery of the drywell has eight vent pipes that connect to the suppression chamber. Each vent pipe is provided with a jet deflector to protect the pipe inlet. About one-third of the length of the jet deflectors are buried in the deposits from below (especially deflectors C through F). It was confirmed that deposits also exist behind the jet deflectors. This shows that fuel debris is likely to have entered the suppression chamber.

TEPCO says that the piping and valves of the reactor auxiliary cooling system and the piping of the reactor recirculation system are not seriously damaged.

However, as those photographs show, the piping and valves of the reactor auxiliary cooling system are covered with deposits, while keeping their original shape. Especially, the greater part of the piping looks to be buried under the deposits, and it is unknown whether the piping is damaged or not (Photograph 2).

The valves and piping of recirculation system B do not look seriously damaged as far as the released videos and photographs show. The valves and piping of system A on the opposite side look vague, and it is unknown whether they are damaged or not. It seems possible that there is an anomaly in the proximity of the piping elbow near the pedestal opening.

The pedestal opening lies nearly halfway around from the underwater ROV entry position. Before the 2011 accident, operators entered the space below the reactor through this opening to inspect and maintain the control rod drive and neutron instrumentation.

Currently there is no concrete on either side of the pedestal opening, which must have been there before the accident. As the photographs show, the reinforcing steel skeletons are exposed, and deposits have settled on them (Photographs 3 and 4). The sheet-steel cylindrical structure called the inner skirt, built inside the pedestal, is also exposed.

This means that, on both the sides of the opening, the originally 120-centimeter-thick concrete wall of the pedestal has completely vanished down to the height of about 100 centimeters from the base floor of the PCV. The data by TEPCO and IRID, as shown in Figure 1, indicates the approximate positions of the exposed reinforced steel, but we believe that these are not the only positions where steel is exposed.

The Unit 1 pedestal and lower part of the PCV have the construction shown in Figure 2. The wall of the pedestal base is about 120 centimeters thick. According to the report of the Nuclear Regulation Authority’s investigative hearing with TEPCO, the inner skirt was originally buried in the pedestal base down to about the height of about 100 centimeters.

This means that, on both the sides of the opening, the originally 120-centimeter-thick concrete wall of the pedestal has completely vanished down to the height of about 100 centimeters from the base floor of the PCV. The data by TEPCO and IRID, as shown in Figure 1, indicates the approximate positions of the exposed reinforced steel, but we believe that these are not the only positions where steel is exposed.

How did the concrete vanish?

Concrete is produced from cement and aggregates such as sand and crushed stones, which are mixed with water and then solidified. Concrete and cement are known to have the following characteristics under elevated temperature (Kasami and Ohno, “Solid-state Properties of Concrete in High-temperature Ranges”).

  • When placed in a high-temperature range for a brief period, such as when exposed to a fire, concrete may flake off or explosively crack.

The characteristics of concrete and cement under more moderate temperature changes can be explained as follows:

  • When a hydration reaction has continued sufficiently in the hardened cement body, free water and gel water are lost at about 105°C.
  • When the body is further heated, part of the chemically bound water starts to be given off, and in the temperature range from approximately 250°C to 350°C, calcium silicate hydrates in the cement lose about 20% of their retained moisture.
  • Between 400°C and 700°C, the moisture remaining in the calcium silicate hydrates is mostly lost. Calcium hydroxides are dehydrated and decomposed.

Melted nuclear fuel that consists mostly of uranium dioxide may reach 2,800°C. The melting temperature for concrete is about 1,200°C (which may differ depending on the amount of aggregates).

The core and concrete reaction analysis conducted by TEPCO in 2011 assumed that concrete erosion started when the temperature was at 1,500 K (approximately 1,227°C), concluding that the pedestal concrete floor was eroded down to a depth of sixty-five centimeters.

Did the melted nuclear fuel blow out from the bottom of the Unit 1 RPV, drop down to the floor inside the pedestal, spread over the floor, and attack the concrete wall of the pedestal, causing concrete flaking or explosive cracking? It is also possible that while such a process went ahead, the concrete, heated to 400°C through 700°C, became progressively weaker and fell apart little by little.

The reinforcing steel and inner skirt are not significantly deformed or melted as far as the videos and photographs show. However, the condition of other structures and to what extent the reinforcing concrete fell apart are also unknown at present.

Can the RPV tolerate a massive earthquake?

The loss of the concrete of the pedestal base presents a concern: The RPV, standing on the pedestal, may collapse or fall.

TEPCO, referring to the results of the RPV and PCV seismic assessment conducted by IRID in 2016, is extremely optimistic, stating that, even if a part of the pedestal is deteriorated or damaged, the pedestal can retain the function of supporting the RPV against an assumed earthquake, using the criteria at the time, of a ground motion Ss of 600 Gal.

However, a close examination of IRID’s assessment and TEPCO’s perspective show that their assumptions are overly optimistic. As an example, the model used for the seismic assessment is incorporated into the function of the containment vessel stabilizer and pressure vessel stabilizer, which control the lateral movement of the containment vessel and pressure vessel respectively, but the integrity of those stabilizers is unknown at present.

The TEPCO and IRID analysis concludes, based only on the observed ranges, that the reinforcing steel of the pedestal base does not show damage such as buckling, and that the function of the inner skirt has not deteriorated. The conditions used for the analysis lack discreteness. These conditions may change as the survey is continued in the future. As an example, greater damage in the concrete walls and floor may be discovered. In that case, completely different results may be derived from the seismic assessment.

References (all in Japanese)

  • 東京電力, 福島第一原子力発電所1~3号機の炉心状態について, 2011年11月30日

TEPCO. “Fukushima Daiichi Nuclear Power Station Units 1, 2 and 3 Reactor Core Conditions,” Nov. 30, 2011.

www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_09-j.pdf

  • IRID, 2014年度補正予算廃炉・汚染水対策事業費補助金, 圧力容器/格納容器の耐震性・影響評価手法の開発 (2016年度成果報告), 2017年7月

IRID. “Fiscal 2014 Supplementary Budget Grant for Decommissioning and Contaminated Water Countermeasures — Development of RPV and PCV Earthquake Resistance and Impact Evaluation Methods (Fiscal 2016 Achievement Report),” July 2017.

irid.or.jp/wp-content/uploads/2017/06/20160000_11.pdf

  • 東京電力・IRID・日立GEニュークリアエナジー, 福島第一原子力発電所1号機原子炉格納容器内部調査の実施状況 (2月9日調査分) について, 2022/2/10

TEPCO, IRID and Hitachi-GE Nuclear Energy. “Updates on Fukushima Daiichi Nuclear Power Station Unit 1 Reactor PCV Interior Survey (of Feb. 9)” [Video], Feb. 10, 2022.

www.tepco.co.jp/library/movie/detail-j.html?catid=107299&video_uuid=k593g02e

  • 東京電力・IRID・日立GEニュークリアエナジー, 福島第一原子力発電所1号機原子炉格納容器内部調査(ROV-A2) の実施状況 (3月14~16日の作業状況), 2022/3/24

TEPCO, IRID and Hitachi-GE Nuclear Energy. “Updates on Fukushima Daiichi Nuclear Power Station Unit 1 Reactor PCV Interior Survey (ROV-A2) (Mar. 14–16)” [Video], Mar. 24, 2022.

www.tepco.co.jp/library/movie/detail-j.html?catid=107299&video_uuid=s19dq021

  • 東京電力・IRID・日立GEニュークリアエナジー, 福島第一原子力発電所1号機原子炉格納容器内部調査(ROV-A2)の実施状況 (2022年5月17~19日の作業状況), 2022/5/23

TEPCO, IRID and Hitachi-GE Nuclear Energy. “Updates on Fukushima Daiichi Nuclear Power Station Unit 1 Reactor PCV Interior Survey (ROV-A2) (May 17–19)” [Video], May 23, 2022.

www.tepco.co.jp/library/movie/detail-j.html?catid=107299&video_uuid=og07od6u

  • 東京電力・IRID, 廃炉・汚染水・処理水対策チーム会合/事務局会議 (第102回), 1号機 PCV内部調査の状況について, 2022年5月26日

TEPCO and IRID. “Updates on Unit 1 PCV Interior Survey,” Decommissioning, Contaminated Water and Treated Water Team Secretariat Meeting (102nd), May 26, 2022.

www.meti.go.jp/earthquake/nuclear/decommissioning/committee/osensuitaisakuteam/2022/05/3-3-2.pdf

  • 東京電力・IRID, 第100回特定原子力施設監視・評価検討会, 資料3: 1号機原子炉格納容器内部調査の状況 [東京電力], 2022年6月20日

TEPCO and IRID. “Document No. 3: Updates on Unit 1 Reactor PCV Interior Survey,” 100th Meeting of Specific Nuclear Facility Monitoring and Evaluation Study Group, June 20, 2022.

www.nra.go.jp/data/000393949.pdf

  • 東京電力・IRID, 第30回東京電力福島第一原子力発電所における事故の分析に係る検討会, 資料1-1: 1号機PCV内部調査の状況について, 2022年6月30日

TEPCO and IRID. “Document 1-1: Updates on Unit 1 PCV Interior Survey,” 30th Meeting of TEPCO FDNPS Accident Analysis Study Group, June 30, 2022.

www.nra.go.jp/data/000395861.pdf

  • 東京電力・IRID, 第30回東京電力福島第一原子力発電所における事故の分析に係る検討会, ・補足説明資料1: 1号機PCV内部調査の状況について, 2022年6月30日

TEPCO and IRID. “Supplement 1: Updates on Unit 1 PCV Interior Survey,” 30th Meeting of TEPCO FDNPS Accident Analysis Study Group, June 30, 2022.

www.nra.go.jp/data/000395885.pdf

  • 原子力規制委員会, 第30回東京電力福島第一原子力発電所における事故の分析に係る検討会, 追加説明資料, 2022年6月30日

NRA. “Additional Explanatory Document,” 30th Meeting of TEPCO FDNPS Accident Analysis Study Group, June 30, 2022.

www.nra.go.jp/data/000395866.pdf

  • 嵩英雄, 大野定俊, 高温下コンクリートの物性、 コンクリート工学 Concrete Journal, 1984年22巻3号, p. 13–20

Kasami, H. and Ohno S. (1984). Solid-state Properties of Concrete in High-temperature Ranges, Concrete Journal, 22 (3), pp. 13–20.

www.jstage.jst.go.jp/article/coj1975/22/3/22_13/_article/-char/ja/

Source: https://cnic.jp/english/?p=6276

October 1, 2022 Posted by | Fuk 2022 | , , | Leave a comment

Fukushima reactor sitting on shaky base raises quake concerns

The exposed metal framework of the base supporting the pressure vessel at the No. 1 reactor of the Fukushima No. 1 nuclear power plant (Provided by IRID and Hitachi-GE Nuclear Energy Ltd.)

May 28, 2022

Alarm bells are sounding over signs the heavily damaged structure of the Fukushima No. 1 nuclear power plant may be too flimsy to withstand another major earthquake.

Photos taken by a remote-controlled robotic device sent into the No. 1 reactor found that a large portion of the concrete base supporting the pressure vessel appears to have melted, leaving only a metal framework holding up the pressure vessel.

Experts are now saying the remaining structure may not be strong enough to withstand a big earthquake, a troubling prediction given that the region has been hit by a number of strong temblors in recent months.

An official with the Agency for Natural Resources and Energy who is handling decommissioning work said at a May 26 news conference the remaining structure could not be described as safe, noting that a large portion of the concrete base only had the metal framework remaining.

At a news conference the previous day, Toyoshi Fuketa, chairman of the Nuclear Regulation Authority, said, “We remain concerned about whether it will withstand a strong quake.”

The Fukushima plant went into triple meltdown after the magnitude-9.0 Great East Japan Earthquake in 2011 that generated devastating tsunami. 

The No. 1 reactor bore the brunt of the damage at the nuclear complex. Photos taken by the remote-controlled robot showed not only the exposed metal framework but what looked like a pile of melted fuel on top of the framework.

Officials believe the meltdown at the No. 1 reactor caused most of the fuel to melt through the bottom of the pressure vessel. The plant’s operator, Tokyo Electric Power Co., suspects the tremendous heat from the nuclear fuel may have melted the concrete of the base supporting the pressure vessel.

The cylindrical base is 1.2 meters thick with a diameter of about 6 meters. It supports the pressure vessel, which weighs about 440 tons.

A fiscal 2016 estimate by the International Research Institute for Nuclear Decommissioning said that the seismic resistance of the structure would not be an issue even if one-quarter of the base was structurally compromised, along with other damage to the interior of the pressure vessel.

But the latest photos captured only about 25 percent of the base, prompting the agency official to speculate the concrete around the entire base had melted.

TEPCO officials plan to send in another robot to take photos of the interior of the base to better grasp the seismic resistance of the structure.

Fumiya Tanabe, a former senior researcher at what is now the Japan Atomic Energy Agency, offered an even scarier possibility.

Noting that the interior of the base lies directly under the reactor core there, he said it was possible that piping hot nuclear fuel flowed into the interior.

“The metal framework in the interior of the base may even have melted,” Tanabe said.

That is a particularly worrisome thought in light of the fact that quakes with a seismic intensity of upper 6 on Japan’s maximum scale of 7 hit off the coast of Fukushima Prefecture in February 2021 and March 2022.

Tanabe said that in a worst-case scenario, another strong quake could cause the pressure vessel to topple over, making work to remove the melted fuel that much more difficult.

He recommended that work start quickly to assess the extent of damage.

The No. 1 reactor at the Fukushima No. 1 nuclear power plant (Asahi Shimbun file photo)

https://www.asahi.com/ajw/articles/14632301

May 29, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

Debris in sediment, bottom of Fukushima Unit 1 Neutron radiation detected at high levels

Debris deposits at the bottom of the containment vessel of the Fukushima Daiichi Unit 1 reactor on March 17 (International Nuclear Decommissioning Research and Development Organization, Hitachi GE Nuclear Energy, Inc. (Courtesy of International Nuclear Decommissioning Research and Development Institute, Hitachi GE Nuclear Energy)

May 26, 2022
On May 26, TEPCO announced that it had detected high levels of neutron radiation, which is emitted when uranium and plutonium contained in nuclear fuel undergo nuclear fission, in sediment found at the bottom of the containment vessel at the Fukushima Daiichi Nuclear Power Plant’s Unit 1 reactor. TEPCO announced that it had detected high levels of neutron radiation, which is emitted when uranium and plutonium contained in nuclear fuel fuse. A TEPCO representative said, “It is presumed to be derived from molten nuclear fuel (debris). It is natural to assume that the debris is contained in the sediment.
 TEPCO will focus on examining the thickness of the deposits near where the neutron rays were detected and the types of radioactive materials contained in the deposits.
 According to TEPCO, on March 20 and 21, underwater robots were used to survey four locations at the bottom of the containment vessel, and neutron rays were detected in all of them. The values at three locations near the openings in the base of the pressure vessel were particularly high.
https://www.tokyo-np.co.jp/article/179742?fbclid=IwAR0oljxEJF2Q5XzUE859cfr1DfSmtvct8xkg6FcU2uIEpIKvtlrh3qm9aag

May 29, 2022 Posted by | Fuk 2022 | , , , , , , | Leave a comment

If a major earthquake were to occur… “Will it be safe?” concerns the chairman of the regulatory committee after the damage to the foundation of the pressure vessel at the Fukushima Daiichi Unit 1 reactor is discovered

The foundation supporting the pressure vessel has lost its concrete, leaving the rebar exposed inside the reactor of TEPCO’s Fukushima Daiichi Nuclear Power Plant Unit 1 (courtesy of the International Nuclear Decommissioning Research and Development Organization and Hitachi GE Nuclear Energy).

May 25, 2022
At a press conference on May 25, Chairman Toyoshi Sarada of the Nuclear Regulation Authority of Japan (NRAJ) said, in response to an investigation that found rebar exposed in part of the reinforced concrete foundation supporting the Unit 1 reactor pressure vessel at TEPCO’s Fukushima Daiichi Nuclear Power Plant (Okuma and Futaba, Fukushima Prefecture), “I have concerns about whether it will be safe when a major earthquake occurs. I have concerns about whether it will be safe in the event of a major earthquake. If we could reinforce it, we would.
 Sarada pointed out that “it is possible to speculate” about the possibility that nuclear fuel (debris) melted down during the accidental meltdown (core meltdown) and broke through the pressure vessel, melting the concrete (1.2 meters thick) of the foundation. He expressed a sense of crisis, saying, “It is necessary to consider what would happen if the foundation collapsed.
 He also recognized that it would be difficult to reinforce the foundation in a nuclear reactor with extremely high radiation levels, and said, “We cannot take too long when considering earthquake resistance, and we should remove the debris as soon as possible, even if it is just an earpick, and analyze its condition.
 TEPCO placed an underwater robot into the containment vessel from March 17 to 21 to investigate its interior. Near the base of the bottom of the containment vessel, several lumpy deposits were found that appeared to be debris. Although the accident caused the meltdown of Units 1-3, this was the first time that the exposure of rebar inside the concrete was confirmed. (Kenta Onozawa)
https://www.tokyo-np.co.jp/article/179502?fbclid=IwAR1Oq1_rEddpUnUyTDUjJXd494WNQk3_XfAyPMVz3zFFWVqZGcsV3X10qSY

May 29, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

TEPCO to Remove Contaminated Pipes at Fukushima Daiichi Nuclear Power Plant by “First Half of FY2022” Due to Continuing Troubles

A cutting device lifted by a large crane grabs a 30-centimeter-diameter pipe at the Fukushima Daiichi Nuclear Power Plant on March 2, 2022 (photo by Takeshi Yamakawa)

April 18, 2022
On April 18, at a meeting of the Nuclear Regulation Authority to review the status of the accident at the Fukushima Daiichi Nuclear Power Plant, TEPCO announced that it had changed its target date for the completion of work to “the first half of FY2022 (April to September)” regarding the removal of pipes between Units 1 and 2 that were contaminated with high concentrations of radioactive materials. Previously, the target was “within FY 2009. The scope of the removal work includes the areas that interfere with the installation of rainwater inflow countermeasures in the waste treatment buildings of Units 1 and 2 and the installation of a large cover in Unit 1.
 The removal work began on February 24, but has not progressed at all due to a series of problems with the cutting equipment. The timing for the resumption of work is not clear, as investigations are still underway to determine whether the cutting equipment and method used to lift the pipes up by a large crane are appropriate.
 The pipes to be removed were used in the venting process immediately after the accident to release contaminated air inside the reactor to prevent the containment vessel from rupturing. The pipes are 30 cm in diameter and measure 65 meters on the Unit 1 side and 70 meters on the Unit 2 side. The current plan is to cut the piping into 26 sections and remove them. The surface dose at the connection with the exhaust stack is 4 sievert per hour, which is high enough to kill a person if he or she stays there for several hours. For this reason, all work will be carried out remotely. (Shinichi Ogawa)
https://www.tokyo-np.co.jp/article/172472?rct=national&fbclid=IwAR1DYTcIpK–IpNqQfheOVBWKG8-G1Eonb274DLuS8FOMWxZ9ciYQLdmaiM

April 23, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

Latest look inside Fukushima’s ruins shows mounds of melted nuclear fuel

About 900 tons of melted nuclear fuel remain inside the plant’s three damaged reactors.

February 16, 2022

A remote-controlled robot has captured images of melted nuclear fuel inside Japan’s wrecked Fukushima nuclear plant.

A massive earthquake and tsunami in 2011 damaged cooling systems at the power plant, causing the meltdown of three reactor cores.

Most of their highly radioactive fuel fell to the bottom of their containment vessels, making its removal extremely difficult.

A previous attempt to send a small robot with cameras into the Unit 1 reactor failed, but images captured this week by a ROV-A robot show broken structures, pipes and mounds of what appears to be melted fuel.

Other debris was also submerged in cooling water, according to Tokyo Electric Power Company Holdings (TEPCO), the plant operator.

About 900 tonnes of melted nuclear fuel remain inside the plant’s three damaged reactors, including about 280 tons in Unit 1.

Its removal is a daunting task that officials say will take 30-40 years. Critics say that’s overly optimistic.

The robot, carrying several tiny cameras, obtained the internal images of the reactor’s primary containment vessel while on a mission to establish a path for subsequent probes, TEPCO said.

TEPCO spokesperson Kenichi Takahara said the piles of debris rose from the bottom of the container, including some inside the pedestal — a structure directly beneath the core — suggesting the mounds were melted fuel that fell in the area.

Takahara said further probes will be needed to confirm the objects in the images.

At one location, the robot measured a radiation level of 2 sievert, which is fatal for humans, Takahara said. The annual exposure limit for plant workers is set at 50 millisievert.

Images from a remote-controlled submersible robot show damaged areas inside the Fukushima nuclear power plant damaged in the 2011 earthquake and tsunami in Fukushima, Japan.

The robot probe of the Unit 1 reactor began on Tuesday and was the first since 2017 when an earlier robot failed to obtain any images of melted fuel because of the extremely high radiation and interior structural damage.

The fuel at Unit 1 is submerged in highly radioactive water as deep as 2 meters (6.5 feet).

TEPCO said it will conduct additional probes after analyzing the data and images collected by the first robot.

The investigation at Unit 1 aims to measure the melted fuel mounds, map them in three dimensions, analyze isotopes and their radioactivity, and collect samples, TEPCO officials said.

Those are key to developing equipment and a strategy for the safe and efficient removal of the melted fuel, allowing the reactor’s eventual decommissioning.

Details of how the highly radioactive material can be safely removed, stored and disposed of at the end of the cleanup have not been decided.

TEPCO hopes to use a robotic arm later this year to remove an initial scoop of melted fuel from Unit 2, where internal robotic probes have made the most progress.

February 20, 2022 Posted by | Fuk 2022 | , , | Leave a comment

Robot photos appear to show melted fuel at Fukushima reactor

MARI YAMAGUCHI – February 10, 2022

TOKYO (AP) — A remote-controlled robot has captured images of what appears to be mounds of nuclear fuel that melted and fell to the bottom of the most damaged reactor at Japan’s wrecked Fukushima nuclear plant, officials said Thursday.

A massive earthquake and tsunami in 2011 damaged cooling systems at the power plant, causing the meltdown of three reactor cores. Most of their highly radioactive fuel fell to the bottom of their containment vessels, making its removal extremely difficult.

A previous attempt to send a small robot with cameras into the Unit 1 reactor failed, but images captured this week by a ROV-A robot show broken structures, pipes and mounds of what appears to be melted fuel and other debris submerged in cooling water, plant operator Tokyo Electric Power Company Holdings said Thursday.

About 900 tons of melted nuclear fuel remain inside the plant’s three damaged reactors, including about 280 tons in Unit 1. Its removal is a daunting task that officials say will take 30-40 years. Critics say that’s overly optimistic.

The robot, carrying several tiny cameras, obtained the internal images of the reactor’s primary containment vessel while on a mission to establish a path for subsequent probes, TEPCO said.

TEPCO spokesperson Kenichi Takahara said the piles of debris rose from the bottom of the container, including some inside the pedestal — a structure directly beneath the core — suggesting the mounds were melted fuel that fell in the area.

Takahara said further probes will be needed to confirm the objects in the images.

At one location, the robot measured a radiation level of 2 sievert, which is fatal for humans, Takahara said. The annual exposure limit for plant workers is set at 50 millisievert.

The robot probe of the Unit 1 reactor began Tuesday and was the first since 2017, when an earlier robot failed to obtain any images of melted fuel because of the extremely high radiation and interior structural damage.

The fuel at Unit 1 is submerged in highly radioactive water as deep as 2 meters (6.5 feet).

TEPCO said it will conduct additional probes after analyzing the data and images collected by the first robot.

Five other robots, co-developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning, a government-funded consortium, will be used in the investigation over the next several months.

The investigation at Unit 1 aims to measure the melted fuel mounds, map them in three dimensions, analyze isotopes and their radioactivity, and collect samples, TEPCO officials said.

Those are key to developing equipment and a strategy for the safe and efficient removal of the melted fuel, allowing the reactor’s eventual decommissioning.

Details of how the highly radioactive material can be safely removed, stored and disposed of at the end of the cleanup have not been decided.

TEPCO hopes to use a robotic arm later this year to remove an initial scoop of melted fuel from Unit 2, where internal robotic probes have made the most progress.

https://www.yahoo.com/now/robot-photos-appear-show-melted-134212334.html

February 13, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

Delayed robot probe of Fukushima reactor begins

Feb. 8, 2022

The operator of the damaged Fukushima Daiichi nuclear power plant has begun its delayed robot probe of the inside of the facility’s No.1 reactor.

Tokyo Electric Power Company, or TEPCO, had planned to start the survey of the reactor’s containment vessel on January 12, but postponed it due to mechanical trouble.

Engineers noticed during preparations that data from radiation-measuring equipment installed in a robot was not shown correctly.

The engineers later found out that electromagnetic waves emitted from the robot’s device for extending and winding up cables had affected its radiometers. They solved the problem, and confirmed that the data was then shown accurately.

TEPCO started the survey on Tuesday morning. Officials of the utility say they initially planned to end the probe by August, but that the schedule will be moved back due to the delay.

The probe is part of efforts to remove molten fuel debris from inside the reactor.

https://www3.nhk.or.jp/nhkworld/en/news/20220208_26/

February 10, 2022 Posted by | Fuk 2022 | , , | Leave a comment

Fukushima Operators Send Robot Into Worst-Hit Melted Reactor

The damaged Unit 1 reactor, back, and the exhaust stack shared with the Unit 1 and 2 reactors at the Fukushima Daiichi nuclear power plant stand along the coast of Okuma town, Fukushima prefecture, northeastern Japan, Saturday, Feb. 27, 2021. A remote-controlled robot was used on Tuesday, Feb. 8, 2022, to probe the hardest-hit nuclear reactor at Japan’s wrecked Fukushima plant, as officials push forward with recovery and clean-up operations that have been mired in delays and controversy. (AP Photo/Hiro Komae, File)

Feb. 8, 2022

By MARI YAMAGUCHI, Associated Press

TOKYO (AP) — A remote-controlled robot on Tuesday was used to probe the hardest-hit nuclear reactor at Japan’s wrecked Fukushima plant, as officials push forward with clean-up operations that have been mired in delays and controversy.

An earthquake and tsunami in 2011 unleashed a disastrous meltdown at Fukushima Daiichi’s three reactors that partly sunk their radioactive cores into the plant’s concrete foundations, making removal extremely difficult.

The plant’s operator, Tokyo Electric Power Company Holdings, said the submersible robot was sent into Unit 1’s primary containment vessel to install a guiding path for five subsequent robots, which will attempt to asses and take samples of the melted fuel that emits fatally high radiation.

Tuesday’s probe followed five years after the operators sent another robot into the same and badly-damaged reactor, but failed to get any images of the melted fuel.

The robot-led work, which was postponed from mid-January due to mechanical glitches, is expected to last for a few days before full-fledged probes begin.

Earlier probes showed that the fuel at Unit 1 is submerged by highly radioactive water as deep as 2 meters (6.5 feet).

Five other robots, co-developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning, a government-funded consortium, will be separately sent in for the investigation over the next several months.

The probe at Unit 1 aims to measure the melted fuel mounds, map them in three dimensions, analyze isotopes and their radioactivity, and collect samples, Tokyo Electric officials said.

Those are key to developing equipment and a strategy for a safe and efficient melted fuel removal.

About 900 tons of melted nuclear fuel remain inside the plant’s three reactors, including about 280 tons in Unit 1, and its removal is a daunting task that officials say will take 30-40 years. Critics say that’s overly optimistic.

Remote-controlled robots with cameras have provided only a limited view of the melted fuel in areas too dangerous for humans to reach. In 2017, super-high levels of radiation and structural damage hampered investigating Unit 1.

Details of how the highly radioactive material can be safely removed, stored and disposed at the end of the cleanup have not been decided.

Tokyo Electric hopes to use a robotic arm to remove a first scoop of melted fuel later this year from Unit 2, where internal robotic probes have made the most progress.

Fisherman and residents of Fukushima’s outlying areas have protested the operator’s plans to discharge into the nearby sea radioactive waters from the reactors, after treating and diluting them to safely releasable levels.

https://www.usnews.com/news/news/articles/2022-02-08/fukushima-operators-send-robot-into-worst-hit-melted-reactor

February 10, 2022 Posted by | Fuk 2022 | , , | Leave a comment

“We don’t know if it’s debris.” Bumpy deposits at the bottom of the reactor.

February 9, 2022
 On February 9, Tokyo Electric Power Company (TEPCO) released a video of the bottom of the containment vessel of the Unit 1 reactor at the Fukushima Daiichi Nuclear Power Plant (Okuma and Futaba towns, Fukushima Prefecture) taken by an underwater robot during an internal investigation. From the images, it was confirmed that orangeish bumpy deposits were spreading and adhering to the structure inside the vessel. It is possible that it is nuclear fuel (debris) that melted down during the accident. We don’t know if it is debris at this stage,” said Kenichi Takahara, a spokesman, at a press conference.

A video of the bottom of the containment vessel of the Unit 1 reactor shows a bumpy deposit spreading from the bottom center to the right side of the vessel at TEPCO’s Fukushima Daiichi Nuclear Power Plant (Courtesy of TEPCO)

According to TEPCO, it is unclear how high the confirmed deposit is; a survey in March 2017 confirmed a deposit of 90 centimeters high near this location. According to TEPCO, the height of the debris is unknown.

A part of the piping that was cut off for the introduction of the robots has sunk to the bottom of the containment vessel of the Unit 1 reactor (Courtesy of TEPCO)

By around 1:50 p.m. on the 9th, the underwater robot that was deployed on the afternoon of the 8th had moved through the water inside the containment vessel and attached four guide rings with a diameter of 30 centimeters at intervals to the structure inside the vessel. The purpose of these rings was to prevent cables from getting tangled in the structure when the robot, which will be used in the future, moves around, and we were finally ready for a full-scale investigation.

In the containment vessel of the Unit 1 reactor, an underwater robot moves through the vessel while attaching rings to the structure (TEPCO)

Oil-like suspended matter was observed on the water surface inside the containment vessel of the Unit 1 reactor. The yellow glow in the center is a pipe illuminated by a light (TEPCO)

 The radiation level in the water was 1 to 2 sievert per hour. The radiation level in the water was 1 to 2 sievert per hour. The exposure limit for workers at the nuclear power plant is 50 millisieverts per year, and even if one were to enter the water, it would take only 1 to 3 minutes to reach the exposure limit, so people are not allowed to go near the water.

A worker opens a valve leading to the containment vessel of the Unit 1 reactor to insert a robot (Courtesy of TEPCO)

Workers insert an underwater robot outside the containment vessel of the Unit 1 reactor (Courtesy of TEPCO)

 Of the three reactors that suffered core meltdowns in the March 2011 accident, video footage shows deposits of what appears to be debris in Units 2 and 3, but no debris was found in Unit 1 during the 2005 survey.
 Removing the debris is the most difficult task, and it is estimated that a total of 880 tons has melted down in Units 1-3. TEPCO is aiming to collect a few grams of debris from the Unit 2 reactor by the end of this year. (Shinichi Ogawa, Kenta Onozawa)
https://www.tokyo-np.co.jp/article/159265?fbclid=IwAR08nc1U0duYKVLHyBgjGnoRnhVI944BMtWrN-6F8HNVGUlKXTpkkFAItm4

February 10, 2022 Posted by | Fuk 2022 | , , | Leave a comment

Fukushima Unit 1: First internal investigation in 5 years

Underwater robot captures images of reactor containment vessel

2022/02/08
The Tokyo Electric Power Company (TEPCO) began an internal investigation of the containment vessel at the Unit 1 reactor of the Fukushima Daiichi Nuclear Power Plant on February 8. An underwater robot was used to collect information on the sediment accumulating at the bottom of the vessel and the molten nuclear fuel (debris) underneath. This is the first time in about five years since March 2017.

 According to the images taken by the camera mounted on the robot, the bottom of the containment vessel was bumpy, as if something had accumulated there. A TEPCO official said, “We don’t know yet whether it is a deposit or not, and we will proceed with the investigation.

 The investigation was scheduled to start on January 12, but was postponed due to problems during the preparation work. TEPCO is now reconsidering the process, which was set to last until August.
https://www.minpo.jp/globalnews/moredetail/2022020801001260?fbclid=IwAR0YiLHqKhJNuprOuxehkLnPzsAYBMFHgQ_0hcLHnWwpllUn9CFD2zSjR10

February 9, 2022 Posted by | Fuk 2022 | , , | Leave a comment

Robotic failure: “We don’t know the cause, and the outlook is unclear…” High barrier to internal investigation of high radiation dose at Fukushima Daiichi Nuclear Power Plant Unit 1

January 15, 2022

Due to a robot malfunction, an internal inspection of the Unit 1 reactor at TEPCO’s Fukushima Daiichi Nuclear Power Plant (located in the towns of Okuma and Futaba in Fukushima Prefecture) has not been able to begin. The radiation level inside the containment vessel, where melted nuclear fuel (debris) remains, is too high for people to approach. The work, which requires remote control, has had a series of problems. As the eleventh anniversary of the accident approaches, a high wall continues to block the way. (Kenta Onozawa)


Advance preparations were too lax.
 We didn’t know the cause of the accident. We don’t know the cause, we don’t know the prospects for countermeasures, and we haven’t decided when to resume the investigation.
 At a press conference on March 13, a TEPCO spokesman gave a vague answer. The internal investigation of the Unit 1 reactor, which was delayed for more than two years from the original plan, was supposed to start on the 12th, but it stalled right from the start.
 Of the three reactors that suffered meltdowns, Unit 1 is the only one where no debris has been found. The survey this time has been planned with a lot of effort to make up for the delay, including the use of six different types of robots with multiple functions, and the survey will take about seven months.
 The first underwater robot (25 centimeters in diameter and 111 centimeters in length) will be used to create a survey route. A 30-centimeter-diameter guide ring will be attached to the robot so that subsequent robots can pass through it to prevent cables from getting tangled, which the spokesperson stresses is essential for the survey.

Status of Containment Vessel Survey at Fukushima Daiichi Nuclear Power Plant


However, the preparations in advance were lax. The preliminary tests were limited to confirming the operation of each piece of equipment, and the team was unable to immediately respond to problems with the dosimeters that occurred when they were operated simultaneously.


In the past, there have been cases of “leaving things behind.
 It is expected to take some time to identify the cause of the problem. If similar problems occur with other robots, plans to take images of the inside of the containment vessel, grasp its three-dimensional structure, and collect sand-like deposits in the water will not be able to proceed and may be abandoned.
 We know from previous studies that complex devices are less effective, such as the underwater robot that photographed debris deposits inside the containment vessel of Unit 3 in 2017. The underwater robot that photographed the debris in the containment vessel of the Unit 3 reactor in 2017 was about a quarter of the length and had a simpler structure. It also focused on photographing as its main purpose.
 In the 2006 survey that succeeded in photographing the debris in the Unit 2 reactor, a worker inserted a pipe (13 meters long) with a camera attached to the end, rather than a robot. In the previous year, a camera-equipped pipe was inserted. In the previous year, a camera-equipped robot called a “scorpion” was deployed, but it climbed up on the sediment and could not be retrieved, remaining in the reactor.


Although “human power” can be used to deal with the problem outdoors…
 Remote-controlled operations are always fraught with difficulties, even outside the building where the reactor is located.

TEPCO’s Fukushima Daiichi Nuclear Power Plant, where work to bring the accident under control is underway. From left: Unit 1 and Unit 2 in Okuma Town, Fukushima Prefecture.


 The exhaust stack near the Unit 1 and 2 buildings, which was in danger of collapsing due to the earthquake and was highly contaminated, was cut down to about 60 meters, half the height of the original stack (1 In one case, the saw blade of a cutting device lifted by a large crane got stuck in the cylinders and could not be moved. At that time, a worker climbed up to the cutting device installed at the top of the 110-meter-high cylinder with a crane and cut it with a power tool.
 In late January, they plan to cut the contaminated pipes leading to this exhaust stack. The project was originally supposed to start four months ago, but there was a problem with the remote-controlled cutting device and the crane broke down, delaying the plan.
 Debris collection is planned for Unit 2 by the end of the year. If a problem occurs in the reactor, we cannot rely on human power.
https://www.tokyo-np.co.jp/article/154269?fbclid=IwAR2E55S3DYLr7KiroYjxza6u_MX67pvMdrWioFykfOwgoxBdOlqhOraX9WI

Translated with http://www.DeepL.com/Translator (free version)

January 15, 2022 Posted by | Fuk 2022 | , , | Leave a comment

TEPCO to begin robot probe of Fukushima reactor

Jan. 6, 2022

The operator of the crippled Fukushima Daiichi Nuclear Power Station says it will launch a probe of the inside of the No.1 reactor on Wednesday using robots. The firm is seeking to clear debris from the reactor interior as part of the decommissioning process.

Tokyo Electric Power Company, or TEPCO, says the probe will involve six types of robots, each with a different function.

It says the survey will continue for more than six months. It will use ultrasonic devices to locate and measure the thickness of debris believed to be submerged under water inside the reactor containment vessel.

The utility says it also hopes to collect small samples of the debris.

TEPCO says it will use a robot to install a cover on a path for the survey machines to move smoothly under water.

The No.1, 2 and 3 reactors of the plant suffered meltdowns in the massive earthquake and tsunami of 2011.

TEPCO confirmed the existence of what is believed to be solid fuel debris inside the No.2 and 3 reactors, but not inside the No.1 reactor. The debris consists of molten nuclear fuel and metal parts.

Fukushima Daiichi Decontamination & Decommissioning Engineering Company, which was established by TEPCO, said on Thursday it will use the robots to gather information before considering how to remove the debris.

https://www3.nhk.or.jp/nhkworld/en/news/20220107_02/

January 8, 2022 Posted by | Fuk 2022 | , , | Leave a comment