Nuke fuel debris from Fukushima more brittle than experts expected
Melted fuel debris retrieved from a crippled reactor at the Fukushima No. 1 nuclear power plant was found to be more brittle than expected, which experts said may offer new ways to tackle the decommissioning process.
The fragment weighs just 700 milligrams. It was removed from the No. 2 reactor containment vessel last November.
Plant operator Tokyo Electric Power Co. and the Japan Atomic Energy Agency said July 31 the surprise findings could lead to development of new methods and tools to remove the rest of the melted fuel from the plant's hobbled reactors in years to come.
The melted fuel, the first to be removed from any of the crippled reactors at the plant, has been under analysis at the JAEA's Oarai Nuclear Engineering Institute, in Ibaraki Prefecture, and elsewhere.
TEPCO and JAEA officials said the fragment broke into smaller lumps and grains when it was whacked with a stainless-steel rod.
A compositional study showed that uranium, the key ingredient of the nuclear fuel, makes up the bulk of the sample.
The fragment contained zirconium alloy, commonly used in nuclear reactors as fuel cladding, and iron and nickel, typically found in structural components. The materials were likely caught up in the mixture when the molten fuel broke through the bottom of the reactor core.
Experts had assumed the piece of fuel debris, with its strong metal content, would be hard to break.
The unexpected brittleness is partly due to the porous structure of the sample material, the officials said.
PULVERIZATION AS AN OPTION
On July 29, TEPCO released a provisional plan to retrieve fuel debris from the plant's No. 3 reactor, starting in fiscal 2037 or later. It aims to accomplish that by pulverizing the melted fuel and removing it from the side of the reactor.
TEPCO said it is weighing the option of using a waterjet or laser to pulverize the debris.
However, a JAEA official who analyzed a sample of the fragment said there was no way of telling whether the fuel debris buried deeper is of similar consistency.
Pulverization has the advantage of reducing debris grain size with little force being applied only if the material crumbles easily, the JAEA official explained.
An estimated 880 tons of melted fuel debris remain inside the No. 1, 2 and 3 reactors at the plant. The facility went into a triple meltdown after being swamped by tsunami triggered by the Great East Japan Earthquake of 2011.
A second batch of fuel debris, weighing a total of 200 milligrams, was retrieved in April, also from the No. 2 reactor.
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Asahi Shimbun
3 days ago
- Asahi Shimbun
Nuke fuel debris from Fukushima more brittle than experts expected
Melted fuel debris retrieved from the Fukushima No. 1 nuclear power plant's No. 2 reactor in November after it was crushed into pieces for analysis (Provided by the Japan Atomic Energy Agency) Melted fuel debris retrieved from a crippled reactor at the Fukushima No. 1 nuclear power plant was found to be more brittle than expected, which experts said may offer new ways to tackle the decommissioning process. The fragment weighs just 700 milligrams. It was removed from the No. 2 reactor containment vessel last November. Plant operator Tokyo Electric Power Co. and the Japan Atomic Energy Agency said July 31 the surprise findings could lead to development of new methods and tools to remove the rest of the melted fuel from the plant's hobbled reactors in years to come. The melted fuel, the first to be removed from any of the crippled reactors at the plant, has been under analysis at the JAEA's Oarai Nuclear Engineering Institute, in Ibaraki Prefecture, and elsewhere. TEPCO and JAEA officials said the fragment broke into smaller lumps and grains when it was whacked with a stainless-steel rod. A compositional study showed that uranium, the key ingredient of the nuclear fuel, makes up the bulk of the sample. The fragment contained zirconium alloy, commonly used in nuclear reactors as fuel cladding, and iron and nickel, typically found in structural components. The materials were likely caught up in the mixture when the molten fuel broke through the bottom of the reactor core. Experts had assumed the piece of fuel debris, with its strong metal content, would be hard to break. The unexpected brittleness is partly due to the porous structure of the sample material, the officials said. PULVERIZATION AS AN OPTION On July 29, TEPCO released a provisional plan to retrieve fuel debris from the plant's No. 3 reactor, starting in fiscal 2037 or later. It aims to accomplish that by pulverizing the melted fuel and removing it from the side of the reactor. TEPCO said it is weighing the option of using a waterjet or laser to pulverize the debris. However, a JAEA official who analyzed a sample of the fragment said there was no way of telling whether the fuel debris buried deeper is of similar consistency. Pulverization has the advantage of reducing debris grain size with little force being applied only if the material crumbles easily, the JAEA official explained. An estimated 880 tons of melted fuel debris remain inside the No. 1, 2 and 3 reactors at the plant. The facility went into a triple meltdown after being swamped by tsunami triggered by the Great East Japan Earthquake of 2011. A second batch of fuel debris, weighing a total of 200 milligrams, was retrieved in April, also from the No. 2 reactor.
Yomiuri Shimbun
10-08-2025
- Yomiuri Shimbun
Delay in retrieving nuclear debris: Take practical, realistic steps toward decommissioning
Given the difficult road ahead toward decommissioning the Fukushima No. 1 nuclear power plant, revising the plan at this point seems to be a realistic decision. Operator Tokyo Electric Power Company Holdings, Inc. has announced that it has significantly delayed the start of the full-scale retrieval of melted nuclear fuel from the plant, originally scheduled for the early 2030s, to between 2037 and 2040. The retrieval of the debris is the most difficult task in the entire decommissioning process. The total amount of debris is estimated to be 880 tons for the Nos. 1, 2 and 3 reactors at the plant, but only about 1 gram was retrieved during two trial attempts last year and this year. It has been highlighted once again that safely retrieving debris amid high radiation levels is quite challenging. In addition, in order to begin the major task of retrieving the debris, it will be necessary to remove adjacent buildings to secure space to work and then, a structure to serve as a work platform must also be constructed above the reactor building. A considerable amount of preparation time will inevitably be required. TEPCO has set a target of completing the decommissioning by 2051, but once it is believed that the retrieval work can be carried out, it will be necessary to review the plan. The current plan was established amid the confusion following the 2011 Great East Japan Earthquake that triggered the meltdown, and it is only natural for it be updated as work progresses. Meanwhile, TEPCO has decided on specific methods for retrieving the debris. Robotic arms or other devices will be inserted into the containment vessel of the No. 3 reactor from above or from the side, and debris will be retrieved by injecting filler material to solidify it as necessary. At this point, this method appears to be the most feasible. Last year, the Nuclear Damage Compensation and Decommissioning Facilitation Corporation, a specialized government agency, proposed three different methods, including flooding the entire reactor building. However, enclosing the entire reactor with a new structure and filling it with water was deemed to be difficult, and the submersion method was not adopted. Since water, which is highly effective in blocking radiation, cannot be used, work must be carried out with greater caution in order to minimize the amount of radiation that workers are exposed to. The analysis of debris extracted on a trial basis revealed that it was more fragile than expected and could be broken by human force. It may be possible to combine existing technologies such as high-pressure water jets and lasers to cut and suction the debris. TEPCO has recorded an extraordinary loss of ¥903 billion based on the new plan. The total cost of decommissioning is estimated at ¥8 trillion, but there is a possibility that this figure will increase further. The outlook for restarting TEPCO's Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture remains uncertain, and TEPCO is facing a difficult business environment. The company is encouraged to manage its operations with a sense of urgency to fulfill its responsibility for decommissioning the plant in Fukushima Prefecture. (From The Yomiuri Shimbun, Aug. 10, 2025)
Asahi Shimbun
01-08-2025
- Asahi Shimbun
VOX POPULI: Fukushima debris removal is a task that will likely take eons
Decommissioning work continues around the No. 3 reactor at Tokyo Electric Power Co.'s Fukushima No. 1 nuclear power plant. (Tsubasa Setoguchi) Buddhism uses its own unique units to express vast spans of time and numbers. Imagine a colossal castle, seven kilometers long, wide, and tall, its interior completely filled with poppy seeds. Once every hundred years, a single seed is removed. The time it would take to empty the castle—removing one seed every century until none remain—would still be shorter than what Buddhism calls a kalpa, or 'ko' in Japanese. Often translated as an eon, a ko represents an unfathomably long stretch of time, used to convey the sense of an almost inconceivable duration. The term also appears in the expression 'mirai eigo,' meaning 'an eternal future' or 'for all eternity,' evoking something that continues without end. How long, then, will it take to remove the fuel debris from the Fukushima No. 1 nuclear power plant, which suffered triple meltdowns in the 2011 disaster? The debris—which was once nuclear fuel that overheated, melted and fused with structural materials inside the reactors—was originally scheduled for removal beginning in 2021. Yet immense technical challenges delayed the start until last year. Tokyo Electric Power Co., the plant's operator, recently announced that full-scale debris removal for reactor No. 3 will begin in fiscal 2037 or later. For reactors No. 1 and No. 2, no timeline has even been set. Of an estimated 880 tons of debris, only 0.9 gram has been recovered to date. A simple calculation based on the time since the accident suggests the removal process could take another 13.6 billion years to complete. Critics rightly argue that such an estimate is absurdly simplistic and misleading. But then, what would a realistic projection look like? Despite knowing full well the near impossibility of the task, authorities and TEPCO continue to uphold the goal of 'completing reactor decommissioning by 2051'—a timeline that seems more like sleight of hand than sincere policy, meant to lull the public into a false sense of reassurance. Even as Japan struggles to dismantle the legacy of Fukushima, the nation has pivoted boldly toward the 'maximum use' of nuclear energy. Kansai Electric Power Co. is now preparing to construct an entirely new plant. Has the landscape really shifted so dramatically—can a country's stance reverse so completely—in just the 14 years since the Great East Japan Earthquake? There's a word for something that defies belief: 'fukashigi.' Bizarre, inconceivable. Fittingly, this term too originated as a unit of measure in Buddhist cosmology—used to signify numbers so vast they dwell beyond comprehension. —The Asahi Shimbun, Aug. 1 * * * Vox Populi, Vox Dei is a popular daily column that takes up a wide range of topics, including culture, arts and social trends and developments. Written by veteran Asahi Shimbun writers, the column provides useful perspectives on and insights into contemporary Japan and its culture.
